Heat shock improves recovery and provides protection against global ischemia after hypothermic storage

Background. Improved methods of donor heart preparation before preservation could allow for prolonged storage and permit remote procurement of these organs. Previous studies have shown that overexpression of heat-shock protein 72 provides protection against ischemic cardiac damage. We sought to determine whether rats subjected to heat stress with only 6-hour recovery could acquire protection to a subsequent heart storage for 12 hours at 4°C.

Methods. Three groups of animals (n = 10 each) were studied: control, sham-treated, and heat-shocked rats (whole-body hyperthermia 42°C for 15 minutes). After 12-hour cold ischemia hearts were reperfused on a Langendorff column. To confirm any differences in functional recovery, hearts were then subjected to an additional 15-minute period of warm global ischemia after which function and lactate dehydrogenase enzyme leakage were measured.

Results. Heat-shocked animals showed marked improvements compared with controls in left ventricular developed pressure (63 ± 4 mm Hg versus 44 ± 4 mm Hg, p < 0.05) heart rate × developed pressure (13,883 ± 1,174 beats per minute × mm Hg versus 8,492 ± 1,564 beats per minute × mm Hg, p < 0.05), rate of ventricular pressure increase (1,912 ± 112 mm Hg/second versus 1,215 ± 162 mm Hg/second, p < 0.005), rate of ventricular pressure decrease (1,258 ± 89 mm Hg/second versus 774 ± 106 mm Hg/second, p < 0.005). Diastolic compliance and lactate dehydrogenase release were improved in heat-shocked animals compared with controls and sham-treated animals. Differences between heat-shocked animals and control or sham-treated animals were further increased after the additional 15-minute period of warm ischemia. Western blot experiments confirmed increased heat-shock protein 72 levels in heat-shocked animals (> threefold) compared with sham-treated animals and controls.

Conclusions. Heat shock 6 hours before heart removal resulted in marked expression of heat-shock protein 72 and protected isolated rat hearts by increased functional recovery and decreased cellular necrosis after 12-hour cold ischemia in a protocol mimicking that of heart preservation for transplantation. Protection was further confirmed after an additional 15-minute period of warm ischemia.     

Studies of myocardial protection in the immature heart. III. Models of ischemic and hypoxic/ischemic injury in the immature puppy heart

This study compares the metabolic and functional effects of three different models of ischemia in the immature heart. The intent was (1) to develop a model of energy-depleted and functionally depressed heart to be used in subsequent studies of myocardial protection and (2) to characterize the biochemical changes following different interventions. Forty-five minutes of normothermic global ischemia produced severe depletion of adenosine triphosphate and creatine phosphate (greater than 70%) but was associated with 85% +/- 10% recovery of left ventricular function. Postischemic functional depression (less than 30% recovery) could be produced by either (1) extending the ischemic duration to 60 minutes or (2) preceding 45 minutes of ischemia by 60 minutes of hypoxic stress (oxygen tension 25 to 30 mm Hg). Neither of these more severe interventions caused more profound depletion of adenosine triphosphate or creatine phosphate, but hypoxic stress produced marked tissue depletion of glutamate (52%) and aspartate (48%) before aortic clamping. Longer ischemia or preceding hypoxia led to greater myocardial accumulation of lactate (greater than 250 versus 104 mumol/gm dry weight) and succinate (18 versus 11 mumol/gm dry weight) during aortic clamping, p less than 0.05 versus 45 minutes of ischemia) and greater postischemic depression and amino acid (greater than 65% aspartate depletion) and carbohydrate (greater than 50% glycogen depletion) metabolism, p less than 0.05 versus simple ischemia. These findings suggest that more severe ischemic/hypoxic models are needed in immature hearts to produce functional depression, and the biochemical analyses suggest the characteristics of metabolic defects that must be corrected to resuscitate these hearts during surgical correction of congenital defects.     

Adverse effects of low-pressure reperfusion after hypothermic cardioplegia in normal and hypertrophic hearts.

The aim of this study was to determine the effect of low-pressure and high-pressure reperfusion, with and without ventricular fibrillation, on the recovery of hypertrophic and normal hearts after hypothermic cardioplegia. Fourteen hearts rendered hypertrophic by valvular aortic stenosis and 18 normal canine hearts were subjected to 1 hour of cardioplegic arrest at 28 degrees C during cardiopulmonary bypass. Each heart was then reperfused at a coronary pressure of either 40 mm Hg (low) or 80 mm Hg (high), initially in the empty beating state and then during ventricular fibrillation. Low-pressure reperfusion produced left ventricular subendocardial ischemia in hypertrophic and in normal hearts, shown by marked depression of subendocardial blood flow, myocardial pH, and myocardial oxygen consumption. In hypertrophic hearts the ischemia was more severe and resulted in a persistent depression of left ventricular function and myocardial oxygen consumption even when coronary pressure was returned to normal levels. High-pressure reperfusion was associated with rapid and complete recovery of myocardial metabolism and function in hypertrophic and in normal hearts. During low-pressure reperfusion, ventricular fibrillation exacerbated ischemia in hypertrophic and in normal hearts. During high-pressure reperfusion, a short period of ventricular fibrillation produced no adverse effects either in hypertrophic or in normal hearts. We conclude that low-pressure reperfusion produces subendocardial ischemia in normal and in hypertrophic hearts even in the empty beating state; in hypertrophic hearts it also impairs recovery of myocardial metabolism and function. The adverse effects of low-pressure reperfusion are exacerbated by ventricular fibrillation.     

Metabolic and functional effects of creatine phosphate in cardioplegic solution. Studies on rat hearts during and after normothermic ischemia

Creatine phosphate is a precursor molecule for ATP synthesis, even under ischemic conditions. We investigated its functional and metabolic effects when added to cardioplegic solution. Rat hearts were subjected to normothermic ischemia for 15 or 30 min and then freeze-clamped. During ischemia there was gradual reduction of high-energy phosphates, but the hearts with creatine phosphate supplement showed higher myocardial content of ATP and of the creatine compound. Other hearts, subjected to 20 min of ischemia, were reperfused with blood for 40 min. Creatine phosphate supplementation resulted in better left ventricular isovolumic work during spontaneous activity, but in paced activity (400 beats/min) no significant differences were seen. After reperfusion, supplemented hearts showed a tendency to higher levels of ATP and creatine phosphate. In all three groups the hearts with cardioplegic supplement had significantly increased myocardial content of pyruvate without proportional lactate increase. The results indicate that creatine phosphate may be an effective constituent in cardioplegic solution.     

Calcitonin Gene-Related Peptide-Induced Preconditioning Improves Preservation With Cardioplegia

Background. Our recent work has shown that calcitonin gene-related peptide (CGRP) may play an important role in mediation of ischemic preconditioning. Therefore, we tested the hypothesis that CGRP-induced preconditioning protects against myocardial damage after prolonged cardioplegic arrest in isolated rat hearts.

Methods. Six groups were studied: the control, ischemic preconditioning, and CGRP-pretreated groups for both 4- and 8-hour hypothermic ischemia. All hearts were arrested using St. Thomas Hospital cardioplegia, and then reperfused with normothermic Krebs-Henseleit solution for 60 minutes after the 4- or 8-hour hypothermic ischemic period. Hearts were subjected to two cycles of 5-minute ischemia and 10-minute reperfusion in the ischemic preconditioning group. In the CGRP-pretreated group, Krebs-Henseleit solution containing CGRP (5 × 10⁻⁹ mol/L) was substituted for the ischemic period.

Results. At 30 minutes of reperfusion after 4-hour storage, left ventricular pressure (mm Hg) and its first derivative (dp/dt_max, mm Hg/s) in the control, ischemic preconditioning, and CGRP groups were 65.2 ± 5.93 and 1,170 ± 119, 94.13 ± 4.93 and 1,825 ± 145.83, and 85.47 ± 4.17 and 1,900 ± 123.13, respectively (p < 0.01). After 8-hour storage, left ventricular pressure (mm Hg) and dp/dt_max (mm Hg/s) in the same groups were 51.07 ± 5.83 and 815 ± 107.17, 83.47 ± 6.54 and 1,480 ± 120.91, and 84.8 ± 8.49 and 1,396 ± 126.16 (p < 0.01). Ischemic preconditioning and CGRP-induced preconditioning also significantly reduced the release of myocardial enzymes.

Conclusions. The present studies suggest that ischemic preconditioning protects against ischemia-reperfusion injury even after 8 hours of hypothermic preservation in isolated rat hearts, and that CGRP exerts preconditioning-like cardioprotection.     

Recovery of the failing canine heart with biventricular support in a previously fatal experimental model

Prolonged normothermic ischemia in the canine model is generally fatal with standard resuscitative techniques. To determine whether such myocardial injury is recoverable with biventricular support, we subjected 10 dogs to 45 minutes of ischemia at 37 degrees C. After ischemia, the animals were supported for 24 hours with biventricular assist with the centrifugal pump. During early reperfusion, none of the hearts could sustain a stable rhythm or blood pressure. Myocardial adenosine triphosphate concentration, expressed as micromoles per gram of heart protein, was dramatically reduced from a control of 31.5 +/- 2.4 to 14.6 +/- 2.9 (p less than 0.01 versus control), a 54% reduction. Ultrastructural analysis did not reveal the explosive cell swelling of irreversible cell injury. After 12 hours of biventricular assist, developed pressure partially recovered to 60.0 +/- 10 mm Hg (p less than 0.01 versus control) and maximal positive dP/dt measured 2,649 +/- 412 mm Hg/sec (p less than 0.01 versus control). Adenosine triphosphate concentration increased to 25.2 +/- 5.5 (p less than 0.01 versus control). Electron microscopic examination showed less chromatin clumping, no further mitochondrial distortion, and more abundant glycogen. After 24 hours of biventricular assist, cardiac output in the seven dogs successfully weaned from biventricular assist measured 3.6 +/- 0.6 L/min, developed pressure recovered to 76.3 +/- 8.9 mm Hg, and its first derivative recovered to 4,282 +/- 585 mm Hg/sec (all measurements not significant compared with control). Examination by an electron microscope revealed no severe mitochondrial injury.     

Myocardial protection in cyanotic neonatal lambs

To investigate the susceptibility of cyanotic neonatal myocardium to ischemia and the effectiveness of cardioplegia for protection, we induced cyanosis in 2- to 5-day-old lambs (n = 16) by connecting the left atrial appendage to the main pulmonary artery with a 4 mm polytetrafluoroethylene graft, which produced an arterial oxygen tension of 34.1 +/- 1.2 torr. Seven to 10 days after creation of the model, isolated perfused hearts from cyanotic animals were subjected to 2 hours of ischemia with topical cooling or crystalloid cardioplegia (K = 30 mEq/L) for myocardial protection (both at 15 degrees C). Identical studies were performed on hearts from 16 normoxemic neonatal lambs 5 to 14 days old. The overall effect of cyanosis was to produce a significant impairment in recovery of maximum developed pressure (p less than 0.05) after ischemia. The overall effect of cardioplegia was to produce a significant improvement in recovery of maximum developed pressure, developed pressure at V10 (the balloon volume to produce an end-diastolic pressure of 10 mm Hg during the preischemic period), and peak rate of pressure rise at V10 (p less than 0.05). The protective effect of cardioplegia was more prominent in cyanotic hearts than in normoxemic hearts for recovery of maximum of peak rate of pressure rise and peak rate of pressure rise at V10 (p less than 0.05). End-diastolic pressure at V10 and the diastolic stiffness constant at 10 and 20 mm Hg were all significantly higher after ischemia in the cyanotic hearts than in the normoxemic hearts (p less than 0.05). We conclude that in neonatal hearts cyanosis may increase the vulnerability to ischemia and cardioplegia appears to enhance the recovery of systolic but not diastolic function in these hearts.     

Oxygen utilization during isovolumic pressure-volume loading: effects of prolonged extracorporeal circulation and cardioplegic arrest

In canine hearts supported by cardiopulmonary bypass, isovolumic peak developed pressure (PDP, mm Hg) and myocardial oxygen consumption (MVO2, ml O2 X 10(-2)/beat/100 gm left ventricular [LV] weight) were determined at 5-ml increments of LV balloon inflation before and after either 2 hours of potassium cardioplegic arrest (ischemia, N = 7) or a comparable period of normothermic perfusion without ischemia (control, N = 6). The sensitivity of MVO2 as a marker of ischemic injury was compared with preservation of both adenosine triphosphate (ATP) stores and systolic pump function. Over a physiological range of end-diastolic volumes (5 to 35 ml) and end-diastolic pressures (0 to 18 mm Hg), the Frank-Starling curves were not depressed following both cardioplegic arrest and prolonged nonischemic perfusion. Although ATP stores decreased by 26% and 22% (ischemia and control groups, respectively; not significant), these levels did not distinguish the effects of cardioplegic arrest from prolonged perfusion. At the preinterventional measurement in both groups, PDP between 50 and 200 correlated with MVO2 from 3.0 to 10.0 (r = +0.84). Following cardioplegic arrest, postischemic MVO2 increased 137 +/- 6% when measured over the PDP range of 75 to 200 mm Hg (p less than 0.01). This change was not evident at a PDP of less than 75, in the empty beating heart, or in control hearts subjected to nonischemic extracorporeal perfusion. These data suggest that increased utilization of oxygen to develop physiological pressures may be a more sensitive indicator of ischemic injury than shifts in the pressure-volume relationship or depletion of adenine nucleotide stores.     

Muscle metabolic changes in induced subtotal ischemia of the leg in a pig model

In nine pigs the arterial blood flow to one hind leg was reduced to 5% of resting values during 8 hours in order to study changes in muscle energy metabolism. Biopsy samples from the gastrocnemius muscle were analyzed for ATP, ADP, AMP, PC, Cr, lactate, pyruvate, glycogen and pH before ischemia, at the end of the ischemic period and during 2.5 hours of reperfusion. During ischemia ATP/TCr decreased to 25%, ECP to 80% and PC/TCr to 6% of preischemic values. Lactate increased eightfold and glycogen fell to 40%. In the reperfusion period, lactate decreased to 1/3 of the end-ischemic value, PC/TCr showed threefold rise and ATP/Cr doubled. TCr fell to 66% of preischemic value. Other changes were not significantly affected by reperfusion. The end-ischemic values indicated severe ischemia, but some improvement of metabolism occurred during early reperfusion. The pig model is suitable for further studies aiming to improve the energy state of the cells during ischemia.     

Myocardial protection by coronary washout during global ischemic cardiac arrest

The effect of intermittent coronary washout (WO) during global ischemic cardiac arrest (ICA) was evaluated in isolated blood perfused dog hearts undergoing 90 min normothermic ICA and 90 min reperfusion. WO consisted of infusion of 100 ml normothermic dog plasma at 100 mm Hg every 10 min during ICA. Systolic and diastolic pressures were measured at constant volume with a left ventricular balloon. Coronary blood flow (CBF) was measured, and transmyocardial oxygen, lactate, and glucose differences were calculated. Adenosine triphosphate (ATP), creatine phosphate (CP), calcium (Ca²⁺), glycogen, and water content were measured from left ventricular biopsies. During 90 min of WO, hearts extracted glucose (15 ± 4 mg/g dry wt LV) and lost lactate (90 ± 5 μmole/g dry wt LV). ATP and CP were significantly depressed at arrest in both groups although WO resulted in significantly higher levels of ATP and CP. CP returned to control levels at 90 min reperfusion in the WO group but remained depressed in the ICA group. Calcium accumulation was greater in hearts with ICA. With reperfusion, both ICA and WO groups demonstrated early hyperemia and rapid lactate washout. There were no differences in total CBF, AVO₂, MOV₂, and myocardial glycogen or water content. Systolic performance was equally depressed in both groups at 90 min of reperfusion. Diastolic compliance, while still impaired, was better preserved in WO when measured in the arrested heart at 90 min ICA (P < 0.01) and in the contracting heart after 90 min reperfusion (P < 0.02). Normothermic coronary washout during 90 min of normothermic ischemic arrest without cardioplegic agents produces improved ventricular compliance and energy metabolism, and reduces myocardial calcium accumulation.     

Intravenous Phenylephrine Preconditioning of Cardiac Grafts From Non–Heart-Beating Donors

Background. Hypoxia and warm ischemia produce severe injury to cardiac grafts harvested from non-heart-beating donors. To potentially improve recovery of such grafts, we studied the effects of intravenous phenylephrine preconditioning.

Methods. Thirty-seven blood-perfused rabbit hearts were studied. Three groups of non-heart-beating donors underwent intravenous treatment with phenylephrine at 12.5 (n = 8), 25 (n = 7), or 50 μg/kg (n = 7) before initiation of apnea. Non-heart-beating controls (n = 8) received saline vehicle. Hypoxic cardiac arrest occurred after 6 to 12 minutes of apnea, followed by 20 minutes of warm in vivo ischemia. A 45-minute period of ex vivo reperfusion ensued. Nonischemic controls (n = 7) were perfused without antecedent hypoxia or ischemia.

Results. Phenylephrine 25 μg/kg significantly delayed the onset of hypoxic cardiac arrest compared with saline controls (9.6 ± 0.5 versus 7.7 ± 0.4 minutes; p = 0.00001), yet improved recovery of left ventricular developed pressure compared with saline controls (57.1 ± 5.3 versus 41.0 ± 3.4 mm Hg; p = 0.04). Phenylephrine 25 μg/kg also yielded a trend toward less myocardial edema than saline vehicle (p = 0.09).

Conclusions. Functional recovery of nonbeating cardiac grafts is improved by preconditioning. We provide evidence that the myocardium can be preconditioned with phenylephrine against hypoxic cardiac arrest.     

Is hyperglycemia seen in children during cardiopulmonary bypass a result of hyperoxia?

OBJECTIVE: We sought to identify whether elevated PaO (2) itself can directly cause hyperglycemia in newborns and to document any additional effects of cardiopulmonary bypass on this response. METHODS: Piglets were exposed to either normoxia (88 +/- 6 mm Hg) or hyperoxia (470 +/- 28 mm Hg) in the following studies. Anesthetized 3-day-old neonatal pigs were either ventilated for 2 hours of normoxia (n = 5) or hyperoxia (n = 5) or placed on normothermic, normoxic cardiopulmonary bypass (n = 6) and then randomly assigned to either undergo a 2-hour normoxic period or a 1-hour hyperoxic episode, followed by a return to normoxia for an additional hour. Blood glucose levels were measured in all animals. RESULTS: No significant changes were observed in blood glucose levels in neonatal pigs that underwent 2 hours of normoxic ventilation (5.0 +/- 0.6 mmol/L) or cardiopulmonary bypass (6.6 +/- 1.6 mmol/L). However, the ventilatory model showed a significant and sustained (P <.001) hyperglycemic response after both 1 hour (8.6 +/- 1.0 mmol/L) and 2 hours (9.8 +/- 1.6 mmol/L) of hyperoxia. In the cardiopulmonary bypass model, exposure to 1 hour of hyperoxia elicited a significant (P <.05) hyperglycemic response (10.3 +/- 1.2 mmol/L), followed by a return to normal blood glucose levels (6.6 +/- 1.6 mmol/L) with a return to normoxia. This hyperoxia-mediated hyperglycemic response was confirmed when data examined from children undergoing cardiopulmonary bypass for primary repair of their congenital defects also identified a significant positive correlation (r = 0.72, P =.02) between oxygen levels and blood glucose levels measured before and at the end of cardiopulmonary bypass. CONCLUSIONS: Hyperoxia triggers a hyperglycemic response in both ventilatory and bypass models. Cardiopulmonary bypass does not exacerbate this response, as shown by the similar levels of hyperglycemia sustained for the duration of the hyperoxic exposure in both experimental models. Therefore, not only may hyperoxia play a crucial role in the hyperglycemic response seen during neonatal cardiopulmonary bypass, but its effect on glucose homeostasis should be considered whenever children are exposed to hyperoxia.     

Effects of coronary perfusion during myocardial hypoxia. Comparison of metabolic and hemodynamic events with global ischemia and hypoxemia.

The effects of metabolic accumulation on myocardial metabolism during global heart oxygen deprivation were evaluated in a working in situ swine heart preparation with controlled total coronary blood flow. Myocardial oxygen consumption was depressed to a similar extent by either reducing total coronary flow 60 per cent (ischemia, low coronary perfusion) in 10 swine or by decreasing coronary perfusate PO2 to 30 mm. Hg at normal flows (hypoxemia, high coronary perfusion) in 13 swine. Compared with findings in 13 control hearts, ischemia significantly (p less than 0.05) decreased myocardial oxygen consumption (640 to 390 mumole per hour per gram), glucose uptake (185 to 16 mumole per hour per gram), and free fatty acid consumption (32 to 17 mumole per hour per gram). ttissue levels of glycogen, creatine phosphate, and adenosine triphosphate (tatp) were significantly reduced (p less than 0.005), and tissue lactate, adenosine diphosphate (ADP), and adenosine monophosphate (AMP) were increased (p less than 0.001). During hypoxemia, glucose uptake was increased (240 mumole per hour per gram) and free fatty acid consumption was somewhat less depressed (19 mumole per hour per gram). Creatine phosphate and ATP were higher than with ischemia (p less than 0.01), and lactate, ADP, and AMP accumulations were less (p less than 0.01). Thus, in the period immediately following myocardial oxygen deprivation, inadequate coronary perfusion caused greater metabolic buildup which inhibited myocardial substrate utilization and energy production. High coronary perfusion, even though the perfusate was unoxygenated, was associated with greater preservation of substrate utilization, higher levels of high-energy phosphates, less accumulation of metabolic products, and a longer survival. These data suggest a critical role of coronary perfusion in protecting myocardial metabolism in the immediate period following global heart hypoxia.     

Donor hearts with impaired hemodynamics. Benefit of warm substrate-enriched blood cardioplegic solution for induction of cardioplegia during cardiac harvesting.

Brain-dead donors frequently show circulatory deterioration and often require so much inotropic support that the donor heart is of questionable value. This experimental study quantifies the cardiac metabolic consequences of brain death and the role of warm blood cardioplegic solution for induction of cardioplegia to improve the quality of potential donor hearts with impaired hemodynamics. Twelve dogs were subjected to brain death by interrupting cerebral blood flow (ligation of innominate artery, carotid arteries, and superior vena cava) and were followed up for as long as 6 hours. Each showed progressive hemodynamic deterioration, necessitating inotropic support (dopamine, calcium, and epinephrine) and large amounts of volume replacement (hetastarch; Hespan) to support the circulation (maintain mean arterial blood pressure greater than 60 mm Hg). Biopsy specimens were taken after 6 hours, or when irreversible ventricular fibrillation occurred, and were analyzed for adenosine triphosphate, creatine phosphate, glycogen, glutamate, and lactate. In six dogs the aorta was then clamped, and a 10-minute infusion of warm (37 degrees C) substrate-enriched aspartate/glutamate blood cardioplegic solution (with the dog's own blood) was given by roller pump to simulate warm induction during the harvesting process. Biopsies were then repeated. Myocardial metabolism, expressed as percent of control values, during brain death was characterized by the following: (1) moderate energy depletion (adenosine triphosphate fell 25% +/- 8%, creatine phosphate fell 55% +/- 15%; p less than 0.05 versus control: mean +/- standard error of the mean); (2) substrate depletion (tissue glutamate fell 48% +/- 9.5%, glycogen fell 66% +/- 7.5%; p less than 0.05 versus control: mean +/- standard error of the mean); and (3) evidence of anaerobic metabolism (lactate increased 374% +/- 95%; p less than 0.05 versus control: mean +/- standard error of the mean). Warm induction of blood cardioplegia in these energy- and substrate-depleted ischemic hearts showed (1) return of creatine phosphate levels to normal (113% +/- 16.8%), (2) replenishment of glutamate (201% +/- 24% of control; p less than 0.05 versus control: mean +/- standard error of the mean), and (3) 43% +/- 14% reduction in myocardial lactate content; (p less than 0.05 versus brain-dead animals). These data suggest that brain-dead donors requiring inotropic support sustain energy and substrate depletion and ischemic damage that can be reversed by a brief period of induction of cardioplegia with a warm substrate-enriched blood cardioplegic solution before harvesting.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evaluation of a new preservative solution for cardiac graft during hypothermia.

BACKGROUND: Reports conflict on the beneficial effects of several cardioplegic solutions such as University of Wisconsin and St. Thomas' Hospital solutions. Therefore our objective was to assess the efficacy of several cardioplegic solutions for cardiac preservation by comparing University of Wisconsin modified solution (UW-1 and UW-1 + calcium = UW-2), St. Thomas' Hospital solution N degrees 1 (STH-1), Celsior solution, and a solution from our laboratory, Lyon preservation solution (LYPS). METHODS: We randomized male rats (n = 70) to 7 groups: LYPS, Celsior, STH-1, UW-1, UW-2, normal saline solution, and control. All hearts, except control hearts were preserved by cold storage (8 hours, 4 degrees C) in the various solutions. We used isolated non-working-heart preparations (left ventricular function evaluation, n = 5/group) or biopsy specimens (energetic store evaluation, n = 5/group) to assess quality of heart preservation. RESULTS: Hearts stored with the saline solution had a mean left ventricular developed pressure (LVDP) of 3.6 +/- 1.3 mm Hg. In contrast, LYPS and Celsior hearts had mean LVDP close to that of the control hearts (97 +/- 2.6, 92.1 +/- 2.2, and 122 +/- 1.9 mm Hg, respectively), whereas STH-1, UW-1, and UW-2 hearts presented an intermediate functional response (48 +/- 4, 39.9 +/- 4.1, and 69 +/- 1.8 mm Hg, respectively). The STH-1 and saline hearts showed increased release of creatine kinase (541.9 +/- 168 and 1,080.8 +/- 126.2 UI/liter, respectively). The energetic charge (EC = [(0.5 ADP + ATP)/ATP + ADP + AMP]) in Celsior, UW-2, and saline was significantly lower (p < 0.001) than in the other groups. CONCLUSION: The composition of the preservation solutions had a notable effect on myocardial viability. Our results indicated that LYPS and Celsior solutions had comparable efficacy for left ventricular function. However these solutions may offer better preservation than do UW-1, UW-2, or STH-1 solutions.     

Potassium-channel opener cardioplegia is superior to St. Thomas' solution in the intact animal.

BACKGROUND: In isolated hearts, the potassium-channel opener pinacidil is an effective cardioplegic agent. This study tested the hypothesis that pinacidil is superior to St. Thomas' solution in the more clinically relevant intact animal. METHODS: Sixteen pigs were placed on full cardiopulmonary bypass. Hearts underwent 2 hours of global ischemia (10 degrees to 15 degrees C). Either St. Thomas' or 100 micromol/L pinacidil was administered every 20 minutes (10 mL/kg). Preischemic and postreperfusion slopes of the preload-recruitable stroke work relationship were determined. Changes in myocardial adenine nucleotide levels and cellular ultrastructure were analyzed. RESULTS: Pinacidil cardioplegia resulted in an insignificant change in the slope of the preload-recruitable stroke work relationship (40.6+/-2.1 mm Hg/mm before ischemia and 36.5+/-3.7 mm Hg/mm after ischemia; p = 0.466). In contrast, St. Thomas' solution resulted in a significant decrease in the slope after reperfusion (34.3+/-5.5 mm Hg/mm and 13.5+/-2.3 mm Hg/mm; p = 0.003). Adenine nucleotide levels, myocardial tissue water, and ultrastructural changes were similar between groups. CONCLUSIONS: Pinacidil ameliorated myocardial stunning associated with traditional hyperkalemic cardioplegia without causing significant differences in cellular metabolism.     

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).     

The effect of lidocaine on myocardial ischemia with asanguinous reperfusion. An in vitro study

The effect of lidocaine on the ischemic nor-mothermic rat heart was studied in a Langendorff preparation. Ventricular fibrillation, total retrograde coronary flow and effluent lactate concentration were monitored in preischemia (control), ischemia (20 min) and reperfusion (20 min). Myocardial metabolites were determined in specimens excised at termination of reperfusion. Six hearts were infused with lidocaine in Ringer solution at onset of ischemia (group A) and six with only Ringer solution (group B). Sinus rhythm proceeded directly to diastolic arrest after 17 sec in group A, while all group B hearts showed ventricular fibrillation before arrest at 174 sec. Effluent lactate concentration was reduced in group A during the first 10 min of ischemia, but not subsequently. After 10 min of reperfusion, coronary flow was reduced by 12% in group A and 20% in group B. ATP was higher and ADP, AMP and IMP were lower in group A than in group B after 20 min of reperfusion. Creatine phosphate showed no intergroup difference, but creatine was higher in group B. Cardiac arrest with lidocaine thus reduced lactate formation during ischemia and lessened high-energy phosphate depletion after reperfusion.     

Influence of initial reperfusion pressure after hypothermic cardioplegic ischemia on endothelial modulation of coronary tone in neonatal lambs. Impaired coronary vasodilator response to acetylcholine

To examine the effect of initial coronary reperfusion pressure on endothelial function, we subjected 16 isolated perfused neonatal lamb hearts to 2 hours of ischemia with potassium cardioplegic solution followed by reperfusion for 1 hour. Before ischemia both acetylcholine, an endothelium-dependent vasodilator, and nitroglycerin, and endothelium-independent vasodilator, caused coronary vasodilation. After ischemia the response to acetylcholine was impaired in the eight hearts with high initial reperfusion pressure (60 mm Hg) but was intact in the eight hearts with low initial reperfusion pressure (20 mm Hg for 10 minutes, 40 mm Hg for 10 minutes, and then 60 mm Hg thereafter). The response to nitroglycerin, however, remained intact regardless of initial reperfusion pressure. Recovery of resting coronary flow and myocardial oxygen consumption was lower in the group with high pressure reperfusion than in the group with low pressure reperfusion. On reperfusion a transient burst of coronary flow was exhibited by the hearts reperfused at high pressure. These results suggest that high initial reperfusion pressure impairs the endothelial modulation of coronary tone; this may be related to the effects on the coronary vasculature of the "burst" of coronary flow associated with high intravascular pressure.     

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.