Celsior versus custodiol: early postischemic recovery after cardioplegia and ischemia at 5 degrees C

BACKGROUND: The aim of this experimental study was to compare the protective efficacy of the cardioplegic solutions Celsior and Custodiol. Canine hearts were examined with regard to energy metabolism and early postischemic recovery after 8 or 12 hours of ischemia at 5 degrees C. METHODS: Canine hearts were preserved with Celsior or Custodiol (each n = 19). Five hearts of each group were used to determine myocardial content of energy-rich phosphates immediately after preservation and after 8 and 12 hours of ischemia at 5 degrees C; the remainder were reperfused after 8 and 12 hours of ischemia. Control variables during reperfusion were myocardial content of energy-rich phosphates, myocardial K+ uptake, left ventricular dP/dtmax and dP/dtmin, and incidence of arrhythmias in percentage of heart rate. RESULTS: Custodiol-preserved hearts contained more ATP than Celsior-preserved hearts after 8 and 12 hours of ischemia (8 hours p = ns, 12 hours, p < 0.05). During reperfusion after 8 hours of ischemia, dP/dtmax and dP/dtmin showed the same values for both solutions, after 12 hours values were significantly higher in Custodiol-preserved hearts (p < 0.005). The incidence of reperfusion arrhythmias was higher in hearts of the Celsior group (8 hours p < 0.01, 12 hours p = ns). Myocardial K+ uptake during reperfusion after 8 and 12 hours of ischemia was about twice as high in Celsior-preserved compared to Custodiol-preserved hearts (p < 0.005). CONCLUSIONS: In the Langendorff model of the canine heart, cardioplegia with Celsior showed no advantage over cardioplegia with Custodiol. Differences were observed, however, which may be clinically important, especially in the case of long cold-storage times.     

Evaluation of myocardial preservation using 31P NMR

The purpose of this study was (1) to monitor myocardial high-energy phosphate content and recovery of left ventricular (LV) contractile function following normothermic graded cardiac ischemia and single-dose hypothermic potassium cardioplegia, and (2) to assess the temporal limits of LV functional recovery during single-dose cardioplegia maintained at 17 degrees C. Rabbit hearts (30) were perfused, equipped with an LV balloon, paced at 240 beats/min, and placed in a nuclear magnetic resonance (NMR) magnet. Hearts underwent either graded, global normothermic ischemia or potassium cardioplegia arrest maintained at 17 degrees C for 1 hr. Myocardial high-energy phosphate level, LV contractility, and temperature were monitored continuously. Phosphocreatine (PCr) fell to 10 +/- 2, 2 +/- 1, and 0% of control and ATP to 70 +/- 3, 19 +/- 7, and 0% of control at 10, 40, and 60 min of 37 degrees C ischemia. After 1 hr of reperfusion, regression analysis of final developed pressure (DP) on end ischemic ATP (EIATP) content revealed: DP = 1.02 EIATP + 18 (r = 0.95). Following single-dose cardioplegia, maintained at 17 degrees C, PCr fell to 16 +/- 3% of control at 60 min while ATP fell only to 92 +/- 5% control. With reperfusion, recovery of DP was 100%. It was concluded that (1) PCr serves as an energy buffer for ATP, (2) EIATP predicts recovery of LV function, (3) single-dose cardioplegia maintained at 17 degrees C provides complete myocardial preservation for up to 60 min.     

Alterations in the beta-adrenergic receptor system after hypothermic ischemia in hearts with preischemic beta-receptor desensitization.

Although hypothermic cardioplegic arrest is a basic method of myocardial protection in cardiac surgery, the beta-adrenergic receptor (BAR) system has been little investigated in the heart subjected to hypothermic ischemia. Additionally, although the hypothermic arrest is often induced in hearts with preischemic desensitization of the BAR system by preceding congestive heart failure, the functional state of the BAR system after ischemia has not been studied in these hearts. We investigated alterations in the BAR system after hypothermic ischemia in normal rat hearts and in those with preischemic desensitization of the BAR system produced with isoproterenol (ISP: 400 micrograms/kg/hr for 24 hr). Both normal and BAR-desensitized hearts were isolated and subjected either to 40 min of hypothermic (10 degrees C) global ischemia followed by 40 min of reperfusion or subjected to time-matched aerobic perfusion with modified Krebs-Henseleit solution. At the end of perfusion (1) BAR binding properties with [3H]CGP-12177 and adenylate cyclase activity were measured in crude membrane fraction and (2) the inotropic response to ISP (delta LV + dP/dtmax) was evaluated in an isovolumetric contracting heart preparation. Following reperfusion, normal hearts without desensitized BAR showed a higher Bmax value than those of nonischemic time-matched hearts (41.8 +/- 3.1 vs 35.4 +/- 2.4 fmole/mg protein, P less than 0.05), whereas the Kd value was in a similar range in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preventive effect of post-ischemic reperfusion injury by terminal Nicorandil-Mg cardioplegia

In this study, we evaluated the preventive effect of post-ischemic reperfusion injury by Nicorandil-Mg cardioplegia (Nic: 8 mg/l, Mg: 20 mEq/l) given just prior to reperfusion as "terminal cardioplegia". Nineteen dogs were placed on cardiopulmonary bypass and the aorta was cross-clamped for 90 min under hypothermic (17-19 degrees C) cardioplegic arrest. The hearts of ten dogs were reperfused without terminal cardioplegia (Group A). In the other nine dogs, terminal cardioplegia was given for 2 min prior to reperfusion (Group B). During and after a period of ischemia, myocardial tissue calcium ion (t-Ca) and PCO2 (t-PCO2) were continuously monitored by ISFET (ion sensitive filed effective transistor) sensor. Myocardial tissue blood flow, oxygen consumption and lactate flux were calculated at 5, 10, 20, 40 min of reperfusion. And myocardial function was evaluated at 45 min of reperfusion. In the initial reperfusion period, Group B showed an improved myocardial tissue blood flow compared to group A (at 5 min of reperfusion in group A: 29.4% of control, in group B: 42.7% of control, p less than 0.025). T-Ca and T-PCO2 in Group B were rapidly and significantly decreased at 5 min of reperfusion (t-Ca in group A: 2.8 +/- 0.5 mM----1.7 +/- 0.5 mM, in group B: 3.1 +/- 0.6----1.2 +/- 0.4, p less than 0.05; t-PCO2 in group A: 117.5 +/- 23.0 mmHg----82.5 +/- 17.4 mmHg, in group B: 127.5 +/- 22.5----42.5 +/- 9.7, p less than 0.001), and group B had better metablic recovery evaluated by myocardial oxygen consumption and lactate flux.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced functional recovery with venting during cardioplegic arrest in chronically damaged hearts

Thirty dogs with experimental myocardial infarction underwent cardiopulmonary bypass, hypothermic asanguineous K+ cardioplegia (1 hour), and reperfusion (30 minutes). Ten hearts were vented throughout, 5 only during arrest, and 5 only during reperfusion; 10 were not vented. Left ventricular (LV) performance and compliance were assessed by isovolumic (LV balloon) indexes before bypass and after reperfusion. Vented hearts recovered 116 +/- 8.3% of prearrest developed LV systolic pressure (DLVSP) and 131 +/- 13.6% of prearrest rate of rise of LV pressure (dP/dt). Nonvented hearts allowed to develop pressure during arrest (11.6 +/- 1.6 mm Hg) and reperfusion (65 +/- 4 mm Hg) recovered 50 +/- 3.9% of prearrest DLVSP and 55 +/- 5% of prearrest dP/dt (p less than 0.05). Reduction in LV compliance was comparable in both groups. Mitochondrial architecture (electron microscopy) was preserved in vented hearts, but was modestly disrupted in nonvented hearts, thus suggesting slight metabolic impairment. Functional recovery was nearly complete in hearts vented only during reperfusion (DLVSP, 94 +/- 10.4%; dP/dt, 89 +/- 12.6%), but venting only during arrest led to functional depression (DLVSP, 50 +/- 6.6%; dP/dt, 51 +/- 8%; p = 0.01). We conclude that venting chronically infarcted hearts during cardiac operations affords better myocardial protection by avoiding the damage that occurs during nonvented reperfusion.     

Captopril improves oxygen and glucose extraction in pig hearts during reperfusion after cold cardioplegic storage

The purpose of this study was to evaluate the haemodynamic and metabolic effects of captopril during reperfusion of pig hearts following 360 min global hypothermic cardioplegia and storage (HCS). The hearts were perfused with one litre of cold crystalloid cardioplegia (Bretschneider solution no. 3), excised and stored in saline at 4 degrees C for 360 min. The hearts were then reperfused with blood in a modified Langendorff model for 60 min. Left ventricular function, myocardial blood flow, and arteriovenous differences in oxygen, glucose and lactate were monitored intraoperatively and during reperfusion. Two groups of hearts were studied. Group I (captopril treated, n = 9): the pigs were pre-medicated with increasing oral doses of captopril for 3 weeks (12.5 mg-150 mg daily) and an intravenous dose (25 mg) upon arrival at the laboratory. Captopril was added to the cardioplegia (1000 microg/l) and to the reperfusion media (1000 microg/l). Group II (controls, n = 8): the pigs were given no premedication, captopril-free cardioplegia and the hearts were reperfused with captopril-free blood. Captopril increased myocardial oxygen and glucose extraction during reperfusion (p < 0.05 for both) while lactate remained unchanged after 360 min HCS. Treatments with captopril increased developed left ventricular pressure (DLVP) and relaxation (-dP/dtmax) during reperfusion (p < 0.05 for both), while contractility (+dP/dtmax) was unchanged. Heart rate was reduced in captopril-treated hearts (p < 0.05) while myocardial blood flow (MBF) was similar in the two groups. Captopril administration prior to and during HCS and postcardioplegic reperfusion improves oxygen and glucose extraction in large spontaneously beating porcine hearts during reperfusion. The underlying mechanisms seem to involve metabolic modulation, since myocardial uptake of oxygen and glucose was increased in the absence of changes in myocardial blood flow.     

Temperature-response studies of the detrimental effects of multidose versus single-dose cardioplegic solution in the rabbit heart

Both single-dose and multidose cardioplegia are protective in the ischemic adult heart under normothermic and hypothermic conditions, but in the hypothermic neonatal rabbit heart single-dose cardioplegia only is protective, whereas multidose cardioplegia is damaging. The present studies in the isolated perfused working heart from neonatal rabbits (aged 7 to 10 days) were designed to characterize the interrelationships between temperature, frequency of cardioplegic infusion, and tissue protection. Hearts (n = 8/group) were subjected to 1, 1.5, 1.5, 3, 10, 12, or 18 hours of ischemia at 37.0 degrees, 34.5 degrees, 32.0 degrees, 28.0 degrees, 20.0 degrees, 15.0 degrees, or 10.0 degrees C, respectively. These times were selected to achieve approximately 55% to 75% recovery of cardiac output in hearts during normothermic reperfusion when single-dose (2 minutes) St. Thomas' Hospital cardioplegic solution was given at the onset of each ischemic period. Under these conditions actual recoveries of cardiac output were 55.7% +/- 5.6%, 68.5% +/- 6.8%, 73.8% +/- 4.1%, 54.6% +/- 5.3%, 56.3% +/- 7.5%, 59.5% +/- 7.7%, and 81.3% +/- 2.3% of the preischemic control values, respectively. By contrast, with multidose cardioplegia (given every 60 minutes in the 3- to 18-hour experiments and every 30 minutes in the 1- and 1.5-hour experiments) there was a temperature-dependent loss of protection when compared with single-dose cardioplegia; the recoveries of cardiac output were 75.7% +/- 1.5%, 78.4% +/- 4.8%, 65.0% +/- 5.8%, 36.7% +/- 5.8%, 34.6% +/- 7.5%, 25.9% +/- 6.0%, and 9.6% +/- 6.4%, respectively. These results were reflected in other indices of cardiac function and in changes in vascular resistance during cardioplegic infusion and reperfusion. To ascertain whether the progressive loss of protection was related to the degree of hypothermia or the duration of ischemia (which had to be increased as the temperature was lowered to permit a 55% to 75% recovery in the single-dose cardioplegia group), we conducted studies at a fixed temperature (20 degrees C) with variable durations of ischemia (6, 8, 10, and 12 hours). Finally, multidose and single-dose cardioplegia at 10.0 degrees, 20.0 degrees, and 37.0 degrees C were compared with hypothermia alone. We concluded that in the neonatal (in contrast to the adult) rabbit heart the protective properties of multidose cardioplegia relative to single-dose cardioplegia are progressively lost.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of heat stress on metabolism of high-energy phosphates. Comparison of normothermic and hypothermic ischemia.

BACKGROUND: Alterations in metabolic pathways may contribute to the cardioprotective effects of heat stress (HS). We investigated the effects of HS on ATP and phosphocreatine (PCr) levels in the ischemic rat myocardium, after both normothermic and hypothermic ischemia. METHODS: Two protocols were used: (1) normothermic ischemia (20 min at 37 degrees C) with no myocardial protection (n=6 HS; n=6 control); (2) hypothermic ischemia (4 hrs at 4 degrees C) after cardioplegic arrest (n=6 HS; n=6 control). ATP and PCr levels in the heart were measured using 31P nuclear magnetic resonance spectroscopy. RESULTS: At the end of normothermic ischemia, ATP levels were better maintained in HS hearts (C vs HS: 4.51+/-0.66 vs 7.81+/-1.06 micromol/g dry wt+/-SEM, p=0.04). A trend for higher ATP content in HS hearts was observed after 40 min of reperfusion (C vs HS: 11.7+/-1.5 vs 16.9+/-2.0 micromol/g dry wt+/-SEM, p=0.09). PCr content was also higher at the end of 40 minutes of reperfusion in HS hearts (C vs HS: 46.4+/-2.9 vs 56.9+/-3.0 micromol/g dry wt+/-SEM, p=0.03). After prolonged hypothermic ischemia under cardioplegic arrest, heat stress again led to better preservation of ATP levels at the end of ischemia (C vs HS: 5.71+/-0.88 vs 9.23+/-1.38 micromol/g dry wt+/-SEM, p=0.05) and after 40 minutes of reperfusion (C vs HS: 16.8+/-1.4 vs 24.6+/-2.8 micromol/g dry wt+/-SEM, p=0.03). PCr levels were also better maintained at the end of ischemia (C vs HS: 4.87+/-0.77 vs 12.4+/-3.0 micromol/g dry wt+/-SEM, p=0.03) and after 40 minutes of reperfusion in HS hearts (C vs HS: 55.1+/-7.0.vs 79.8+/-7.3 micromol/g dry wt+/-SEM, p=0.03). CONCLUSIONS: Heat stress induces changes in the energy profile of the heart which results in better preservation of ATP and phosphocreatine levels. These changes could be observed after brief normothermic ischemia and also after prolonged hypothermic ischemia under cardioplegic arrest, mimicking conditions of preservation for cardiac transplantation.     

Cardioplegia-induced damage to ischemic immature myocardium is independent of oxygen availability

The known benefits of hypothermic pharmacological cardioplegia in protecting the ischemic adult heart may not extend to children. Protection of the ischemic immature rabbit heart with hypothermic Krebs-Henseleit bicarbonate buffer is better than with hypothermic St. Thomas' II cardioplegic solution. We investigated whether the availability of oxygen in the preischemic perfusate is responsible for the increased tolerance to ischemia of immature (7- to 10-day-old) hearts perfused with Krebs buffer in comparison with St. Thomas' II solution immediately before ischemia. After obtaining preischemic control data in the "working" mode, we perfused hearts (n = 8 per group) for 3 minutes with hypothermic (14 degrees C) Krebs buffer or hypothermic St. Thomas' II solution saturated with 0%, 25%, or 95% oxygen. This was followed by 2 hours of global ischemia at 14 degrees C. Hearts were reperfused for 15 minutes in the Langendorff mode and 35 minutes in the working mode, and recovery of function was measured. For preischemic oxygen concentrations of 0%, 25%, and 95%, recovery of aortic flow in hearts protected by hypothermia alone during ischemia was 74% +/- 9%, 82% +/- 4%, and 99% +/- 2% of preischemic values, respectively. In hearts protected by hypothermia plus cardioplegia, the values were 69% +/- 6%, 72% +/- 3%, and 86% +/- 5%, respectively. Thus, at equal oxygen concentrations, recovery of postischemic function was better in hearts protected by hypothermia alone compared with hypothermia plus cardioplegia. We conclude that factors other than oxygen availability are responsible for the damaging effect of St. Thomas' II solution on the ischemic immature rabbit heart.     

Coronary blood flow and myocardial metabolism during reperfusion after hypothermic cardioplegia in the dog

There have been many studies of reperfusion injury after normothermic ischemia. However, there have been few clinically relevant studies on the nature and time course of recovery of the myocardium during reperfusion after hypothermic cardioplegia. We studied reperfusion in the isolated dog heart supported by another dog. After 2 h of cardioplegic arrest at 20 degrees C, 11 normal hearts were reperfused for 30 min at optimal coronary pressures (60-100 mm Hg mean). The following events occurred: rapid rewarming, a transient hyperemia followed by a rapid return of both coronary blood flow and myocardial oxygen consumption to normal, washout of lactate, recovery of contractility and a slight decline in ATP. Most of these events occurred during the first 15 min of reperfusion. We concluded that, in normal hearts which are well protected during hypothermic cardioplegia, reperfusion at optimal coronary pressure results in recovery of the myocardium within 15 min, with the exception of recovery of ATP levels.     

Effects of adenosine and defibrotide adjunct to a standard crystalloid cardioplegic solution

AIM: Adenosine has many actions potentially useful as adjunct to a cardioplegia. Defibrotide was recently shown to have protective effects during cardiac arrest. The aim of this study was to compare these 2 substances to delineate their profile of action in the setting of cardioplegic arrest. METHODS: A Langendorff model for isolated rat hearts was employed: 3 groups of 8 hearts each were used, respectively with plain St.Thomas cardioplegia as control (group C), and the same solution added with adenosine (group A) or defibrotide (group D). The hearts had a baseline perfusion for 30 minutes with Krebs-Henseleit solution at 37 degrees C, cardioplegia administration for 3 minutes, then 30 minutes of ischemia without any perfusion and finally 30 minutes of reperfusion with Krebs-Henseleit solution at 37 degrees C. RESULTS: The time to attain heart arrest was 20% shorter in group A, but this difference did not reach statistical significance (A: 13.6+/-1.5; D: 16.8+/-2.7; C: 17.3+/-2.2 s). The heart rate during reperfusion in group A was almost identical to baseline, while in both group C and D it was significantly lower (A: 101%, D: 93.4%, C: 82.4%, p<0.01).A and D decreased significantly the release of creatine phospokinase compared to group C (p=0.006). Lactate dehydrogenase release was lower in both treatment groups, although statistical significance was not reached. Peak positive dP/dT decreased more in controls during reperfusion (A: -23+/-6%, D: -17+/-5%, C: -31+/-5%, p=ns). Negative dP/dT was significantly worse in controls compared to both treatments (A: -19+/-6%, D: -12+/-5%, C: -34+/-7%, p=0.035). CONCLUSIONS: Both adenosine and defibrotide have protective effects in an isolated model of cardioplegic arrest. Adenosine is significantly more active on heart rate while defibrotide is more active on contractily. Further studies are justified in order to test the combination of these 2 drugs.     

ATP precursor depletion and postischemic myocardial recovery

Although cardioplegia reduces myocardial metabolism during ischemia, adenosine triphosphate (ATP) depletion occurs, which may contribute to poor functional recovery after reperfusion. Augmenting myocardial adenosine during ischemia is successful in improving ATP repletion and myocardial recovery following ischemia. If adenosine is an important determinant of ischemic tolerance, then depletion or elimination of myocardial adenosine should lead to poor functional and metabolic recovery after ischemia. To test this hypothesis, isolated, perfused rabbit hearts were subjected to 120 min of 34 degrees C ischemia. Hearts received St. Thomas cardioplegia alone or cardioplegia containing 200 microM adenosine, or cardioplegia containing 15, 5, 2.5, or 0.025 micrograms/ml adenosine deaminase (ADA), which catalyzes the breakdown of adenosine to inosine, making adenosine unavailable as an ATP precursor. Functional recovery was determined and myocardial nucleotide levels were measured before, during, and after ischemia. Following ischemia and reperfusion, control hearts recovered to 51 +/- 3% of preischemic developed pressure (DP). There was significantly better recovery in adenosine-augmented hearts (68 +/- 7%), while ADA hearts had significantly worse recovery. Hearts treated with 0.025 microgram/ml ADA recovered to only 29 +/- 5% of DP and higher dose ADA hearts failed to demonstrate any recovery of systolic function. Furthermore, adenosine enhanced metabolic recovery, whereas ADA resulted in greatly depleted ATP and precursor reserves. Postischemic developed pressure closely paralleled the availability of myocardial adenosine, consistent with the hypothesis that myocardial adenosine levels at end ischemia and early reperfusion are important determinants of functional recovery after global ischemia.     

Modified reperfusate after long-term preservation of the heart

Warm (30 degrees C) blood cardioplegia (K = 22 mEq/L) with glutamate (26 mmol/L) as a reperfusate was compared with unmodified blood reperfusion after prolonged hypothermic storage of the isolated canine heart. After cardioplegic arrest, three groups of hearts (n = 5 each) were excised and stored at 2 degrees C. In groups 1 and 2, reperfusion with unmodified blood was undertaken after six and 24 hours of storage, respectively, and in group 3, reperfusion with modified warm blood cardioplegia containing glutamate was administered after 24 hours of storage. After reperfusion, no significant difference in left ventricular developed pressure was noted between groups 1 (110 +/- 15 mm Hg), 2 (127 +/- 14 mm Hg), and 3 (98 +/- 13 mm Hg). Similarly, no difference in maximum rate of rise of left ventricular pressure was noted between groups 1 (1,456 +/- 171 mm Hg/s), 2 (1,905 +/- 395 mm Hg/s), and 3 (1,450 +/- 291 mm Hg/s). Group 3 (modified reperfusate) had improved diastolic compliance compared with group 2 (0.776 mm Hg/mL versus 1.395 mm Hg/mL; p less than 0.02). We conclude that our modified reperfusate improves diastolic function after 24 hours of hypothermic storage, but does not result in improved systolic function.     

Effect of diltiazem on functional recovery and myocardial metabolism during hypothermic global ischemia and normothermic reperfusion

An isolated working rat heart preparation was used to determine the effect of diltiazem, a calcium antagonist, on the myocardial metabolism and functional recovery in the ischemic and reperfused heart, under conditions of 15 degrees C of topical hypothermia. The hearts were divided into two groups according to the solution injected into aortic root at the onset of ischemia. Group I (25 hearts) were given 3 ml of cold Krebs-Henseleit bicarbonate buffer solution (KHB), and Group II (25 hearts) were given the same dose of KHB containing 300 micrograms of diltiazem. After 30 min of reperfusion following 120 min of ischemia, cardiac output (ml/min) was significantly better in Group II (24.1 +/- 3.2) than in Group I (9.5 +/- 2.5). There were no differences between the groups with regard to tissue levels of creatine phosphate, adenosine triphosphate (ATP), total adenine nucleotide (TAN), glucose-6-phosphate and lactate during the ischemia. However, ATP and TAN levels were significantly higher in Group II after 30 min of reperfusion. These data show that, although diltiazem has little effect in preventing the catabolism of high-energy phosphates during hypothermic ischemia, there was an improvement in myocardial metabolism and an enhanced functional recovery during reperfusion in the diltiazem-treated hearts.     

Is protection of ischemic neonatal myocardium by cardioplegia species dependent?

Hypothermia combined with pharmacologic cardioplegia protects the globally ischemic adult heart, but this benefit may not extend to children, resulting in poor postischemic recovery of function and increased mortality. The relative susceptibilities to ischemia modified by hypothermia alone and by hypothermia plus cardioplegia were assessed in isolated perfused neonatal (3- to 4-day-old) rabbit and pig hearts. Hearts were perfused aerobically with Krebs buffer solution in the working mode for 30 minutes and aortic flow was recorded. This was followed by 3 minutes of hypothermic (14 degrees C) coronary perfusion with either Krebs or St. Thomas' Hospital cardioplegic solution No. 2 followed by hypothermic (14 degrees C) global ischemia (rabbits 2, 4, and 6 hours; pigs 2 and 4 hours). Hearts were reperfused for 15 minutes in the Langendorff mode and 30 minutes in the working mode, and recovery of postischemic aortic flow was measured. Hypothermia alone provided excellent protection of the ischemic neonatal rabbit heart, with recovery of aortic flow after 2 and 4 hours of ischemia at 91% +/- 4% and 87% +/- 5% (mean +/- standard deviation) of its preischemic value. Recovery after 6 hours of ischemia was depressed to 58% +/- 9% of its preischemic value. Ischemic neonatal pig hearts protected with hypothermia alone recovered 94% +/- 3% of preischemic aortic flow after 2 hours; none was able to generate flow after 4 hours. St. Thomas' Hospital solution No. 2 decreased postischemic aortic flow after 4 hours of ischemia in rabbit hearts from 87% +/- 5% to 70% +/- 7% (p less than 0.05, hypothermia alone versus hypothermia plus cardioplegia) but improved postischemic recovery of aortic flow in pig hearts after 4 hours of ischemia from 0 to 73% +/- 13% (p less than 0.0001, hypothermia alone versus hypothermia plus cardioplegia). This effect was dose related in both species. We conclude that the neonatal pig heart is more susceptible to ischemia modified by hypothermia alone than the neonatal rabbit and that St. Thomas' Hospital solution No. 2 improves postischemic recovery of function in the neonatal pig but decreases it in the neonatal rabbit. This species-dependent protection of the neonatal heart may be related to differences in the extent of myocardial maturity at the time of study.     

Optimal hypothermic preservation of arrested myocardium in isolated perfused rabbit hearts: a 31P NMR study

The purpose of this study was to (1) relate myocardial high-energy phosphate stores to functional recovery after ischemia and reperfusion, (2) assess the bioenergetics and functional influence of clinically relevant myocardial hypothermia, and (3) examine tissue pH as an independent indicator of postischemic recovery of function. Rabbit hearts were perfused via a modified Langendorff technique, monitored for developed pressure (DP) and left ventricular end-diastolic pressure (LVEDP) via an isovolumic left ventricular balloon catheter, and placed in a Brucker NMR magnet (4.7 tesla) to measure phosphocreatine (PCr), adenosine triphosphate (ATP), and pH. Hearts underwent 1 hour of global ischemia at 7 degrees, 17 degrees, 27 degrees and 37 degrees C initiated by one dose of K+ cardioplegia followed by 30 minutes of reperfusion. After reperfusion, DP (expressed as a percentage of preischemic control) and LVEDP (mm Hg) in 7 degrees and 17 degrees C hearts were no different (96 + 5% vs 97 +/- 3%; 5 +/- 2 mm Hg vs 6 +/- 2 mm Hg; p = NS), but were better (p less than 0.01) than 27 degree hearts (72 +/- 6%, 17 +/- 6 mm Hg) and 37 degree hearts (31 +/- 7%, 60 +/- 6 mm Hg). PCr was severely depleted in all groups. ATP was 90 +/- 7% and 87 +/- 5% of preischemic control in the 7 degree and 17 degree hearts, which was significantly better than the 68 +/- 3% and 21 +/- 3% in the 27 degree and 37 degree groups (p less than 0.01). The pH at end ischemia was 6.83, 6.89, 6.54, and 5.86 for the 7 degree, 17 degree, 27 degree, and 37 degree hearts, respectively (7 degrees vs 27 degrees or 37 degrees, p less than 0.01; 17 degrees vs 27 degrees or 37 degrees, p less than 0.01). Linear regression of DP on end-ischemic ATP (EIATP) and end-ischemic pH revealed: DP = 0.96 (EIATP) + 20 (r = 0.92) and DP = 60 (pH) -317 (r = 0.86). We conclude that (1) end-ischemic ATP predicts recovery of ventricular function, and, furthermore, there appears a threshold ATP concentration (80% of control) below which full recovery of function will not occur; (2) end-ischemic pH predicts recovery of ventricular function; (3) 7 degrees C hypothermic ischemia does not cause a clinically significant cold injury; and (4) in a single-dose crystalloid cardioplegia model, end-ischemic pH is linearly related to recovery of function (r = 0.86).     

Cardioplegia and ischemia in the canine heart evaluated by 31P magnetic resonance spectroscopy

BACKGROUND: Warm continuous blood cardioplegia provides excellent protection, but must be interrupted by ischemic intervals to aid visualization. We hypothesized that (1) as ischemia is prolonged, the reduced metabolic rate offered by cooling gives the advantage to hypothermic cardioplegia; and (2) prior cardioplegia mitigates the deleterious effects of normothermic ischemia. METHODS: Isolated cross-perfused canine hearts underwent cardioplegic arrest followed by 45 minutes of global ischemia at 10 degrees C or 37 degrees C, or 45 minutes of normothermic ischemia without prior cardioplegia. Left ventricular function was measured at baseline and during 2 hours of recovery. Metabolism was continuously evaluated by phosphorus-31 magnetic resonance spectroscopy. RESULTS: Adenosine triphosphate was 71% +/- 4%, 71% +/- 7%, and 38% +/- 5% of baseline at 30 minutes, and 71% +/- 4%, 48% +/- 5%, and 39% +/- 6% at 42 minutes of ischemia in the cold ischemia, warm ischemia, and normothermic ischemia without prior cardioplegia groups, respectively. Left ventricular systolic function, left ventricular relaxation, and high-energy phosphate levels recovered fully after cold cardioplegia and ischemia. Prior cardioplegia delayed the decline in intracellular pH during normothermic ischemia initially by 9 minutes, and better preserved left ventricular relaxation during recovery, but did not ameliorate the severe postischemic impairment of left ventricular systolic function, marked adenosine triphosphate depletion, and creatine phosphate increase. Left ventricular distensibility decreased in all groups. CONCLUSIONS: When cardioplegia is followed by prolonged ischemia, better protection is provided by hypothermia than by normothermia. Prior cardioplegia confers little advantage on recovery after prolonged normothermic ischemia but delays initial ischemic metabolic deterioration, which would contribute to the safety of brief interruptions of warm cardioplegia.     

Age-related changes in the ability of hypothermia and cardioplegia to protect ischemic rabbit myocardium

Hypothermia combined with pharmacologic cardioplegia protects the globally ischemic adult heart, but this benefit may not extend to children; poor postischemic recovery of function and increased mortality may result when this method of myocardial protection is used in children. The relative susceptibilities to ischemia-induced injury modified by hypothermia alone and by hypothermia plus cardioplegia were assessed in isolated perfused immature (7- to 10-day-old) and mature (6- to 24-month-old) rabbit hearts. Hearts were perfused aerobically with Krebs-Henseleit buffer in the working mode for 30 minutes, and aortic flow was recorded. This was followed by 3 minutes of hypothermic (14 degrees C) coronary perfusion with either Krebs or St. Thomas' Hospital cardioplegic solution No. 2, followed by hypothermic (14 degrees C) global ischemia (mature hearts 2 and 4 hours; immature hearts 2, 4, and 6 hours). Hearts were reperfused for 15 minutes in the Langendorff mode and 30 minutes in the working mode, and recovery of postischemic function was measured. Hypothermia alone provided excellent protection of the ischemic immature rabbit heart, with recovery of aortic flow after 2 and 4 hours of ischemia at 97% +/- 3% and 93% +/- 4% (mean +/- standard deviation) of the preischemic value. Mature hearts protected with hypothermia alone recovered only minimally, with 22% +/- 16% recovery of preischemic aortic flow after 2 hours; none were able to generate flow at 4 hours. St. Thomas' Hospital solution No. 2 improved postischemic recovery of aortic flow after 2 hours of ischemia in mature hearts from 22% +/- 16% to 65% +/- 6% (p less than 0.05), but actually decreased postischemic aortic flow in immature hearts from 97% +/- 3% to 86% +/- 10% (p less than 0.05). To investigate any dose-dependency of this effect, we subjected hearts from both age groups to reperfusion with either Krebs solution or St. Thomas' Hospital solution No. 2 for 3 minutes every 30 minutes throughout a 2-hour period of ischemia. Reexposure to Krebs solution during ischemia did not affect postischemic function in either age group. Reexposure of immature hearts to St. Thomas' Hospital solution No. 2 caused a decremental loss of postischemic function in contrast to incremental protection with multidose cardioplegia in the mature heart. We conclude that immature rabbit hearts are significantly more tolerant of ischemic injury than mature rabbit hearts and that, unexpectedly, St. Thomas' Hospital solution No. 2 damages immature rabbit hearts.     

Effects of inhibition of myocardial extracellular-responsive kinase and P38 mitogen-activated protein kinase on mechanical function of rat hearts after prolonged hypothermic ischemia

BACKGROUND: Mitogen-activated protein kinases (MAPKs), including extracellular-responsive kinase (ERK) and p38 MAPK, are activated by stresses associated with hypothermia-rewarming and ischemia-reperfusion. Their activation in heart is associated with beneficial (preconditioning) and adverse effects (apoptosis and impaired contractility). This study determined whether ERK and p38 MAPK activities are altered by hypothermic ischemia and normothermic reperfusion and the consequences of their inhibition on recovery of myocardial function. METHODS: Left ventricular work (L x min(-1) x mm Hg) was assessed during normothermic perfusion (30 min) of isolated rat hearts that were either freshly excised or previously subjected to hypothermic storage (8 hr, 3 degrees C) and rewarming (10 min, 37 degrees C) before normothermic reperfusion (30 min). Phospho-specific immunoblot analysis of p38 MAPK was performed in hearts and various cultured cells. RESULTS: Compared with fresh hearts, hearts subjected to hypothermia and rewarming demonstrated impaired left ventricular work (1.96+/-0.53, n=12 vs. 8.37+/-0.46, n=4, <0.05) during reperfusion. The ERK inhibitor, PD98059 (20 microM), present during storage and rewarming, caused modest improvement (3.66+/-0.75, n=9, <0.05). The p38 MAPK inhibitor, SB202190 (10 microM), when present during reperfusion, improved recovery (to 6.12+/-0.75, n=6, <0.05); it was ineffective if present only during rewarming (1.52+/-0.88, n=4). In rat2 fibroblasts, hypothermia and rewarming activated p38 MAPK and its downstream kinase MAPK-activated protein kinase 2, but not c-Jun N-terminal kinase/stress-activated protein kinase. CONCLUSIONS: Myocardial p38 MAPK and MAPK-activated protein kinase 2 are stimulated by hypothermia, ischemia, and rewarming and are detrimental to recovery of mechanical function of hearts subjected to prolonged hypothermic storage. Inhibition of p38 MAPK may be useful in protocols to improve the recovery of mechanical function of cold-stored hearts.     

Effect of ATP synthesis promoters on postischemic myocardial recovery

The use of cardioplegia during surgically induced ischemia greatly reduces myocardial metabolic requirements. However, adenosine triphosphate (ATP) depletion may occur, resulting in poor functional recovery after ischemia. This study investigated if augmentation of intracellular ATP could be achieved by delivering known ATP synthesis promoters (adenosine and/or phosphate) during cardioplegic arrest, and whether this could enhance myocardial functional and metabolic recovery following ischemia. Isolated, perfused rabbit hearts were subjected to 120 min of hypothermic (34 degrees C) cardioplegia-induced ischemia. Controls received St. Thomas cardioplegia (CTL); remaining hearts received cardioplegia containing 200 microM adenosine (ADO), or 25 microM phosphate (PO4), or both ADO and PO4. Following ischemia and reperfusion, recovery of developed pressure (%DP) and postischemic diastolic stiffness was significantly better in adenosine hearts when compared with control or PO4 hearts. To determine if ADO or PO4 minimized depletion of ATP during ischemia or accelerated synthesis of ATP in the postischemic period, nucleotide levels were obtained before, during, and after ischemia. During ischemia, ATP fell equally in all groups, indicating that ADO and PO4 did not alter ischemia-induced depletion of ATP. However, intracellular adenosine was augmented during ischemia in adenosine-treated hearts. Consequently, during reperfusion, ADO and ADO/PO4 hearts had significantly enhanced ATP levels, suggesting that augmenting myocardial adenosine accelerated synthesis of ATP postischemia. The addition of phosphate, a stimulus for ATP synthesis, did not augment postischemic ATP. In fact, the beneficial effect of adenosine may have been decreased when phosphate was added to adenosine. In conclusion, adenosine but not PO4 augments intracellular ATP by allowing better metabolic repletion following ischemia, thereby improving postischemic myocardial functional recovery.