Ischemic Cardioplegic Arrest Research Articles

Hypothermic protection of the ischemic heart via alterations in apoptotic pathways as assessed by gene array analysis.

Hypothermia improves resistance to ischemia in the cardioplegia-arrested heart. This adaptive process produces changes in specific signaling pathways for mitochondrial proteins and heat-shock response. To further test for hypothermic modulation of other signaling pathways such as apoptosis, we used various molecular techniques, including cDNA arrays. Isolated rabbit hearts were perfused and exposed to ischemic cardioplegic arrest for 2 h at 34 degrees C [ischemic group (I); n = 13] or at 30 degrees C before and during ischemia [hypothermic group (H); n = 12]. Developed pressure, the maximum first derivative of left ventricular pressure, oxygen consumption, and pressure-rate product (P < 0.05) recovery were superior in H compared with in I during reperfusion. mRNA expression for the mitochondrial proteins, adenine translocase and the beta-subunit of F1-ATPase, was preserved by hypothermia. cDNA arrays revealed that ischemia altered expression of 13 genes. Hypothermia modified this response to ischemia for eight genes, six related to apoptosis. A marked, near fivefold increase in transformation-related protein 53 in I was virtually abrogated in H. Hypothermia also increased expression for the anti-apoptotic Bcl-2 homologue Bcl-x relative to I but decreased expression for the proapoptotic Bcl-2 homologue bak. These data imply that hypothermia modifies signaling pathways for apoptosis and suggest possible mechanisms for hypothermia-induced myocardial protection.

Lactate accumulation rather than ATP depletion predicts ischemic myocardial necrosis: Implications for the development of lethal myocardial injury

In ischemia, the myocardial metabolic status determines the expansion of necrosis. Decreased ATP levels and increased lactate contents in ischemic myocardium undergoing lethal injury are known to be related to the expansion of irreversible damage. However, their individual contributions have not yet been firmly established. Using two differently effective protocols of ischemic preconditioning (IP short and IP long), ischemic cardioplegic arrest (CP) and their combination (IP+CP) to directly influence the metabolic status of porcine myocardium, graded preservations in ATP content and decreases in lactate accumulation during 45 min ischemia could be achieved (control: ATP, 0.15±0.03; lactate, 60.53±4.89 μmol/g wet weight; IP short, 0.33±0.10/27.42±3.90; IP long, 0.60±0.10/17.49±2.14; CP, 0.98±0.12/11.82±0.96; IP+CP, 2.24±0.28/10.88±0.89; all P<0.001 vs. control). At the same time, a graded reduction of myocardial necrosis was observed (90.0±3.1 vs. 31.7±4.55 vs. 5.05±2.1 vs. 0.0 [isolated patchy necroses] vs. none). Regression analysis revealed only a weak correlation of infarct size and ATP preservation ( r=0.567). In fact, there was a biphasic relation: with ATP levels above 1 μmol/g wet weight, no infarction occurred. ATP levels below this threshold value were associated with steep increase in infarct size. However, even for this latter range, the regression coefficient remained low ( r=0.654). Instead, over the entire range, there was a close, rectilinear correlation of infarct size and lactate accumulation ( r=0.939). These data indicate that lactate accumulation rather than ATP depletion determines the development of lethal myocardial injury. However, the biphasic relation between ATP depletion and infarct size suggests the latter to play a permissive role, since above a threshold value of 1 μmol/g wet weight neither substantial lactate accumulation nor infarction was observed. Below this threshold, however, infarct size increased as lactate accumulated.

Experimental study of intermittent crossclamping with fibrillation and myocardial protection: Reduced injury from shorter cumulative ischemia or intrinsic protective effect?

Objective: During coronary artery revascularization, some surgeons favor intermittent crossclamping with ventricular fibrillation in preference to cardioplegic ischemic arrest for myocardial protection. It is unclear, however, whether intermittent crossclamping with fibrillation is equally protective or whether ischemic injury is reduced as a consequence of shorter cumulative ischemia. Methods: We used isolated, Langendorff-perfused rat hearts, measured preischemic function (left ventricular developed pressure) with an intraventricular balloon, and then subjected the hearts to either (1) 40 minutes of global ischemia, (2) a 2-minute infusion of cardioplegic solution and 40 minutes of ischemia, (3) multidose (every 10 minutes) infusions of cardioplegic solution during 40 minutes of ischemia, (4) continuous ventricular fibrillation during 40 minutes of ischemia, (5) intermittent (4 × 10 minutes) ischemia with 10 minutes of reperfusion, (6) intermittent (4 × 10 minutes) ischemia preceded by intermittent cardioplegia, (7) intermittent (4 × 10 minutes) ischemia with ventricular fibrillation, (8) continuous (40 minutes) ventricular fibrillation during coronary perfusion, or (9) intermittent (4 × 10 minutes) ventricular fibrillation (with perfusion). All protocols were followed by 60 minutes of reperfusion. Results: After 60 minutes of reperfusion, the percentage recovery of left ventricular developed pressure for groups 1 through 9 was as follows: 32% ± 2%, 57% ± 6%, 82% ± 3%, 19% ± 3%, 73% ± 3%, 70% ± 3%, 78% ± 4%, 55% ± 2%, and 57% ± 3%, respectively. No significant differences were identified among groups 3, 5, and 7, but the percentage recovery of developed pressure in group 3 was significantly higher than that in group 6; the degree of recovery in groups 3 and 5 to 7 was significantly (P <.05) higher than in groups 1, 2, 4, 8, and 9. Early recovery was significantly (P <.05) more rapid in groups 3 and 5 to 9, reaching a plateau (of 55%-80%) by 10 minutes of reperfusion; in groups 1, 2, and 4, the recovery plateau occurred after 50 minutes. Left ventricular end-diastolic pressure was elevated in groups 1, 2, and 4 but was almost unchanged from baseline in the other groups. Conclusions: A similar level of myocardial protection was achieved with multidose (intermittent) cardioplegia or intermittent crossclamping (with or without fibrillation), indicating that intrinsic preservation by intermittent crossclamping with fibrillation does not exacerbate ischemic injury. (J Thorac Cardiovasc Surg 2000;120:528-37)

Protection of hearts from reperfusion injury by propofol is associated with inhibition of the mitochondrial permeability transition

Diminishing oxidative stress may protect the heart against ischaemia-reperfusion injury by preventing opening of the mitochondrial permeability transition (MPT) pore. The general anaesthetic agent propofol, a free radical scavenger, has been investigated for its effect on the MPT and its cardioprotective action following global and cardioplegic ischaemic arrest. Isolated perfused Wistar rat hearts were subjected to either warm global ischaemia (Langendorff) or cold St. Thomas' cardioplegia (working heart mode) in the presence or absence of propofol. MPT pore opening was determined using [3H]-2-deoxyglucose-6-phosphate ([3H]-DOG-6P) entrapment. The respiratory function of isolated mitochondria was also determined for evidence of oxidative stress. Propofol (2 micrograms/ml) significantly improved the functional recovery of Langendorff hearts on reperfusion (left ventricular developed pressure from 28.4 +/- 6.2 to 53.3 +/- 7.3 mmHg and left ventricular end diastolic pressure from 52.9 +/- 4.3 to 37.5 +/- 3.9 mmHg). Recovery was also improved in propofol (4 micrograms/ml) treated working hearts following cold cardioplegic arrest. External cardiac work on reperfusion improved from 0.42 +/- 0.05 to 0.60 +/- 0.03 J/s, representing 45-64% of baseline values, when compared to controls (P < 0.05). Propofol inhibited MPT pore opening during reperfusion, [3H]-DOG-6P entrapment being 16.7 vs. 22.5 ratio units in controls (P < 0.05). Mitochondria isolated from non-ischaemic, propofol-treated hearts exhibited increased respiratory chain activity and were less sensitive to calcium-induced MPT pore opening. Propofol confers significant protection against global normothermic ischaemia and during cold cardioplegic arrest. This effect is associated with less opening of mitochondrial MPT pores, probably as a result of diminished oxidative stress. Propofol may be a useful adjunct to cardioplegic solutions in heart surgery.

Mitochondrial protein and HSP70 signaling after ischemia in hypothermic-adapted hearts augmented with glucose.

Hypothermia improves resistance to subsequent ischemia in the cardioplegic-arrested heart (CAH). This adaptive process produces mRNA elevation for heat shock protein (HSP) 70-1 and mitochondrial proteins, adenine nucleotide translocator (ANT(1)), and beta-F(1)-ATPase. Glucose in cardioplegia also enhances myocardial protection. These processes might be linked to reduced ATP depletion. To assess for synergism between these protective processes, isolated rabbit hearts (n = 91) were perfused at 37 degrees C and exposed to ischemic cardioplegic arrest for 2 h. Hearts were in four groups: control (C), hypothermia adapted (H) perfused to 31 degrees C 20 min before ischemia, 22 mM glucose (G) in cardioplegia, and hypothermic adaptation and glucose (HG). Developed pressure (DP), dP/dt(max), and pressure-rate product (PRP) improved (P < 0.05) in G, H, and HG compared with C during reperfusion. DP and PRP were elevated in HG over H and G. ATP was higher in G, H, and HG, although no additional increase in HG over H was found. Lactate and CO(2) production were elevated in G only. The mRNA expression for HSP70-1, ANT(1), and beta-F(1)-ATPase was elevated severalfold in H and HG, but not G over C during reperfusion. In conclusion, glucose provides additional functional improvement in H. Additionally, neither ATP levels nor anaerobic metabolism are linked to mRNA expression for HSP70, ANT(1), or beta-F(1)-ATPase in CAH.

Temperature Threshold and Preservation of Signaling for Mitochondrial Membrane Proteins during Ischemia in Rabbit Heart

Temperature modulates both myocardial energy requirements and production. We have previously demonstrated that myocardial protection induced by hypothermic adaptation preserves expression of genes regulating heat shock protein and the nuclear-encoded mitochondrial proteins, the adenine nucleotide translocator isoform 1 (ANT1), and the β subunit of F1-ATPase (βF1-ATPase). This preservation is associated with a reduction in ATP depletion similar to that noted in cardioplegic arrested hearts preserved at a critical temperature (30°C) or below. We tested the hypothesis that expression of these genes may also be subject to this temperature threshold phenomenon. Isolated perfused rabbit hearts were subjected to ischemic cardioplegic arrest at 4, 30, or 34°C for 120 min. Cardiac function indices and steady-state mRNA levels for ANT1, βF1-ATPase, and HSP70-1 were measured prior to ischemia (B) and after 45 min of reperfusion. Cardiac function was significantly depressed in the 34°C group. Ischemia at 34°C reduced steady-state mRNA levels for ANT1and βF1-ATPase from B, but these levels were similarly preserved at 4 and 30°C. HSP70-1 levels were mildly elevated (fourfold) above B to similar levels at all three temperatures. These results indicate that mRNA expression for ANT1and βF1-ATPase is specifically preserved in a pattern consistent with the temperature threshold phenomenon. HSP70-1 expression is not influenced by ischemic temperature. Preservation of gene expression for these mitochondrial proteins implies that signaling for mitochondrial biogenesis or resynthesis is maintained after ischemic insult.

The mechanism of cardioprotection by S-nitrosoglutathione monoethyl ester in rat isolated heart during cardioplegic ischaemic arrest.

1. This study was designed (i) to assess the effect of S-nitrosoglutathione monoethyl ester (GSNO-MEE), a membrane-permeable analogue of S-nitrosoglutathione (GSNO), on rat isolated heart during cardioplegic ischaemia, and (ii) to monitor the release of nitric oxide (.NO) from GSNO-MEE in intact hearts using endogenous myoglobin as an intracellular .NO trap and the hydrophilic N-methyl glucamine dithiocarbamate-iron (MGD-Fe2+) complex as an extracellular .NO trap. 2. During aerobic perfusion of rat isolated heart with GSNO-MEE (20 mumol 1(-1), there was an increase in cyclic GMP from 105 +/- 11 to 955 +/- 193 pmol g-1 dry wt. (P < 0.05), and a decrease in glycogen content from 119 +/- 3 to 96 +/- 2 mumol g-1 dry wt. (P < 0.05), and glucose-6-phosphate concentration from 258 +/- 22 in control to 185 +/- 17 nmol g-1 dry wt. (P < 0.05). During induction of cardioplegia, GSNO-MEE caused the accumulation of cyclic GMP (100 +/- 6 in control vs. 929 +/- 168 pmol g-1 dry wt. in GSNO-MEE-treated group, P < 0.05), and depletion of glycogen from 117 +/- 3 to 103 +/- 2 mumol g-1 dry wt. (P < 0.05) in myocardial tissue. 3. Inclusion of GSNO-MEE (20 mumol l-1) in the cardioplegic solution improved the recovery of developed pressure (46 +/- 8 vs. 71 +/- 3% of baseline, P < 0.05), and rate-pressure product from 34 +/- 6 to 63 +/- 5% of baseline (P < 0.05), and reduced the diastolic pressure during reperfusion from 61 +/- 7 in control to 35 +/- 5 mmHg (P < 0.05) after 35 min ischaemic arrest. GSH-MEE (20 mumol l-1) in the cardioplegic solution did not elicit the protective effect. 4. During cardioplegic ischaemia, GSNO-MEE (20-200 mumol l-1) induced the formation of nitrosylmyoglobin (MbNO), which was detected by electron spin resonance (ESR) spectroscopy. Inclusion of MGD-Fe2+ (50 mumol l-1 Fe2+ and 500 mumol l-1 MGD) in the cardioplegic solution along with GSNO-MEE yielded an ESR signal characteristic of the MGD-Fe2+ -NO adduct. However, the MGD-Fe2+ trap did not prevent the formation of the intracellular MbNO complex in myocardial tissue. During aerobic reperfusion, denitrosylation of the MbNO complex slowly occurred as shown by the decrease in ESR spectral intensity. GSNO-MEE treatment did not affect ubisemiquinone radical formation during reperfusion. 5. GSNO-MEE (20 microliters l-1) treatment elevated the myocardial cyclic GMP during ischaemia (47 +/- 3 in control vs. 153 +/- 34 pmol g-1 dry wt. after 35 min ischaemia, P < 0.05). The cyclic GMP levels decreased in the control group during ischaemia from 100 +/- 6 after induction of cardioplegia to 47 +/- 3 pmol g-1 dry wt. at the end of ischaemic duration. 6. Glycogen levels were lower in GSNO-MEE (20 mumol l-1)-treated hearts throughout the ischaemic duration (26.7 +/- 3.1 in control vs. 19.7 +/- 2.4 mumol g dry-t wt. in GSNO-MEE-treated group at the end of ischaemic duration), because of rapid depletion of glycogen during induction of cardioplegia. During ischaemia, the amounts of glycogen consumed in both groups were similar. Equivalent amounts of lactate were produced in both groups (148 +/- 4 in control vs. 141 +/- 4 mumol g-1 dry wt. in GSNO-MEE-treated group after 35 min in ischaemia). 7. The mechanism(s) of myocardial protection by GSNO-MEE against ischaemic injury may involve preischaemic glycogen reduction and/or elevated cyclic GMP levels in myocardial tissue during ischaemia.

Reduction of oxidative tissue injury and endothelial dysfunction by graduated reperfusion after cardioplegic arrest in isolated rat hearts

The aim of this study was to investigate whether or not a graduated resumption of the perfusion pressure after cardioplegic ischaemic arrest will reduce the impact of oxygen free radicals on myocardium and the cardiovasculature. Langendorff-perfused rat hearts were subjected to cardioplegia and subsequent 40 min of global ischaemia at 25°C. Reperfusion was carried out either abruptly (AR) or gradually (i.e., perfusion pressure stepwise increased from 40 to 75 mmHg whithin 30 min -GR). GR resulted in a significant improvement of percentage recovery of left ventricular systolic pressure as compared to AR. A marked increase of thiobarbituric acid reactive substances (TBARS) was detected in the effluent during AR, accompanied by an impaired release of the endothelial vasodilator NO and diminished coronary flow rates compared to the baseline values. GR resulted in a significant reduction of TBARS in the effluent and promoted a better recovery of coronary flow as well as endothelial release of NO during the later phase of reperfusion. It is concluded that graduated reperfusion is beneficial in reducing free radical mediated peroxidative tissue injury and endothelial dysfunction upon reoxygenation.

Studies on the role of sodium/hydrogen exchange system in myocardial ischemia-reperfusion injury.

This study aimed at the exploration of the relationship between Na(+)-H+ exchange system and myocardial ischemia-reperfusion injury (MRI) in an attempt to provide a theoretic basis for the prevention and treatment of MRI. We used the isolated working guinea pig hearts as the experimental model to mimick cardiopulmonary bypass, which included 120 min hypothermic ischemic cardioplegic arrest followed by 60 min normothermic reperfusion. The hearts were divided into 2 groups: the control group receiving St. Thomas' Hospital Solution (STS) and the treated group receiving STS + amiloride, a Na(+)-H+ exchange blocker. The results showed that during reperfusion, [Na+]i and [Ca2+]i overloads, poor recovery of cardiac function, increases in CPK release and OFR generation, reduction of ATP content and serious damage of ultrastructure were seen in group 1; whereas there were no [Na+]i and [Ca2+]i overloads and better recovery of cardiac function accompanied by improved results of biochemical assay and less damage of ultrastructure was found in group 2. Our study indicates that amiloride can inhibit Na(+)-H+ exchange system in cardiac cells during early reperfusion period, which prevents [Na+]i overload produced by Na(+)-H+ exchange, and stops Na(+)-Ca2+ exchange activated by high level of [Na+]i, thus attenuating [Ca2+]i overload caused by Na(+)-Ca2+ exchange and myocardial injury. Therefore, we conclude that Na(+)-H+ exchange blocker, amiloride, can exert significant protective effects on MRI and its use may prove to be a new clinical approach to prevention and cure of MRI.

Hypothermic Ventricular Fibrillation with Pulsatile Coronary Perfusion during Repair of Ventricular Septal Perforation following Infarction

Emergency or urgent surgery for ventricular septal perforation (VSP) following acute myocardial infarction still carries a high operative mortality rate. Hypothermic fibrillatory arrest studies without aortic cross-clamping and using continuous pulsatile coronary flow were performed to improve this result. Of 19 patients suffering from VSP. 12 underwent hypothermic (mean(s.d.) blood temperature 23.5(1.7)°C) ventricular fibrillation with concomitant pulsatile systemic and continuous coronary perfusion (group 1), and seven underwent deep hypothermic cardioplegic ischaemic arrest with systemic pulsatile perfusion alone (group 2). The two groups were comparable in terms of age, sex. location of infarction, number of coronary arteries involved, interval between infarction and surgery, and preoperative maximum enzyme levels and haemodynamics. Pulsatile flow with a mean(s.d.) pulse pressure of 48(13)mmHg was produced by an intra-aortic balloon pumping device in both groups. Operative exposure In the two groups was comparable. In group 1. mean(s.d.) cardiac output in the early postoperative period (within 3 h of procedure) was significantly higher than in group 2 (4.2(0.9) versus 2.6(0.7)Imin−1 m−2, P&lt;0.01). The 30-day operative mortality rate was significantly lower in group 1 (8% (80% confidence interval 1–29%)) than in group 2 (57% (80% confidence interval 28–83%)) ( P&lt;0.05). On the basis of these results, hypothermic fibrillatory arrest with continuous pulsatile coronary perfusion can be recommended for myocardial protection during surgery for VSP associated with severe heart failure or cardiogenic shock.

Intracellular Catalase Inhibition Does not Predispose Rat Heart to Ischemia-Reperfusion and Hydrogen Peroxide-Induced Injuries

The objective of this study was to determine whether inhibition of intracellular catalase would decrease the tolerance of the heart to ischemia-reperfusion and hydrogen peroxide-induced injuries. Isolated bicarbonate buffer-perfused rat hearts were used in the study. Intracellular catalase was inhibited with 3-amino-1,2,4-triazole (ATZ, 1.5 g/kg body weight, two hours prior to heart perfusion). In the ischemia-reperfusion protocol, hearts were arrested with St. Thomas'II cardioplegic solution, made ischemic for 35 min at 37 degrees C, and reperfused with Krebs-Henseleit buffer for 30 min. The extent of ischemic injury was assessed using postischemic contractile recovery and lactate dehydrogenase (LDH) leakage into reperfusate. In the hydrogen peroxide infusion protocol, hearts were perfused with increasing concentrations of hydrogen peroxide (inflow rates 0.05-1.25 mumol/min). Inhibition of catalase activity (30.4 +/- 1.8 mU/mg protein in control vs 2.4 +/- 0.3 mU/mg in ATZ-treated hearts) affected neither pre-ischemic aerobic cardiac function nor post-ischemic functional recovery and LDH release in hearts subjected to 35 min cardioplegic ischemic arrest. Myocardial contents of lipid hydroperoxides were similar in control and ATZ-treated animals after 20 min aerobic perfusion, ischemia, and ischemia-reperfusion. During hydrogen peroxide perfusion, there was an increase in coronary flow rate followed by an elevation in diastolic pressure and inhibition of contractile function in comparison with control hearts. The functional parameters between control and ATZ-treated groups remained unchanged. The concentrations of myocardial lipid hydroperoxides were the same in both groups. We conclude that inhibition of myocardial catalase activity with ATZ does not predispose the rat heart to ischemia-reperfusion and hydrogen peroxide-induced injury.

Improvement in contractile recovery of isolated rat heart after cardioplegic ischaemic arrest with endogenous phosphocreatine: involvement of antiperoxidative effect?

The aim was to attempt to get further insight into the mechanism of the cardioprotective action of phosphocreatine (PCr). Three experimental protocols were used: (1) The effect was examined of exogenous PCr (10 mmol.litre-1) on myocardial oxidative damage produced by H2O2 perfusion (90 mumol.litre-1) of isolated rat heart. (2) Isolated rat hearts were subjected to 35 min cardioplegic ischaemia followed by reperfusion. A control group was studied along with two PCr groups, one corrected for Ca2+ to compensate its binding with PCr (1.4 mmol.litre-1 CaCl2 in St Thomas's Hospital cardioplegic solution), and the other not (1.2 mmol.litre-1). (3) The effect was studied of PCr alone and in combination with the antioxidant tocopherol phosphate (0.1 mumol.litre-1) on contractile and metabolic recovery of isolated rat heart reperfused after 40 min cardioplegic ischaemia. Studies were performed on hearts of 84 male Wistar rats, weighing 250-300 g. (1) Oxidative stress resulted in irreversible contracture and impairment of sarcolemmal integrity revealed by using the transmembrane tracer ionic lanthanum. These effects coincided with the decrease of developed pressure from 116 (SEM 3) to 38(3) mm Hg and rate-pressure product from 498(13) to 165(16) mm Hg.s-1. The Ca2+ binding property of PCr was estimated experimentally and the stability constant of the complex CaPCr was found to be 35.4(0.7) mmol; from this the Ca2+ bound by PCr was calculated to be 14% in the experimental conditions used. Ca2+ concentration in K-H buffer containing PCr was increased to compensate its binding with PCr. PCr prevented H2O2 induced contracture, preserved sarcolemmal integrity, and attenuated H2O2 induced decrease in developed pressure and rate-pressure product [73(6) mm Hg and 340(28) mm H.s-1, respectively, p less than 0.05 compared with control]. (2) PCr reduced the diastolic pressure [29(10) v 68(10) mm Hg in control group at 30 min of reperfusion, p less than 0.05] and enhanced the developed pressure [81(10) v 46(10) mm Hg in controls, p less than 0.05] and rate-pressure product [325(44) v 158(40) mm Hg.s-1 in controls, p less than 0.05]. When CaCl2 was increased to 1.4 mmol.litre-1 the protective effect of PCr was not abolished. (3) PCr resulted in improvement of developed pressure [49(7) v 18(5) mm Hg in controls at 40 min of reperfusion, p less than 0.05] and rate-pressure product [184(27) v 71(20) mm Hg.s-1 in controls, p less than 0.05]. The degree of contractile recovery in the tocopherol group was almost the same as in the PCr group. Combined addition of PCr and tocopherol further increased the developed pressure and rate-pressure product to 72(4) mm Hg and 284(23) mm Hg.s-1, respectively. Similarly, PCr and tocopherol in combination provided substantial inhibition of creatine kinase release into perfusate, at 3.8(0.4) v 10.9(2.5) IU in controls, p less than 0.05. PCr decreases the vulnerability of myocardium to oxidative stress and ischaemic damage. These effects cannot be explained by PCr induced shifts in Ca2+ concentration. Protective effects of PCr and tocopherol are quantitatively additive, most probably due to their different mechanisms of action, and tocopherol may be effective in extending the ability of PCr to stabilise cell membrane structure.

Warm induction blood cardioplegia in the infant: A technique to avoid rapid cooling myocardial contracture

The use of profound hypothermia and total circulatory arrest for repair of heart defects in neonates usually involves a period of systemic and myocardial bypass cooling. Rapid cooling of muscle (skeletal, smooth, and myocardial) can result in contracture through elevation of cytosolic calcium levels. The increased myocardial tone caused by cooling might render the heart more vulnerable to a subsequent period of cardioplegic ischemic arrest. Infants may be more susceptible to contracture because their small body mass allows more rapid myocardial temperature change when prearrest bypass cooling is used. The influence of avoiding rapid myocardial cooling before induced cardioplegic arrest was analyzed in a group of infants weighing less than 6 kg at the time of open cardiac operation. Myocardial ischemic arrest by warm (37 degrees C) induction blood cardioplegia was used in 57 infants and compared with results in 440 infants treated with standard blood cardioplegia. Multivariate logistic regression analysis revealed that patient diagnosis, weight, and age at operation were significant risk factors for operative mortality. The use of warm induction blood cardioplegia had a strongly positive independent effect on survival (p = 0.0003) for any patient weight, age, or diagnostic group. We recommend the avoidance of rapid myocardial cooling on bypass in all patients before induction of cardioplegic ischemic arrest.

Rapid cooling contracture of the myocardium: The adverse effect of prearrest cardiac hypothermia

Hypothermic total circulatory arrest for repair of congenital heart lesions in neonates requires a period of rapid core cooling on cardiopulmonary bypass during which the myocardium is also exposed to hypothermic perfusion. Myocardial hypothermia in the nonarrested state results in an increase in contractility due to elevation of intracellular calcium levels. This study was designed to test the hypothesis that rapid myocardial cooling before cardioplegic ischemic arrest results in damage, with impaired recovery during reperfusion. Two groups of 10 rabbit hearts were perfused on an isolated Langendorff apparatus. Group N (normothermia) was perfused at 37 degrees C before 2 hours of cardioplegic ischemic arrest at 10 degrees C. Group C (cooling) was perfused at 15 degrees C in the unarrested state for 20 minutes before the same cardioplegic arrest conditions as group N. Left ventricular isovolumic pressure measurements, biochemical measurements from right ventricular biopsy specimens, and ventricular necrosis as defined by tetrazolium staining were used to compare the groups at 30 and 60 minutes of normothermic reperfusion. Developed pressure at a constant volume was preserved in group N at 90.7 +/- 4.5 mm Hg versus 76.9 +/- 6.3 in group C after reperfusion (p less than 0.05). Diastolic compliance showed significant deterioration in group C, with marked elevation of diastolic pressure during reperfusion (group N = 6.8 +/- 2.5 mm Hg versus group C = 38.9 +/- 6.1 after reperfusion; p less than 0.001). Adenosine triphosphate levels were significantly higher in group N both at end-ischemia and after reperfusion versus group C (group N = 17.0 +/- 1.1 nmol/mg protein versus group C = 7.7 +/- 1.0 after reperfusion; p less than 0.001). Group N had 0.4% +/- 0.4% necrosis of ventricular mass versus 19.3% +/- 2.2% with prearrest cooling in group C (p less than 0.0001). These results indicate that, when combined with cardioplegic ischemic arrest, rapid myocardial cooling in the unarrested state results in significant damage. The mechanism may be related to the cytosolic calcium loading effect of hypothermia that is not relieved during the subsequent period of cardioplegic arrest. Although hypothermia is an essential component to ischemic preservation, rapid cooling contracture can adversely influence cardioplegic myocardial protection.

Effects of Initial Reperfusion Temperature and Pressure After Prolonged Cardioplegic Ischemic Arrest: A Metabolic and Functional Study in Rat Hearts

The effects of temperature and pressure during early cardiac reperfusion after 3.5 hours of hypothermic, cardioplegic ischemia were investigated in isolated Langendorff-perfused rat hearts. The hearts were randomized in two groups and subjected to different techniques of reperfusion. The group I hearts were exposed to rapidly rising perfusion pressure and temperature, and in group II slowly rising pressure and temperature were employed. After 60 min of reperfusion, left ventricular developed pressure, coronary flow and tissue content of high-energy phosphates were evaluated. Left ventricular pressure and coronary flow were significantly better preserved in group II. Recovery of adenosine triphosphate and creatine phosphate was significantly lower in group I (5.27 +/- 0.38 and 8.72 +/- 0.62 mumol x g dry weight-1) than in group II (9.31 +/- 0.41 and 14.97 +/- 0.62). The study thus demonstrated that functional recovery, restoration of coronary flow and normalization of high-energy phosphate stores after long periods of hypothermic cardioplegic ischemia can be considerably influenced by the employed reperfusion technique.

Preservation of high energy phosphates during ischaemic cardiac arrest with glucose.

The possible myocardial protection by glucose-insulin-potassium infusion prior to cardioplegic ischaemic arrest was studied in rats. One group of animals was given intravenous infusions of high concentrations of glucose during 3 days. A control group received the same amount of saline. The isolated hearts were subjected to Langendorff perfusion followed by cardioplegic arrest at 15 degrees C for a period of 2 or 3.5 hours. The hearts were then subjected to reperfusion for a period of 45 min for those sustaining 2 hours of ischaemia and 60 min for those sustaining 3.5 hours of ischaemia. In the hearts that suffered 2 hours of ischaemia there were no differences in myocardial content of high energy phosphate compounds between the pretreated and controls, and there was no evidence of creatine kinase release. In the hearts exposed to 3.5 hours ischaemia, myocardial content of high energy phosphates was significantly higher in the pretreated than in the controls. The release of creatine kinase was also less, but this difference was not significant. The study indicates that preoperative treatment with glucose-insulin-potassium may improve myocardial tolerance to ischaemia.

Effect of reperfusion temperature and pressure on the functional and metabolic recovery of preserved hearts

Reperfusion conditions significantly affect recovery following global myocardial ischemia. Using an isolated dog heart model, we investigated the effect of initial (first 10 minutes) reperfusion temperature and pressure on the metabolic and functional recovery of the preserved heart. Four groups of five or six dogs each underwent 2 hours of ischemic cardioplegic arrest at 15 degrees C following single-dose crystalloid cardioplegia. Hearts were initially reperfused at 37 degrees C (high temperature) or 28 degrees C (low temperature) and at 50 mm Hg (low pressure) or 80 mm Hg (high pressure), giving four groups: (1) high-temperature, high-pressure; (2) high-temperature, low-pressure; (3) low-temperature, high-pressure; and (4) low-temperature, low-pressure. Septal temperatures were continuously recorded. Ventricular function curves 1 and 2 hours following reperfusion were significantly depressed in the high-temperature, high-pressure group (70%, p less than 0.01, and 83%, p less than 0.02) and the low-temperature, high-pressure group (78%, p less than 0.03, and 85%, p less than 0.03) but were normal in the low-temperature, low-pressure and the high-temperature, low-pressure groups. All groups showed edema 1/2 hour after reperfusion as measured by water and sodium content in myocardial biopsy specimens but only the high-temperature, high-pressure and the low-temperature, high-pressure groups showed persistent edema at 3 hours (3.95 +/- 0.2 ml H2O/gm dry weight, p less than 0.03 and 3.99 +/- 0.16 ml/gm, p less than 0.02, respectively). Only low-temperature, high-pressure reperfusion resulted in statistically significant reductions in adenosine triphosphate (ATP) 1/2 hour and 2 hours following reperfusion (a 15% reduction from baseline). Maximum rewarming rates were measured for each group. High-temperature, high-pressure = 2 degrees C per second; low-temperature, high-pressure = 1 degree C per second; high-temperature, low-pressure = 0.75 degrees C per second; and low-temperature, low-pressure = 0.4 degrees C per second. High-pressure reperfusion following global myocardial ischemia results in rapid rewarming and is associated with prolonged myocardial edema, depressed ATP levels, and delayed functional recovery. Therefore, we employ 10 minutes of low-pressure reperfusion in our patients undergoing potassium cardioplegic arrest.

Myocardial protection during coronary surgery. Getting the maximum advantage of both cardioplegia and hypothermia.

The author presents a specially timed protocol of a combination of cold cardioplegic arrest and deep total body hypothermia designed to include the best features and to eliminate some of the principal short-comings of these 2 commonly used methods of myocardial preservation. According to this protocol, the operations were divided into 3 periods: (1) About half the number of the peripheral anastomoses are done in the first period while the body is cooled to 20 degrees C and the during which the heart is in cold ischemic cardioplegic arrest. (2) Most or all proximal anastomoses are done in the second period during which body temperature is kept at 20 degrees C and the heart is in a per vias naturales perfused cold arrest. (3) During the third period, the remaining anastomoses are completed while the heart is again in cold ischemic cardioplegic arrest and the body is rewarmed. This method was used in excess of 100 myocardial revascularization procedures with satisfactory clinical results.

The temperature dependence of recovery of metabolic function following hypothermic potassium cardioplegic arrest

A study was performed to define the influence of reperfusate temperature on the recovery of high-energy phosphate compounds following hypothermic ischemic cardioplegic arrest. Two groups, each consisting of six pigs, were subjected to 1 hour of hypothermic potassium cardioplegic arrest (myocardial temperature 10 degrees to 15 degrees C). In one group, the arrest period was followed by a 30 minute period of normothermic reperfusion (37 degrees C) followed by a second hour of hypothermic cardioplegic arrest and a second 30 minute normothermic reperfusion period. The second group of pigs was reperfused after the first hour of arrest for 30 minutes with a cold blood (10 degrees to 14 degrees C) followed by an additional hour of hypothermic cardioplegic arrest and a second 30 minute hypothermic reperfusion period. Myocardial biopsy specimens for adenosine triphosphate (ATP) and creatine phosphate (CP) were obtained at the beginning of perfusion (control studies), at the end of each hour of the arrest interval, and at the end of each 30 minutes of reperfusion. The ATP and CP levels were significantly higher after normothermic reperfusion than after hypothermic reperfusion. After normothermic reperfusion the CP level exceeded control; following hypothermic reperfusion CP remained less than 70% of the control level. On the basis of these results, it is proposed that hypothermic reperfusion does not permit the same level of high-energy phosphorylation that is provided with normothermic reperfusion and may therefore adversely affect hemodynamic recovery of the heart after cardioplegic arrest.

Influence of the initial reperfusate composition on myocardial function following cardioplegic ischemic arrest

Influence of the initial reperfusate composition on myocardial function following cardioplegic ischemic arrest