Nifedipine and cardioplegia: rat heart studies with the St Thomas' cardioplegic solution.

The ability of nifedipine to enhance myocardial protection was assessed using an isolated rat heart model of cardiopulmonary bypass and ischaemic cardiac arrest. With normothermic ischaemic arrest (35 min, 37 degrees C), nifedipine addition improved the protective properties of the St Thomas' cardioplegic solution. Optimal protection was observed with 0.075 mumol nifedipine X litre-1, where post-ischaemic recovery of aortic flow was improved from 47.9 +/- 5.2% to 76.7 +/- 2.9% (P less than 0.001) and creatine kinase leakage was reduced by approximately 50%. Despite the marked additional protection under normothermic conditions the drug was unable to improve contractile recovery after a period of hypothermic ischaemic arrest (150 min, 20 degrees C) although it did allow a significant reduction (22%) in creatine kinase leakage. In other studies, the ability of nifedipine to replace the cardioplegic solution was examined. Under normothermic conditions, it showed a good ability to protect against ischaemia, but this protection did not match that afforded by the St Thomas' cardioplegic solution. Under hypothermic conditions the drug failed to substitute for the cardioplegic solution, suggesting that a common modality between hypothermia and nifedipine-induced protection.

Free radicals and cardioplegia: organic anti-oxidants as additives to the St Thomas' Hospital cardioplegic solution.

The isolated perfused working rat heart model of cardiopulmonary bypass and ischaemic cardiac arrest has been used to investigate whether addition of various organic anti-oxidants to the St Thomas' Hospital cardioplegic solution can enhance the recovery of function of the rat myocardium after normothermic (37 degrees C) global ischaemic arrest. Five anti-oxidants were studied: (i) ascorbate (1.0 and 10.0 mmol.litre-1), (ii) methionine (1.0 and 10.0 mmol.litre-1), (iii) reduced glutathione (1.0 and 10.0 mmol.litre-1), (iv) dimethylthiourea (0.1, 1.0, 10.0 and 50.0 mmol.litre-1), (v) N-2-mercaptopropionyl glycine (0.1, 1.0 and 10.0 mmol.litre-1). The recovery of aortic flow in control hearts which were free of anti-oxidant was 50.7(SEM 0.5)%; ascorbate (1.0 or 10.0 mmol.litre-1) improved this recovery to 72.1(1.7) and 70.2(0.3)% respectively; methionine (1.0 and 10.0 mmol.litre-1) improved the recovery to 74.1(5.7)% and 67.7(1.7)%, respectively; reduced glutathione (1.0 and 10.0 mmol.litre-1) improved the recovery to 66.7(1.4)% and 74.0(1.7)% respectively. In further studies, the addition of dimethylthiourea (0.1, 1.0 and 10.0 mmol.litre-1) to the cardioplegic solution failed to improve recovery of aortic flow [47.3(8.0), 24.6(7.3), 48.0(7.7)% respectively] when compared to its anti-oxidant free control value of 40.4(6.1)% and at a concentration of 50.0 mmol.litre-1 a very poor recovery of aortic flow of 7.7(4.8)% was observed. Mercaptopropionyl glycine (0.1, 1.0 and 10.0 mmol.litre-1) also failed to improve the recovery of aortic flow [34.7(1.6), 34.7(7.7) and 25.6(5.4)% respectively.2+ Since biological membranes are highly permeable to dimethylthiourea and mercaptopropionyl glycine, it is possible that they accumulate in the intracellular compartment.(ABSTRACT TRUNCATED AT 250 WORDS)

Equipment for inducing cold cardioplegic arrest.

A technique for the infusion of the cardioplegic solution used at St. Thomas' Hospital is described. A flanged aortic root needle is used for patients with competent aortic valves and hand-held metal cannulas for those with aortic regurgitation.

Protection of the pediatric myocardium. Differential susceptibility to ischemic injury of the neonatal rat heart.

Myocardial protection during pediatric cardiac operations has been suggested to be less successful than in adult hearts. In the present study we have compared the resistance of adult, infant, and neonatal rat hearts to various periods of ischemic arrest with normothermic (37 degrees C) crystalloid cardioplegia. Isolated hearts with intraventricular balloons, from adult (50 to 60 days of age, heart weight 865 +/- 13 mg), infant (20 to 25 days of age, heart weight 251 +/- 3 mg), and neonatal rats (3 to 5 days of age, heart weight 40 +/- 1 mg) were subjected to 10, 20, 30, 40, 50, 60, 80, and 100 minutes of ischemia (n = 6 hearts for each time point and for each age group). St. Thomas' Hospital cardioplegic solution was infused at the onset of the period of arrest. With increasing durations of ischemia there was a declining postischemic recovery of function. Up to 40 minutes of ischemia there was no significant difference between the three age groups in postischemic recovery of left ventricular developed pressure: 40.3% +/- 4.4%, 45.4% +/- 6.5%, and 44.4% +/- 2.2% of preischemic control for adult, infant, and neonatal hearts, respectively. Beyond 40 minutes adult and infant hearts showed an identical deterioration with effectively no recovery beyond 60 minutes of ischemia. By contrast, neonatal hearts were much more resistant to ischemia. After 100 minutes of ischemia the mean recovery of left ventricular developed pressure was 20.9% +/- 1.1%, whereas in infant and adult hearts the values were 0.6% +/- 0.3% after 80 minutes of ischemia and 0% after 100 minutes, respectively. Analysis of creatine kinase leakage also indicated that with ischemic durations in excess of 40 minutes, the neonatal heart was far more resistant to ischemia, and creatine kinase leakage per gram dry weight was much less than in infant or adult rats. Analysis of the rates of recovery during reperfusion again revealed differences between neonatal hearts and hearts from the other two age groups. We conclude that in the normal rat the neonatal heart has a greater inherent tolerance to ischemia than that of the infant or adult rat.

Myocardial protection during ischemic cardiac arrest. A possible hazard with calcium-free cardioplegic infusates.

A number of cardioplegic and protective solutions have been described for the reduction of cellular damage during ischemic cardiac arrest. These solutions are designed to induce diastolic arrest rapidly and to combat the various deleterious effects of ischemia. The efficacy of three different infusates (Bretschneider, Kirsch and St. Thomas' Hospital) has been compared. The results indicate that, whereas some solutions are able to afford striking protection, others may be ineffective and may exacerbate damage. Until the mechanisms underlying ischemic damage and its prevention are understood, it would seem undesirable to advocate the use of solutions containing extremes of concentration or solutions devoid of ions normally found in the extracellular fluid.

Protection of the ischemic myocardium. Volume-duration relationships and the efficacy of myocardial infusates.

In studies in the isolated rat heart that were designed to optimize the composition of the infusion conditions for a cardioplegic protective solutuin, we have observed a complex relationship between the duration and volume of infusion and the extent of tissue protection. Our results would indicate that solutions, such as that formulated at St. Thomas' Hospital, which are based on extracellular electrolyte content, afford (after a brief equilibration period) a constant degree of protection, irrespective of infusion volume or duration. In contrast other solutions, such as the Bretschneider solution, which have extremes of electrolyre concentration, are associated with a complex dose-response relationship. In the latter instance, infusion of small volumes for short durations affords an increasing degree of protection against ischemia. Increasing the infusate volume may result in a progressive loss of protection. Excessive infusion may lead to an exacerbation of ischemia-induced damage. Our studies suggest that the relative patterns and rates of re-equilibration of various ions, especially sodium and calcium, during infusion may play a major role in determining the efficacy of the infusate.

Calcium and cardioplegia. The optimal calcium content for the St. Thomas' Hospital cardioplegic solution.

The relationship between the calcium content of the St. Thomas' Hospital cardioplegic solution and the degree of tissue protection it affords has been characterized by means of an isolated working rat heart preparation subjected to normothermic ischemic arrest. With a 3 minute period of preischemic infusion of solutions containing calcium chloride concentrations of 0, 0.6, 1.0, 1.1, 1.2, 1.3, 1.4, and 2.4 mmol/L and 35 minutes of normothermic ischemic arrest, postischemic creatine kinase leakage was 562.3 +/- 26.7, 64.8 +/- 12.1, 63.3 +/- 9.9, 37.5 +/- 5.4, 33.4 +/- 3.1, 41.2 +/- 4.1, 58.6 +/- 7.4, and 65.7 +/- 9.1 IU/15 min/gm dry weight, respectively. The postischemic recovery of aortic flow was 0%, 29.2% +/- 6.8%, 29.0% +/- 3.3%, 45.8% +/- 4.9%, 55.5% +/- 1.4%, 38.5% +/- 2.7%, 27.8% +/- 8.6%, and 19.5 +/- 7.1%, respectively. The results indicate optimal protection with a calcium concentration of 1.2 mmol/L and a rapid decline in protection with even small changes in concentration either side of the optimum. The hazard of total absence of calcium was confirmed by the induction of the calcium paradox. This study shows that under normothermic conditions a calcium concentration of 1.2 mmol/L is optimal for the St. Thomas' Hospital solution. This study reinforces the importance of undertaking dose-response studies for all components of all cardioplegic solutions.

Long-term preservation of the mammalian myocardium. Effect of storage medium and temperature on the vulnerability to tissue injury.

Human heart preservation for transplantation commonly involves infusion of cold cardioplegic solutions and subsequent immersion in the same solution. The objectives of the present study were (1) to establish the temporal relationship between storage time (at 10 degrees C) and the postischemic recovery of function in the isolated rat heart, (2) to assess, by metabolic and functional measurements, whether storing the heart in fluid as opposed to moist air had any effect on the viability of the preparation, and (3) to ascertain the optimal storage temperature. Isolated rat hearts (at least 6 in each group) were infused for 3 minutes with St. Thomas' Hospital cardioplegic solution No. 2 at 10 degrees C, stored at 10 degrees C for 6, 12, 18, or 24 hours, and then reperfused at 37 degrees C. Mechanical function, assessed by construction of pressure-volume curves (balloon volumes: 20, 40, 60, 80, 100, and 120 microliters), was measured before ischemia and storage and after 60 minutes of reperfusion. Function deteriorated in a time-dependent manner; thus at a balloon volume of 60 microliters the recovery of left ventricular developed pressure was 84.2% +/- 5.3% after 6 hours (p = not significant when compared with preischemic control); 69.1 +/- 3.3% after 12 hours (p less than 0.05); 55.6% +/- 4.4% after 18 hours (p less than 0.05), and 53.0% +/- 6.8% (p less than 0.05) after 24 hours of storage. Other indices of cardiac function, together with creatine kinase leakage and high-energy phosphate content, supported these observations. Since the recovery of the left ventricular developed pressure balloon volume curves were essentially flat after 18 and 24 hours of storage, either 6 or 12 hours of storage were therefore used in subsequent studies. Comparison of storage environment (hearts either immersed in St. Thomas Hospital cardioplegic solution No. 2 or suspended in moist air at 10 degrees C for 6 or 12 hours) revealed no significant differences in functional recovery between the groups. Thus hearts recovered 94.9% +/- 3.5% and 113.7% +/- 12.4%, respectively, after 6 hours of storage and 71.6% +/- 2.4% and 54.2% +/- 7.9%, respectively, after 12 hours of storage. Enzyme leakage and tissue water gain were also similar in both groups of hearts. Finally, hearts (n = 6 per group) were subjected to 12 hours' storage at 1.0 degree, 5.0 degrees, 7.5 degrees, 10.0 degrees, 12.5 degrees, 15.0 degrees, and 20.0 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)

The St. Thomas' Hospital cardioplegic solution. A comparison of the efficacy of two formulations.

Two commercially available formulations of St. Thomas' Hospital cardioplegic solutions, known as No. 1 (MacCarthy) and No. 2 (Plegisol, Abbott Laboratories, North Chicago, Ill.), were compared in the isolated working rat heart subjected to a long period (3 hours) of hypothermic ischemic arrest with multidose infusion. Solution No. 2 was found to be superior in nearly all respects. Of the 10 hearts infused with solution No. 1, persistent ventricular fibrillation during postischemic reperfusion occurred in six. Two of the six hearts, still in fibrillation after 15 minutes of reperfusion, were returned to regular rhythm by electrical defibrillation but failed to maintain an output. In contrast, in the 10 hearts infused with solution No. 2, ventricular fibrillation was short lasting (p less than 0.01). In comparing mechanical function in all hearts returning to regular rhythm (either spontaneously or after electrical defibrillation), the mean postischemic recoveries for aortic flow and rate of rise of left ventricular pressure (expressed as a percentage of its preischemic control) were significantly greater with solution No. 2 than with solution No. 1 (74.3% +/- 6.9% compared with 18.7% +/- 8.9%, p less than 0.01, and 98.0% +/- 6.0% compared with 63.0% +/- 9.0%, p less than 0.005, respectively). Creatine kinase leakage tended to be lower in hearts infused with solution No. 2 (19.7 +/- 4.7 IU/15 min/gm dry weight as opposed to 27.5 +/- 4.7 IU/15 min/gm dry weight), although this difference did not achieve a level of statistical significance. Consideration is given to the differences in formulation between solutions, which might account for the improved performance with solution No. 2, and it is concluded that the lower calcium content of solution No. 2 (1.2 as opposed to 2.4 mmol/L) is likely to be the most important factor.

Improved myocardial protection by oxygenation of St. Thomas' Hospital cardioplegic solutions. Studies in the rat.

The effect of oxygenation (100% oxygen) of the St. Thomas' Hospital cardioplegic solutions No. 1 (MacCarthy) and No.2 (Plegisol, Abbott Laboratories, North Chicago, Ill.) was examined in the isolated working rat heart subjected to long periods (3 hours for studies with solution No. 1 and 4 hours for studies with solution No. 2) of hypothermic (20 degrees C) ischemic arrest with multidose (every 30 minutes) cardioplegic infusion. At the aortic infusion point the oxygen tension of the oxygenated solutions (measured at 20 degrees C) was in the range of 320 to 560 mm Hg whereas that of the nonoxygenated solutions was less than 150 mm Hg. Twenty hearts (10 oxygenated and 10 nonoxygenated) were studied for each solution. The studies with solution No. 1 demonstrated that oxygenation led to a significant (p less than 0.05) reduction in the incidence of persistent ventricular fibrillation during postischemic reperfusion. Oxygenation of the cardioplegic solution also improved postischemic functional recovery so that the recovery of aortic flow was improved from 18.7% +/- 8.9% (of its preischemic control level) in the nonoxygenated group to 54.6% +/- 6.6% in the oxygenated group (p less than 0.025). Creatine kinase leakage was also significantly reduced from 27.5 +/- 4.8 to 9.9 +/- 0.6 IU/15 min/gm dry weight (p less than 0.005). Studies with solution No. 2 indicated that protection was better than with solution No. 1, even in the absence of oxygenation. A better degree of functional recovery was obtained after 4 hours of arrest with solution No. 2 than that obtained after only 3 hours of arrest with solution No. 1, and persistent ventricular ventricular fibrillation was never observed with solution No. 2. However, despite the superior performance with solution No. 2, further improvements could be obtained by oxygenation, with that time from the onset of reperfusion to the return of regular sinus rhythm being reduced from 55 +/- 8 to 35 +/- 2 seconds (p less than 0.01), postischemic recovery of aortic flow increasing from 59.8% +/- 7.4% to 85.7% +/- 2.5% (p less than 0.005), and creatine kinase leakage being reduced from 38.1 +/- 7.3 to 16.2 +/- 1.5 IU/15 min/gm dry weight (p less than 0.005). It is concluded that oxygenation of the St. Thomas' Hospital cardioplegic solutions improves their ability to protect the heart against long periods of ischemia and that this is manifested by improved postischemic electrical stability, functional recovery, and reduced creatine kinase leakage.

Enhanced myocardial protection with high-energy phosphates in St. Thomas' Hospital cardioplegic solution. Synergism of adenosine triphosphate and creatine phosphate.

The potential for improving myocardial protection with the high-energy phosphates adenosine triphosphate and creatine phosphate was evaluated by adding them to the St. Thomas' Hospital cardioplegic solution in the isolated, working rat heart model of cardiopulmonary bypass and ischemic arrest. Dose-response studies with an adenosine triphosphate range of 0.05 to 10.0 mmol/L showed 0.1 mmol/L to be the optimal concentration for recovery of aortic flow and cardiac output after 40 minutes of normothermic (37 degrees C) ischemic arrest (from 24.1% +/- 4.4% and 35.9% +/- 4.1% in the unmodified cardioplegia group to 62.6% +/- 4.7% and 71.0% +/- 3.0%, respectively, p less than 0.001). Adenosine triphosphate at its optimal concentration (0.1 mmol/L) also reduced creatine kinase leakage by 39% (p less than 0.001). Postischemic arrhythmias were also significantly reduced, which obviated the need for electrical defibrillation and reduced the time to return of regular rhythm from 7.9 +/- 2.0 minutes in the control group to 3.5 +/- 0.4 minutes in the adenosine triphosphate group. Under more clinically relevant conditions of hypothermic ischemia (20 degrees C, 270 minutes) with multidose (every 30 minutes) cardioplegia, adenosine triphosphate addition improved postischemic recovery of aortic flow and cardiac output from control values of 26.8% +/- 8.4% and 35.4% +/- 6.3% to 58.0% +/- 4.7% and 64.4% +/- 3.7% (p less than 0.01), respectively, and creatine kinase leakage was significantly reduced. Parallel hypothermic ischemia studies (270 minutes, 20 degrees C) using the previously demonstrated optimal creatinine phosphate concentration (10.0 mmol/L) gave nearly identical improvements in recovery and enzyme leakage. The combination of the optimal concentrations of adenosine triphosphate and creatine phosphate resulted in even greater myocardial protection; aortic flow and cardiac output improved from their control values of 26.8% +/- 8.4% and 35.4% +/- 6.3% to 79.7% +/- 1.1 and 80.7% +/- 1.0% (p less than 0.001), respectively. In conclusion, both extracellular adenosine triphosphate and creatine phosphate alone markedly improve the cardioprotective properties of the St. Thomas' Hospital cardioplegic solution during prolonged hypothermic ischemic arrest, but together they act additively to provide even greater protection.

Optimal myocardial protection during crystalloid cardioplegia. Interrelationship between volume and duration of infusion.

There is often a large difference between volumes of crystalloid cardioplegic solution used clinically (2 to 4 ml/gm myocardium) and experimentally (in rat heart preparations, volumes of 30 ml/gm or more are used). In an attempt to reconcile these differences and define the minimum volume and/or duration of infusion of the St. Thomas' Hospital cardioplegic solution consistent with maximal myocardial protection, we have used the isolated working rat heart to characterize the relationships between myocardial protection and (1) the duration of cardioplegic infusion and (2) the volume of cardioplegic infusion. Hearts (n = 6 per group, weighing 0.90 +/- 0.06 gm) were subjected to 0, 5, 10, 15, 30, 45, 60, 120, 180, 240, or 300 seconds of cardioplegic infusion (mean infusion volumes = 0, 1.3 +/- 0.1, 2.0 +/- 0.1, 2.8 +/- 0.2, 5.0 +/- 0.1, 8.3 +/- 0.2, 10.5 +/- 0.8, 21.8 +/- 2.1, 22.7 +/- 1.3, 32.3 +/- 2.1, and 39.1 +/- 1.8 ml per heart, respectively) before 30 minutes of normothermic ischemia. They recovered 3.9% +/- 2.3%, 9.7% +/- 5.0%, 22.8% +/- 5.8%, 34.6% +/- 4.6%, 54.7% +/- 6.6%, 64.0% +/- 5.0%, 67.4% +/- 4.0%, 56.6% +/- 11.1%, 60.0% +/- 5.8%, 51.6% +/- 7.0%, and 68.0% +/- 7.8% of their preischemic cardiac output on reperfusion. Creatine kinase leakage, tissue adenosine triphosphate and creatine phosphate content, and other indices of cardiac function supported this observation. To assess volume of infusion rather than duration, we infused hearts (n = 6 per group) with 1.0, 1.5, or 2.0 ml of cardioplegic solution over 120 seconds. Although recovery of cardiac output with 2.0 ml (56.2% +/- 6.8%) was not significantly different from that (56.6% +/- 11.1%) observed with large volumes of solution (21.9 +/- 2.1 ml), infusion of 1.5 and 1.0 ml resulted in poor recovery of cardiac output (40.1% +/- 4.6% and 21.8% +/- 3.9%, respectively). To assess duration (with low volumes) rather than volume of infusion, we infused hearts (n = 6 per group) with 2.0 ml of cardioplegic solution over 10, 30, 60, or 120 seconds. Maximal protection was observed with 30, 60, and 120 seconds of infusion (recovery of cardiac output = 56.7% +/- 5.9%, 45.1% +/- 7.9%, and 56.2% +/- 6.8%, respectively). Our results suggest that, for maximum myocardial protection, the St. Thomas' Hospital solution should be infused at a rate of not less than 2.0 ml/gm wet weight of heart and that the duration of infusion should be not less than 30 seconds.

Protection of the myocardium during ischemic arrest. Dose-response curves for procaine and lignocaine in cardioplegic solutions.

The dose-response curve of procaine or lignocaine (lidocaine) added to the St. Thomas' Hospital cardioplegic solution was investigated with an isolated working rat heart preparation. In the absence of any cold cardioplegic protection, hearts failed to recover after as little as 30 minutes of ischemia. A single infusion (20 degrees C) of the basic St. Thomas' Hospital cardioplegic solution allowed hearts to recover to 60% or more of their preischemic control aortic flow after a 120 minute period of ischemia. Addition of procaine to the cardioplegic solution either increased or reduced the apparent protective properties of the solution with a bell-shaped dose-response curve being obtained. The optimum procaine concentration was 0.05 mM/L. At this concentration the protection afforded by the St. Thomas' Hospital solution was increased by up to two thirds. Substitution of lignocaine for procaine resulted in a similar dose-response curve with its optimum also at 0.05 mM/L. If a similar optimum exists for the human heart, the doses in current clinical use would appear to be too high. These results argue for determining the dose-response characteristics of all substances used in cardioplegic solutions.

Cardioplegia and slow calcium-channel blockers. Studies with verapamil.

The ability of dl-verapamil to enhance myocardial protection when given before, during, or after myocardial ischemia was assessed with the use of an isolated working rat heart model of cardiopulmonary bypass and ischemic cardiac arrest. Under conditions of normothermic ischemic arrest (30 minutes at 37 degrees C), the addition of verapamil enhanced the protective properties of the St. Thomas' Hospital cardioplegic solution. Optimal protection was observed with verapamil concentrations of 0.5 mg/L (1.09 mumol/L) of cardioplegic solution. Under these conditions, postischemic enzyme leakage was reduced by 32.2% and the postischemic recovery of aortic flow was improved by 18.7%. Despite the additional protection at normothermia, the drug at several concentrations appeared unable to improve functional recovery after an extended period of hypothermic arrest (150 minutes at 20 degrees C), although under these conditions its inclusion in the cardioplegic solution could substantially reduce enzyme leakage. In other studies, the ability of various doses of verapamil alone as a substitute for the cardioplegic solution was examined. At the optimal dose (again 0.5 mg/L), and under normothermic conditions, verapamil alone was a good protection against ischemic injury, although this protection did not match that afforded by the St. Thomas' Hospital cardioplegic solution. In similar studies under hypothermic conditions, the drug failed to afford tissue protection, perhaps indicating some common modality between hypothermia and verapamil-induced protection. Pretreatment with verapamil (0.1 mg/L) prior to ischemia offered moderate additional protection, but its use during reperfusion failed to enhance overall recovery.

Myocardial protection during ischemic cardiac arrest. The importance of magnesium in cardioplegic infusates.

The increasing use of coronary infusates for the protection of the human heart drug ischemic cardiac arrest has placed great emphasis on the need for a rational and safe formulation of any infusion solution. Using a rat heart model of cardiopulmonary bypass and ischemic cardiac arrest, we have found magnesium to be a highly effective component of protective infusates which can be additive to hypothermia and other protective agents. However, the concentration of magnesium bears a complex relationship to the degree of protection, a fact which stresses the need for the establishment of the correct concentration for optimal protection.

Myocardial protection during ischemic cardiac arrest. Possible deleterious effects of glucose and mannitol in coronary infusates.

Cardioplegic protective infusates are designed to induce rapid diastolic arrest and also to reduce or delay the onset of ischemic damage. As this study shows, the use of such infusates can greatly improve postischemic recovery of cardiac function. A number of investigators include glucose, insulin, or mannitol in their infusates in an attempt to increase the amount of protection afforded to the ischemic myocardium. Using an isolated, working rat heart model of cardiopulmonary bypass and ischemic cardiac arrest, we have shown that under certain conditions these additives can be deterimental to tissue protection. The deleterious effects of glucose and mannitol are dose dependent and can be modified by the inclusion of insulin in the infusate. The damaging effects of glucose appear to be both osmotic and metabolic in origin and those of mannitol, purely osmotic. The effects of insulin are complex and may affect a number of cellular processes.

The potential hazard of particulate contamination of cardioplegic solutions.

The potential hazard of particulate debris in unfiltered cardioplegic solutions was assessed using the isolated rat heart preparation. Five intravenous solutions were evaluated: These were manufactured by three pharmaceutical firms (two United States and one British) and are commonly used as bases for preparing clinical cardioplegic solutions. Particles were counted in each solution, and each fell well within the limits for particle contamination defined by both the United States and the British Pharmacopoeias. Intracoronary continuous infusion of each solution over 20 minutes at constant temperature and pressure (20 degrees C, 60 cm H2O) resulted in a progressive reduction in coronary flow (mean reduction 55.7% +/- 6.6%) due to a rise in coronary vascular resistance; filtration of these same solutions through a 0.8 micron filter just prior to their entry into the heart largely prevented these coronary vascular changes. The filter was examined by scanning electron microscopy and showed amorphous and crystalline debris. Nifedipine (0.1 mumol/L) added to the cardioplegic solution reduced by almost 50% the impairment in coronary flow seen in the unfiltered group. In more clinically relevant studies of 180 minutes of hypothermic (20 degrees C) ischemia using multidose cardioplegia (3 minutes every 30 minutes), hearts infused with filtered solution recovered almost 90% of their preischemic functional capacity. Hearts receiving identical but unfiltered solution, however, essentially failed to recover (p less than 0.001) and had significantly higher levels of creatine kinase leakage. These results suggest that commercially produced solutions conforming to limits of particulate contamination acceptable for intravenous administration may prove harmful if given unfiltered directly into coronary arteries, with the likely mechanism of action being particle-induced coronary vasoconstriction.

Creatine phosphate: an additive myocardial protective and antiarrhythmic agent in cardioplegia.

The potential for enhancing myocardial protection by adding high-energy phosphates to cardioplegic solutions was investigated in a rat heart model of cardiopulmonary bypass and ischemic arrest. Creatine phosphate (CP) was evaluated as an additive to the St. Thomas' Hospital cardioplegic solution. Dose-response studies (CP 0 to 50 mmol/L) revealed 10.0 mmol/L as the optimal concentration which improved recovery of aortic flow and cardiac output after a 40 minute period of normothermic (37 degrees C) ischemic arrest from 21.2% +/- 5.4% and 32.8% +/- 4.6% in the CP-free control group to 82.5% +/- 3.7% and 82.6% +/- 4.2% (p less than 0.001), respectively. Creatine kinase (CK) leakage was reduced by 68.7% (p less than 0.001) in the CP group. With hypothermic (20 degrees C) ischemia (240 minutes) and multidose (every 30 minutes) cardioplegia, recoveries of aortic flow and cardiac output were improved from 33.1% +/- 8.4% and 42.2% +/- 7.7% in the CP-free control group to 77.9% +/- 4.2% and 79.6% +/- 4.3% (p less than 0.001), respectively, in the drug group. In addition to improving function and decreasing CK release, CP reduced reperfusion arrhythmias, significantly decreasing the time between cross-clamp removal and return of regular rhythm and also completely obviating the need for electrical defibrillation. 51Chromium-ethylenediaminetetraacetic acid (51Cr-EDTA), an extracellular space marker, was used to study the disappearance of CP from the cardioplegic solution during its stasis in the heart. Upon reperfusion, two thirds of the infused dose appeared unchanged in the coronary effluent; the remainder was either degraded or accumulated by the myocardium. Despite its alleged inability to enter the myocardial cell, exogenous CP exerts potent protective and antiarrhythmic effects when added to the St. Thomas' Hospital cardioplegic solution. Although the mechanism of action remains to be elucidated, it may involve binding or uptake of the drug.

The additive protective effects of hypothermia and chemical cardioplegia during ischemic cardiac arrest in the rat.

In a rat heart model of cardiopulmonary bypass and ischemic cardiac arrest the potential additive protective effects of hypothermia and chemical cardioplegia have been investigated. Isolated rat hearts were subjected to a 2 minute period of coronary infusion with a cardioplegic or a noncardioplegic solution immediately before and also at the midpoint of a 2 hour period of hypothermic (20 degrees C) ischemic cardiac arrest. In the hypothermia plus cardioplegia group postischemic aortic flow recovered to more than 50% of its preischemic control value, myocardial energy phosphate content returned to near preischemic control levels, and creatine kinase leakage was moderate. By contrast, in the hypothermia alone group (coronary infusion with non cardioplegic solution) the postischemic functional recovery was less than 30% of its preischemic control value, cellular high-energy phosphate content was considerably reduced, and creatine kinase leakage was more than twice that observed in the hypothermia plus cardioplegia group. In addition to illustrating the additive nature and powerful protective properties of hypothermia and cardioplegia these studies serve to illustrate the utility of the isolated rat heart model for the primary assessment of procedures designed to protect the myocardium during ischemic cardiac arrest. The results and conclusions derived from this study were quantitatively and qualitatively similar to those obtained in a parallel study in the dog.

Harvesting hearts for long-term preservation. Detrimental effects of initial hypothermic infusion of cardioplegic solutions.

Current procedure for harvesting human donor hearts for long-term storage before transplantation involves direct infusion of a hypothermic (4 degrees C) crystalloid cardioplegic solution into the normothermic (37 degrees C) heart in situ. We used the isolated perfused working rat heart preparation to investigate whether infusing cold crystalloid solutions into normothermic blood-containing hearts was consistent with maximal myocardial protection. Hearts (n = 6 per group) were excised and subjected to a primary (1 minute) infusion with either the St. Thomas' Hospital cardioplegic solution or a bicarbonate buffer solution, at 7.5 degrees C, 22 degrees C, or 37 degrees C. This was followed by a secondary infusion (2 minutes) with cold (7.5 degrees C) cardioplegic solution, after which all hearts were stored at 7.5 degrees C for 6 hours and then reperfused at 37 degrees C for 60 minutes, during which time creatine kinase leakage and cardiac function were measured. Primary infusion with warm solutions resulted in (1) decreased coronary vascular resistance during cardioplegic infusion and (2) greater postischemic cardiac function. This suggests that their use, before the standard cold infusion, might be beneficial to the long-term preservation of transplant donor hearts.