Importance of reperfusion on thromboxane metabolite excretion after thrombolysis
A2
Fibrinolytic therapy is a major advance in the treatment of coronary artery disease. A marked elevation in plasma and urinary metabolites of thromboxane A2 (TXA2 ) after administration of thrombolytic therapy has been observed and has been related to a direct effect of thrombolytic drugs on platelets. To test this hypothesis we evaluated the 1 1-dehydrothromboxane B2 (1 l-d-TXB2) level, as an index of platelet activation, in 20 healthy subjects and in 30 patients with acute myocardial infarction (AM). Patients with infarction received streptokinase (n = 8), recombinant tissue-type plasminogen activator (rt-PA) (n = 8), or thrombolytic therapy preceded by acetylsalicylic acid (n = 7) or were treated without thrombolytic therapy (n = 7). The urinary 1 l-d-TXB2 level in healthy control subjects was 327 + 128 pg/mg creatinine. A significant increase was observed in patients with AMI with no difference between those who received no thromboiytic therapy (873 -t 283 pg/mg creatinine in the first 12 hours) and those who received streptokinase (833 + 813 pg/mg creatinine) or rt-PA (838 ? 853 pg/mg creatinine). Patients pretreated with acetylsalicylic acid had urinary 1 I-d-TXB2 values ranging between 381 and 155 pg/mg creattnine. A significant difference in 1 l-d-TXB2 values was observed only when patients who were reperfused were separated from those who remained occluded according to angiographic criteria (1085 + 498 vs 391 + 227 pg/mg creatinine in the first 12 hours, p < 0.001). We conclude that reperfusion and not thrombolytic agents per se appears to be the factor that induces platelet activation and consequently facilitates reocclusion. (AM HEART J 1992; 123:580.)
Antonio Giuseppe Rebuzzi, MD, Andrea Santino Albanese, MD, Gaetano Antonio Giovanni Ciabattoni, MD. Rome, Italy
Natale, MD, Claudio Bianchi, MD, Lanza, MD, Elda Coppola, MD, and
The goal of thrombolytic therapy is to restore coronary artery flow in the shortest possible time to prevent or limit myocardial necrosis. However, thrombolytic therapy is limited by failure to reperfuse the occluded artery in up to 50% of patients1 and by reocclusion in up to 30 % of the initially reperfused patients. Thus the ideal thrombolytic drug should produce the highest rate of reperfusion but also the lowest rate of reocclusion. The mechanisms of delayed or unsuccessful reperfusion and reocclusion are not completely understood, but studies on experimental models strongly suggest a role for platelets. 2-4Provocative experimental and clinical studies5-g have suggested an increase in platelet activation and in thrombin activity after
From the Institute the Sacred Heart.
of Cardiology
Supported
by grant
Received
for publication
73501
from April
and Pharmacology, the Ministry 15, 1991;
Catholic
University
of Education.
accepted
Sept.
3, 1991.
Reprint requests: Antonio G. Rebuzzi, MD, Istituto di Cardiologia, Universita’ Cattolica de1 S. Cuore, L.go A. Gemelli, 8, 00168 Roma, Italy. 4/l/34417
580
of
thrombolysis. Fitzgerald et a1.5 observed a marked elevation in plasma and urinary metabolites of thromboxane A2 (TXA2) after administration of streptokinase in six patients with acute myocardial infarction (AMI). An increase in thromboxane biosynthesis during coronary thrombolysis with intravenous tissue-type plasminogen activator (rt-PA) in a chronic canine model of coronary thrombosis was also observed.‘O In another study6 an increase in fibrinopeptide A (which is released by the action of thrombin on fibrinogen) has been shown after thrombolytic therapy with streptokinase in patients with AMI. Although these studies may suggest a direct stimulative effect of thrombolysis on platelet activity, some investigators believe that the prothrombotic events seen after thrombolysis may reflect the thrombogenic effect exerted by the residual thrombus on both platelet@ and thrombin activity.” In this study we evaluated urinary 11-dehydrothromboxane B2 (ll-d-TXBz) as an index of platelet activation12 in patients with AM1 treated with intravenous streptokinase or rt-PA, and compared them with patients treated with aspirin and thrombolysis and patients not treated with thrombolytic agents.
Volume
123
Number
3
METHODS The study consisted of 50 subjects: 20 healthy subjects and 30 patients admitted to the coronary care unit of our hospital with ECG and symptomatic evidence of AMI. Patients were excluded if they had received any antiaggregating agents or anticoagulant therapy in the last 10 days, had a history of previous AMI, had symptoms for longer than 6 hours before entering the coronary care unit, or were more than 75 years of age. Four groups of patients were considered for the study. Group 1 consisted of eight patients who received streptokinase administered intravenously in a dose of 1,500,OOO units over 60 minutes. Group 2 consisted of eight patients who were given an intravenous bolus of 10 mg of rt-PA (Actilyse, Boehringer Ingelheim, Florence, Italy) followed by intravenous infusion of 50 mg in the first hour and 40 mg over the next 2 hours. Group 3 included seven consecutive patients with AMI, who had contraindications to thrombolytic therapy13 and were treated with conventional therapy (not thrombolysis or aspirin). Finally, to exclude the possibility that an increase in TXA2 metabolite excretion could reflect the metabolism of preformed inactive TXBz washed out from the coronary circulation and not an increase in TXAs biosynthesis, we also evaluate urinary excretion of ll-d-TXBs in seven patients with AM1 treated with thrombolytic therapy (rt-PA in three patients and streptokinase in four) after the administration of an intravenous bolus of acetylsalicylic acid (250 mg) (group 4). Consecutive patients with AM1 who received thrombolytic therapy were randomly allocated to groups 1,2, and 4. Heparin (a bolus of 5000 U followed by 20,000 to 30,000 U/day by continuous drip) was started at the end of thrombolysis in all of the patients, and infusion was maintained according to activated partial thromboplastin time to achieve therapeutic anticoagulation (prolongation of activated partial thromboplastin time to 1.5 to 2.5 the normal values). In all patients plasma creatine kinase levels were determined every 4 hours during the first 36 hours. Urine was collected from the patients every 12 hours up to 72 hours for determination of ll-d-TXBs values, one of the most abundant enzymatic metabolites of TXAs.i4 Urine from 20 healthy subjects (aged 27 to 70 years) was also collected over a 12-hour period for determination of ll-d-TXBz values in a control group. None of them was taking any drugs. All urine samples were immediately frozen and kept at -40° C until assay. Coronary angiography was performed in all patients 5 to 7 days after the onset of AMI, and on the basis of the results patients were divided into those who were reperfused and those who were not. Evidence of reperfusion was also evaluated in the acute phase according to the following indirect criteria: time to peak creatine kinase less than 12 hours and/or sudden normalization of ST segment after the start of thrombolytic infusion (within 1 hour).15-17 The protocol was approved by the ethics committee of our institution, and all the subjects gave informed consent. Urinary l l-d-TXB2 assay. Measurement of urinary ll-
Thrombolysis-reperfusion
Table
I. Main Clinical
Age
clinical data
(yr)
Sex (M/F) Location of AM1 Anterior Inferior Secondary diagnosis Hypertension Diabetes Hyperlipidemia Additional medication Diuretics P-Blockers Calcium antagonists Lidocaine Hospital death
on thromboxane
56 1
data of patients Group 1
Group 2
Group 3
Group 4
64 + 3 618
60 f 2 718
61 k 6 517
65 + 4 717
6 2
7 1
6 1
7 3
2
1
1
2
3
3 2
1
3
3 2
2 2
3 3
3 3
3
2
-
-
2 1
-
1
3
-
Group 1, Streptokinase-treated patients; group 2, rt-PA-treated patients; group 3, patients not treated with thrombolysis or aspirin; group 4, patients treated with aspirin and thrombolytic therapy.
d-TXBs was performed by previously validated radioimmunoassay techniques.1s-21 Immunoreactive ll-d-TXBz was extracted from 20 ml aliquots of each urine specimen collected (pH adjusted to 4.0 to 4.5 with formic acid) run on SEP-PAK Cl8 cartridges (Waters Associates, Milford, Mass,), and eluted with ethyl acetate. The eluate was subjected to silicic acid column chromatography and further eluted with benzene:ethyl acetate:methanol (60:40:30). The overall recovery rate, as assessed by Il-d-(3H)-TXBs levels, averaged 80 f 6%. Immunoreactive ll-d-TXBs eluted in the radioimmunoassay system from silicic acid columns was assayed at a final dilution of 1:15 to 1:lOOO. ll-d-(3H)-TXBs (160 Ci/nmol) was purchased by Amersham Corp. (Arlington Heights, Ill.). The authentic ll-dTXBs employed as a standard was provided by The Upjohn Co. (Kalamazoo, Mich.). The urinary creatinine value was determined in every urine specimen collected, and the results are reported in picograms of urinary ll-d-TXBs per milligram of creatinine. Statistical analysis. Results were analyzed by means of analysis of variance with Student-Newman-Keuls test for multiple comparisons. The t test for unpaired data was utilized for comparison of two groups when indicated. The chi-square test for contingency tables 2 x 4 was used for ratio comparisons. All values are reported as means + SD: Statistical significance was defined as p < 0.05. RESULTS Clinical data of the patients with AM1 are shown in Table I. Age distribution was similar in the four groups, and there were no significant differences among groups with regard to infarct location, secondary diagnosis, or additional medication. None of the patients underwent cardiac catheterization dur-
562
Rebuzzi
et al.
American
U-d-TX82
(pg/mg
March 1992 Heart Journal
creatinine)
800 600
o-12
12-24
24-36
36-48
48-60
60-72
HOURS m
Group
1
m
Group
2
/Group
3
Group
4
Fig. 1. Urinary ll-d-TXBZ in patients with AM1 after streptokinase (group I), rt-PA (group 2), no treatment (group 3), and thrombolytic therapy and aspirin (group 4). No significant differenceswere observed among groups 1, 2, and 3. Aspirin prevented increasein TXBz observed in other groups.
II. Clinical findings of patients
Table
Onsetof
Group 1 2 3 4
symptoms to therapy (min) 150 176 198 144
+ f ? rf:
71 87 96 102
Peak CK (U/L) 2,973 3,915 3,287 2,976
+ * + ?I
950 1,577 1,541 1,134
Time to peak CK (hr) 12.4 11.3 17.3 10.1
f * + i-
8.8 7.7 6.7 6.1
For description of groups, see Table I. CK, Creatine kinase.
ing the period of sample collection. None of the patients died during the study period, but one patient treated with streptokinase died of myocardial rupture on the eleventh day after the acute event. None of the patients had cardiogenic shock or pulmonary edema. There were no differences among the groups with regard to time from the onset of symptoms to therapy or time to peak of the creatine kinase level (Table II). Coronary angiography performed 5 to 7 days after the acute event demonstrated vessel patency in four patients in group l(50 % ), five in group 2 (71%), two in group 3 (28%), and six in group 4
(86%). Evidence of early reperfusion based on indirect criteria was observed in four patients in group 1
(50%)), six in group 2 (75%), one in group 3 (14%), and six in group 4 (86%). Indirect criteria correctly identified all reperfused and nonreperfused patients in groups 1 and 4, whereas only one patient in group 2 and one in group 3 were not correctly classified as reperfused or nonreperfused by indirect criteria. Thus a substantial agreement was observed between results of coronary angiography performed late after thrombolysis and reperfusion evaluated in the acute phase of myocardial infarction by indirect criteria. The urinary ll-d-TXBZ level in the 20 healthy control subjects was 327 + 126 pg/mg creatinine. In patients with AM1 who did not receive thrombolytic therapy (group 3)) a significant increase was observed in the first 12 hours (673 * 283 pg/mg creatinine, p < 0.001). Also patients in groups 1 and 2 showed an increase in urinary ll-d-TXB:! values (833 t 613 and 836 t 653 pg/mg creatinine, respectively, in the first urine specimens collected) that were significantly higher than the values measured in normal subjects (p < 0.001 and p < 0.002, respectively). Conversely, the differences in ll-d-TXBZ values among groups 1, 2, and 3 were not significant (Fig. 1). However, when the 11 patients in groups 1, 2, and 3 who were reperfused were compared with the 12 patients in the same groups who remained occluded according to angiographic criteria, a significant difference in ll-d-TXBZ values was found in all urine specimens (Fig. 2). Similar results were obtained in
Volume
123
Number
3
Thrombolysis-reperfusion
11-d-TxB2
(pg/mg
on thromboxane
563
creatinine)
1400 1200 1000 800 600 400 200 0
I
o-12
12-24
36-48
24-36
48-60
60-72
HOURS m
Reperfused
pts.
b%# Not reperfused
pts.
2. Urinary ll-d-TXBZ in reperfusedand nonreperfusedpatients with AM1 who were not treated with aspirin (groups 1,2, and 3). Values were significantly higher in reperfusedpatients independent of thrombolytic therapy. Fig.
a comparison of only nine reperfused and seven nonreperfused patients treated with thrombolytic agents (groups 1 and 2). Finally, no significant difference in ll-d-TXBs excretion was found both between the subgroups of patients treated with streptokinase or rt-PA who were reperfused and between the subgroups of patients treated with the two thrombolytic drugs who were not reperfused (Fig. 3). Patients pretreated with aspirin (group 4) had urinary ll-d-TXBs values ranging from 155 to 361 pglmg creatinine, which turned out to be significantly lower than the values in patients receiving only thrombolytic therapy (groups 1 and 2) (Table III); notwithstanding, reperfusion occurred in six of seven patients treated with aspirin. The values for urinary ll-d-TXBs detected in the first 12 hours in this group were not significantly different from those in normal subjects. In the other three groups urinary ll-d-TXBs excretion returned to values in the normal range within 60 to 72 hours after AMI. DISCUSSION
Results of our study show an increase in urinary excretion of ll-d-TXBs during the first 36 to 48 hours and a return to normal values by day 3 in all patients with AM1 who were not pretreated with aspirin. Although in patients who received thrombolytic therapy (groups 1 and 2) there was a higher increase in TXAs metabolites compared with values in patients
Ill. Urinary ll-d-TXBZ in patients with AM1 who received only thrombolytic therapy (groups 1 and 2) and patients who received aspirin and thrombolytic therapy Table
(group
Hours o-12 12-24 24-36 36-48 48-60 60-72
4) Thrombolysis (groups l-2) 834 703 923 827 656 379
rt t + f t t
633 477 767 767 571 145
Thrombolysis aspirin (group 4) 239 361 200 191 159 155
k + + + -t k
165 276 100 70 68 54
+ p Value 0.02 0.09 0.02 0.04 0.03 0.0001
not receiving thrombolytic infusion (group 3), the difference was not significant. Neither has a significant difference been shown between patients who received either streptokinase or rt-PA. On the other hand, significantly higher ll-d-TXB2 values were observed when reperfused and nonreperfused patients were compared. This finding was independent of the type of thrombolytic drug, inasmuch as no difference was found in ll-d-TXBZ values between those patients in groups 1 and 2 who were reperfused and those in the two groups who were not reperfused (Fig. 3). Therefore our data suggest that not thrombolytic therapy itself but a residual stenosis at the site of clot
564
Rebuzzi
ltd-7x82 4
lW9
et al.
(pg/mg
American
cralnhw)
1400 1200 1000 000 wo 400 200 0 12-24
24-M
30-48
80-72
48-60
00-72
48-00
HOURS m
ii-d-lx82
Stroptokln~r*
tBrt-PA
(pg/mgcrrtlnlnd
1000 I 1400 1200 1000 800 800 400 200 0 12-24
24-30
30-48
HOURS m
Stnptokln~r*
FB rt-PA
3. Urinary ll-d-TXB2 in patients treated with streptokinase or rt-PA with coronary patency (upper panel) or coronary occlusion (lower panel) at late angiography.
Fig.
lysis probably plays a major role in the observed higher platelet activation. As an alternative, platelet activation after restoration of vessel patency might be a reaction resulting from the release of toxic metabolites accumulated at the site of occlusion or a consequence of reperfusion damage related to oxygen-derived free radicals increased at the time of reperfusion.22s23 In addition, our data indicate that aspirin given intravenously immediately before thrombolytic infusion (group 4) completely prevented the increase in TXAs metabolites observed in the other groups, although a higher rate of reperfusion occurred. To our knowledge this is the first study in which consecutive patients were randomly assigned to different treatment groups and urine and blood samples were collected following the same protocol. Our data do not completely agree with those of other investigators who demonstrated a marked increase in urinary 2,3-dinor-TXBs in patients with AM1 treated with streptokinase5 or rt-PA24 com-
March1992 Heart Journal
pared with patients not receiving thrombolytic therapy. Our different results may be due to the fact that in previous studies patients with AM1 treated without thrombolytic therapy were included later than the treated patients and their urinary metabolite excretion peak may have occurred before they were admitted to the study. Control patients also differed in that the majority of them did not receive heparin, which has been shown to activate platelets in vitro, although it has also been demonstrated that heparin does not alter TXAz biosynthesis in humans.“4 Our findings might also be related to the fact that we measured urinary ll-d-TXBs differently from Fitzgerald et al., 5,lo who analyzed urinary 2,3-dinorTXBz and plasmatic ll-d-TXBs. However, a similar pattern in urinary and plasma concentrations of lld-TXB2 has been demonstrated during infusion of TXBz at the same rate into healthy male volunteers.25 On the other hand, it is well known that TXB2 has two major pathways of metabolism in humans: P-oxidation, resulting in the formation of 2, 3-dinorTXB2, and dehydrogenation, resulting in the formation of ll-d-TXB2. Although 2, 3-dinor-TXBz was originally described as the prevailing pathway of enzymatic degradation of infused TXB2 in humans, it has recently been demonstrated that ll-d-TXB:! has a substantially longer plasma half-life (i.e., 45 minutes vs 15 minutes)14 and is at least as abundant a conversion product of exogenously infused TXBz as262 3-dinor-TXBs . Alihough in the above-mentioned studies, human platelets incubated with streptokinase seemed to show an enhancement of the sensitivity to aggregation inducers,5s27it has also been reported that human platelets incubated with streptokinase or rt-PA lose their ability to aggregate in response to adenosine diphosphate and collagen.28-32On the other hand, the fact that two thrombolytic agents (one with a direct and one with an indirect mechanism of action on plasminogen) have the same effect on TXAs metabolite production may support the hypothesis that activation of platelets may occur mostly because of the exposure of platelets to the injured vascular bed after reperfusion and not because of a direct action of streptokinase and rt-PA on platelet aggregation. Our data comparing reperfused and nonreperfused patients seem to confirm this hypothesis. Limitations of the study. A possible limitation of our study might be constituted by the fact that we do not have information on pretreatment coronary vessel anatomy. Consequently we cannot directly attribute restoration of blood flow in the occluded vesselsto the effect of thrombolytic therapy. Furthermore, we performed coronary angiography late after AM1 (5 to 7
Volume Number
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Thrombolysis-reperfision
days) so we cannot exclude the possibility of spontaneous delayed reperfusion. However, this is unlikely since reperfusion established in the acute phase according to an early (less than 12 hours) peak in the creatinine kinase level and ECG criteria15-17 occurred essentially in the same patients who showed a patent vessel at angiography. In addition, in one patient in the group that did not receive thrombolytic therapy (group 3), we observed an early peak in the creatinine kinase level and restored vessel flow, suggesting early reperfusion associated with two- to threefold higher excretion of urinary ll-d-TXB2 with respect to the other subjects in the same group. Thus our data indicate that platelet activation seems to occur as new surfaces are exposed on the clot during thrombolysis and/or by reperfusion of the injured vascular bed and not because of a direct effect of thrombolytic drugs. However, although our data support this hypothesis, further studies are needed to confirm these observations. Conclusions. Thrombolytic infusion does not seem to significantly increase urinary ll-d-TXBs excretion and therefore platelet aggregation unless reperfusion occurs. Thus reperfusion and not thrombolytic agents per se turns out to be the most important factor inducing platelet activation and consequently facilitating reocclusion. Aspirin administration appears to be effective in reducing the extent of this phenomenon. We thank the nursing able assistance.
staff of our coronary
care unit
for invalu-
REFERENCES
1. TIM1 Study Group. The Thrombolysis in Myocardial Infarction trial: phase 1 findings. N Engl J Med 1985;312:932-6. 2. Yasuda T, Gold HL, Fallon JT, Leinbach RC, Guerrero JL, Scudder LE, Kanke M, Shealy D, Ross MJ, Collen D, Coller BS. Monoclonal antibody against the platelet glycoprotein (GP) IIb/IIIa receptor prevents coronary artery reocclusion after reperfusion with recombinant tissue-type plasminogen activator in dogs. J Clin Invest 1988;81:1284-91. 3. Gold HK, Coller BS, Yasuda T, Saito T, Allon JT, Guerrero JL, Leinbach RC, Ziskind AA, Collen D. Rapid and sustained coronary artery recanalization with combined bolus injection of recombinant tissue-type plasminogen activator and monoclonal antiplatelet GPIIbiIIIa antibody in a canine preparation. Circulation 1988;77:670-7. 4. Golino P, Ashton JH, Glas-Greenwalt P, McNatt J, Buja LM, Willerson JT. Mediation of reocclusion by thromboxane As and serotonin after thrombolysis with tissue-type plasminopen activator in a canine preparation of coronary thrombosis. Circulation 1988;77:678-84. 5. Fitzgerald DJ. Catella F. Rov L. FitzGerald GA. Marked platilet activation in vitro after intravenous streptokinase in patients with acute myocardial infarction. Circulation 1988; 77~142-54. 6. Eisenberg PR, Sherman LA, Jaffe AS. Paradoxic elevation of fibrinopeptide A after streptokinase: evidence for continued thrombosis despite intense fibrinolysis. J Am Co11 Cardiol 1987;10:527-9.
on thromboxane
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7. Vaughan DE, Kirshenbaum JM, Loscalzo J. Streptokinaseinduced antibody-mediated platelet aggregation: a potential cause of clot propagation in vivo. J Am Co11 Cardiol 1988;11:1343-8. 8. Fitzgerald DJ, Roy L, Wright F, FitzGerald GA. Functional significance of platelet activation following coronary thrombolysis [Abstract]. Circulation 1987;76(suppl IV):IV-151. 9. Ohlstein EH, Shebuski RJ. Tissue-type plasminogen activator (tPA) increases plasma thromboxane levels which is associated with platelet hyperaggregation [Abstract]. Circulation 1987;76(suppl IV):IV-100. 10. Fitzgerald DJ, Wright F, FitzGerald GA. Increased thromboxane biosynthesis during coronary thrombolysis. Evidence that platelet activation and thromboxane Az modulate the response to tissue-type plasminogen activator in vivo. Circ Res 1989;65:83-94. 11. Francis CW, Markham RE, Barlow GH, Florack TM, Dobrzynsky DM, Marder VJ. Thrombin activity of fibrin thrombi and soluble plasmic derivatives. J Lab Clin Med 1983;102:220-30. 12. Fitzeerald DJ. Rov L. Catella F. Fitzgerald GA. Platelet activation in unstable coronary diseasi N Engl J Med 1986; 315:983-9. 13. Guidelines for the early management of patients with acute myocardial infarction. Circulation 1990;82:664-707. 14. Lawson JA, Patron0 C, Ciabattoni G, FitzGerald GA. Longlived enzymatic metabolites of thromboxane Az in the human circulation. Anal Biochem 1986,155:198-205. 15. The ISAM Study Group. A prospective trial of intravenous streptokinase in acute myocardialinfarction (ISAM). Mortality, morbidity, and infarct size at 21 davs. N Enel J Med 1986;314:1465-71. 16. Hogg KJ, Hornung RS, Howie CA, Hockings N, Dunn FG, Hillis WS. Electrocardiogrpahic prediction of coronarv arterv patency after thromboly% treatment in acute myocardial in”farction: use of the ST segment as a noninvasive marker. Br Heart J 1988;60:275-80. 17. Zabel M, Hohnloser SH, Kasper W, Meinertz T, Just H. Combined analysis of three noninvasive markers for better prediction of reperfusion after thrombolytic therapy for acute myocardial infarction. J Am Co11 Cardiol 1991;17:67A. 18. Ciabattoni G, Maclouf J, Catella F, FitzGerald GA, Patron0 C. Radioimmunoassay of ll-dehydrothromboxane Bz in human plasma and urine. Biochim Biophys Acta 1987;918:293-7. 19. Patron0 C, Ciabattoni G, Remuzzi G, Gotti E, Bombardieri S, Di Munno 0, Tartarelli G. Cinotti GA. Simonetti BM. Pierucci A. Functional significance of renal prostacyclin and thromboxane AZ production in patients with systemic lupus erythematosus. J Clin Invest 1985;76:1011-8. 20. Ciabattoni G, Pugliese F, Davi G, Pierucci A. Simonetti BM, Patron0 C. Fractional conversion of thromboxane Bs in man. Biochim Biophvs Acta 1989:992:66-70. 21. Ciabattoni G; Patrignani P, Patron0 C. Radioimmunoassay of ll-dehydro-thromboxane Bz. In: Murphy RC, Fitzpatrick FA, eds. Methods in enzymology. New York: Academic Press, Inc, 1987:34-41. 22. Lucchesi BR. Modulation of leukocyte-mediated myocardial reperfusion injury. Annu Rev Physiol 1990;52:561-76. 23. Fox KAA. Thrombolysis: adjuvant therapy and the role of complement. Eur Heart J 199O;ll(suppl F):36-42. 24. Kerins DM. Rov L. Fitzgerald GA. FitzGerald DJ. Platelet and vascular function during coronary thrombolysis with tissuetype plasminogen activator. Circulation 1989;80:1718-25. 25. Patron0 C. Thromboxane biosynthesis and metabolism in health and disease. In: Strano A, Novo S, eds. Advances in vascular pathology. Amsterdam: Elsevier Science Publishers BV, 19891407-10. 26. Ciabattoni G, Pugliese F, Davi G, Pierucci A, Simonetti BM, Patron0 C. Fractional conversion of thromboxane Bs to lldehydrothromboxane Bz in mm. Biochim Biophys Acta 1989; 992:66-70. 27. Griguer P, Brochier M, Leroy J, et al. Platelet aggregation after thrombolytic therapy. Angiology 1980;31:91-9.
Rebuzzi et al. 28. Fry ETA, Grace AM, Sobel BE. Interactions between pharmacologic concentrations of plasminogen activators and platelets. Fibrinolysis 1989;3:127-36. 29. Mizuta T, Imai C. Tissue-type plasminogen activator inhibits aggregation of platelets in vitro. Life Sci 1988;43:955-63. 30. Loscalzo J, Vaughan DE. Tissue plasminogen activator promotes platelet disaggregation in plasma. J Clin Invest 1987; 79:1749-55.
American
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31. Grace AM, Fry ETA, Sobel BE. Decreased aggregation of platelets induced by exposure to pharmacologic concentrations of t-PA in whole blood. Circulation 1987;76(suppl IV):307-11. 32. Hoffmann JJML. Blood viscosity and platelet function in thrombolytic therapy of acute myocardial infarction. Eur Heart J 199O;ll(suppl F):29-35.
Regional redistribution of myocardial by UL-FS 49, a selective bradycardic
perfusion agent
The effects of UL-FS 49, a specific bradycardlc agent, on systemic hemodynamics, regional myocardial function (sonomicrometry, percentage of segment shortening), and regional coronary blood flow (radioactive microspheres) were studied in open-chest, anesthetized dogs with severe left circumflex cororiary artery (LCX) stenosis. UL-FS 49 was admlnlstered as two sequential bolus injections of 0.25 mg/kg. Heart rate decreased from 149 + 13 beats/min to 102 + 6 and 77 f. 4 beats/min after 0.25 and 0.5 mg/kg cumulative doses of UL-FS 49, respectively. The reduction in heart rate was not associated with any significant change in left ventricular pressure or mean arterial pressure, left ventricular dp/dt, or coronary vascular resistance. Similarly no hemodynamic changes occurred with atrial pacing to the initial heart rate. Application of an LCX stenosis of sufficient severity to produce a 50% reduction in mean LCX blood flow (44 + 4 to 22 + 2 ml/min) resulted in a significant reduction in the percentage of segment shortening in the ischemic zone (9.8 + 1.6% to 6.5 + 1.1%). The percentage of segment shortening in the ischemic zone progressively improved to 8.4 f 1.2% and 9.4 + 0.5% after 0.25 and 0.5 mg/kg UL-FS 49, respectively. Subepicardial perfusion in the ischemic zone was decreased and subendocardial perfusion was increased after administration of UL-FS 49. Consequently the ischemic zone endocardial/epicardlal ratio increased from 0.43 2 0.08 to 1.12 ? 0.22 and 1.48 t 0.32 with low and high doses of UL-FS 49. Atrial pacing to the control heart rate abolished the effects of UL-FS 49 on regional myocardial blood flow and percentage of segment shortening. These data indicate that UL-FS 49 is a selective bradycardlc agent that can improve ischemic myocardlal function distal to severe coronary stenosis. The data suggest that UL-FS 49 Improves the relationship between myocardial oxygen supply and demand by negative chronotropic actions and by favorably redistributing ischemic blood flow. (AM HEART J 1992;123:566.)
Patrick Harold
O’Brien, MD, David Drage, BA, Kooroush Saeian, MD, L. Brooks, MD, and David C. Warltier, MD, PhD. Milwaukee,
Heart rate is a major determinant of myocardial oxygen demand.lM3 It has been demonstrated that regional myocardial contractile dysfunction, ECG ab-
From the Departments of Medicine/Division of Cardiology, Anesthesiology, and Pharmacology, Medical College of Wisconsin. Received for publication April 15, 1991; accepted Aug. 12, 1991. Reprint requests: David C. Warltier, MD, PhD, Medical College of Wisconsin, MFRC, Room AlOOO, 8701 W. Watertown Plank Rd., Milwaukee, WI 53226. 4/l/34416
566
Wis.
normalities, and altered myocardial lactate metabolism accompany atria1 pacing-induced elevations of heart rate.4-7 Thus pharmacologic reduction of heart rate represents an important form of therapy in patients with coronary artery disease. Two classes of drugs, /3-adrenergic receptor antagonists and slow inward calcium channel-blocking agents, are frequently used in the treatment of ischemic heart disease. The effects of bradycardia produced by these drugs on blood flow to an ischemic zone and myocardial function have been studied in both conscious and
A2
Fibrinolytic therapy is a major advance in the treatment of coronary artery disease. A marked elevation in plasma and urinary metabolites of thromboxane A2 (TXA2 ) after administration of thrombolytic therapy has been observed and has been related to a direct effect of thrombolytic drugs on platelets. To test this hypothesis we evaluated the 1 1-dehydrothromboxane B2 (1 l-d-TXB2) level, as an index of platelet activation, in 20 healthy subjects and in 30 patients with acute myocardial infarction (AM). Patients with infarction received streptokinase (n = 8), recombinant tissue-type plasminogen activator (rt-PA) (n = 8), or thrombolytic therapy preceded by acetylsalicylic acid (n = 7) or were treated without thrombolytic therapy (n = 7). The urinary 1 l-d-TXB2 level in healthy control subjects was 327 + 128 pg/mg creatinine. A significant increase was observed in patients with AMI with no difference between those who received no thromboiytic therapy (873 -t 283 pg/mg creatinine in the first 12 hours) and those who received streptokinase (833 + 813 pg/mg creatinine) or rt-PA (838 ? 853 pg/mg creatinine). Patients pretreated with acetylsalicylic acid had urinary 1 I-d-TXB2 values ranging between 381 and 155 pg/mg creattnine. A significant difference in 1 l-d-TXB2 values was observed only when patients who were reperfused were separated from those who remained occluded according to angiographic criteria (1085 + 498 vs 391 + 227 pg/mg creatinine in the first 12 hours, p < 0.001). We conclude that reperfusion and not thrombolytic agents per se appears to be the factor that induces platelet activation and consequently facilitates reocclusion. (AM HEART J 1992; 123:580.)
Antonio Giuseppe Rebuzzi, MD, Andrea Santino Albanese, MD, Gaetano Antonio Giovanni Ciabattoni, MD. Rome, Italy
Natale, MD, Claudio Bianchi, MD, Lanza, MD, Elda Coppola, MD, and
The goal of thrombolytic therapy is to restore coronary artery flow in the shortest possible time to prevent or limit myocardial necrosis. However, thrombolytic therapy is limited by failure to reperfuse the occluded artery in up to 50% of patients1 and by reocclusion in up to 30 % of the initially reperfused patients. Thus the ideal thrombolytic drug should produce the highest rate of reperfusion but also the lowest rate of reocclusion. The mechanisms of delayed or unsuccessful reperfusion and reocclusion are not completely understood, but studies on experimental models strongly suggest a role for platelets. 2-4Provocative experimental and clinical studies5-g have suggested an increase in platelet activation and in thrombin activity after
From the Institute the Sacred Heart.
of Cardiology
Supported
by grant
Received
for publication
73501
from April
and Pharmacology, the Ministry 15, 1991;
Catholic
University
of Education.
accepted
Sept.
3, 1991.
Reprint requests: Antonio G. Rebuzzi, MD, Istituto di Cardiologia, Universita’ Cattolica de1 S. Cuore, L.go A. Gemelli, 8, 00168 Roma, Italy. 4/l/34417
580
of
thrombolysis. Fitzgerald et a1.5 observed a marked elevation in plasma and urinary metabolites of thromboxane A2 (TXA2) after administration of streptokinase in six patients with acute myocardial infarction (AMI). An increase in thromboxane biosynthesis during coronary thrombolysis with intravenous tissue-type plasminogen activator (rt-PA) in a chronic canine model of coronary thrombosis was also observed.‘O In another study6 an increase in fibrinopeptide A (which is released by the action of thrombin on fibrinogen) has been shown after thrombolytic therapy with streptokinase in patients with AMI. Although these studies may suggest a direct stimulative effect of thrombolysis on platelet activity, some investigators believe that the prothrombotic events seen after thrombolysis may reflect the thrombogenic effect exerted by the residual thrombus on both platelet@ and thrombin activity.” In this study we evaluated urinary 11-dehydrothromboxane B2 (ll-d-TXBz) as an index of platelet activation12 in patients with AM1 treated with intravenous streptokinase or rt-PA, and compared them with patients treated with aspirin and thrombolysis and patients not treated with thrombolytic agents.
Volume
123
Number
3
METHODS The study consisted of 50 subjects: 20 healthy subjects and 30 patients admitted to the coronary care unit of our hospital with ECG and symptomatic evidence of AMI. Patients were excluded if they had received any antiaggregating agents or anticoagulant therapy in the last 10 days, had a history of previous AMI, had symptoms for longer than 6 hours before entering the coronary care unit, or were more than 75 years of age. Four groups of patients were considered for the study. Group 1 consisted of eight patients who received streptokinase administered intravenously in a dose of 1,500,OOO units over 60 minutes. Group 2 consisted of eight patients who were given an intravenous bolus of 10 mg of rt-PA (Actilyse, Boehringer Ingelheim, Florence, Italy) followed by intravenous infusion of 50 mg in the first hour and 40 mg over the next 2 hours. Group 3 included seven consecutive patients with AMI, who had contraindications to thrombolytic therapy13 and were treated with conventional therapy (not thrombolysis or aspirin). Finally, to exclude the possibility that an increase in TXA2 metabolite excretion could reflect the metabolism of preformed inactive TXBz washed out from the coronary circulation and not an increase in TXAs biosynthesis, we also evaluate urinary excretion of ll-d-TXBs in seven patients with AM1 treated with thrombolytic therapy (rt-PA in three patients and streptokinase in four) after the administration of an intravenous bolus of acetylsalicylic acid (250 mg) (group 4). Consecutive patients with AM1 who received thrombolytic therapy were randomly allocated to groups 1,2, and 4. Heparin (a bolus of 5000 U followed by 20,000 to 30,000 U/day by continuous drip) was started at the end of thrombolysis in all of the patients, and infusion was maintained according to activated partial thromboplastin time to achieve therapeutic anticoagulation (prolongation of activated partial thromboplastin time to 1.5 to 2.5 the normal values). In all patients plasma creatine kinase levels were determined every 4 hours during the first 36 hours. Urine was collected from the patients every 12 hours up to 72 hours for determination of ll-d-TXBs values, one of the most abundant enzymatic metabolites of TXAs.i4 Urine from 20 healthy subjects (aged 27 to 70 years) was also collected over a 12-hour period for determination of ll-d-TXBz values in a control group. None of them was taking any drugs. All urine samples were immediately frozen and kept at -40° C until assay. Coronary angiography was performed in all patients 5 to 7 days after the onset of AMI, and on the basis of the results patients were divided into those who were reperfused and those who were not. Evidence of reperfusion was also evaluated in the acute phase according to the following indirect criteria: time to peak creatine kinase less than 12 hours and/or sudden normalization of ST segment after the start of thrombolytic infusion (within 1 hour).15-17 The protocol was approved by the ethics committee of our institution, and all the subjects gave informed consent. Urinary l l-d-TXB2 assay. Measurement of urinary ll-
Thrombolysis-reperfusion
Table
I. Main Clinical
Age
clinical data
(yr)
Sex (M/F) Location of AM1 Anterior Inferior Secondary diagnosis Hypertension Diabetes Hyperlipidemia Additional medication Diuretics P-Blockers Calcium antagonists Lidocaine Hospital death
on thromboxane
56 1
data of patients Group 1
Group 2
Group 3
Group 4
64 + 3 618
60 f 2 718
61 k 6 517
65 + 4 717
6 2
7 1
6 1
7 3
2
1
1
2
3
3 2
1
3
3 2
2 2
3 3
3 3
3
2
-
-
2 1
-
1
3
-
Group 1, Streptokinase-treated patients; group 2, rt-PA-treated patients; group 3, patients not treated with thrombolysis or aspirin; group 4, patients treated with aspirin and thrombolytic therapy.
d-TXBs was performed by previously validated radioimmunoassay techniques.1s-21 Immunoreactive ll-d-TXBz was extracted from 20 ml aliquots of each urine specimen collected (pH adjusted to 4.0 to 4.5 with formic acid) run on SEP-PAK Cl8 cartridges (Waters Associates, Milford, Mass,), and eluted with ethyl acetate. The eluate was subjected to silicic acid column chromatography and further eluted with benzene:ethyl acetate:methanol (60:40:30). The overall recovery rate, as assessed by Il-d-(3H)-TXBs levels, averaged 80 f 6%. Immunoreactive ll-d-TXBs eluted in the radioimmunoassay system from silicic acid columns was assayed at a final dilution of 1:15 to 1:lOOO. ll-d-(3H)-TXBs (160 Ci/nmol) was purchased by Amersham Corp. (Arlington Heights, Ill.). The authentic ll-dTXBs employed as a standard was provided by The Upjohn Co. (Kalamazoo, Mich.). The urinary creatinine value was determined in every urine specimen collected, and the results are reported in picograms of urinary ll-d-TXBs per milligram of creatinine. Statistical analysis. Results were analyzed by means of analysis of variance with Student-Newman-Keuls test for multiple comparisons. The t test for unpaired data was utilized for comparison of two groups when indicated. The chi-square test for contingency tables 2 x 4 was used for ratio comparisons. All values are reported as means + SD: Statistical significance was defined as p < 0.05. RESULTS Clinical data of the patients with AM1 are shown in Table I. Age distribution was similar in the four groups, and there were no significant differences among groups with regard to infarct location, secondary diagnosis, or additional medication. None of the patients underwent cardiac catheterization dur-
562
Rebuzzi
et al.
American
U-d-TX82
(pg/mg
March 1992 Heart Journal
creatinine)
800 600
o-12
12-24
24-36
36-48
48-60
60-72
HOURS m
Group
1
m
Group
2
/Group
3
Group
4
Fig. 1. Urinary ll-d-TXBZ in patients with AM1 after streptokinase (group I), rt-PA (group 2), no treatment (group 3), and thrombolytic therapy and aspirin (group 4). No significant differenceswere observed among groups 1, 2, and 3. Aspirin prevented increasein TXBz observed in other groups.
II. Clinical findings of patients
Table
Onsetof
Group 1 2 3 4
symptoms to therapy (min) 150 176 198 144
+ f ? rf:
71 87 96 102
Peak CK (U/L) 2,973 3,915 3,287 2,976
+ * + ?I
950 1,577 1,541 1,134
Time to peak CK (hr) 12.4 11.3 17.3 10.1
f * + i-
8.8 7.7 6.7 6.1
For description of groups, see Table I. CK, Creatine kinase.
ing the period of sample collection. None of the patients died during the study period, but one patient treated with streptokinase died of myocardial rupture on the eleventh day after the acute event. None of the patients had cardiogenic shock or pulmonary edema. There were no differences among the groups with regard to time from the onset of symptoms to therapy or time to peak of the creatine kinase level (Table II). Coronary angiography performed 5 to 7 days after the acute event demonstrated vessel patency in four patients in group l(50 % ), five in group 2 (71%), two in group 3 (28%), and six in group 4
(86%). Evidence of early reperfusion based on indirect criteria was observed in four patients in group 1
(50%)), six in group 2 (75%), one in group 3 (14%), and six in group 4 (86%). Indirect criteria correctly identified all reperfused and nonreperfused patients in groups 1 and 4, whereas only one patient in group 2 and one in group 3 were not correctly classified as reperfused or nonreperfused by indirect criteria. Thus a substantial agreement was observed between results of coronary angiography performed late after thrombolysis and reperfusion evaluated in the acute phase of myocardial infarction by indirect criteria. The urinary ll-d-TXBZ level in the 20 healthy control subjects was 327 + 126 pg/mg creatinine. In patients with AM1 who did not receive thrombolytic therapy (group 3)) a significant increase was observed in the first 12 hours (673 * 283 pg/mg creatinine, p < 0.001). Also patients in groups 1 and 2 showed an increase in urinary ll-d-TXB:! values (833 t 613 and 836 t 653 pg/mg creatinine, respectively, in the first urine specimens collected) that were significantly higher than the values measured in normal subjects (p < 0.001 and p < 0.002, respectively). Conversely, the differences in ll-d-TXBZ values among groups 1, 2, and 3 were not significant (Fig. 1). However, when the 11 patients in groups 1, 2, and 3 who were reperfused were compared with the 12 patients in the same groups who remained occluded according to angiographic criteria, a significant difference in ll-d-TXBZ values was found in all urine specimens (Fig. 2). Similar results were obtained in
Volume
123
Number
3
Thrombolysis-reperfusion
11-d-TxB2
(pg/mg
on thromboxane
563
creatinine)
1400 1200 1000 800 600 400 200 0
I
o-12
12-24
36-48
24-36
48-60
60-72
HOURS m
Reperfused
pts.
b%# Not reperfused
pts.
2. Urinary ll-d-TXBZ in reperfusedand nonreperfusedpatients with AM1 who were not treated with aspirin (groups 1,2, and 3). Values were significantly higher in reperfusedpatients independent of thrombolytic therapy. Fig.
a comparison of only nine reperfused and seven nonreperfused patients treated with thrombolytic agents (groups 1 and 2). Finally, no significant difference in ll-d-TXBs excretion was found both between the subgroups of patients treated with streptokinase or rt-PA who were reperfused and between the subgroups of patients treated with the two thrombolytic drugs who were not reperfused (Fig. 3). Patients pretreated with aspirin (group 4) had urinary ll-d-TXBs values ranging from 155 to 361 pglmg creatinine, which turned out to be significantly lower than the values in patients receiving only thrombolytic therapy (groups 1 and 2) (Table III); notwithstanding, reperfusion occurred in six of seven patients treated with aspirin. The values for urinary ll-d-TXBs detected in the first 12 hours in this group were not significantly different from those in normal subjects. In the other three groups urinary ll-d-TXBs excretion returned to values in the normal range within 60 to 72 hours after AMI. DISCUSSION
Results of our study show an increase in urinary excretion of ll-d-TXBs during the first 36 to 48 hours and a return to normal values by day 3 in all patients with AM1 who were not pretreated with aspirin. Although in patients who received thrombolytic therapy (groups 1 and 2) there was a higher increase in TXAs metabolites compared with values in patients
Ill. Urinary ll-d-TXBZ in patients with AM1 who received only thrombolytic therapy (groups 1 and 2) and patients who received aspirin and thrombolytic therapy Table
(group
Hours o-12 12-24 24-36 36-48 48-60 60-72
4) Thrombolysis (groups l-2) 834 703 923 827 656 379
rt t + f t t
633 477 767 767 571 145
Thrombolysis aspirin (group 4) 239 361 200 191 159 155
k + + + -t k
165 276 100 70 68 54
+ p Value 0.02 0.09 0.02 0.04 0.03 0.0001
not receiving thrombolytic infusion (group 3), the difference was not significant. Neither has a significant difference been shown between patients who received either streptokinase or rt-PA. On the other hand, significantly higher ll-d-TXB2 values were observed when reperfused and nonreperfused patients were compared. This finding was independent of the type of thrombolytic drug, inasmuch as no difference was found in ll-d-TXBZ values between those patients in groups 1 and 2 who were reperfused and those in the two groups who were not reperfused (Fig. 3). Therefore our data suggest that not thrombolytic therapy itself but a residual stenosis at the site of clot
564
Rebuzzi
ltd-7x82 4
lW9
et al.
(pg/mg
American
cralnhw)
1400 1200 1000 000 wo 400 200 0 12-24
24-M
30-48
80-72
48-60
00-72
48-00
HOURS m
ii-d-lx82
Stroptokln~r*
tBrt-PA
(pg/mgcrrtlnlnd
1000 I 1400 1200 1000 800 800 400 200 0 12-24
24-30
30-48
HOURS m
Stnptokln~r*
FB rt-PA
3. Urinary ll-d-TXB2 in patients treated with streptokinase or rt-PA with coronary patency (upper panel) or coronary occlusion (lower panel) at late angiography.
Fig.
lysis probably plays a major role in the observed higher platelet activation. As an alternative, platelet activation after restoration of vessel patency might be a reaction resulting from the release of toxic metabolites accumulated at the site of occlusion or a consequence of reperfusion damage related to oxygen-derived free radicals increased at the time of reperfusion.22s23 In addition, our data indicate that aspirin given intravenously immediately before thrombolytic infusion (group 4) completely prevented the increase in TXAs metabolites observed in the other groups, although a higher rate of reperfusion occurred. To our knowledge this is the first study in which consecutive patients were randomly assigned to different treatment groups and urine and blood samples were collected following the same protocol. Our data do not completely agree with those of other investigators who demonstrated a marked increase in urinary 2,3-dinor-TXBs in patients with AM1 treated with streptokinase5 or rt-PA24 com-
March1992 Heart Journal
pared with patients not receiving thrombolytic therapy. Our different results may be due to the fact that in previous studies patients with AM1 treated without thrombolytic therapy were included later than the treated patients and their urinary metabolite excretion peak may have occurred before they were admitted to the study. Control patients also differed in that the majority of them did not receive heparin, which has been shown to activate platelets in vitro, although it has also been demonstrated that heparin does not alter TXAz biosynthesis in humans.“4 Our findings might also be related to the fact that we measured urinary ll-d-TXBs differently from Fitzgerald et al., 5,lo who analyzed urinary 2,3-dinorTXBz and plasmatic ll-d-TXBs. However, a similar pattern in urinary and plasma concentrations of lld-TXB2 has been demonstrated during infusion of TXBz at the same rate into healthy male volunteers.25 On the other hand, it is well known that TXB2 has two major pathways of metabolism in humans: P-oxidation, resulting in the formation of 2, 3-dinorTXB2, and dehydrogenation, resulting in the formation of ll-d-TXB2. Although 2, 3-dinor-TXBz was originally described as the prevailing pathway of enzymatic degradation of infused TXB2 in humans, it has recently been demonstrated that ll-d-TXB:! has a substantially longer plasma half-life (i.e., 45 minutes vs 15 minutes)14 and is at least as abundant a conversion product of exogenously infused TXBz as262 3-dinor-TXBs . Alihough in the above-mentioned studies, human platelets incubated with streptokinase seemed to show an enhancement of the sensitivity to aggregation inducers,5s27it has also been reported that human platelets incubated with streptokinase or rt-PA lose their ability to aggregate in response to adenosine diphosphate and collagen.28-32On the other hand, the fact that two thrombolytic agents (one with a direct and one with an indirect mechanism of action on plasminogen) have the same effect on TXAs metabolite production may support the hypothesis that activation of platelets may occur mostly because of the exposure of platelets to the injured vascular bed after reperfusion and not because of a direct action of streptokinase and rt-PA on platelet aggregation. Our data comparing reperfused and nonreperfused patients seem to confirm this hypothesis. Limitations of the study. A possible limitation of our study might be constituted by the fact that we do not have information on pretreatment coronary vessel anatomy. Consequently we cannot directly attribute restoration of blood flow in the occluded vesselsto the effect of thrombolytic therapy. Furthermore, we performed coronary angiography late after AM1 (5 to 7
Volume Number
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Thrombolysis-reperfision
days) so we cannot exclude the possibility of spontaneous delayed reperfusion. However, this is unlikely since reperfusion established in the acute phase according to an early (less than 12 hours) peak in the creatinine kinase level and ECG criteria15-17 occurred essentially in the same patients who showed a patent vessel at angiography. In addition, in one patient in the group that did not receive thrombolytic therapy (group 3), we observed an early peak in the creatinine kinase level and restored vessel flow, suggesting early reperfusion associated with two- to threefold higher excretion of urinary ll-d-TXB2 with respect to the other subjects in the same group. Thus our data indicate that platelet activation seems to occur as new surfaces are exposed on the clot during thrombolysis and/or by reperfusion of the injured vascular bed and not because of a direct effect of thrombolytic drugs. However, although our data support this hypothesis, further studies are needed to confirm these observations. Conclusions. Thrombolytic infusion does not seem to significantly increase urinary ll-d-TXBs excretion and therefore platelet aggregation unless reperfusion occurs. Thus reperfusion and not thrombolytic agents per se turns out to be the most important factor inducing platelet activation and consequently facilitating reocclusion. Aspirin administration appears to be effective in reducing the extent of this phenomenon. We thank the nursing able assistance.
staff of our coronary
care unit
for invalu-
REFERENCES
1. TIM1 Study Group. The Thrombolysis in Myocardial Infarction trial: phase 1 findings. N Engl J Med 1985;312:932-6. 2. Yasuda T, Gold HL, Fallon JT, Leinbach RC, Guerrero JL, Scudder LE, Kanke M, Shealy D, Ross MJ, Collen D, Coller BS. Monoclonal antibody against the platelet glycoprotein (GP) IIb/IIIa receptor prevents coronary artery reocclusion after reperfusion with recombinant tissue-type plasminogen activator in dogs. J Clin Invest 1988;81:1284-91. 3. Gold HK, Coller BS, Yasuda T, Saito T, Allon JT, Guerrero JL, Leinbach RC, Ziskind AA, Collen D. Rapid and sustained coronary artery recanalization with combined bolus injection of recombinant tissue-type plasminogen activator and monoclonal antiplatelet GPIIbiIIIa antibody in a canine preparation. Circulation 1988;77:670-7. 4. Golino P, Ashton JH, Glas-Greenwalt P, McNatt J, Buja LM, Willerson JT. Mediation of reocclusion by thromboxane As and serotonin after thrombolysis with tissue-type plasminopen activator in a canine preparation of coronary thrombosis. Circulation 1988;77:678-84. 5. Fitzgerald DJ. Catella F. Rov L. FitzGerald GA. Marked platilet activation in vitro after intravenous streptokinase in patients with acute myocardial infarction. Circulation 1988; 77~142-54. 6. Eisenberg PR, Sherman LA, Jaffe AS. Paradoxic elevation of fibrinopeptide A after streptokinase: evidence for continued thrombosis despite intense fibrinolysis. J Am Co11 Cardiol 1987;10:527-9.
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7. Vaughan DE, Kirshenbaum JM, Loscalzo J. Streptokinaseinduced antibody-mediated platelet aggregation: a potential cause of clot propagation in vivo. J Am Co11 Cardiol 1988;11:1343-8. 8. Fitzgerald DJ, Roy L, Wright F, FitzGerald GA. Functional significance of platelet activation following coronary thrombolysis [Abstract]. Circulation 1987;76(suppl IV):IV-151. 9. Ohlstein EH, Shebuski RJ. Tissue-type plasminogen activator (tPA) increases plasma thromboxane levels which is associated with platelet hyperaggregation [Abstract]. Circulation 1987;76(suppl IV):IV-100. 10. Fitzgerald DJ, Wright F, FitzGerald GA. Increased thromboxane biosynthesis during coronary thrombolysis. Evidence that platelet activation and thromboxane Az modulate the response to tissue-type plasminogen activator in vivo. Circ Res 1989;65:83-94. 11. Francis CW, Markham RE, Barlow GH, Florack TM, Dobrzynsky DM, Marder VJ. Thrombin activity of fibrin thrombi and soluble plasmic derivatives. J Lab Clin Med 1983;102:220-30. 12. Fitzeerald DJ. Rov L. Catella F. Fitzgerald GA. Platelet activation in unstable coronary diseasi N Engl J Med 1986; 315:983-9. 13. Guidelines for the early management of patients with acute myocardial infarction. Circulation 1990;82:664-707. 14. Lawson JA, Patron0 C, Ciabattoni G, FitzGerald GA. Longlived enzymatic metabolites of thromboxane Az in the human circulation. Anal Biochem 1986,155:198-205. 15. The ISAM Study Group. A prospective trial of intravenous streptokinase in acute myocardialinfarction (ISAM). Mortality, morbidity, and infarct size at 21 davs. N Enel J Med 1986;314:1465-71. 16. Hogg KJ, Hornung RS, Howie CA, Hockings N, Dunn FG, Hillis WS. Electrocardiogrpahic prediction of coronarv arterv patency after thromboly% treatment in acute myocardial in”farction: use of the ST segment as a noninvasive marker. Br Heart J 1988;60:275-80. 17. Zabel M, Hohnloser SH, Kasper W, Meinertz T, Just H. Combined analysis of three noninvasive markers for better prediction of reperfusion after thrombolytic therapy for acute myocardial infarction. J Am Co11 Cardiol 1991;17:67A. 18. Ciabattoni G, Maclouf J, Catella F, FitzGerald GA, Patron0 C. Radioimmunoassay of ll-dehydrothromboxane Bz in human plasma and urine. Biochim Biophys Acta 1987;918:293-7. 19. Patron0 C, Ciabattoni G, Remuzzi G, Gotti E, Bombardieri S, Di Munno 0, Tartarelli G. Cinotti GA. Simonetti BM. Pierucci A. Functional significance of renal prostacyclin and thromboxane AZ production in patients with systemic lupus erythematosus. J Clin Invest 1985;76:1011-8. 20. Ciabattoni G, Pugliese F, Davi G, Pierucci A. Simonetti BM, Patron0 C. Fractional conversion of thromboxane Bs in man. Biochim Biophvs Acta 1989:992:66-70. 21. Ciabattoni G; Patrignani P, Patron0 C. Radioimmunoassay of ll-dehydro-thromboxane Bz. In: Murphy RC, Fitzpatrick FA, eds. Methods in enzymology. New York: Academic Press, Inc, 1987:34-41. 22. Lucchesi BR. Modulation of leukocyte-mediated myocardial reperfusion injury. Annu Rev Physiol 1990;52:561-76. 23. Fox KAA. Thrombolysis: adjuvant therapy and the role of complement. Eur Heart J 199O;ll(suppl F):36-42. 24. Kerins DM. Rov L. Fitzgerald GA. FitzGerald DJ. Platelet and vascular function during coronary thrombolysis with tissuetype plasminogen activator. Circulation 1989;80:1718-25. 25. Patron0 C. Thromboxane biosynthesis and metabolism in health and disease. In: Strano A, Novo S, eds. Advances in vascular pathology. Amsterdam: Elsevier Science Publishers BV, 19891407-10. 26. Ciabattoni G, Pugliese F, Davi G, Pierucci A, Simonetti BM, Patron0 C. Fractional conversion of thromboxane Bs to lldehydrothromboxane Bz in mm. Biochim Biophys Acta 1989; 992:66-70. 27. Griguer P, Brochier M, Leroy J, et al. Platelet aggregation after thrombolytic therapy. Angiology 1980;31:91-9.
Rebuzzi et al. 28. Fry ETA, Grace AM, Sobel BE. Interactions between pharmacologic concentrations of plasminogen activators and platelets. Fibrinolysis 1989;3:127-36. 29. Mizuta T, Imai C. Tissue-type plasminogen activator inhibits aggregation of platelets in vitro. Life Sci 1988;43:955-63. 30. Loscalzo J, Vaughan DE. Tissue plasminogen activator promotes platelet disaggregation in plasma. J Clin Invest 1987; 79:1749-55.
American
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31. Grace AM, Fry ETA, Sobel BE. Decreased aggregation of platelets induced by exposure to pharmacologic concentrations of t-PA in whole blood. Circulation 1987;76(suppl IV):307-11. 32. Hoffmann JJML. Blood viscosity and platelet function in thrombolytic therapy of acute myocardial infarction. Eur Heart J 199O;ll(suppl F):29-35.
Regional redistribution of myocardial by UL-FS 49, a selective bradycardic
perfusion agent
The effects of UL-FS 49, a specific bradycardlc agent, on systemic hemodynamics, regional myocardial function (sonomicrometry, percentage of segment shortening), and regional coronary blood flow (radioactive microspheres) were studied in open-chest, anesthetized dogs with severe left circumflex cororiary artery (LCX) stenosis. UL-FS 49 was admlnlstered as two sequential bolus injections of 0.25 mg/kg. Heart rate decreased from 149 + 13 beats/min to 102 + 6 and 77 f. 4 beats/min after 0.25 and 0.5 mg/kg cumulative doses of UL-FS 49, respectively. The reduction in heart rate was not associated with any significant change in left ventricular pressure or mean arterial pressure, left ventricular dp/dt, or coronary vascular resistance. Similarly no hemodynamic changes occurred with atrial pacing to the initial heart rate. Application of an LCX stenosis of sufficient severity to produce a 50% reduction in mean LCX blood flow (44 + 4 to 22 + 2 ml/min) resulted in a significant reduction in the percentage of segment shortening in the ischemic zone (9.8 + 1.6% to 6.5 + 1.1%). The percentage of segment shortening in the ischemic zone progressively improved to 8.4 f 1.2% and 9.4 + 0.5% after 0.25 and 0.5 mg/kg UL-FS 49, respectively. Subepicardial perfusion in the ischemic zone was decreased and subendocardial perfusion was increased after administration of UL-FS 49. Consequently the ischemic zone endocardial/epicardlal ratio increased from 0.43 2 0.08 to 1.12 ? 0.22 and 1.48 t 0.32 with low and high doses of UL-FS 49. Atrial pacing to the control heart rate abolished the effects of UL-FS 49 on regional myocardial blood flow and percentage of segment shortening. These data indicate that UL-FS 49 is a selective bradycardlc agent that can improve ischemic myocardlal function distal to severe coronary stenosis. The data suggest that UL-FS 49 Improves the relationship between myocardial oxygen supply and demand by negative chronotropic actions and by favorably redistributing ischemic blood flow. (AM HEART J 1992;123:566.)
Patrick Harold
O’Brien, MD, David Drage, BA, Kooroush Saeian, MD, L. Brooks, MD, and David C. Warltier, MD, PhD. Milwaukee,
Heart rate is a major determinant of myocardial oxygen demand.lM3 It has been demonstrated that regional myocardial contractile dysfunction, ECG ab-
From the Departments of Medicine/Division of Cardiology, Anesthesiology, and Pharmacology, Medical College of Wisconsin. Received for publication April 15, 1991; accepted Aug. 12, 1991. Reprint requests: David C. Warltier, MD, PhD, Medical College of Wisconsin, MFRC, Room AlOOO, 8701 W. Watertown Plank Rd., Milwaukee, WI 53226. 4/l/34416
566
Wis.
normalities, and altered myocardial lactate metabolism accompany atria1 pacing-induced elevations of heart rate.4-7 Thus pharmacologic reduction of heart rate represents an important form of therapy in patients with coronary artery disease. Two classes of drugs, /3-adrenergic receptor antagonists and slow inward calcium channel-blocking agents, are frequently used in the treatment of ischemic heart disease. The effects of bradycardia produced by these drugs on blood flow to an ischemic zone and myocardial function have been studied in both conscious and
