Gen. Pharmac. Vol. 23, No. 5, pp. 909-913, 1992 Printedin Great Britain.All rights reserved
0306-3623/92$5.00+ 0.00 Copyright © 1992PergamonPress Ltd
EFFECT OF ATP AND VERAPAMIL AS CARDIOPLEGIC ADDITIVES IN THE ISOLATED GUINEA PIG HEART H. SONCUL,L. GOKGOZ,K. AYRANCIOGLU,(~. KARASU,S. KALAYCIOGLUand A. EF,.SOz Department of Thoracic and Cardiovascular Surgery of Gazi University Medical School, Be~evler, Ankara, Turkey (Received 3 December 1991) Al~traet--1. A comparative study on isolated guinea pig hearts was carried out to determine the effects of ATP and verapamil as cardioplegic additives. 2. The hearts were arrested by one of the plegic solutions: I, potassium 20 retool/l; II, potassium 20 mmol/l + verapamil 1.I #mol/1; III, potassium 20 mmol/l + ATP 10 mmol/1.After 45 rain of hypothermic isehemia, the hearts were reperfused by Krebs-Henseleit buffer. 3. Postischemic percentage change of myocardial functions (heart rate, contractility, heart work) and tissue enzymes (LDH, SGOT, SGPT) were compared between the groups. 4. Although a rapid cardiac arrest could be obtained by verapamil added cardioplegia. Postischemic myocardial recovery was much better with ATP added cardiopleglc solutions.
INTRODUCTION The problem of myocardial protection and a rapid cardiac arrest during cardiac surgery led to several investigations on cardioplegic solutions (Bourdillon and Peele-Wilson, 1980; Brandt, 1981). It is shown that calcium influx into myocardial cells is associated with increased adenosine triphosphate (ATP) consumption and contracture formation (Fleckenstein, 1977). Therefore intracellular calcium overload plays an important role in myocardial ischemic injury (Bretsehnei et aL, 1975; Hearse et aL, 1980). Although their value is controversial, calcium channel blockers such as verapamil, nifedipine and diltiazem which inhibit the influx of calcium by blockage of the "slow channel" and arrest the plateau phase of electrical depolarization, have been evaluated as cardioplegic additives (Magovern et al., 1981; Yamamato et aL, 1985). On the other hand to supply the demands of ischemic myocardium by high energy compounds has also been investigated (Parrat and Marshall, 1974; Bernard et al., 1988). Several studies have focused on the possibility of saving myocardial high energy phosphates by using ATP as an additive to cardioplegic solutions (Thelin et al., 1986, 1987). ATP and other adenine derivatives have negative chronotropic, negative dromotropic and antiarrythmic effects on myocardium. They inhibit sinoatrial and atrioventricular nodes, thereby potentially inducing cardiac arrest (Ward et al., 1983). ATP also decreases calcium influx into the cell and reduces cellular calcium loading caused by cathecolamines (Wayne et al., 1949; Thelin et al., 1985). In the present experimental study we have specifically compared the effects of verapamil and ATP as cardioplegic additives on cardiac arrest and myocardial recovery. 909
MATERIALSAND METHODS Animals Hearts were obtained from male guinea pigs (N = 30) weighing 280-370 g. All animals received humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by the National Institutes of Health (NIH Publication No. 80-23, revised 1978). The animals were anesthetized by ether and given 200 units of beparin into the femoral vein. The hearts (1.8-2.4 g) were rapidly removed and cannulated via the aorta. Perfusion techniques and plegic solutions The hearts were mounted on a modified Langendorf perfusion apparatus and perfused by a gassed (oxygen95%, carbondioxide 5%) Krebs-Henseleit solution at a rate of 2 ml/min at 37°C. (Mean arterial pressure = 80 mmHg.) The composition of the solution (in retool/l) was NaHCO3, 25; NaCI, 118; KH2PO4, 1.2; KC1, 4.8; MgSO+, 1.2; CaC12, 1.2; and glucose, 11.1. Three different cardioplegic solutions (10 experiments in each group) were used to arrest the hearts. The composition of these solutions were: Group 1, NaC1 123retool/I, KCI 20mmol/l, MgCI 8 retool/l, glucose 11.1 retool/l, NaHCO 3 9 retool/l, pH 7.6; Group 2, the same solution in Group I + verapamil 1.0 #reel/l; Group 3, the same solution in Group 1 + ATP 10 mmol/l. Protocol After 10 min of a stabilization period, we recorded the contractility, heart rate and also collected perfusate samples from the fight atrium to determine tissue enzymes. The hearts were arrested by infusion of one of the cardioplegic solutions from the aortic root at a rate of 2 ml/min for 3 min at 4°C. Over this 3 min of plegic infusion the arrest time and number of beats were assessed. Following cardiac arrest the plegic solution was removed by infusion of 2 ml isotonic
H.SONCUL et
910
Perfu$ion of Krebs solution
Rel)erfusion of Krebs solution
Hypot hermlc
Cordioplegl¢ infusion
3 minutes
al.
Ischemlo
[~
10 minutes/
45 minutes
Recording mechanical
Washout of cardioplegJc
Recording mechanical data and collectinq
[
data and collecting perfusate samples
perfusate samples
Fig. 1. Experimental protocol.
saline from the aortic root. During the ischemic period the hearts were kept at 8-10°C by topical cooling with isotonic saline. After 45 min of ischemia the reperfusion was begun by the same buffer at 37°C. At the 10th min of reperfusion again the contractility and heart rate were recorded and perfusate samples were collected (Fig. 1). Calculations The following calculations were made. Arrest time: time (sec) from the onset of cardioplegic infusion until the heart arrests. Arrest beats: number of heart beats during 3 rain of cardioplegic infusion.
Percentage recovery of heart rate = Postischemic heart rate × 100 Preischemic heart rate Percentage recovery of ventricular contractions = Postischemic contractions × 100 Preischemic contractions
Percentage recovery of heart work = Postischemic heart rate x postischemic contractions x 100 Preischemic heart rate x preischemic contractions Percentage change of tissue enzymes = Postischemic enzyme (LDH, SGOT, SGPT) concentrations x 100 Preischemic enzyme concentrations Data and statistics Ventricular contractility (in g) and heart rate (beats/rain) were recorded through (UGO BASILE 7004) isometric force transducer connected to a microdynomometer (UGO BASILE 7050). The biochemical parameters (LDH, SGOT, SGPT) were calculated by "Technican RA-1000" autoanalyzer using "Chromatest" kits. The results are presented as mean and SEM. Overall significance of difference between groups was determined by t-test using "Microstat" PC program.
60
Dl~a
! 40
30
20 10
Arrest
time
(sec)
Arrest
beats
(no)
Fig. 2. Arrest time: time between the onset of cardioplegic infusion and cardiac asystole. Arrest beats: number of heart beats during cardioplegic infusion. *Indicates significant difference between indicated group and potassium (control) group (P < 0.05). Values are mean + SEM.
ATP and verapamil in cardioplegia
911
120
100
80
40
20
Heart
rate
Contractility
Heart
work
Fig. 3. Postischemic recovery of heart rate, ventricular contractions and heart work according to their preischemic values. *Indicates significant difference between value indicated and potassium (control) group (P < 0.05). Values are mean + SEM.
RESULTS
Effect of verapamil and A TP on cardiac arrest From the beginning of the cardioplegic infusion, the time to cardiac arrest was significantly reduced by verapamil containing solution and the number of beats during the 3 min of cardioplegic infusion were reduced by both verapamil and ATP containing solutions. Time to cardiac arrest was reduced from 52.6 ± 14.1 see in potassium group to 19.3 ± 2.4see in vvrapamil group and to 35.8 ± 11.1 sec in ATP group (P < 0.05 for comparisons between verapamil and potassium groups).
The number of beats during cardioplegic infusion was reduced from 38.7 ± 8.3 in potassium group to 16.8 ± 2.6 in verapamil group and to 15.0 ± 2.6 in ATP group (P < 0.05 for both verapamil and ATP groups when compared with potassium group). (See Fig. 2.)
Effect of verapamil and A TP on myocardial recovery Mechanical parameters. There was no significant difference between the three groups for final recovery of the heart rate. The percentage change of the heart rate was, 95.1 ± 8 . 4 % in potassium group where it was 102.5±11.1% in verapamil group and 108.9 ± 10.3% in ATP group.
250
150-
~47
100-
50-
0 LDH
SGOT
SGPT
Fig. 4. Postischemic concentrations of lactic dehydrogenase (LDH), serum glutamic pyruvate transaminase (SGPT), serum glutamic oxalic transaminase (SGOT) of the perfusate as percentage change of their preischemic values. *Indicates significant difference between indicated group and potassium (control) group (P < 0.05). Values are mean + SEM.
912
H. SONCULet al.
Postischemic recovery of the left ventricular contractility was significantly better in ATP group 71.5-t-5.3% when compared with the potassium group 53.7 __. 5.0% and also with the verapamil group 45.1 + 4.1% (P < 0.05 for both comparisons). Although the percentage recovery of contractility was slightly better in potassium group compared to verapamil group, the difference was not significant statistically (Fig. 3). Postischemic recovery of cardiac work as a percentage of the preischemic calculation was expressively better in ATP group 88.7 + 6.4% compared with the potassium 45.7 + 3.1°/'o and the verapamil 46.6 + 2.7% groups (P < 0.05 for both comparisons) (Fig. 3). Biochemical parameters. Postischemic percentage changes of LDH and SGPT concentrations were significantly higher in potassium group when compared with ATP and verapamil groups (P < 0.05 for both comparisons). There was no significant difference among the three groups for SGOT concentrations (Fig. 4). DISCUSSION Decreasing myocardial energy consumption and increasing myocardial energy stores are the two major ways of myocardial protection during global ischemia. The most effective and commonly used techniques like hypothermia and potassium arrest to decrease myocardial energy consumption still cannot preclude significant depression of myocardial function and high energy phosphate stores flyers, 1988). There is a conception that better myocardial protection and a rapid cardiac arrest can be achieved by adding verapamil or other calcium blockers to plegic solutions because of their theoretical advantages such as decreasing calcium influx into the cell, protection of arrythmias, decreasing ATP consumption and coronary vasodilatation (Henry, 1980; Clark et al., 1981; Yamamato et ai., 1983). Although it is controversial, recent evidence shows that calcium blocking agents have cardioprotective effect in normothermic ischemia, but in hypothermic conditions they fail to afford additional protection (Johnson et al., 1982; Prasad and Bharadwaj, 1987). Corroborating with these previous data, our study shows that addition of verapamil to cardioplegic solutions supplies a rapid cardiac arrest and decreases myocardial injury (elevation of enzyme levels are significantly less in verapamil group when compared with potassium group). But it has no beneficial effect on postischemic myocardial recovery. ATP which is a high energy phosphate itself has also nearly the same theoretical effects of verapamil, mentioned above (Ward et al., 1983). Our study corroborates previous conclusions that high energy phosphates could be effective on postischemic recovery as cardioplegic additives (Thelin et ai., 1986). Our data shows that, postiscbemic left ventricular contractility and cardiac work are much better and also the elevation of enzyme levels, which represent tissue injury (for LDH and SGPT) are significantly less when ATP is added to cardioplegia. We also confirmed that ATP containing solution can decrease the number of beats during the cardioplegic infusion. However it can be argued that
decreasing the energy consumption by a rapid cardiac arrest, maintains better myocardial protection. It was controversial to our data with verapamil that caused rapid cardiac arrest (decreases both arrest time and arrest beats) without any additional effect on myocardial recovery. CONCLUSION Finally according to our study, we can argue that verapamil, which is a useful agent for cardiac arrest, shows no additional effect for myocardial protection in hypothermic conditions. On the other hand ATP as an additive to cardioplegia has beneficial protective effects on myocardium. SUMMARY
In order to determine the role of verapamil and adenosine triphosphate (ATP), as cardioplegic additives on cardiac arrest and postischemic myocardial recovery, a comparative study has been undertaken in isolated guinea pig hearts using Langcndorf technique as a model of cardio-pulmonary bypass. The hearts (n = 10 in each group) previously being perfused by Krebbs solution were arrested by one of the subsequent solutions. I, potassium 20 mmol/l; II, potassium 20 mmol/l + verapamil 1 #mol/l; III, potassium 20 mmol/l + ATP 10 mmol/1. After 45 rain of hypothermic ischemia, postischemic recovery of heart rate, ventricular contractility heart work and postischemic changes of tissue enzymes (LDH, SGOT, S GPT) were compared between the groups. Also arrest time and number of arrest beats were recorded and compared. Even though cardiac arrest was achieved more rapidly with verapamil group, postischemic myocardial recovery was significantly better in ATP group when compared with verapamil and potassium 20 mmol/I groups. REFERENCES
Bernard B., Aaro (3. and Shlomo L. (1988) Comparative clinical and electrophysiologic effects of adenosine triphosphate and verapamil on paroxysmal reciprocating junctional tachycardia. Circulation 77, 795-805. Bourdillon P. D. and Poole-Wilson P. A. (1980) Effects of verapamil and cardioplegia on calcium exchange and mechanical function in myocardial ischemia. Circulation 42, 31. Brandt B., Richardson R. V., O'Bryan P. and Ehrenhaft J. L. (1981) Intramyocardial electrical and metabolic activity during hypothermia and potassium cardioplegia. Ann. Thorac. Surg. 31, 117-121. Bretschneider H. J., Hubner G., Knoll D., Lohr B., Nordbeck H. and Spieckerman P. G. (1975) Myocardial resistance and tolerance to ischemia: physiological and biochemical basis. J. cardiovasc. Surg. 16, 241-260. Clark R. E., Christlieb I. Y., Spratt J. A., Henry P, D., Fischer A. E., Williamson J. R. and Sob¢l E. B. (1981) Myocardial preservation with nifedipine: a comparative study at normothermia. Ann. thorac. Surg. 31, 315-327. Fleckenstein A. (1977) Specific pharmacology of calcium in myocardium, cardiac pacemakers, and vascular smooth muscle. A. Rev. Pharmac. Toxic. 17, 149. Hearse D. J., Stewart D. A. and Braimbridge M. V. (1980) The additive protective effects of hypothermia and chemical cardioplegia during ischemic cardiac arrest in the rat. J. thorac, cardiovasc. Surg. 79, 39-43.
ATP and verapamil in cardioplegia Henry P. D. (1980) Comparative pharmacology of calcium antagonists: nifedipine, verapamil and diltiazem. Am. J. Cardiol. 46, 1047-1056. Johnson R., Jacoks A., Arets T., Gillian G., Geffin M. B., Dennis D., Laurence W., Guyton R., Fallon J. and Dagget W. M. (1982) Comparison of myocardial preservation with hypothermic potassium and nifedipine arrest. Circulation Suppl.l 66, 73-80. Magovern O. J., Dixon C. M. and Burkholder J. A. (1981) Improved myocardial protection with nifedipine and potassium based cardioplegia. J. thorac, cardiovasc. Surg. 82, 239-244. Parrat J. R. and Marshall R. J. (1974) The response of isolated cardiac muscle to acute anoxia: protective effect of adenosine tripbosphate and creatine phosphate. J. Pharmac. 26, 427-433. Prasad K. and Bharadwaj B. (1987) Effect of crystalloid cardioplegia and verapamil on cardiac function and cellular biochemistry during hypothermic cardiac arrest. Can. J. CardioL 3, 293-299. Thelin S., Hultman J., Ronquist G. and Hansson H. E. (1985) Metabolic and functional effects of phosphoenolpyruvate and adenosine triphosphate upon rat hearts subjected to global ischemia. Scand. J. thorac, cardiovasc. Surg. 19, 237-245. Thelin S., Hultman J., Ronquist G. and Hansson H. E. (1986) Enhanced protection of rat hearts during ischemia
913
by phosphoenolpyruvate and A l P in cardioplegia. Thorac. cardiovasc. Surg. 34, 104-109. Thelin S., Hultman J., Ronquist G. and Hansson H. E. (1987) Myocardial high-energy phosphates, lactate and pyruvate during moderate or severe normothermic ischemia in rat hearts perfused with phosphoenolpyruvate and ATP in cardioplegic solution. Scand. J. thorac. cardiovasc. Surg. 21, 245-249. Tyers G. F. (1988) Verapamil and calcium free cardioplegia Can. J. Cardiol. 4, 6-8. Ward H. B., Kriett J. B., Einzig S., Bianco R. V., Anderson R. W. and Folker J. E. (1983) Adenine nucleotides and cardiac function following global myocardial ischemia. Surg. Forum. 34, 264-266. Wayne E. J., Goodwin J. F. and Stoner H. B. (1949) The effects of adenosine triphosphate on the electrocardiogram of man and animals. Br. heart J. 1, 55-67. Yamamato F., Manning A. S., Braimbridge. M. V. and Hearse D. J. (1983) Cardioplegia and slow calcium channel blockers: studies with verapamil. J. thorac, cardiovasc. Surg. 86, 252-261. Yamamato F., Manning A. S., Braimbridge M. V. and Hearse D. J. (1985) Calcium antagonists and myocardial protection: a comparative study of the functional, metabolic and electrical consequences of verapamil and nifedipine as additives to the St Thomas cardioplegic solution. Thorac. cardiovaac. Surg. 33, 354-359.
0306-3623/92$5.00+ 0.00 Copyright © 1992PergamonPress Ltd
EFFECT OF ATP AND VERAPAMIL AS CARDIOPLEGIC ADDITIVES IN THE ISOLATED GUINEA PIG HEART H. SONCUL,L. GOKGOZ,K. AYRANCIOGLU,(~. KARASU,S. KALAYCIOGLUand A. EF,.SOz Department of Thoracic and Cardiovascular Surgery of Gazi University Medical School, Be~evler, Ankara, Turkey (Received 3 December 1991) Al~traet--1. A comparative study on isolated guinea pig hearts was carried out to determine the effects of ATP and verapamil as cardioplegic additives. 2. The hearts were arrested by one of the plegic solutions: I, potassium 20 retool/l; II, potassium 20 mmol/l + verapamil 1.I #mol/1; III, potassium 20 mmol/l + ATP 10 mmol/1.After 45 rain of hypothermic isehemia, the hearts were reperfused by Krebs-Henseleit buffer. 3. Postischemic percentage change of myocardial functions (heart rate, contractility, heart work) and tissue enzymes (LDH, SGOT, SGPT) were compared between the groups. 4. Although a rapid cardiac arrest could be obtained by verapamil added cardioplegia. Postischemic myocardial recovery was much better with ATP added cardiopleglc solutions.
INTRODUCTION The problem of myocardial protection and a rapid cardiac arrest during cardiac surgery led to several investigations on cardioplegic solutions (Bourdillon and Peele-Wilson, 1980; Brandt, 1981). It is shown that calcium influx into myocardial cells is associated with increased adenosine triphosphate (ATP) consumption and contracture formation (Fleckenstein, 1977). Therefore intracellular calcium overload plays an important role in myocardial ischemic injury (Bretsehnei et aL, 1975; Hearse et aL, 1980). Although their value is controversial, calcium channel blockers such as verapamil, nifedipine and diltiazem which inhibit the influx of calcium by blockage of the "slow channel" and arrest the plateau phase of electrical depolarization, have been evaluated as cardioplegic additives (Magovern et al., 1981; Yamamato et aL, 1985). On the other hand to supply the demands of ischemic myocardium by high energy compounds has also been investigated (Parrat and Marshall, 1974; Bernard et al., 1988). Several studies have focused on the possibility of saving myocardial high energy phosphates by using ATP as an additive to cardioplegic solutions (Thelin et al., 1986, 1987). ATP and other adenine derivatives have negative chronotropic, negative dromotropic and antiarrythmic effects on myocardium. They inhibit sinoatrial and atrioventricular nodes, thereby potentially inducing cardiac arrest (Ward et al., 1983). ATP also decreases calcium influx into the cell and reduces cellular calcium loading caused by cathecolamines (Wayne et al., 1949; Thelin et al., 1985). In the present experimental study we have specifically compared the effects of verapamil and ATP as cardioplegic additives on cardiac arrest and myocardial recovery. 909
MATERIALSAND METHODS Animals Hearts were obtained from male guinea pigs (N = 30) weighing 280-370 g. All animals received humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by the National Institutes of Health (NIH Publication No. 80-23, revised 1978). The animals were anesthetized by ether and given 200 units of beparin into the femoral vein. The hearts (1.8-2.4 g) were rapidly removed and cannulated via the aorta. Perfusion techniques and plegic solutions The hearts were mounted on a modified Langendorf perfusion apparatus and perfused by a gassed (oxygen95%, carbondioxide 5%) Krebs-Henseleit solution at a rate of 2 ml/min at 37°C. (Mean arterial pressure = 80 mmHg.) The composition of the solution (in retool/l) was NaHCO3, 25; NaCI, 118; KH2PO4, 1.2; KC1, 4.8; MgSO+, 1.2; CaC12, 1.2; and glucose, 11.1. Three different cardioplegic solutions (10 experiments in each group) were used to arrest the hearts. The composition of these solutions were: Group 1, NaC1 123retool/I, KCI 20mmol/l, MgCI 8 retool/l, glucose 11.1 retool/l, NaHCO 3 9 retool/l, pH 7.6; Group 2, the same solution in Group I + verapamil 1.0 #reel/l; Group 3, the same solution in Group 1 + ATP 10 mmol/l. Protocol After 10 min of a stabilization period, we recorded the contractility, heart rate and also collected perfusate samples from the fight atrium to determine tissue enzymes. The hearts were arrested by infusion of one of the cardioplegic solutions from the aortic root at a rate of 2 ml/min for 3 min at 4°C. Over this 3 min of plegic infusion the arrest time and number of beats were assessed. Following cardiac arrest the plegic solution was removed by infusion of 2 ml isotonic
H.SONCUL et
910
Perfu$ion of Krebs solution
Rel)erfusion of Krebs solution
Hypot hermlc
Cordioplegl¢ infusion
3 minutes
al.
Ischemlo
[~
10 minutes/
45 minutes
Recording mechanical
Washout of cardioplegJc
Recording mechanical data and collectinq
[
data and collecting perfusate samples
perfusate samples
Fig. 1. Experimental protocol.
saline from the aortic root. During the ischemic period the hearts were kept at 8-10°C by topical cooling with isotonic saline. After 45 min of ischemia the reperfusion was begun by the same buffer at 37°C. At the 10th min of reperfusion again the contractility and heart rate were recorded and perfusate samples were collected (Fig. 1). Calculations The following calculations were made. Arrest time: time (sec) from the onset of cardioplegic infusion until the heart arrests. Arrest beats: number of heart beats during 3 rain of cardioplegic infusion.
Percentage recovery of heart rate = Postischemic heart rate × 100 Preischemic heart rate Percentage recovery of ventricular contractions = Postischemic contractions × 100 Preischemic contractions
Percentage recovery of heart work = Postischemic heart rate x postischemic contractions x 100 Preischemic heart rate x preischemic contractions Percentage change of tissue enzymes = Postischemic enzyme (LDH, SGOT, SGPT) concentrations x 100 Preischemic enzyme concentrations Data and statistics Ventricular contractility (in g) and heart rate (beats/rain) were recorded through (UGO BASILE 7004) isometric force transducer connected to a microdynomometer (UGO BASILE 7050). The biochemical parameters (LDH, SGOT, SGPT) were calculated by "Technican RA-1000" autoanalyzer using "Chromatest" kits. The results are presented as mean and SEM. Overall significance of difference between groups was determined by t-test using "Microstat" PC program.
60
Dl~a
! 40
30
20 10
Arrest
time
(sec)
Arrest
beats
(no)
Fig. 2. Arrest time: time between the onset of cardioplegic infusion and cardiac asystole. Arrest beats: number of heart beats during cardioplegic infusion. *Indicates significant difference between indicated group and potassium (control) group (P < 0.05). Values are mean + SEM.
ATP and verapamil in cardioplegia
911
120
100
80
40
20
Heart
rate
Contractility
Heart
work
Fig. 3. Postischemic recovery of heart rate, ventricular contractions and heart work according to their preischemic values. *Indicates significant difference between value indicated and potassium (control) group (P < 0.05). Values are mean + SEM.
RESULTS
Effect of verapamil and A TP on cardiac arrest From the beginning of the cardioplegic infusion, the time to cardiac arrest was significantly reduced by verapamil containing solution and the number of beats during the 3 min of cardioplegic infusion were reduced by both verapamil and ATP containing solutions. Time to cardiac arrest was reduced from 52.6 ± 14.1 see in potassium group to 19.3 ± 2.4see in vvrapamil group and to 35.8 ± 11.1 sec in ATP group (P < 0.05 for comparisons between verapamil and potassium groups).
The number of beats during cardioplegic infusion was reduced from 38.7 ± 8.3 in potassium group to 16.8 ± 2.6 in verapamil group and to 15.0 ± 2.6 in ATP group (P < 0.05 for both verapamil and ATP groups when compared with potassium group). (See Fig. 2.)
Effect of verapamil and A TP on myocardial recovery Mechanical parameters. There was no significant difference between the three groups for final recovery of the heart rate. The percentage change of the heart rate was, 95.1 ± 8 . 4 % in potassium group where it was 102.5±11.1% in verapamil group and 108.9 ± 10.3% in ATP group.
250
150-
~47
100-
50-
0 LDH
SGOT
SGPT
Fig. 4. Postischemic concentrations of lactic dehydrogenase (LDH), serum glutamic pyruvate transaminase (SGPT), serum glutamic oxalic transaminase (SGOT) of the perfusate as percentage change of their preischemic values. *Indicates significant difference between indicated group and potassium (control) group (P < 0.05). Values are mean + SEM.
912
H. SONCULet al.
Postischemic recovery of the left ventricular contractility was significantly better in ATP group 71.5-t-5.3% when compared with the potassium group 53.7 __. 5.0% and also with the verapamil group 45.1 + 4.1% (P < 0.05 for both comparisons). Although the percentage recovery of contractility was slightly better in potassium group compared to verapamil group, the difference was not significant statistically (Fig. 3). Postischemic recovery of cardiac work as a percentage of the preischemic calculation was expressively better in ATP group 88.7 + 6.4% compared with the potassium 45.7 + 3.1°/'o and the verapamil 46.6 + 2.7% groups (P < 0.05 for both comparisons) (Fig. 3). Biochemical parameters. Postischemic percentage changes of LDH and SGPT concentrations were significantly higher in potassium group when compared with ATP and verapamil groups (P < 0.05 for both comparisons). There was no significant difference among the three groups for SGOT concentrations (Fig. 4). DISCUSSION Decreasing myocardial energy consumption and increasing myocardial energy stores are the two major ways of myocardial protection during global ischemia. The most effective and commonly used techniques like hypothermia and potassium arrest to decrease myocardial energy consumption still cannot preclude significant depression of myocardial function and high energy phosphate stores flyers, 1988). There is a conception that better myocardial protection and a rapid cardiac arrest can be achieved by adding verapamil or other calcium blockers to plegic solutions because of their theoretical advantages such as decreasing calcium influx into the cell, protection of arrythmias, decreasing ATP consumption and coronary vasodilatation (Henry, 1980; Clark et al., 1981; Yamamato et ai., 1983). Although it is controversial, recent evidence shows that calcium blocking agents have cardioprotective effect in normothermic ischemia, but in hypothermic conditions they fail to afford additional protection (Johnson et al., 1982; Prasad and Bharadwaj, 1987). Corroborating with these previous data, our study shows that addition of verapamil to cardioplegic solutions supplies a rapid cardiac arrest and decreases myocardial injury (elevation of enzyme levels are significantly less in verapamil group when compared with potassium group). But it has no beneficial effect on postischemic myocardial recovery. ATP which is a high energy phosphate itself has also nearly the same theoretical effects of verapamil, mentioned above (Ward et al., 1983). Our study corroborates previous conclusions that high energy phosphates could be effective on postischemic recovery as cardioplegic additives (Thelin et ai., 1986). Our data shows that, postiscbemic left ventricular contractility and cardiac work are much better and also the elevation of enzyme levels, which represent tissue injury (for LDH and SGPT) are significantly less when ATP is added to cardioplegia. We also confirmed that ATP containing solution can decrease the number of beats during the cardioplegic infusion. However it can be argued that
decreasing the energy consumption by a rapid cardiac arrest, maintains better myocardial protection. It was controversial to our data with verapamil that caused rapid cardiac arrest (decreases both arrest time and arrest beats) without any additional effect on myocardial recovery. CONCLUSION Finally according to our study, we can argue that verapamil, which is a useful agent for cardiac arrest, shows no additional effect for myocardial protection in hypothermic conditions. On the other hand ATP as an additive to cardioplegia has beneficial protective effects on myocardium. SUMMARY
In order to determine the role of verapamil and adenosine triphosphate (ATP), as cardioplegic additives on cardiac arrest and postischemic myocardial recovery, a comparative study has been undertaken in isolated guinea pig hearts using Langcndorf technique as a model of cardio-pulmonary bypass. The hearts (n = 10 in each group) previously being perfused by Krebbs solution were arrested by one of the subsequent solutions. I, potassium 20 mmol/l; II, potassium 20 mmol/l + verapamil 1 #mol/l; III, potassium 20 mmol/l + ATP 10 mmol/1. After 45 rain of hypothermic ischemia, postischemic recovery of heart rate, ventricular contractility heart work and postischemic changes of tissue enzymes (LDH, SGOT, S GPT) were compared between the groups. Also arrest time and number of arrest beats were recorded and compared. Even though cardiac arrest was achieved more rapidly with verapamil group, postischemic myocardial recovery was significantly better in ATP group when compared with verapamil and potassium 20 mmol/I groups. REFERENCES
Bernard B., Aaro (3. and Shlomo L. (1988) Comparative clinical and electrophysiologic effects of adenosine triphosphate and verapamil on paroxysmal reciprocating junctional tachycardia. Circulation 77, 795-805. Bourdillon P. D. and Poole-Wilson P. A. (1980) Effects of verapamil and cardioplegia on calcium exchange and mechanical function in myocardial ischemia. Circulation 42, 31. Brandt B., Richardson R. V., O'Bryan P. and Ehrenhaft J. L. (1981) Intramyocardial electrical and metabolic activity during hypothermia and potassium cardioplegia. Ann. Thorac. Surg. 31, 117-121. Bretschneider H. J., Hubner G., Knoll D., Lohr B., Nordbeck H. and Spieckerman P. G. (1975) Myocardial resistance and tolerance to ischemia: physiological and biochemical basis. J. cardiovasc. Surg. 16, 241-260. Clark R. E., Christlieb I. Y., Spratt J. A., Henry P, D., Fischer A. E., Williamson J. R. and Sob¢l E. B. (1981) Myocardial preservation with nifedipine: a comparative study at normothermia. Ann. thorac. Surg. 31, 315-327. Fleckenstein A. (1977) Specific pharmacology of calcium in myocardium, cardiac pacemakers, and vascular smooth muscle. A. Rev. Pharmac. Toxic. 17, 149. Hearse D. J., Stewart D. A. and Braimbridge M. V. (1980) The additive protective effects of hypothermia and chemical cardioplegia during ischemic cardiac arrest in the rat. J. thorac, cardiovasc. Surg. 79, 39-43.
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