Coronary following
hemodynamics acute coronary
during reperfusion ligation in dogs
Paul E. Parker, Ph.D. F. A. Bashour, M.D., Ph.D. H. Fred Downey, Ph.D. Sarkis J. Kechejian, M.D. Arthur G. Williams, B.S. Dallus, Texas
Recently, surgical techniques were developed in human beings to re-establish myocardial blood flow distal to a coronary obstruction. The availability of these techniques to patients with acute myocardial infarction has directed several investigators to evaluate various factors potentially capable of limiting the extent of myocardial damage following an acute coronary artery occlusion.1-4 Although some histologic and histochemical studies have demonstrated that experimental coronary artery reperfusion would reduce myocardial cell death,‘, 2. 5 other studies indicate that additional irreversible cardiac damage occurs after the re-establishment of coronary blood flow 3. 1, 6-S The purposes of the present study were to elucidate the coronary hemodynamic effects of re-establishing coronary blood flow to a region of the myocardium rendered ischemic by the acute occlusion of a coronary artery and to assess the regional distribution of the myocardial flow during coronary reperfusion. Materials
and methods
Adult mongrel dogs of either sex with an average weight of 21 kilograms were anesthetized with sodium pentobarbital (30 mg. per kilogram of body weight) and ventilated with room air by a From the Cardiopulmonary Institute and the Departments cine and Physiology, University of Texas Health Science Dallas, Texas.
of MediCenter at
Work supported in part, by Cardiology Fund, and Grants from (HL-05396) and American Heart Association, Texas Affiliate. Received
for publication
Reprint requests tute. Methodist 75222.
November,
NIH
Sept. 26, 1974.
to: Paul E. Parker, Hospital of Dallas.
Ph.D., Cardiopulmonary P.O. Box 5999, Dallas,
1975, Vol. 90, No. 5, pp. 593-599
InstiTexas
Harvard respirator. After the heart had been exposed through a left thoracotomy in the fifth intercostal space, the left circumflex (LC) and the left anterior descending (LAD) coronary arteries were isolated 1 to 2 cm. from their origins. Electromagnetic flow transducers (Micron RClOOO) were placed around the LC and LAD and loose ligatures were placed around each artery 1 to 2 cm. beyond the flow transducer. By temporarily constricting these ligatures, reactive hyperemic responses to 10 sec. and 90 sec. occlusions were elicited. Following the determination of control reactive hyperemic responses, an occlusive ligature was secured around the LAD just distal to the flow transducer, causing a large portion of the left ventricular wall to become cyanotic. Simultaneous measurements of mean aortic pressure, left ventricular end-diastolic pressure, LC and LAD flows, and limb Lead II electrocardiogram were continuously made. Systemic arterial blood gases, pH, and rectal temperature of the animal were monitored and kept within normal physiological limits by adjusting the respirator and using a heating pad. Experimental protocol consisted of a 2 hr. period of LAD occlusion followed by a 4 hr. period of observation after release of this occlusion. Throughout these 6 hours, in 20 dogs, the reactive hyperemic responses to a 10 sec. occlusion of LAD and LC were obtained at 30 min. intervals except in the LAD during the 2 hr. period when it was occluded. In an additional group of 6 animals, the reactive hyperemic responses to a 90 sec. occlusion of the LAD were also obtained at 30 min. intervals during reperfusion. To define the minimal resistance of the reperfused bed, 90 sec. occlusions were used, since in preliminary experi-
American
Heart
-lownal
593
Parker
et al.
DESCENDING
9 z
(LAD)
0121234 *LAD---+-------LADOCCLUDED
REPERFUSED
TIME Wrs.1 Fig. 1. Coronary vascular resistance (in millimeters of mercury per milliliter per minute) in left anterior descending (LAD) and left circumflex coronary arteries during LAD occlusion and reperfusion (n = 20).
ments we observed that occlusions longer than 60 sec. did not result in significantly greater dilation of the coronary vasculature. Coronary vascular resistances during reactive hyperemia in the LAD and LC vascular beds were computed by dividing the mean aortic pressure (in millimeters of mercury) by the peak reactive hyperemic coronary blood flow (in milliliters per minute) as measured by flowmeter following the release of the 10 sec. or 90 sec. occlusions of these arteries. Regional distribution of coronary blood flow was determined during the period of reperfusion of the LAD from tissue content of radioactive microspheres of 8 to 10~ diameter administered into the left atrium.“~ lo In 18 of the dogs used in the hyperemic study, one injection of radiomicrospheres was made at the fourth hour of reperfusion. In seven of these dogs, two additional measurements of regional blood flow were made by injecting microspheres at 5 minutes and 2 hours of reperfusion. These microspheres were labeled with different isotopes,Y!e, YSc, and Wr. Following the last isotope administration, the heart was excised and frozen for sampling. Myocardial tissue samples from the free wall of the left ventricle were obtained from both the normal myocardium (control), area supplied by the LC coronary artery, and the reperfused region of the left ventricle, area supplied by the LAD. Visually, these samples were divided transmu-
594
rally into three thirds: epicardial, midmyocardial, and endocardial layers. The samples were weighed individually and their respective radioactivities were measured by scintillation counting in a three-channel gamma detector (Nuclear Chicago 4233). Standard techniques for isotope separation were utilized with the aid of a minicomputer (DEC8E). Regional blood flow was calculated by relating the radioactivity per gram of myocardial tissue to that of a reference sample of arterial blood collected during each administration of microspheres.” Cardiac arrhythmias, mainly ventricular in origin, were usually observed to accompany the occlusion of the LAD and the resumption of the blood flow to the occluded vessels. To minimize the frequency of these arrhythmias or prevent their occurrence, lidocaine was infused at a rate of 1 mg. per minute throughout the experiment. This dosage of lidocaine produces no significant systemic hemodynamic effects2 and if it did influence the coronary vascular system’” it would be expected to affect both the LAD and LC coronary vascular beds. Results Coronary resistances. Coronary vascular resistances in both the LAD and LC were calculated in 20 dogs and are illustrated in Fig. 1. Fifteen minutes after re-establishing flow to LAD, the coronary vascular resistance of this bed was practically unchanged (97 per cent of the control), but it rose gradually to 156 per cent of the control at the end of 4 hours of reperfusion. Statistically significant (P < 0.05) increases in LAD resistances became apparent by 1 hour after establishing flow. Coronary resistance in the LC was not changed significantly during LAD occlusion or reperfusion. Representative tracings showing the reactive hyperemic flow responses to a 10 sec. occlusion of both the LAD and LC coronary arteries are presented in Fig. 2. There the peak hyperemic responses of the LAD after 1 hour and 4 hours of reperfusion can be compared with the preocclusion response of the LAD and that of the LC during the period of LAD reperfusion. In the LAD, the peak responses became progressively attenuated following reperfusion (upper panel), with little or no change in the LC reactive hyperemic responses (lower panel). In 20 dogs, the reactive hyperemic resistances
November,
1975, Vol. 90, No. 5
LEFT
ANTERIOR
DESCENDING
E&-JyGk*v ; lll[& 0
LEcEx,L 240 min 60 min Post-Reperfusion
Pre-Occlusion
Fig. 2. Representative descending (LAD) reperfusion.
tracings showing and left circumflex
reactive coronary
hyperemic flow responses to 10 sec. occlusions of the left anterior arteries before LAD occlusion and at 1 and 4 hours during LAD
I. Statistical analysis of transmural distribution of myocardial blood flow in normal reperfused regions during 5 minutes, 2 hours, and 4 hours of LAD reperfusion
Table
Control Blood flout (ml.lmin./Gm.)
0.98 + 0.13
0.92
+ 0.12
SE.
P, P, P, = probability of statistical or 4 br. vs. 2 hr.: P, = within
0.81
Heart
Journal
t
0.10
L 0.05
N.S.
N.S.
-
N.S.
1.07 k 0.18 N.S. N.S.
1.05 t 0.24 N.S. -
N.S.
0.95
1.13 2 0.19
N.S.
N.S.
+- 0.19
N.S. N.S. N.S.
region 2hr.
5 min.
-
-
1.17 + 0.16
N.S. < 0.01
N.S.
0.59
7- / I
t 0.05
4 hr.
0.54 :k. 0.13
hemodynamics acute coronary
during reperfusion ligation in dogs
Paul E. Parker, Ph.D. F. A. Bashour, M.D., Ph.D. H. Fred Downey, Ph.D. Sarkis J. Kechejian, M.D. Arthur G. Williams, B.S. Dallus, Texas
Recently, surgical techniques were developed in human beings to re-establish myocardial blood flow distal to a coronary obstruction. The availability of these techniques to patients with acute myocardial infarction has directed several investigators to evaluate various factors potentially capable of limiting the extent of myocardial damage following an acute coronary artery occlusion.1-4 Although some histologic and histochemical studies have demonstrated that experimental coronary artery reperfusion would reduce myocardial cell death,‘, 2. 5 other studies indicate that additional irreversible cardiac damage occurs after the re-establishment of coronary blood flow 3. 1, 6-S The purposes of the present study were to elucidate the coronary hemodynamic effects of re-establishing coronary blood flow to a region of the myocardium rendered ischemic by the acute occlusion of a coronary artery and to assess the regional distribution of the myocardial flow during coronary reperfusion. Materials
and methods
Adult mongrel dogs of either sex with an average weight of 21 kilograms were anesthetized with sodium pentobarbital (30 mg. per kilogram of body weight) and ventilated with room air by a From the Cardiopulmonary Institute and the Departments cine and Physiology, University of Texas Health Science Dallas, Texas.
of MediCenter at
Work supported in part, by Cardiology Fund, and Grants from (HL-05396) and American Heart Association, Texas Affiliate. Received
for publication
Reprint requests tute. Methodist 75222.
November,
NIH
Sept. 26, 1974.
to: Paul E. Parker, Hospital of Dallas.
Ph.D., Cardiopulmonary P.O. Box 5999, Dallas,
1975, Vol. 90, No. 5, pp. 593-599
InstiTexas
Harvard respirator. After the heart had been exposed through a left thoracotomy in the fifth intercostal space, the left circumflex (LC) and the left anterior descending (LAD) coronary arteries were isolated 1 to 2 cm. from their origins. Electromagnetic flow transducers (Micron RClOOO) were placed around the LC and LAD and loose ligatures were placed around each artery 1 to 2 cm. beyond the flow transducer. By temporarily constricting these ligatures, reactive hyperemic responses to 10 sec. and 90 sec. occlusions were elicited. Following the determination of control reactive hyperemic responses, an occlusive ligature was secured around the LAD just distal to the flow transducer, causing a large portion of the left ventricular wall to become cyanotic. Simultaneous measurements of mean aortic pressure, left ventricular end-diastolic pressure, LC and LAD flows, and limb Lead II electrocardiogram were continuously made. Systemic arterial blood gases, pH, and rectal temperature of the animal were monitored and kept within normal physiological limits by adjusting the respirator and using a heating pad. Experimental protocol consisted of a 2 hr. period of LAD occlusion followed by a 4 hr. period of observation after release of this occlusion. Throughout these 6 hours, in 20 dogs, the reactive hyperemic responses to a 10 sec. occlusion of LAD and LC were obtained at 30 min. intervals except in the LAD during the 2 hr. period when it was occluded. In an additional group of 6 animals, the reactive hyperemic responses to a 90 sec. occlusion of the LAD were also obtained at 30 min. intervals during reperfusion. To define the minimal resistance of the reperfused bed, 90 sec. occlusions were used, since in preliminary experi-
American
Heart
-lownal
593
Parker
et al.
DESCENDING
9 z
(LAD)
0121234 *LAD---+-------LADOCCLUDED
REPERFUSED
TIME Wrs.1 Fig. 1. Coronary vascular resistance (in millimeters of mercury per milliliter per minute) in left anterior descending (LAD) and left circumflex coronary arteries during LAD occlusion and reperfusion (n = 20).
ments we observed that occlusions longer than 60 sec. did not result in significantly greater dilation of the coronary vasculature. Coronary vascular resistances during reactive hyperemia in the LAD and LC vascular beds were computed by dividing the mean aortic pressure (in millimeters of mercury) by the peak reactive hyperemic coronary blood flow (in milliliters per minute) as measured by flowmeter following the release of the 10 sec. or 90 sec. occlusions of these arteries. Regional distribution of coronary blood flow was determined during the period of reperfusion of the LAD from tissue content of radioactive microspheres of 8 to 10~ diameter administered into the left atrium.“~ lo In 18 of the dogs used in the hyperemic study, one injection of radiomicrospheres was made at the fourth hour of reperfusion. In seven of these dogs, two additional measurements of regional blood flow were made by injecting microspheres at 5 minutes and 2 hours of reperfusion. These microspheres were labeled with different isotopes,Y!e, YSc, and Wr. Following the last isotope administration, the heart was excised and frozen for sampling. Myocardial tissue samples from the free wall of the left ventricle were obtained from both the normal myocardium (control), area supplied by the LC coronary artery, and the reperfused region of the left ventricle, area supplied by the LAD. Visually, these samples were divided transmu-
594
rally into three thirds: epicardial, midmyocardial, and endocardial layers. The samples were weighed individually and their respective radioactivities were measured by scintillation counting in a three-channel gamma detector (Nuclear Chicago 4233). Standard techniques for isotope separation were utilized with the aid of a minicomputer (DEC8E). Regional blood flow was calculated by relating the radioactivity per gram of myocardial tissue to that of a reference sample of arterial blood collected during each administration of microspheres.” Cardiac arrhythmias, mainly ventricular in origin, were usually observed to accompany the occlusion of the LAD and the resumption of the blood flow to the occluded vessels. To minimize the frequency of these arrhythmias or prevent their occurrence, lidocaine was infused at a rate of 1 mg. per minute throughout the experiment. This dosage of lidocaine produces no significant systemic hemodynamic effects2 and if it did influence the coronary vascular system’” it would be expected to affect both the LAD and LC coronary vascular beds. Results Coronary resistances. Coronary vascular resistances in both the LAD and LC were calculated in 20 dogs and are illustrated in Fig. 1. Fifteen minutes after re-establishing flow to LAD, the coronary vascular resistance of this bed was practically unchanged (97 per cent of the control), but it rose gradually to 156 per cent of the control at the end of 4 hours of reperfusion. Statistically significant (P < 0.05) increases in LAD resistances became apparent by 1 hour after establishing flow. Coronary resistance in the LC was not changed significantly during LAD occlusion or reperfusion. Representative tracings showing the reactive hyperemic flow responses to a 10 sec. occlusion of both the LAD and LC coronary arteries are presented in Fig. 2. There the peak hyperemic responses of the LAD after 1 hour and 4 hours of reperfusion can be compared with the preocclusion response of the LAD and that of the LC during the period of LAD reperfusion. In the LAD, the peak responses became progressively attenuated following reperfusion (upper panel), with little or no change in the LC reactive hyperemic responses (lower panel). In 20 dogs, the reactive hyperemic resistances
November,
1975, Vol. 90, No. 5
LEFT
ANTERIOR
DESCENDING
E&-JyGk*v ; lll[& 0
LEcEx,L 240 min 60 min Post-Reperfusion
Pre-Occlusion
Fig. 2. Representative descending (LAD) reperfusion.
tracings showing and left circumflex
reactive coronary
hyperemic flow responses to 10 sec. occlusions of the left anterior arteries before LAD occlusion and at 1 and 4 hours during LAD
I. Statistical analysis of transmural distribution of myocardial blood flow in normal reperfused regions during 5 minutes, 2 hours, and 4 hours of LAD reperfusion
Table
Control Blood flout (ml.lmin./Gm.)
0.98 + 0.13
0.92
+ 0.12
SE.
P, P, P, = probability of statistical or 4 br. vs. 2 hr.: P, = within
0.81
Heart
Journal
t
0.10
L 0.05
N.S.
N.S.
-
N.S.
1.07 k 0.18 N.S. N.S.
1.05 t 0.24 N.S. -
N.S.
0.95
1.13 2 0.19
N.S.
N.S.
+- 0.19
N.S. N.S. N.S.
region 2hr.
5 min.
-
-
1.17 + 0.16
N.S. < 0.01
N.S.
0.59
7- / I
t 0.05
4 hr.
0.54 :k. 0.13
