Myocardial protection in normal and hypoxically stressed neonatal hearts: the superiority of blood versus crystalloid cardioplegia

OBJECTIVES: Blood cardioplegia predominates in the adult because it provides superior myocardial protection, especially in the ischemically stressed heart. However, the superiority of blood over crystalloid cardioplegia in the pediatric population is unproved. Furthermore, because many pediatric hearts undergo a preoperative stress such as hypoxia, it is important to compare the different methods of protection in both normal and hypoxic hearts. METHODS: Twenty neonatal piglets were supported by cardiopulmonary bypass and subjected to 70 minutes of cardioplegic arrest. Of 10 nonhypoxic hearts, five (group 1) were protected with blood cardioplegia and five (group 2) with crystalloid cardioplegia (St. Thomas' Hospital solution). Ten other piglets underwent 60 minutes of ventilator hypoxia (inspired oxygen concentration 8% to 10%) before cardioplegic arrest. Five (group 3) were then protected with blood cardioplegia and the other five (group 4) with crystalloid cardioplegia. Myocardial function was assessed by means of pressure volume loops and expressed as a percentage of control. Coronary vascular resistance was measured with each infusion of cardioplegic solution. RESULTS: No difference was noted between blood (group 1) or crystalloid cardioplegia (group 2) in nonhypoxic hearts regarding systolic function (end-systolic elastance 104% vs 103%), diastolic stiffness (156% vs 159%), preload recruitable stroke work (102% vs 101%), or myocardial tissue edema (78.9% vs 78.9%). Conversely, in hearts subjected to a hypoxic stress, blood cardioplegia (group 3) provided better protection than crystalloid cardioplegia (group 4) by preserving systolic function (end-systolic elastance 106% vs 40%; p < 0.05) and preload recruitable stroke work (103% vs 40%; p < 0.05); reducing diastolic stiffness (153% vs 240%; p < 0.05) and myocardial tissue edema (79.6% vs 80.1%); and preserving vascular function, as evidenced by unaltered coronary vascular resistance (p < 0.05). CONCLUSION: This study demonstrates that (1) blood or crystalloid cardioplegia is cardioprotective in hearts not compromised by preoperative hypoxia and (2) blood cardioplegia is superior to crystalloid cardioplegia in hearts subjected to the preoperative stress of acute hypoxia.     

Rapid cooling contracture with cold cardioplegia

BACKGROUND: Cold cardioplegia can induce rapid cooling contracture. The relations of cardioplegia-induced cooling contracture to myocardial temperature or myocyte calcium are unknown. METHODS: Twelve crystalloid-perfused isovolumic rat hearts received three 2-minute cardioplegic infusions (1 mmol/L calcium) at 4 degrees, 20 degrees, and 37 degrees C in random order, each followed by 10 minutes of beating at 37 degrees C. Finally, warm induction of arrest by a 1-minute cardioplegic infusion at 37 degrees C was followed by a 1-minute infusion at 4 degrees C. Indo-1 was used to measure the intracellular Ca2+ concentration in 6 of these hearts. Additional hearts received hypoxic, glucose-free cardioplegia at 4 degrees or 37 degrees C. RESULTS: After 1 minute of cardioplegia at 4 degrees, 20 degrees, and 37 degrees C, left ventricular developed pressure rose rapidly to 54% +/- 3%, 43% +/- 3%, and 18% +/- 1% of its prearrest value, whereas the intracellular Ca2+ concentration reached 166% +/- 23%, 94% +/- 4%, and 37% +/- 10% of its prearrest transient. Coronary flow was 5.7 +/- 0.2, 8.7 +/- 0.3, and 12.6 +/- 0.6 mL/min, respectively. Warm cardioplegia induction at 37 degrees C reduced left ventricular developed pressure and [Ca2+]i during subsequent 4 degrees C cardioplegia by 16% (p = 0.001) and 34% (p = 0.03), respectively. Adenosine triphosphate and phosphocreatine contents were lower after 4 degrees C than after 37 degrees C hypoxic, glucose-free cardioplegia. CONCLUSIONS: Rapid cooling during cardioplegia increases left ventricular pressure, [Ca2+]i and coronary resistance, and is energy consuming. The absence of rapid cooling contracture may be a benefit of warm heart operations and warm induction of cardioplegic arrest.     

Cerebellar granule cell GABA(A) receptors studied at the single-channel level: modulation by protein kinase G

BACKGROUND: This study was designed to evaluate the adenosine-triphosphate-sensitive potassium channel opener pinacidil as a blood cardioplegic agent. METHODS: Using a blood-perfused, parabiotic, Langendorff rabbit model, hearts underwent 30 minutes of normothermic ischemia protected with blood cardioplegia (St. Thomas' solution [n = 8] or Krebs-Henseleit solution with pinacidil [50 micromol/L, n = 81) and 30 minutes of reperfusion. Percent recovery of developed pressure, mechanical arrest, electrical arrest, reperfusion ventricular fibrillation, percent tissue water, and myocardial oxygen consumption were compared. RESULTS: The percent recovery of developed pressure was not different between the groups (52.3 +/- 5.9 and 52.8 +/- 6.9 for hyperkalemic and pinacidil cardioplegia, respectively). Pinacidil cardioplegia was associated with prolonged electrical and mechanical activity (14.4 +/- 8.7 and 6.1 +/- 3.9 minutes), compared with hyperkalemic cardioplegia (1.1 +/- 0.6 and 1.1 +/- 0.6 minutes, respectively; p < 0.05). Pinacidil cardioplegia was associated with a higher reperfusion myocardial oxygen consumption (0.6 +/- 0.1 versus 0.2 +/- 0.0 mL/100 g myocardium/beat; p < 0.05) and a higher percent of tissue water (79.6% +/- 0.7% versus 78.6% +/- 1.2%; p < 0.05). CONCLUSIONS: Systolic recovery was not different between groups, demonstrating comparable effectiveness of pinacidil and hyperkalemic warm blood cardioplegia.     

Adenosine-enhanced ischemic preconditioning provides enhanced postischemic recovery and limitation of infarct size in the rabbit heart

OBJECTIVE: The purpose of this study was to determine the effect of an intracoronary bolus injection of adenosine used in concert with ischemic preconditioning on postischemic functional recovery and infarct size reduction in the rabbit heart and to compare adenosine-enhanced ischemic preconditioning with ischemic preconditioning and magnesium-supplemented potassium cardioplegia. METHODS: New Zealand White rabbits (n = 36) were used for Langendorff perfusion. Control hearts were perfused at 37 degrees C for 180 minutes; global ischemic hearts received 30 minutes of global ischemia and 120 minutes of reperfusion; magnesium-supplemented potassium cardioplegic hearts received cardioplegia 5 minutes before global ischemia; ischemic preconditioned hearts received 5 minutes of zero-flow global ischemia and 5 minutes of reperfusion before global ischemia; adenosine-enhanced ischemic preconditioned hearts received a bolus injection of adenosine just before the preconditioning. To separate the effects of adenosine from adenosine-enhanced ischemic preconditioning, a control group received a bolus injection of adenosine 10 minutes before global ischemia. RESULTS: Infarct volume in global ischemic hearts was 32.9% +/- 5.1% and 1.03% +/- 0.3% in control hearts. The infarct volume decreased (10.23% +/- 2.6% and 7.0% +/- 1.6%, respectively; p < 0.001 versus global ischemia) in the ischemic preconditioned group and control group, but this did not enhance postischemic functional recovery. Magnesium-supplemented potassium cardioplegia and adenosine-enhanced ischemic preconditioning significantly decreased infarct volume (2.9% +/- 0.8% and 2.8% +/- 0.55%, respectively; p < 0.001 versus global ischemia, p = 0.02 versus ischemic preconditioning and p = 0.05 versus control group) and significantly enhanced postischemic functional recovery. CONCLUSIONS: Adenosine-enhanced ischemic preconditioning is superior to ischemic preconditioning and provides equal protection to that afforded by magnesium-supplemented potassium cardioplegia.     

Enflurane and isoflurane, but not halothane, protect against myocardial reperfusion injury after cardioplegic arrest with HTK solution in the isolated rat heart

To investigate the effects of halothane, enflurane, and isoflurane on myocardial reperfusion injury after ischemic protection by cardioplegic arrest, isolated perfused rat hearts were arrested by infusion of cold HTK cardioplegic solution containing 0.015 mmol/L Ca2+ and underwent 30 min of ischemia and a subsequent 60 min of reperfusion. Left ventricular (LV) developed pressure and creatine kinase (CK) release were measured as variables of myocardial function and cellular injury, respectively. In the treatment groups (each n = 9), anesthetics were given during the first 30 min of reperfusion in a concentration equivalent to 1.5 minimum alveolar anesthetic concentration of the rat. Nine hearts underwent the protocol without anesthetics (controls). Seven hearts underwent ischemia and reperfusion without cardioplegia and anesthetics. In a second series of experiments, halothane was tested after cardioplegic arrest with a modified HTK solution containing 0.15 mmol/L Ca2+ to investigate the influence of calcium content on protective actions against reperfusion injury by halothane. LV developed pressure recovered to 59%+/-5% of baseline in controls. In the experiments with HTK solution, isoflurane and enflurane further improved functional recovery to 84% of baseline (P < 0.05), whereas halothane-treated hearts showed a functional recovery similar to that of controls. CK release was significantly reduced during early reperfusion by isoflurane and enflurane, but not by halothane. After cardioplegic arrest with the Ca2+-adjusted HTK solution, halothane significantly reduced CK release but did not further improve myocardial function. Isoflurane and enflurane given during the early reperfusion period after ischemic protection by cardioplegia offer additional protection against myocardial reperfusion injury. The protective actions of halothane depended on the calcium content of the cardioplegic solution. IMPLICATIONS: Enflurane and isoflurane administered in concentrations equivalent to 1.5 minimum alveolar anesthetic concentration in rats during early reperfusion offer additional protection against myocardial reperfusion injury even after prior cardioplegic protection. Protective effects of halothane solely against cellular injury were observed only when cardioplegia contained a higher calcium concentration.     

Three-fold effect of lovastatin treatment on low density lipoprotein metabolism in subjects with hyperlipidemia: increase in receptor activity, decrease in apoB production, and decrease in particle affinity for the receptor. Results from a novel triple-tracer approach

OBJECTIVE: This study was designed to determine whether simultaneous antegrade/retrograde cardioplegia improves myocardial perfusion in areas supplied by occluded vessels. METHODS: Isolated pig hearts placed in a Langendorff preparation were divided into two groups. The left anterior descending coronary artery was occluded at its origin. In group 1 (n = 7), simultaneous antegrade/retrograde cardioplegia was conducted with use of a single perfusion unit with tubing in a Y-shaped configuration at the end, joined to the aorta and the coronary sinus. In group 2 (n = 8) simultaneous antegrade/retrograde cardioplegia was performed with two separate units, one for antegrade delivery of cardioplegic solution and the other for retrograde cardioplegic solution delivery. Myocardial perfusion in the region supplied by the left anterior descending artery and the region not supplied by this artery was assessed by magnetic resonance imaging, with use of a magnetic resonance contrast agent. The contrast agent was introduced into the common perfusion line in group 1 and into the aortic line only in group 2. RESULTS: Magnetic resonance images showed that the myocardium in the region supported by the left anterior descending artery could not be perfused with antegrade cardioplegic solution because of occlusion of the artery. During simultaneous antegrade/retrograde cardioplegia, however, the myocardium in the left anterior descending region was perfused by approximately 40% to 50% (group 1) or 20% to 30% (group 2) of the degree of perfusion in the region not perfused by the left anterior descending artery (100%). Almost no cardioplegic solution was delivered to the heart through the coronary sinus route during simultaneous antegrade/retrograde cardioplegia in both groups of hearts. Myocardial perfusion in the region supported by the left anterior descending artery was heterogeneous during simultaneous antegrade/retrograde cardioplegia. CONCLUSIONS: Simultaneous antegrade/retrograde cardioplegia significantly improved myocardial perfusion in jeopardized areas of the myocardium. The jeopardized myocardium was mainly perfused by the solution drained from the adjacent normal tissue. Elevated pressure at the coronary sinus during simultaneous antegrade/retrograde cardioplegia is responsible for the redistribution of antegradely delivered cardioplegic solution.     

Resistance of the failing dystrophic hamster heart to the cardioprotective effects of diltiazem and clentiazem: evidence of coronary vascular dysfunctions

Although hypothermia and cardioplegic cardiac arrest provide effective protection during cardiac surgery, ischemia of long duration, poor preoperative myocardial function, and ventricular hypertrophy may lead to heterogeneous delivery of cardioplegic solutions, incomplete protection, and impaired postischemic recovery. Calcium antagonists are potent cardioprotective agents, but their efficacy in the presence of cold cardioplegia is still controversial, especially in heart failure, since it is often believed that failing hearts are more sensitive to their negative inotropic and chronotropic actions. However, recent data have demonstrated that the benzothiazepine-like calcium antagonists diltiazem and clentiazem, in selected dose ranges, elicit significant cardioprotection independently of intrinsic cardiodepression, thus lending support to their use in cardioprotective maneuvers involving the failing heart. We therefore evaluated the cardioprotective interaction of diltiazem, clentiazem, and cold cardioplegia in both normal and failing ischemic hearts. Hearts were excised from 200- to 225-day-old cardiomyopathic hamsters (CMHs) of the UM-X7.1 line and age-matched normal healthy controls. Ex vivo perfusion was performed at a constant pressure (140 cmH2O; 1 cmH2O = 98.1 Pa) according to the method of Langendorff. Heart rate, left ventricular developed pressure (LVDP), and coronary flow were monitored throughout the study. Global ischemia was produced for 90 min by shutting down the perfusate flow, followed by reperfusion for 30 min. Normal and failing CMH hearts were either untreated (control) or perfused at the onset of global ischemia with one of the following combinations: cold cardioplegia alone (St. Thomas' Hospital cardioplegic solution, 4 degrees C, infused for 2 min), cold cardioplegia + 10 nM diltiazem, or cold cardioplegia + 10 nM clentiazem. The cardiac and coronary dilator properties of 10 nM diltiazem and 10 nM clentiazem alone were investigated in separate groups of isolated preparations. Failing CMH hearts had lower basal LVDP (42 +/- 2 vs. 77 +/- 2 mmHg (1 mmHg = 133.3 Pa) for normal hearts, p < 0.05), while coronary flow was only slightly reduced (5.6 +/- 0.2 vs. 6.2 +/- 0.2 mL/min for normal hearts). Following 90 min global ischemia, coronary flow was increased in both groups, but the peak hyperemic response declined only in failing CMH hearts (+50 +/- 17 vs. +82 +/- 17% in normal hearts). In normal hearts, LVDP virtually recovered within 5 min of reperfusion but steadily decreased thereafter (-37 +/- 4% at 30 min). In contrast, in failing CMH hearts, LVDP significantly decreased early during reperfusion but improved over time (-19 +/- 7% at 30 min). In normal hearts, the addition of diltiazem or clentiazem to cold cardioplegic solutions resulted in improved postischemic contractile function for the duration of reperfusion (85 +/- 4% vs. only 71 +/- 6% for cardioplegia, p < 0.05). The post-ischemic increase in coronary flow was similar in all groups. In failing CMH hearts, the addition of diltiazem or clentiazem afforded no significant contractile benefit at reperfusion. In nonischemic normal hearts, infusion of diltiazem or clentiazem (10 nM) alone increased coronary flow (+6 +/- 1% for diltiazem and +24 +/- 3% for clentiazem) without significant negative inotropic or chronotropic effects. In nonischemic failing CMH hearts, infusion of diltiazem or clentiazem did not elicit cardiodepression. In contrast their coronary dilator actions reverted to vasoconstriction (diltiazem) or were significantly attenuated (clentiazem). From these experiments we can conclude that, compared with the normal heart, the failing CMH heart adapted differently to global ischemia.     

Effect of pinacidil on rat hearts undergoing hypothermic cardioplegia

We studied the effect of pinacidil, a potassium-channel opener, on the hemodynamic, biochemical, and ultrastructural changes in rat hearts undergoing hypothermic cardioplegia. Fifty-four male Wistar rats weighing 250 to 300 g were used. Isolated hearts were prepared for modified Langendorff circulation in the working mode using modified Krebs-Henseleit bicarbonate solution bubbled with a 95% O2 and 5% CO2 gas mixture. Eighty minutes of cardioplegia at 25 degrees C was followed by normothermic reperfusion for 30 minutes. Pinacidil, 5, 10, or 50 mumol/L added to the cardioplegic solution, did not affect heart rate, but is significantly improved the recovery of aortic flow as compared with controls (88.1% +/- 4.3 [5 mumol/L]; 83.2% +/- 8.5% [10 mumol/L]; 90.3% +/- 5.3% [50 mumol/L] compared with 55.6 +/- 4.3% [control]; p < 0.05). Administration of pinacidil during reperfusion did not further enhance the recovery of aortic flow. The dose-response curve of aortic flow to the pinacidil concentrations was flat from 5 to 50 mumol/L. However, preservation of myocardial adenosine triphosphate and calcium concentrations and mitochondrial morphology suggested that the optimal concentration of pinacidil cardioplegia is 10 mumol/L.     

Temporary leukocyte depletion reduces ventricular dysfunction during prolonged postischemic reperfusion

Leukocyte depletion improves early postischemic ventricular performance in neonatal models of global myocardial ischemia. However, the rate of leukocyte reaccumulation after cardiopulmonary bypass and its subsequent impact on myocardial function is not known. This laboratory study examined the effect of leukocyte depletion on myocardial performance during the initial 6-hour period after bypass in an in situ, in vivo porcine model of neonatal cardiac surgery. Fifteen 3- to 5-day-old piglets (eight control and seven leukocyte depleted animals) were instrumented by placement of left ventricular short-axis sonomicrometry crystals and an intraventricular micromanometer catheter. Mechanical leukocyte depletion was achieved with Pall RC100 filters (Pall Biomedical, Inc., Fajardo, Puerto Rico) in the cardiopulmonary bypass circuit. Neonatal hearts were subjected to 90 minutes of hypothermic ischemia after a single dose of cold crystalloid cardioplegia. Two control animals died after the operation and were excluded from data analysis. Leukocyte filtration reduced the granulocyte count during initial myocardial reperfusion to 0.8% of control values. However, circulating granulocyte counts increased in leukocyte depleted animals throughout the postoperative period, reaching 68% of control values by 6 hours. Despite this rapid return of circulating granulocytes, animals subjected to leukocyte depletion had significantly better preservation of left ventricular performance (measured by preload recruitable stroke work, p < or = 0.02), left ventricular systolic function (measured by end-systolic pressure-volume relationship, p < or = 0.05), and ventricular compliance (p < or = 0.04) during the experiment. These changes in ventricular function were associated with a significant increase in left ventricular water content (p < or = 0.02) and tissue myeloperoxidase activity (p < or = 0.005) in control animals compared with leukocyte depleted animals. This study demonstrates that leukocyte depletion during initial reperfusion results in sustained improvement in postischemic left ventricular function despite the rapid return of granulocytes to the circulation.     

Dichloroacetate enhanced myocardial functional recovery post-ischemia : ATP and NADH recovery

This study was undertaken to determine the effect of dichloroacetate (DCA) on myocardial functional and metabolic recovery following global ischemia. Isolated rabbit hearts were subjected to 120 min of mildly hypothermic (34 degrees C), cardioplegic arrest with multidose, modified St. Thomas' cardioplegia. Hearts were reperfused with either physiologic salt solution (PSS) as controls, (CON, n = 10) or PSS containing DCA (DCA, n = 6) at a concentration of 1 mM. Functional and metabolic indices were determined at baseline and at 15, 30, and 45 min of reperfusion. In four DCA and four CON hearts, myocardial biopsies were taken at baseline, end-ischemia, 15 and 45 min for nucleotide levels. Functional recovery was significantly better in hearts reperfused with DCA as demonstrated by recovery of baseline developed pressure (DCA = 69 +/- 5%, CON = 45 +/- 9%) and dP/dt (DCA = 64% +/- 10% versus CON = 48% +/- 10%). Coronary blood flow was not different between groups either at baseline or during reperfusion, but myocardial oxygen consumption (MVO2) was increased in the DCA versus CON hearts (79% +/- 20% of baseline vs 50% +/- 18%). Recovery of myocardial adenylate energy status was improved in the DCA versus CON hearts (ATP recovered to 45% +/- 20% versus 8% +/- 6% of baseline). Coronary sinus lactate concentration was decreased in DCA perfused hearts at 45 min of reperfusion. Percent of baseline NADH values was similar at 15 min of reperfusion, but at 45 min, DCA hearts showed a decrease in NADH levels, while CON hearts showed an increase (DCA = 48%; CON = 121%). The enhanced myocardial function and improved metabolic status noted with DCA may result from increased oxidative phosphorylation due to altered pyruvate dehydrogenase (PDH) activity.     

Complete unloading alone may not adequately protect the left ventricle

BACKGROUND: The benefit of left ventricular (LV) unloading for preserving LV function is commonly accepted, but its efficacy remains incompletely defined. METHODS: We studied the influence of complete LV unloading on LV systolic and diastolic mechanics using an in situ isovolumic preparation with two different coronary perfusion pressures (CPPs) in 12 dogs during prolonged normothermic cardiopulmonary bypass. RESULTS: Multivariate analysis of covariance with time as a covariate revealed that a high CPP (143 +/- 36 mm Hg; n = 6) was associated with better preservation of systolic LV function over time as assessed by LV end-systolic elastance (p < 0.001) and the end-systolic pressure-volume relation physiologic intercept (p < 0.001) compared with a moderate CPP (107 +/- 18 mm Hg; p < 0.005 versus a high CPP by t-test; n = 6). Dobutamine (2 micrograms.kg-1.min-1) improved LV end-systolic elastance (p < 0.005) and LV physiologic intercept (p < 0.01) only in the high-CPP group. Conversely, impaired LV diastolic function (as measured by LV stiffness) was observed (p < 0.001) with a high CPP, but did not change with a moderate CPP. CONCLUSIONS: These observations in canine hearts suggest that complete LV unloading may not preserve LV systolic function adequately over time when CPP is maintained in the accepted clinical range. A higher CPP is required to prevent deterioration over prolonged cardiopulmonary bypass times, but diastolic dysfunction still occurs.     

The superiority of pinacidil over adenosine cardioplegia in blood-perfused isolated hearts

BACKGROUND: Our laboratory has shown that the potassium-channel opener pinacidil is an effective cardioplegic agent. A theoretical benefit of cardioplegia with potassium-channel openers is that it arrests the heart at hyperpolarized membrane potentials, a state of minimal metabolic requirement. This study was designed to examine another nondepolarizing agent, adenosine, and to test the hypothesis that it could provide comparable cardioprotection or augment potassium-channel opener cardioplegia. METHODS: Using the blood-perfused Langendorff technique, isolated rabbit hearts were arrested for 30 minutes of global normothermic ischemia. Cardioplegia consisted of either Krebs-Henseleit solution alone (control) or with pinacidil (50 micromol/L), adenosine (200 micromol/L to 1 mmol/ L), or pinacidil + adenosine (200 micromol/L). Recovery of developed pressure and coronary flow were recorded. RESULTS: Postischemic functional recovery for control, pinacidil, adenosine, and adenosine + pinacidil groups was 44.1%+/-3.4%, 59.5%+/-5.2% (p < 0.05 versus control), 37.0%+/-4.5%, and 56.0%+/-2.9%, respectively. CONCLUSIONS: Adenosine, alone or as adjunct to pinacidil cardioplegia, was not an effective cardioplegic agent, despite shorter times to electromechanical arrest than control. The ineffectiveness of adenosine suggests that the cardioprotective properties of potassium-channel openers involve mechanisms other than the avoidance of membrane depolarization.     

Controlled reperfusion of cardiac grafts from non-heart-beating donors

BACKGROUND: Hearts harvested from non-heart-beating donors sustain severe injury during procurement and implantation, mandating interventions to preserve their function. We tested the hypothesis that limiting oxygen delivery during initial reperfusion of such hearts would reduce free-radical injury. METHODS: Rabbits sustained hypoxic arrest after ventilatory withdrawal, followed by 20 minutes of in vivo ischemia. Hearts were excised and reperfused with blood under conditions of high arterial oxygen tension (PaO2) (approximately 400 mm Hg), low PaO2 (approximately 60 to 70 mm Hg), high pressure (80 mm Hg), and low pressure (40 mm Hg), with or without free-radical scavenger infusion. Non-heart-beating donor groups were defined by the initial reperfusion conditions: high PaO2/ high pressure (n = 8), low PaO2/high pressure (n = 7), high PaO2/low pressure (n = 8), low PaO2/low pressure (n = 7), and high PaO2/high pressure/free-radical scavenger infusion (n = 7). RESULTS: After 45 minutes of reperfusion, low PaO2/ high pressure and high PaO2/low pressure had a significantly higher left ventricular developed pressure (63.6 +/- 5.6 and 63.1 +/- 5.6 mm Hg, respectively) than high PaO2/high pressure (40.9 +/- 4.5 mm Hg; p < 0.0000001 versus both). However, high PaO2/high pressure/free-radical scavenger infusion displayed only a trend toward improved ventricular recovery compared with high PaO2/ high pressure. CONCLUSIONS: Initially reperfusing nonbeating cardiac grafts at low PaO2 or low pressure improves recovery, but may involve mechanisms other than decreased free-radical injury.     

Depressed myofilament co-operativity associated with post-cardioplegic myocardial depression

The mechanism underlying myocardial depression after procedures involving cardioplegia are unknown. We tested the hypothesis that such depression was associated with altered myofilament interactions, using isolated hearts perfused with warm (37 degreesC), oxygenated (95% O2/5% CO2) Krebs-Ringer's bicarbonate (KRB) buffer. A latex balloon was inserted into the left ventricle (LV) to monitor LV function. All hearts underwent a 30-min equilibration period. One group of hearts (CPL+RPR) were arrested with St Thomas #2 cardioplegic solution (4 degreesC; 3 ml followed by 1 ml every 15 min) for 120 min, followed by reperfusion with warm, oxygenated KRB. A second group underwent cardioplegic arrest with no reperfusion (CPL). A third group underwent 60 min of warm, oxygenated perfusion with KRB beyond the equilibration period (60 MIN). The last group only underwent the equilibration period (EQUIL). LV function was assessed at the end of equilibration, and at 30 and 60 min of reperfusion (or 30 and 60 min additional perfusion in the 60 MIN group). All hearts were frozen at the end of the temporal protocol for each group, and stored at -70 degreesC for later measurement of Ca2+-stimulated Mg2+ ATPase activity after isolation of myofibrils. CPL+RPR hearts demonstrated significant depression of systolic pressure and elevation diastolic pressure at fixed volumes, compared to baseline and 60 MIN group values. There were no significant changes in the amount of constituent myofilament proteins, as assessed by densinometric analyses of Western blots. There were also no changes in the minimal or maximal ATPase activities, nor in the pCa50, indicating no effect of cardioplegic arrest on myofilament sensitivity to calcium. However, all hearts that underwent cardioplegic arrest were found to have significantly lower Hill coefficients (1.85+/-0.09 and 1.85+/-0.13 v 2.31+/-0.13 and 2.34+/-0. 14 in CPL+RPR and CPL v 60 MIN and EQUIL hearts, respectively), suggesting decreased co-operativity of the actomyosin interaction. Such a decrease in co-operativity would contribute to both the systolic and diastolic alterations associated with myocardial depression after cardioplegic arrest. These changes were associated with the cardioplegic event, and appeared to be independent of reperfusion.     

Ischemic intervals during warm blood cardioplegia in the canine heart evaluated by phosphorus 31-magnetic resonance spectroscopy

OBJECTIVE: Warm blood cardioplegia requires interruption by ischemic intervals to aid visualization. We evaluated the safety of repeated interruption of warm blood cardioplegia by normothermic ischemic periods of varying durations. METHODS: In three groups of isolated cross-perfused canine hearts, left ventricular function was measured before and for 2 hours of recovery after arrest, which comprised four 15-minute periods of cardioplegia alternating with three ischemic intervals of 15, 20, or 30 minutes (I15, I20, and I30). Metabolism was continuously measured by phosphorus 31-magnetic resonance spectroscopy. RESULTS: Adenosine triphosphate level fell progressively as ischemia was prolonged; after recovery, adenosine triphosphate was 99% +/- 6%, 90% +/- 1% (p = 0.0004 vs control), and 68% +/- 3% (p = 0.0002) of control levels in I15, I20, and I30, respectively. Intracellular acidosis with ischemia was most marked in I30. After recovery, left ventricular maximal systolic elastance at constant heart rate and coronary perfusion pressure was maintained in I15 but fell to 85% +/- 3% in I20, (p = 0.003) and to 65% +/- 6% (p = 0.003) of control values in I30, while relaxation (tau) was prolonged only in I30 (p = 0.007). CONCLUSIONS: Hearts recover fully after three 15-minutes periods of ischemia during warm blood cardioplegia, but deterioration, significant with 20-minute periods, is profound when the ischemic periods are lengthened to 30 minutes. This suggests that in the clinical setting warm cardioplegia can be safely interrupted for short intervals, but longer interruptions require caution.     

Endothelial stunning and myocyte recovery after reperfusion of jeopardized muscle: a role of L-arginine blood cardioplegia

Ischemia and reperfusion may damage myocytes and endothelium in jeopardized hearts. This study tested whether (1) endothelial dysfunction (reduced nitric oxide release) exists despite good contractile performance and (2) supplementation of blood cardioplegic solution with nitric oxide precursor L-arginine augments nitric oxide and restores endothelial function. Among 30 Yorkshire-Duroc pigs, 6 received standard glutamate/aspartate blood cardioplegic solution without global ischemia. Twenty-four underwent 20 minutes of 37 degrees C global ischemia. Six received normal blood reperfusion. In 18, the aortic clamp remained in place 30 more minutes and all received 3 infusions of blood cardioplegic solution. In 6, the blood cardioplegic solution was unaltered; in 6, the blood cardioplegic solution contained L-arginine (a nitric oxide precursor) at 2 mmol/L; in 6, the blood cardioplegic solution contained the nitric oxide synthase inhibitor L-nitro arginine methyl ester (L-NAME) at 1 mmol/L. Complete contractile and endothelial recovery occurred without ischemia. In jeopardized hearts, complete systolic recovery followed infusion of blood cardioplegic solution and of blood cardioplegic solution plus L-arginine. Conversely, contractility recovered approximately 40% after infusion of normal blood and blood cardioplegic solution plus L-NAME. Postischemic nitric oxide production fell 50% in the groups that received blood cardioplegic solution and blood cardioplegic solution plus L-NAME but was increased in the group that received blood cardioplegic solution L-arginine. In vivo endothelium-dependent vasodilator responses to acetylcholine recovered 75% +/- 5% of baseline in the blood cardioplegic solution plus L-arginine group, but less than 20% of baseline in other jeopardized hearts. Endothelium-independent smooth muscle responses to sodium nitroprusside were relatively unaltered. Myeloperoxidase activity (neutrophil accumulation) was similar in the blood cardioplegic solution (without ischemia) and blood cardioplegic solution plus L-arginine groups (0.01 +/- 0.002 vs 0.013 +/- 0.003 microgram/gm tissue). Myeloperoxidase activity was raised substantially to 0.033 +/- 0.002 microgram/gm after exposure to normal blood and to 0.025 +/- 0.003 microgram/gm after infusion of blood cardioplegic solution and was highest at 0.053 +/- 0.01 microgram/gm with exposure to blood cardioplegic solution plus L-NAME in jeopardized hearts. The discrepancy between contractile recovery and endothelial dysfunction in jeopardized muscle can be reversed by adding L-arginine to blood cardioplegic solution.     

Coronary vascular regulation during postcardioplegia reperfusion

BACKGROUND: This study extends previous investigations of global and regional myocardial blood flow during early postcardioplegia reperfusion. The hypothesis tested is that coronary vascular regulation becomes abnormal within 3 minutes after the start of postcardioplegia reperfusion. METHODS: Pigs (n = 40) were supported by cardiopulmonary bypass and 38 degrees C blood cardioplegic solution was infused. A control preischemic microsphere injection (No. 1) was given in asystolic hearts. Groups 1 to 3 had 1 hour of hypothermic cardioplegic arrest. Group 4 (control group) had 1 hour of perfusion without cardioplegia. A blood cardioplegic solution at 38 degrees C and 70 mm Hg pressure was infused to maintain asystole during the initial 7 to 10 minutes of reperfusion in all groups. Left ventricular intracavitary pressures were set at 0, 10, 20, or 0 mm Hg in groups 1, 2, 3, and 4 (n = 10 pigs per group), respectively, during the initial 7 minutes of reperfusion. The ventricle was then decompressed. At 30 seconds, 3 minutes, and 6 minutes after reperfusion, microsphere injections 2, 3, and 4 were given in asystolic hearts. Microsphere injection No. 5 was given 10 minutes after reperfusion in beating vented hearts. RESULTS: (1) Left ventricular distention during the initial 7 minutes of reperfusion after hypothermic cardioplegic arrest attenuates postischemic hyperemia. (2) Left ventricular intracavitary pressure of 20 mm Hg during reperfusion causes a decrease in endocardial blood flow relative to epicardial blood flow at 6 minutes after reperfusion. (3) Global myocardial blood flow during postcardioplegia reperfusion falls significantly below preischemic control values despite the return of electromechanical activity. INFERENCE: Coronary vascular regulation (i.e., coronary resistance and metabolic flow recruitment) becomes abnormal within 3 minutes after the start of reperfusion after hypothermic blood cardioplegic arrest.     

Comparison of the effects of potential parenteral vehicles for poorly water soluble anticancer drugs (organic cosolvents and cyclodextrin solutions) on cultured endothelial cells (HUV-EC)

Left atrial (LA) adaptation during the development of left ventricular (LV) dysfunction is not fully understood. We performed echocardiographic assessment of LA volumes simultaneously with recordings of pulmonary wedge pressures in 60 patients. Twenty patients had no structural or functional LV abnormalities, 20 had a recent myocardial infarction with LV dysfunction, and 20 suffered from congestive heart failure (CHF). Pressure-volume loops were obtained at baseline and during increases in LA pressure produced by normal saline infusion. LA afterload was estimated by the effective LV elastance (E(LV)). Atrioventricular coupling was calculated by the E(LV)/E(es) ratio (where E(es) is the end-systolic elastance). E(es) increased in patients with myocardial infarction (0.80 +/- 0.09 mm Hg/ml, p <0.001), whereas it decreased in patients with CHF (0.22 +/- 0.05 mm Hg/ml, p <0.001) compared with controls (0.61 +/- 0.07 mm Hg/ml). Similarly, stroke workload increased in patients with myocardial infarction (60.7 +/- 7.3 mm Hg x ml, p <0.001), whereas it decreased in patients with CHF (25.4 +/- 2.2 mm Hg x ml, p <0.001) compared with controls (44.8 +/- 5.5 mm Hg x ml). In all patients LA stiffness (slope of the relation of the filling portion of the pressure-volume loop) was increased compared with controls (controls: 0.13 +/- 0.04, patients with myocardial infarction: 0.22 +/- 0.05, and patients with CHF: 0.27 +/- 0.05 mm Hg/ml, p <0.001 for both comparisons). Moreover, the E(LV)/E(es) ratio increased gradually as LV function deteriorated (controls: 1.06 +/- 0.10, patients with myocardial infarction: 1.35 +/- 0.16, and patients with CHF: 6.90 +/- 0.84, p <0.001). Thus, early in heart failure, LA pump function is augmented but LA stiffness increases and work mismatch occurs. With further progression of LV dysfunction, LA pump function decreases as a result of increased afterload imposed on the LA myocardium.     

Ischemic preconditioning prior to myocardial protection with cold blood cardioplegia in coronary surgery

OBJECTIVE: Encouraging results on myocardial preconditioning in experimental models of infarction, stunning or prolonged ischemia raise the question whether preconditioning techniques may enhance conventional cardioplegic protection used for routine coronary surgery. METHODS: A prospective clinical trial was conducted to investigate the effect of additional ischemic normothermic preconditioning prior to cardioplegic arrest applying cold blood cardioplegia in patients scheduled for routine coronary surgery (3 vessel disease, left ventricular ejection fraction > 50%). Two cross clamp periods of 5 min with the hearts beating in sinus rhythm were applied followed by 10 min of reperfusion, each (n = 7, group I). Inducing moderate hypothermia cold blood cardioplegia was delivered antegradely. In control groups, cold intermittent blood cardioplegia (n = 7, group II) was used alone. Coronary sinus effluents were analyzed for release of creatine kinase (CK), CK-MB, lactate, and troponin T at 1, 3, 6, 9, and 12 h. In addition, postoperative catecholamine requirements were monitored. RESULTS: The procedure was tolerated well, and no perioperative myocardial infarction in any of the groups studied occurred. Concentrations of lactate tended to be higher in group I, but this difference was not significant. In addition, no significant differences for concentrations of CK, CK-MB, and troponin T were found. Following ischemic preconditioning an increased dosage of dopamine was required within the first 12 h postoperatively (group I: 2.63 +/- 1.44 microg/kg/min, group II: 0.89 +/- 1.06 microg/kg/min). CONCLUSIONS: Combining ischemic preconditioning and cardioplegic protection with cold blood cardioplegia does not appear to ameliorate myocardial protection when compared to cardioplegic protection applying cold blood cardioplegia alone. Inversely, contractile function seemed to be impaired when applying this protocol of ischemic preconditioning.     

The effect of coenzyme Q10 and cold cristalloid cardioplegia on hypothermic global ischemia

Coenzyme Q10 (CoQ10, ubiquinone) has been shown to be protective against myocardial ischemia/reperfusion induced injury. The purpose of this study was to investigate the effect of CoQ10 added to cold cristalloid cardioplegia on hypothermic ischemia and normothermic reperfusion using an isolated working rat heart. Hearts (n = 6-9/group) from male Wistar rats were aerobically (37 degrees C) perfused (20 min) with bicarbonate buffer. This was followed by a 3-min infusion of St. Thomas' Hospital cardioplegic solution containing various concentrations of CoQ10 (0, 1, 3, 6, 12, and 58 mumol/L). Hearts were then subjected to 180 min of hypothermic (20 degrees C) global ischemia and 35 min of normothermic (37 degrees C) reperfusion (15 min Langendorff, 20 min working). Ventricular fibrillation (Vf) upon reperfusion was irreversible in the 12 and 58 mumol/ L CoQ10 groups (4/6 and 3/6, respectively). In the hearts which Vf upon reperfusion was not irreversible, the percent recovery of aortic flow (%AF) was 43.3 +/- 5.4% (n = 9) in the control group versus 31.6 +/- 7.7% (n = 6), 38.0 +/- 12.0% (n = 6), 27.2 +/- 6.9% (n = 6), 31.3% (n = 2), and 30.4 +/- 14.2% (n = 3) in the 1, 3, 6, 12, and 58 mumol/L CoQ10 groups, respectively. Creatine kinase leakage during Langendorff reperfusion tended to be greater in the 12 and 58 mumol/L CoQ10 groups than in the control group. Thus, CoQ10 in the cold cristalloid cardioplegic solution induced irreversible Vf upon reperfusion and failed to improve functional recoveries following hypothermic global ischemia.