Coronary artery endothelial dysfunction after global ischemia, blood cardioplegia, and reperfusion

Beating Heart Transplantation: How to Do It

Heart transplantation utilizing deceased after circulatory death (DCD) donors has expanded the donor pool through the use of ex vivo normothermic perfusion. Compared with brain death donation, the conventional method of performing DCD heart transplantation includes an additional period of warm and cold ischemia. We have developed a beating heart implantation technique that obliviates the need for a second cardioplegic arrest and the associated reperfusion injury. We hypothesize this reproducible method may improve short-term and long-term outcomes to mirror results seen in brain death donors and provide details on how to perform beating heart transplantation.

Low-dose spironolactone: effects on artery-to-artery vein grafts and percutaneous coronary intervention sites

The efficacy of vein grafts used in coronary and peripheral artery bypass is limited by excessive hyperplasia and fibrosis that occur early after engraftment. In the present study, we sought to determine whether low-dose spironolactone alleviates maladaptive vein graft arterialization and alters intimal reaction to coronary artery stenting. Yorkshire pigs were randomized to treatment with oral spironolactone 25 mg daily or placebo. All animals underwent right carotid artery interposition grafting using a segment of external jugular vein and, 5 days later, underwent angiography of carotid and coronary arteries. At that time, a bare metal stent was placed in the left anterior descending artery and balloon angioplasty was performed on the circumflex coronary artery. Repeat carotid and coronary angiograms were performed before euthanasia and graft excision at 30 days. Angiography revealed that venous grafts of spironolactone-treated animals had lumen diameters twice the size of controls at 5 days, a finding that persisted at 30 days. However, neointima and total vessel wall areas also were 2- to 3-fold greater in spironolactone-treated animals, and there were no differences in vessel wall layer thicknesses or collagen and elastin densities. In the coronary circulation, there were no differences between treatment groups in any vessel wall parameters in either stented or unstented vessels. Taken together, these observations suggest that low-dose spironolactone may exert a novel protective effect on remodeling in venous arterial grafts that does not depend on the reduction of hyperplastic changes but may involve dilatation of the vessel wall.

Use of warm priming solution in open heart surgery: its effects on hemodynamics and acute inflammation

Cardiac surgery causes an acute inflammatory response and organ damage. In this study, for the first time in the literature, we compared the effects of priming solutions at 20°C and 36°C on acute inflammatory markers and hemodynamic parameters. Forty patients were recruited and randomized into two groups, each consisting of 20 participants who underwent elective coronary artery bypass grafting operation. Groups were primed with the same solution at different temperatures. Hemodynamic parameters were recorded. Blood samples were drawn pre-operatively and at the 15th and 60th minutes of aortic cross-clamping and the 24th hour following surgery. Serum pre-albumin, α-1 antitrypsin, and tumor necrosis factor-α levels were determined. The groups were compared statistically. Both of the groups were comparable for mean aortic cross-clamping time and mean time for cardiopulmonary bypass. Mean blood pressure value was significantly lower and the mean amount of ephedrine hydrochloride used was significantly higher in the cold priming group. Spontaneous beating of the heart after removal of aortic cross-clamp significantly was more frequent in the warm priming group. A significant rise was observed in systemic inflammatory markers in the cold priming group. In our study, the lesser amount of ephedrine hydrochloride used and the higher frequency of spontneous beating of the heart in the warm priming group may be considered as improvements in hemodynamic status. Use of warm priming solution also induced a significant improvement in the acute inflammatory markers. We recommend the use of warm priming solution in open heart surgery.

Cecilie Greig memorial lecture 2002. Myocardial protection: an expanding or contracting discipline?

For the past thirty years cardiac surgeons have had a unique opportunity to study the consequences of myocardial ischemia and reperfusion. With the advent of an ability to intervene in acute myocardial syndromes, cardiologists have vigorously joined that effort as have fundamental scientists. Exogenous myocardial protective strategies have emerged as have novel strategies that take advantage of endogenous mechanisms of myocardial protection. As a consequence of improved myocardial protection, operative mortality and morbidity, in particular the low output syndrome, have diminished. However, despite important increases in the knowledge base referable to myocardial ischemia and reperfusion, major advances in myocardial protection have slowed in the past several years. This article explores potential untapped options for augmenting myocardial protection and focuses on the potential adverse interactions between cardiopulmonary bypass and myocardial protection as a prime target for future investigations leading to improved myocardial management during heart operations.

Controlled intermittent asystole cardiac therapy induced by pharmacologically potentiated vagus nerve stimulation in normal and hibernating myocardium

BACKGROUND

Pharmacologically potentiated electrical stimulation of the right vagus nerve achieves controlled intermittent asystole cardiac therapy. The present study examined pathophysiologic consequences of repetitive intermittent asystoles on contractile function, myocardial blood flow, and vagus nerve function and morphology.

METHODS

Open-chest anesthetized canines, with either normal left anterior descending (LAD) coronary arteries (n = 8) or severely stenotic LADs (n = 8), received pharmacologic pretreatment with pyridostigmine (0.5 mg/kg), propranolol (80 microg/kg), and verapamil (50 microg/kg) before vagus nerve stimulation. Time-matched control animals with normal (n = 4) or severely stenotic LADs (n = 6) received drugs but no vagus nerve stimulation. The vagus nerve was stimulated for 12 seconds ("on") and rested for 15 seconds ("off"). This algorithm was repeated for 15 on-off cycles, simulating using controlled intermittent asystole during the placement of 15 sutures in a distal coronary anastomosis. This 15-cycle sequence was repeated twice more, simulating a three-vessel bypass.

RESULTS

Normal coronary arteries: Ninety minutes after three sets of controlled intermittent asystole, LAD blood flow was unchanged from base line (36.6 +/- 4.5 versus 33.0 +/- 4.2 mL/min, p = 0.4), and global left ventricular performance (impedance catheter, end-systolic pressure-volume relations) was similar to baseline (7.4 +/- 1.2 versus 7.2 +/- 1.0 mm Hg/mL, p = 0.1). Left anterior descending coronary artery stenosis model: Ninety minutes after CIA, there were no significant differences versus control animals in regional LAD blood flow (27 +/- 4 versus 29 +/- 5 mL/min, p = 0.4) or fractional shortening of LAD myocardium (sonomicrometry; 6.2% +/- 1.8% versus 5.4% +/- 1.2%, p = 0.1). Vagus nerve conduction and morphology were unchanged from baseline.

CONCLUSIONS

Repetitive controlled intermittent asystole does not impair poststimulation coronary blood flow, cardiac contractile function, or vagus nerve function. Controlled intermittent asystole may be useful to facilitate off-pump or endoscopic coronary artery bypass grafting.

Continuous tepid blood cardioplegia can preserve coronary endothelium and ameliorate the occurrence of cardiomyocyte apoptosis

OBJECTIVE

In modern cardiac surgery, crystalloid or blood cardioplegic solutions have been used widely for myocardial protection; however, ischemia does occur during protection with intermittent infusion of cold crystalloid or blood cardioplegic solutions. The present study was designed to evaluate the effect of different cardioplegic methods on myocardial apoptosis and coronary endothelial injury after global ischemia, cardiopulmonary bypass (CPB), and reperfusion in anesthetized open-chest dogs.

METHODS

The dogs were classified into five groups to identify the injury of myocardium and coronary endothelium: group 1, normothermic CPB without cardiac arrest; group 2, hypothermic CPB with continuous tepid blood cardioplegia, and with cardiac arrest; group 3, hypothermic CPB with intermittent cold blood cardioplegia, and with cardiac arrest; group 4, hypothermic CPB with intermittent cold crystalloid cardioplegia, and with cardiac arrest; and group 5, sham-operated control group. During CPB, cardiac arrest was achieved with different cardioplegia solutions for 60 min, followed by reperfusion for 4 h before the myocardium and coronary arteries were harvested. Coronary arteries were harvested immediately and analyzed by scanning electron microscopy. Cardiomyocytic apoptosis was detected using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling, Western blot, and DNA ladder methods.

RESULTS

Regardless of the detection method used, significantly higher percentages of apoptotic cardiomyocytes were found in group 3 and group 4 than in other groups. Expression of caspase-3 correlated with increased apoptosis. Scanning electron microscopy revealed severe endothelial injury of coronary arteries in group 3 and group 4.

CONCLUSION

These results point to an important explanation for the difference in cardiac recovery after hypothermic ischemia and arrest with various cardioplegic solutions.

Erythrocyte-containing versus crystalloid cardioplegia in the rat: effects on myocardial capillaries

BACKGROUND

The purpose of this study was to investigate the effects of crystalloid and erythrocyte-containing cardioplegia on capillary morphology of the isolated erythrocyte-perfused rat heart.

METHODS

Hearts from adult Sprague-Dawley rats were perfused throughout with resuspended sheep erythrocytes and subjected to the following protocols (n = 6, all groups): (1) 15 minutes nonworking and 30 minutes working heart mode (control; group 1); (2) as for group 1, with 30 minutes erythrocyte-containing (BL) or crystalloid (CR) cardioplegic arrest without reperfusion (groups 2BL and 2CR); (3) as for group 2, with 30 minutes nonworking reperfusion (groups 3BL and 3CR); and (4) as for group 3, with 30 minutes working heart mode (groups 4BL and 4CR). After each protocol troponin I from coronary effluent was measured. Corrosion casts were then made of the coronary microvasculature. Cast density was calculated as cast volume per left ventricular dry weight. Casts also underwent scanning electron microscopy. Analysis was by analysis of variance. Values are mean +/- standard deviation.

RESULTS

Prearrest working heart coronary flow averaged 15.1 +/- 4.7 mL/min without any differences among groups. Coronary flow in group 4 working hearts was the same before and after either cardioplegia. Cardiac outputs were similarly consistent in all groups. Cast density in group 1 (control) was 9.60 +/- 1.17 x 10(-2) mm3/mg. It was unaltered by erythrocyte-containing cardioplegia, but after crystalloid cardioplegia (group 2CR), it was 6.52 +/- 0.93 x 10(-2) mm3/mg (p = 0.0001 versus group 1 and p = 0.0007 versus group 2BL). With 30 minutes of nonworking reperfusion (group 3CR, there was slight improvement in cast density at 7.60 +/- 0.90 x 10(-2) mm3/mg (p = 0.0072 versus group 1; p = 0.0242 versus group 3BL). No further improvement was seen in group 4CR. Electron micrographs showed circumferential angularities or narrowings in crystalloid-perfused, arrested hearts, consistent with ischemic damage. Troponin I rose significantly after reperfusion in all groups, but it was higher in crystalloid-perfused, arrested hearts: 0.054 +/- 0.013 microg/L versus 0.024 +/- 0.017 microg/L (p = 0.0273).

CONCLUSIONS

Erythrocyte-containing cardioplegia maintained capillary density and morphology. Crystalloid cardioplegia produced capillary loss, visible abnormalities, and higher troponin I release. These hearts may be more vulnerable to myocardial damage during reperfusion than hearts perfused with erythrocyte-containing cardioplegic solution.

Electroplegia: an alternative to blood cardioplegia for arresting the heart during conventional (on-pump) cardiac operation

BACKGROUND

Aortic cross-clamping is contraindicated in patients with severe atherosclerosis of the ascending aorta, and administration of chemical cardioplegia may be cumbersome in these patients. In this study, we demonstrate an alternative method of achieving cardioplegia by electrical stimulation of the vagus nerve.

METHODS

In anesthetized canines, the left anterior descending coronary artery was reversibly ligated for 90 minutes, followed by cardiopulmonary bypass (CPB) and randomization to three groups (n = 8 each): (1) BCP group: 1 hour of intermittent hypothermic (4 degrees C) blood cardioplegia infusion; (2) CPB group: 1 hour of CPB alone; (3) EP group (group receiving electroplegia): 1 hour of intermittent vagal stimulation (total of 60 20-second electrical stimuli at 40 Hz, 6 to 10 V) with adjunctive pyridostigmine (0.5 mg/kg), verapamil (50 microg/kg), and propranolol (80 microg/kg) to potentiate hyperpolarization and suppress ectopic escape beats.

RESULTS

The EP group achieved consistent intervals of arrest with 3.8 +/- 1.2 escape beats per 20-second stimulation period. After 2 hours of reperfusion off CPB, the left anterior descending coronary artery segmental shortening was reduced from baseline in all groups, but the segmental shortening recovered to a greater extent in the EP group than in either the CPB or BCP group (2.4% +/- 1.4% versus -1.3% +/- 1.3% versus -4.0% +/- 0.8%, p < 0.05). Infarct size (TTC stain, percentage of area at risk) was comparable among groups (EP: 20.9% +/- 4.7%; CPB: 29.6% +/- 3.2%; BCP: 25.1% +/- 5.7%). Postischemic left anterior descending coronary artery endothelial function (percent maximum relaxation to acetylcholine) was depressed in the EP group (68.6% +/- 7.6% versus 102.3% +/- 6.4%, p < 0.05), but was comparable versus nonischemic circumflex function in the BCP group (77.1% +/- 11.9% versus 100.4% +/- 10.0%, p = 0.15) and the CPB group (93.8% +/- 6.6% versus 93.3% +/- 6.6%).

CONCLUSIONS

Electroplegia achieves elective intermittent cardiac arrest, avoids hypothermia, chemical cardioplegia, and aortic cross-clamping, with physiological outcomes comparable to blood cardioplegia.

Myocardial protection with leukocyte depletion in cardiac surgery

A role of neutrophils in ischemia-reperfusion injury has been focused on as one of the mediating factors of inflammatory reactions. Current studies have reported the efficacy of leukocyte-depletion in reperfusion by using leukocyte removal filter to attenuate reperfusion injury during open heart surgeries. For clinical application, we have introduced leukocyte-depleted terminal blood cardioplegia (LDTC) in adult patients and leukocyte-depleted blood cardioplegia in pediatric patients. The results of elective surgery in noncompromised LDTC did not significantly alter the results in terms of leakage of creatine kinase (CK)-MB, production of malondialdehyde from myocardium, and dopamine dose required at the weaning from cardiopulmonary bypass compared with the whole-blood reperfusion or with terminal cardioplegia alone. In contrast, the results in emergency coronary artery bypass graft (CABG) patients differed significantly between the LDTC group and the other two groups. Leukocyte-depleted reperfusion was also effective in a similar fashion for patients with severe left ventricular hypertrophy caused by chronic aortic valve disease. Leukocyte-depleted blood cardioplegia was useful in pediatric patients. Thus, leukocyte depletion may be beneficial as an adjunct to terminal blood cardioplegia or blood cardioplegia during cardiac surgery to attenuate leukocyte-mediated ischemia-reperfusion injury in patients with compromised hearts, such as those with preoperative ischemic insults, severe left ventricular hypertrophy, and in pediatric patients.

Glutathione Reverses Endothelial Damage From Peroxynitrite, the Byproduct of Nitric Oxide Degradation, in Crystalloid Cardioplegia

Background —NO has been advocated as an adjunct to cardioplegia solutions. However, NO undergoes a rapid biradical reaction with superoxide anions to produce peroxynitrite (ONOO − ). ONOO − in crystalloid cardioplegia solution induces injury to coronary endothelium and to systolic function after cardioplegia and reperfusion. However, ONOO − may be degraded to less lethal or cardioprotective intermediates with glutathione (GSH) in reactions separate from its well known antioxidant effects. We hypothesized that GSH detoxifies ONOO − and reverses defects in endothelial function and systolic function when present in crystalloid cardioplegia.

Methods and Results —In anesthetized dogs on cardiopulmonary bypass, a 45-minute period of global normothermic ischemia was followed by 60 minutes of intermittent cold crystalloid cardioplegia (Plegisol) and 2 hours of reperfusion. The cardioplegia solution contained 5 μmol/L authentic ONOO − ; catalase was included to attenuate the potential antioxidant effects of GSH and to unmask the effects on ONOO − . In 1 group (CP+GSH, n=5), the cardioplegia contained 500 μmol/L GSH, whereas 1 group received crystalloid cardioplegia without GSH (CCP, n=6). There were no group differences in postcardioplegia left ventricular systolic function (end-systolic pressure-volume relation, impedance catheter: CCP 10.0±2.4 versus CP+GSH 10.6±1.3 mm Hg/mL) or diastolic chamber stiffness (β-coefficient: CCP 0.35±0.2 versus CP+GSH 0.31±0.18). Myocardial neutrophil accumulation (myeloperoxidase activity) was attenuated in CP+GSH versus CCP (2.2±0.7 versus 5.4±1.2, P <0.05). In postexperimental coronary arteries, maximal endothelium-dependent relaxation was greater in CP+GSH than in CCP (118±6% versus 92±5%, P <0.05), with a smaller EC 50 value (−7.10±0.05 versus −6.98±0.03, respectively, P <0.05). Smooth muscle relaxation was complete in both groups. The adherence of neutrophils to postexperimental coronary arteries as a measure of endothelial function was less in CP+GSH than in CCP (98±18 versus 234±36 neutrophils/mm 2 , P <0.05). Nitrosoglutathione, a byproduct of the reaction between ONOO − and GSH, was greater in CP+GSH than in CCP (4.1±2.3 versus 0.4±0.2 μg/mL, P <0.05).

Conclusions —GSH in crystalloid cardioplegia detoxifies ONOO − and forms cardioprotective nitrosoglutathione, resulting in attenuated neutrophil adherence and selective endothelial protection through the inhibition of neutrophil-mediated damage.

Reperfusion injury associated with one-fourth of deaths after coronary artery bypass grafting

BACKGROUND

This study of reperfusion injury after coronary artery bypass grafting focuses on its contribution to fatal outcome, on its connection with myocardial infarction (MI) and on risk factors.

METHODS

A consecutive series of 190 patients (mean age 61.7+/-8.9 years) dying within 30 days following coronary artery bypass grafting was autopsied with concomitant postmortem angiography during 1980 to 1993.

RESULTS

Reperfusion injury was revealed in 49 (25.8%) patients, with concomitant MI in almost all (46 of 49) (p < 0.01). Reperfusion injury occurred in association with preoperative New York Heart Association (NYHA) III classification (p < 0.05), coronary endarterectomy (p < 0.01), long aortic clamping time (p < 0.01), and short postoperative survival (p < 0.05).

CONCLUSIONS

Reperfusion injury was observed in one fourth of the deaths in association with MI. It occurred more often in patients with preoperative NYHA III symptoms and in those in whom endarterectomy was carried out and the anoxic time of the myocardium was longer. The shorter postoperative survival time indicates the lethal nature of this complication.

Clinical evaluation of leukocyte-depleted blood cardioplegia for pediatric open heart operation

BACKGROUND

Blood cardioplegia (BCP) is widely used for myocardial protection during open heart operation. However, BCP may have a chance to induce neutrophil-mediated myocardial injury during aortic cross-clamping. We clinically evaluated the myocardial protective effect of leukocyte-depleted blood cardioplegia (LDBCP) for initial and intermittent BCP administration in pediatric patients.

METHODS

Fifty patients undergoing open heart operation for congenital heart disease between January 1997 and March 1999 were reviewed. Twenty-five were administered LDBCP for myocardial protection during ischemic periods (LDBCP group), and the remaining 25 were given BCP without leukocyte depletion (BCP group).

RESULTS

The difference in plasma concentrations of malondialdehyde between coronary sinus effluent blood and arterial blood just after reperfusion in the LDBCP group (1.68 +/- 0.56 micromol/L) was significantly lower than that in the BCP group (2.35 +/- 0.62 micromol/L; p < 0.01). The LDBCP group showed significantly lower plasma concentrations of human heart fatty acid-binding protein at 50 minutes after reperfusion (LDBCP group, 103.5 +/- 38.7 IU/L; BCP group, 144.8 +/- 48.8 IU/L; p < 0.01) and the peak value of creatine kinase-MB during the first 24 postoperative hours (LDBCP group, 17.0 +/- 8.5 IU/L; BCP group, 26.0 +/- 11.6 IU/L; p < 0.01) than did the BCP group. The maximum dose of catecholamine was significantly smaller in the LDBCP group (LDBCP group, 3.20 +/- 2.18 microg x kg(-1) x min(-1); BCP group, 5.60 +/- 2.83 microg x kg(-1) x min(-1); p < 0.01).

CONCLUSIONS

These results suggest the usefulness of LDBCP for protection from the myocardial injury that can be induced by BCP administration during aortic cross-clamping.

Nitric oxide and the vascular endothelium in myocardial ischemia-reperfusion injury

The normal coronary vascular endothelium (VE) tonically releases nitric oxide (NO) by converting L-arginine to citrulline by a constitutive NO synthase. Reperfusion after myocardial ischemia reduces basal and stimulated release of NO. This "vascular reperfusion injury" is mediated largely by neutrophils (PMN) through specific interactions between adhesion molecules on the endothelium and the PMN, an interaction that precedes myocyte injury. NO inhibits the PMN-mediated reperfusion injury by direct effects on both the PMN and the vascular endothelium. Cardioprotective strategies include augmentation of endogenous NO by the precursor L-arginine and the administration of exogenous NO donors at the time of perfusion, which (1) attenuates PMN adherence to the coronary artery and venous endothelium, (2) reduces PMN-mediated endothelial dysfunction, (3) reduces PMN accumulation in the area at risk, and (4) reduces infarct size. Hence, NO represents a powerful therapeutic tool with which to attenuate the consequences of ischemia-reperfusion injury on vascular injury and infarction.

Coronary microvascular protection with mg2+: effects on intracellular calcium regulation and vascular function

The use of Mg2+-supplemented hyperkalemic cardioplegia preserves microvascular function. However, the mechanism of this beneficial action remains to be elucidated. We investigated the effects of Mg2+ supplementation on the regulation of intracellular calcium concentration ([Ca2+]i) and vascular function using an in vitro microvascular model. Ferret coronary arterioles (80-150 micrometer in diameter) were studied in a pressurized (40 mmHg) no-flow, normothermic (37 degrees C) state. Simultaneous monitoring of internal luminal diameter and [Ca2+]i using fura 2 were made with microscopic image analysis. The microvessels (n = 6 each group) were divided into four groups according to the content of MgCl2 (nominally 0, 1.2, 5.0, and 25.0 mM) in a hyperkalemic cardioplegic solution ([K+] 25.0 mM). After baseline measurements, vessels were subjected to 60 min of hypoxia with hyperkalemic cardioplegia (equilibrated with 95% N2-5% CO2) containing each concentration of Mg2+ ([Mg2+]) and were then reoxygenated. During hyperkalemic cardioplegia, [Ca2+]i increased in a time-dependent manner in all groups. In the lower [Mg2+] cardioplegia groups, [Ca2+]i was significantly increased at the end of the 60-min cardioplegic period (247 +/- 44 nM and 236 +/- 49 nM in [Mg2+] 0 and 1.2 mM groups, respectively; both P < 0.05 vs. baseline) with 19.6-17.2% vascular contraction. Conversely, there was no significant [Ca2+]i increase in the higher [Mg2+] cardioplegia groups and less vascular contraction (5.4-4.1%, both P < 0.05 vs. [Mg2+] 1.2 mM group). After reperfusion, agonist (U-46619, thromboxane A2 analog)-induced vascular contraction was significantly enhanced in the lower [Mg2+] cardioplegia groups (both P < 0.05 vs. control) but was normalized in the higher [Mg2+] cardioplegia groups. Intrinsic myogenic contraction was significantly decreased in the lower [Mg2+] cardioplegia groups (both P < 0.05 vs. control) but was preserved in the higher [Mg2+] cardioplegia groups. These results suggest that supplementation of the solution with >5.0 mM [Mg2+] may prevent hyperkalemic cardioplegia-related intracellular Ca2+ overloading and preserve vascular contractile function in coronary microvessels.

Recombinant human megakaryocyte growth and development factor attenuates postbypass thrombocytopenia

BACKGROUND

Cardiopulmonary bypass contributes to platelet loss and dysfunction by exposure to shear stresses, foreign surfaces, and hypothermia. This study tested the hypothesis that pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) accelerates recovery of the platelet population after hypothermic extracorporeal circulation (HEC).

METHODS

In a blinded study, subcutaneous injections of drug or placebo were given to dogs daily for 3 days preoperatively (day 0, 1, and 2) with no drug on day 3. On day 4, the animal was prepared for arteriovenous HEC. After heparinization, HEC was initiated at 30 to 40 mL x kg(-1) x min(-1). Hypothermic extracorporeal circulation (25 degrees C) was continued for 90 minutes.

RESULTS

Preoperative platelet count (x10(3) platelets/microL) did not differ from predrug count in placebo (256+/-27 versus 255+/-20) or PEG-rHuMGDF (271+/-30 versus 291+/-38). During 60 minutes of HEC, the platelet count decreased to approximately 10% of baseline in placebo (29+/-5) and PEG-rHuMGDF (46+/-8), and recovered to approximately 70% of baseline after rewarming (90 minutes of HEC: placebo, 185+/-17, versus PEG-rHuMGDF, 169+/-22). After HEC, platelet count was greater in PEG-rHuMGDF-treated animals (p < 0.05) without altering function (aggregation responses). Within the first 6 hours after HEC, platelet count in PEG-rHuMGDF-treated animals was rising and increased to 260+/-29 (p < 0.01), but was unchanged in placebo animals (186+/-21). Thereafter, platelet count in placebo animals declined to a nadir of 124+/-15 (72 hours after HEC), whereas platelet count in PEG-rHuMGDF animals approximated the preoperative value (>200) at all times.

CONCLUSIONS

Appropriately timed presurgical administration of PEG-rHuMGDF counteracts post-HEC relative thrombocytopenia without increasing platelet population and enhancing aggregation preoperatively or during extracorporeal circulation.

Effect of pressure on myocardial function after 6-hour preservation with blood cardioplegia

BACKGROUND

This study examined the return of cardiac function in pig hearts after 6 hours' preservation by continuous perfusion with blood cardioplegia at two perfusion pressures compared with preservation with crystalloid solutions.

METHODS

Isolated pig hearts were randomly divided into five groups (n = 8 per group) according to the following treatments: group 1 = fresh hearts (control); group 2 = hearts arrested with Queen's cocktail cardioplegia and then immersion in 0 degrees C saline solution (QS group); group 3 = hearts arrested with (5 degrees C) and simple immersion in 0 degrees C University of Wisconsin solution (UW group); and groups 4 and 5 = hearts arrested with blood cardioplegia at 10 degrees C and then continuously perfused at a pressure of 80 cm H2O or 40 cm H2O, respectively (groups BC80 and BC40). After preservation for 6 hours, donor hearts were reperfused by a cross-circulation support pig. Thereafter, cardiac function and metabolism were examined every half hour for 2 hours. A three-way mixed general linear model was used to analyze data with repeated measures. Bonferroni test was used to determine differences (p < or = 0.05) between groups.

RESULTS

Only 4 hearts recovered electric activity in the BC80 group (p < or = 0.05 versus other groups). There was poor recovery of left ventricular work in the BC80 group compared with the other groups (p < 0.001). Left ventricular work in the QS and UW groups was also lower than in the control and BC40 groups. Left ventricular work in the BC40 group fully recovered. Maximum elastance did not differ between groups. Compliance was reduced in the QS, BC80, and BC40 groups versus controls after preservation (p < 0.006). Coronary flow decreased and coronary vascular resistance increased in the BC80 group versus the other groups (p < or = 0.001). Coronary flow in the QS, UW, and BC40 groups was lower than in the control group (p < 0.001). The magnitude of lactate release was much higher in the BC80 group than in the other groups (p < or = 0.001).

CONCLUSIONS

Continuous perfusion with 10 degrees C blood cardioplegia at 40 cm H2O pressure for 6 hours provided adequate preservation of systolic function in this model. University of Wisconsin solution provided the best protection of diastolic function.

Preconditioning human cardiomyocytes and endothelial cells

BACKGROUND

The effects of simulated "ischemia" and "reperfusion" were evaluated in cell cultures of human ventricular cardiomyocytes and human saphenous vein endothelial cells.

METHODS

Myocyte and endothelial cell cultures were exposed to a low volume (1.5 ml) of either hypoxic (oxygen tension = 16 mm Hg) or anoxic (oxygen tension = 0 mm Hg) phosphate-buffered saline solution for 90 minutes ("ischemia") followed by 30 minutes of simulated "reperfusion." Cell injury was evaluated by trypan blue exclusion. Next, the effects of a preconditioning stimulus were evaluated by a brief (10 minute) exposure to hypoxic or anoxic ischemia and 10 minutes of reperfusion before prolonged (90 minutes) anoxic ischemia. Finally, the effects of anoxic preconditioning on intracellular lactate accumulation and extracellular lactate and acid release were assessed.

RESULTS

"Ischemia" and "reperfusion" resulted in greater injury to endothelial cells than to cardiomyocytes. In both cell types, anoxic ischemia resulted in greater injury than hypoxic ischemia. Preconditioning reduced cell injury in myocytes but not in endothelial cells. Endothelial cells produced more lactate than cardiomyocytes under normoxic conditions. Ischemia increased lactate accumulation and release in cardiomyocytes but not endothelial cells. Preconditioning reduced lactate accumulation and release in cardiomyocytes but not endothelial cells.

CONCLUSIONS

Endothelial cells were more susceptible to the same period of simulated ischemia than cardiomyocytes. Preconditioning protected cardiomyocytes but not endothelial cells from a subsequent prolonged period of ischemia and reperfusion.

Comparative effects of continuous warm blood and intermittent cold blood cardioplegia on coronary reactivity

BACKGROUND

Cardioplegia is known to affect coronary vascular reactivity. We examined the effects of intermittent cold and continuous warm blood cardioplegia on beta-adrenoceptor-mediated, adenosine triphosphate-sensitive K+ (K+ATP)-channel-mediated, and endothelium-dependent relaxation and on the myogenic tone of coronary arterioles.

METHODS

Pigs were placed on cardiopulmonary bypass. Hearts were arrested for 1 hour with a cold blood cardioplegic solution administered intermittently (n = 12; iCB-CP) or with a warm blood cardioplegic solution delivered continuously (n = 12; cWB-CP). Selected hearts (n = 6 in each group) were then reperfused for 1 hour. In vitro relaxation responses of precontracted microvessels (50 to 160 microns) were studied in a pressurized no-flow state.

RESULTS

Relaxation in response to isoproterenol (beta-adrenergic agonist) was similar after iCB-CP and cWB-CP, whereas forskolin (adenylate cyclase activator)-induced relaxation was impaired more after iCB-CP than after cWB-CP. After reperfusion the respective responses were similar. Both iCB-CP and cWB-CP preserved receptor-mediated, endothelium-dependent relaxation in response to adenosine, 5'-diphosphate; non-receptor-mediated endothelium-dependent relaxation in response to A23187; endothelium-independent cyclic guanosine monophosphate-mediated relaxation in response to sodium nitroprusside, and K+ATP-channel-mediated relaxation. Relaxations in response to 8-bromo-cyclic guanosine monophosphate (a cyclic guanosine monophosphate-dependent protein kinase activator) and to 8-bromo-cyclic adenosine monophosphate (a cyclic adenosine monophosphate-dependent protein kinase activator) were impaired after iCB-CP alone and after reperfusion, whereas the respective responses were not affected after cWB-CP. Myogenic tone was decreased similarly after iCB-CP and cWB-CP but was not further altered after reperfusion. Cardiac function was similar after iCB-CP and cWB-CP.

CONCLUSIONS

These results suggest that cWB-CP is similar to iCB-CP in its ability to preserve endothelium-dependent relaxation and K+ATP-channel function. The superior preservation of beta-adrenergic-cyclic adenosine monophosphate-mediated coronary responses after cWB-CP is brief and associated with minimal improvement of myocardial function and myogenic tone.

Cardiopulmonary bypass alters vasomotor regulation of the skeletal muscle microcirculation

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with alterations in the regulation of organ perfusion and vascular permeability. The purpose of this study was to examine the effects of hypothermic CPB on the regulation of the skeletal muscle microcirculation and the modulating influence of the priming solution.

METHODS

Sheep were placed on hypothermic CPB with a prime of either Pentastarch hydroxylethyl starch (HS) solution (n = 7), a solution in which HS is conjugated with deferoxamine (n = 7), or Ringer's lactate solution (n = 7). Sheep were placed on hypothermic CPB (27 degrees C) for 90 minutes while the heart was protected with cold blood cardioplegia. Sheep were then separated from CPB and perfused for an additional 3 hours off CPB. Hemodynamics and total water content were measured.

RESULTS

In vitro relaxation responses of gracilis muscle arterioles (70 to 180 microns) to the endothelium-dependent agent acetylcholine, the endothelium-independent cyclic GMP-mediated vasodilator sodium nitroprusside, the beta-adrenergic agonist isoproterenol, and the adenylate cyclase activator forskolin were studied. No statistically significant hemodynamic differences were observed between groups. However, weight gain was significantly less when the priming solution was HS or HS-deferoxamine compared to when Ringer's lactate was used. Skeletal muscle arteriolar relaxations to the endothelium-dependent vasodilator acetylcholine and the beta-adrenergic agonist isoproterenol were impaired after CPB in the HS and Ringer's lactate groups. Acetylcholine response was preserved in the HS-deferoxamine group, whereas the response to isoproterenol remained impaired. The responses to sodium nitroprusside and forskolin were similar in all groups.

CONCLUSIONS

Skeletal muscle microvascular endothelium-dependent relaxation and beta-adrenergic relaxation are reduced after CPB using either a crystalloid or HS prime. Skeletal muscle microvascular endothelial dysfunction may be attributable to oxygen-derived free radical-mediated injury, whereas altered beta-adrenergic regulation is attributable to mechanisms other than the generation of oxygen-derived free radicals during CPB.

Deoxygenated blood minimizes adherence of sonicated albumin microbubbles during cardioplegic arrest and after blood reperfusion: experimental and clinical observations with myocardial contrast echocardiography

Both administration of cardioplegic solution and blood reperfusion result in endothelial dysfunction. The transit rate of albumin microbubbles during myocardial contrast echocardiography may reflect endothelial injury. Accordingly, we performed myocardial contrast echocardiography in 12 dogs undergoing cardiopulmonary bypass and measured the myocardial transit rate of microbubbles injected into the aortic root during delivery of cardioplegic solutions containing arterial and venous blood and delivery of pure crystalloid cardioplegic solution. The myocardial transit rate of 99mTc-labeled red blood cells was measured and perfusates were sampled for biochemical analysis at each stage. The microbubble transit rate was markedly prolonged during delivery of crystalloid cardioplegic solution and improved significantly during infusion of blood cardioplegic solution (p < 0.001); venous compared with arterial blood in the solution resulted in a greater rate (p < 0.001). The microbubble transit rate did not correlate with pH, oxygen tension or carbon dioxide tension values, or K+ concentration. The red blood cell transit rate remained constant regardless of the cardioplegic perfusate infused. Myocardial contrast echocardiography was also performed in 12 patients undergoing coronary artery bypass who underwent sequential arterial and venous reperfusion after cardioplegic arrest. The microbubble transit rate was faster with venous than arterial blood reperfusion (p = 0.01), although this gain was diminished when arterial blood reperfusion preceded venous blood reperfusion (p = 0.05). Our results indicate that endothelial dysfunction after cardioplegic arrest may be ameliorated by reperfusion with venous rather than arterial blood.

Cardioplegia preserves hypoxic response in isolated coronary arteries but not in isolated hearts

BACKGROUND

Experiments were designed to determine whether hyperkalemic crystalloid cardioplegic solution alters the hypoxic response of isolated segments of rabbit coronary arteries.

METHODS

Coronary arteries were suspended in organ chambers to measure isometric force. We measured the coronary perfusion pressure at a constant flow rate in isolated Langendorff-perfused hearts. Coronary arteries and hearts were preserved in warm (37 degrees C) physiologic solution or in cold (10 degrees C) crystalloid cardioplegic solution.

RESULTS

In all groups of coronary arteries, the acetylcholine-induced relaxation before and after preservation was unchanged (n = 7). Hypoxia (15 mm Hg) caused an endothelium-dependent contraction, the amplitude of which did not change after cardioplegia. Conversely, in coronary arteries preserved in physiologic solution, hypoxic contraction amplitude decreased by 67% +/- 17%. In isolated hearts, hypoxic perfusion (15 mm Hg) induced a vasodilation. In all groups, the second hypoxic vasodilation was significantly greater (group 1, first hypoxic perfusion 2.8% +/- 2.8%, second hypoxic perfusion 18.2% +/- 7.1%; group 2, first hypoxic perfusion 6.8% +/- 1.5%, second hypoxic perfusion 29% +/- 9%).

CONCLUSIONS

The crystalloid cardioplegic solution did not change the hypoxic response in isolated hearts and preserved the endothelium-dependent hypoxic contraction in coronary arteries.

Impaired endothelium-dependent relaxation after cardiac global ischemia and reperfusion: role of warm blood cardioplegia

OBJECTIVES

Experiments were designed to determine whether coronary endothelial dysfunction after cardiac global ischemia and reperfusion could be prevented by warm blood cardioplegic solution.

BACKGROUND

The coronary endothelium produces endothelium-derived relaxing factor (EDRF) to prevent vasospasm and thrombosis. After ischemia and reperfusion, endothelium-dependent relaxation (EDR) is diminished as a result of G-protein dysfunction.

METHODS

Dogs were exposed to extracorporeal circulation in 37 degrees C (group 1) or 28 degrees C (groups 2 and 3). The heart was ischemic for 120 min while continuous warm blood cardioplegic solution (group 1) or intermittent cold (4 degrees C) crystalloid cardioplegic solution was not used in group 3 animals. The heart was then allowed to function for 60 min of reperfusion.

RESULTS

Endothelium-derived relaxation in response to acetylcholine, adenosine diphosphate and sodium fluoride of the coronary rings of group 1 was significantly different from that of groups 2 and 3 but was not significantly different from that of group 4. In contrast, EDR in response to the receptor-independent calcium ionophore agonist A23187 was not significantly different between the four groups. Scanning electron microscopic studies showed that platelet adhesion and aggregation, area of microthrombi, disruption of endothelial cells and separation of the intercellular junction could be found in coronary segments of groups 2 and 3 but not in vessels of groups 1 and 4.

CONCLUSIONS

These experiments suggest that cardiac global ischemia and reperfusion impair receptor-mediated release of EDRF from the coronary endothelium with G-protein dysfunction. This type of coronary endothelial dysfunction can be prevented by continuous anterograde infusion of warm blood cardioplegic solution during global ischemia.

Basal nitric oxide expresses endogenous cardioprotection during reperfusion by inhibition of neutrophil-mediated damage after surgical revascularization

Ischemia-reperfusion damages endothelium and impairs basal production of nitric oxide. Basally released nitric oxide is cardioprotective by its inhibition of neutrophil activities. Loss of endogenous nitric oxide with endothelial injury may occur during two phases: cardioplegic ischemia and reperfusion (aortic declamping). This study tested the hypothesis that inhibition of endogenously released nitric oxide in hearts subjected to regional ischemia, cardioplegic arrest, and reperfusion (1) restricts endogenous cardioprotection and permits neutrophil-mediated damage and (2) expresses damage during the reperfusion phase. L-Nitro-arginine was used to block basal nitric oxide production. In 22 anesthetized dogs, the left anterior descending artery was ligated for 90 minutes followed by 1 hour of arrest with cold multidose (every 20 minutes) blood cardioplegia. Dogs were divided into three groups: the first group received standard unsupplemented blood cardioplegia (group 1, n = 8), in the second group L-nitro-arginine was administered as an additive to blood cardioplegic solution (1 mmol) and as an infusion during reperfusion (34 mg/kg) (group 2, n = 7), and in the third group L-nitro-arginine was administered only at reperfusion (group 3, n = 7). The ligature was released during the second infusion of cardioplegic solution. Infarct size (triphenyltetrazolium chloride) was increased in group 3 (L-nitro-arginine only at reperfusion) compared with that in group 1 (standard blood cardioplegia) (49% +/- 6% vs 34% +/- 2%, respectively), but was not further extended in group 2 (L-nitro-arginine as an additive to blood cardioplegic solution and at reperfusion) (56% +/- 3%, p > 0.05 vs group 3), which suggests primarily a reperfusion process. Polymorphonuclear neutrophil-specific myeloperoxidase activity in the area at risk was elevated comparably in groups 2 and 3 (group 2: 2.9 +/- 0.5 units/gm tissue, p = 0.06 vs group 1; group 3: 3.9 +/- 1.0 units/gm tissue, p < 0.05 vs group 1) compared with that in the standard blood cardioplegia group (1.7 +/- 0.3 units/gm tissue), suggesting polymorphonuclear neutrophil accumulation occurs primarily during reperfusion. Polymorphonuclear neutrophil adherence in ischemic-reperfused left anterior descending artery segments was comparably greater in group 2 (L-nitro-arginine as an additive to blood cardioplegic solution and at reperfusion: 195 +/- 21 polymorphonuclear neutrophils/mm2 of artery, p < 0.05 vs group 1) and group 3 (L-nitro-arginine only at reperfusion: 224 +/- 20 polymorphonuclear neutrophils/mm2 of artery, p < 0.05 vs group 1) relative to that in group 1 (108 +/- 19 polymorphonuclear neutrophils/mm2 of artery). There was no significant adherence to nonischemic circumflex arteries. We conclude that blockade of endogenous nitric oxide augments postischemic injury mediated by polymorphonuclear neutrophils, and this damage is expressed primarily during the reperfusion phase.

The role of nitric oxide in cardiac ischemia-reperfusion injury

During cardiac surgery, ischemia-reperfusion injury (IRI) is thought to be a major factor in intraoperative myocardial damage. Coronary endothelial cells have been thought to play an important role in the pathogenesis of cardiac IRI. Release of nitric oxide (NO) from coronary endothelial cells is impaired following myocardial ischemia, and this may contribute to the vulnerability of the coronary circulation to thrombus-formation and vasospasm. Several experimental studies have found that NO has a cardioprotective effect in myocardial IRI. In this regard, attempts have been made to supplement NO production exogenously during reperfusion, when endogenous NO release from endothelial cells may be diminished. In a blood-reperfused heart model, L-arginine acts cardioprotectively via 2 primary possible mechanisms: (1) by blocking both neutrophil aggregation and neutrophil adherence, and (2) by scavenging oxygen-derived free-radicals. On the other hand, in a non-blood reperfused heart model, the optimal concentration of L-arginine may be low and protection may be due to 2 additional mechanisms: (3) direct coronary vasodilatation and (4) reduced oxygen demand due to vasodilatation-induced hypotension. Other studies have suggested that NO exacerbates IRI and that NO synthase (NOS) inhibitors act cardioprotectively. It has also been suggested that the pharmacological effectiveness of inhibiting NO production may be due to the prevention of peroxinitrite formation from NO and superoxide during reperfusion. This review summarizes the current understanding of the role of NO in IRI.

Effects of blood and crystalloid cardioplegia on adrenergic and myogenic vascular mechanisms

BACKGROUND

This study compares the effects of cold blood and crystalloid cardioplegia on adrenergic and myogenic regulation of the coronary circulation.

METHODS

Pigs were placed on cardiopulmonary bypass and hearts were arrested with a hyperkalemic crystalloid cardioplegic solution (Cryst CP) or blood cardioplegic solution (Blood CP) for 1 hour. Hearts of selected pigs were then reperfused for 1 hour (Rep) and separated from cardiopulmonary bypass. Left ventricular perfusion and contractility and beta- and alpha 2-adrenergic and myogenic responses of the coronary circulation were examined.

RESULTS

Relaxation of isolated, precontracted microvessels to isoproterenol (beta-adrenoceptor agonist) was reduced to a lesser extent after Blood CP as compared with Cryst CP. Relaxation to forskolin (adenylate cyclase activator) was reduced after Cryst CP, but was preserved after Blood CP. After 1 hour of postcardioplegia reperfusion, the respective responses to isoproterenol and forskolin were similar in vessels from the Cryst CP-Rep and Blood CP-Rep groups. The alpha 2-adrenoceptor-mediated, endothelium-dependent vascular relaxation to clonidine was decreased more after Cryst CP than after Blood CP. The relaxation to nitroprusside was not affected by either Cryst CP or Blood CP. Myogenic tone was decreased to a lesser extent after Blood CP versus Cryst CP. Baseline coronary blood flow, isoproterenol-induced increases of coronary blood flow, and indices of myocardial contractility were similar in the Blood CP-Rep and Cryst CP-Rep groups, both 5 and 60 minutes after initiation of reperfusion.

CONCLUSIONS

Although Blood CP was superior to Cryst CP in preserving beta- and alpha 2-adrenoceptor function and myogenic tone in vitro, there was no demonstrable benefit of blood cardioplegia in the preservation of myocardial contractility or perfusion in this model of cardioplegia.

Production of endothelium-derived factors from sodded expanded polytetrafluoroethylene grafts

PURPOSE

Experiments were designed to determine whether endothelium isolated from adipose tissue and sodded onto expanded polytetrafluoroethylene grafts release endothelium-derived vasoactive factors.

METHODS

Thin-walled expanded polytetrafluoroethylene grafts (6 mm internal diameter, 6 cm length, 30 microm pore size), one sodded with autogenous endothelial cells, the other unsodded, were implanted bilaterally in carotid arteries of 30 male mongrel dogs. Dogs were treated with 325 mg aspirin daily. After 6 weeks grafts were excised and perfused in a bioassay system. Effluent from the grafts stimulated with either acetylcholine, thrombin, adenosine 5-diphosphate, or the calcium ionophore A23187 was superfused over rings of canine femoral arteries without endothelium contracted with phenylephrine. Effluent from the grafts was analyzed by radioimmunoassay for thromboxane B2, 6-keto-prostaglandin F1alpha, endothelin-1, and C-type natriuretic peptide.

RESULTS

Ninety percent of the sodded grafts and 87% of the unsodded grafts were patent after 6 weeks. Bioassay rings superfused with effluent from sodded grafts stimulated with acetylcholine relaxed significantly more than rings superfused with effluent from similarly stimulated unsodded grafts. Biochemical analysis of the effluent showed an increase in 6-keto prostaglandin F1alpha and C-type natriuretic peptide and a decrease in endothelin-1 and thromboxane B2 release from the sodded compared with the unsodded grafts. Scanning electron microscopy showed a continuous layer of endothelial cells lining only the sodded grafts. Staining for alpha-actin and heavy-chain myosin showed a differentiated layer of smooth muscle below the endothelial layer on the sodded grafts. Finally, there was positive staining for C-type natriuretic peptide and endothelin-1 in the endothelium of the sodded grafts.

CONCLUSIONS

These results indicate that endothelial cells of sodded expanded polytetrafluoroethylene grafts produce endothelium-derived vasoactive factors. In addition, receptor-coupled synthesis/release of these factors is retained in sodded endothelial cells.

Release of markers of myocardial and endothelial injury following cold cardioplegic arrest in pigs

Cold cardioplegic arrest causes reperfusion injury to both endothelium and myocardium. We investigated release of troponin-T (TnT), tissue plasminogen activator activity (t-PA) and histamine (HA) from the heart before and after 2h of cold crystalloid cardioplegia in eight Swedish landrace pigs. Coronary sinus blood flow was measured in an external shunt between the coronary sinus and the right atrium. TnT, t-PA and HA were measured concomitantly in arterial and coronary sinus plasma, and the cardiac release was calculated. Cardiac release of TnT increased from 18 (15-25) micrograms/min (median (central 90% percentile)) before cold cardioplegia to maximum 281 (132-510) micrograms/min 30 min after aortic declamping (p < 0.02 vs initial value). t-PA rose from -4 (-52-34) to maximum 249 (75-691) IU/min 2 min after declamping (p < 0.01) and thereafter returned to baseline levels. The net cardiac release of HA was 72 (-80-1321) nmol/min before cardioplegia, rising to 234 (-188-524) after 2 min of reperfusion (p < 0.02) and returning to baseline after 30 minutes. We conclude that the porcine heart releases t-PA, Tn-T and HA during postcardioplegic reperfusion. The differing kinetics of their release may indicate different affection of the myocardium and the endothelium. Tn-T, t-PA and HA are potential markers of myocardial and endothelial injury in the porcine heart.

Preservation of endothelium-dependent vasodilation with low-potassium University of Wisconsin solution

University of Wisconsin solution has provided excellent myocardial preservation. However, the high potassium content of the currently available University of Wisconsin solution has been implicated in coronary artery endothelial damage. We placed 16 neonatal (age 1 to 3 days) Duroc piglet hearts on an isolated nonworking perfusion circuit. Endothelium-dependent and endothelium-independent vasodilation were tested by measuring coronary blood flow after intracoronary infusion of bradykinin (10(-6) mol/L) and nitroprusside (10(-6) mol/L), respectively. In addition, nitric oxide levels were measured after bradykinin infusion. The hearts were then arrested blindly with either a modified University of Wisconsin solution (group 1; n = 8, K+ = 25 mEq/L) or standard University of Wisconsin solution (group 2; n = 8, K+ = 129 mEq/L) by infusion of cardioplegic solution every 20 minutes for a total of 2 hours. After bradykinin infusion, the mean coronary blood flow increased by 237.1% +/- 14.0% of baseline valves before arrest and by 232.8% +/- 16.0% after arrest in group 1 (p = not significant). As in the first group, the mean coronary blood flow in group 2 increased by 231.1% +/- 13.7% before arrest; however, the increase in mean coronary blood flow after arrest was significantly attenuated (163.3% +/- 12.8%, p < 0.01). The loss of endothelium-dependent coronary blood flow response in group 2 correlated with a decreased capacity to release nitric oxide after arrest (prearrest 8.25 +/- 2.30 nmol/min per gram versus postarrest -2.46 +/- 2.29 nmol/min per gram, p < 0.01). Endothelium-independent vasodilatory response revealed no significant difference between groups before and after arrest. These results suggest that the low-potassium University of Wisconsin solution provides superior protection of the endothelium by preserving the endothelium-dependent vasodilatory response to nitric oxide release.

Release of tissue plasminogen activator during reperfusion after different times of ischaemia in isolated, perfused rat hearts

Tissue plasminogen activator (t-PA) is a potential marker of endothelial cell activation or injury. The relationship between duration of ischaemia and release of t-PA during reperfusion was investigated in isolated rat hearts exposed to either 5, 10, 20, 30, 40, or 60 min of global, normothermic ischaemia followed by 30 min of reperfusion (n = 8 in each group). t-PA activity was measured (chromogenic peptide substrate assay) in the effluent before ischaemia, and after 2.5, 5, 7.5, 10, 20, and 30 min of reperfusion. Release of lactate dehydrogenase (LD), a marker of myocyte injury, was measured before ischaemia and after 5 min reperfusion. Left ventricular pressures were measured by a balloon in the left ventricle. Ischaemia for 20 min or less had only minor effects on cardiac function. Thirty min or more of ischaemia induced ventricular fibrillation during reperfusion in most hearts. After ischaemia t-PA outflow increased, but without any significant difference between groups. Peak release occurred after either 2.5 or 5 min of reperfusion. After 10 min reperfusion the release was not different from the basal value. In contrast, postischaemic release of LD correlated to the length of ischaemia. To conclude, t-PA release from the ischaemic-reperfused rat heart is independent of the length of ischaemia. Thus the potential of t-PA to quantify endothelial injury appears to be limited.

Effect of L-arginine on metabolic recovery of the ischemic myocardium

BACKGROUND

The release of nitric oxide is decreased after myocardial ischemia and reperfusion. Whereas the precursor L-arginine can stimulate the release of nitric oxide, its effect on metabolic recovery after myocardial ischemia is unknown.

METHODS

To study the effect of L-arginine on metabolic recovery after myocardial ischemia, cardioplegia infusion, and reperfusion, 33 dogs were placed on cardiopulmonary bypass and subjected to a sequence of 30 minutes of normothermic global ischemia, 30 minutes of warm blood cardioplegic arrest, and 30 minutes of reperfusion. A pH probe was inserted in the anterior wall of the left ventricle, and tissue pH was measured throughout the experiment. Coronary blood flow in the left anterior descending coronary artery and the circumflex coronary artery was measured. Blood samples from the coronary sinus were taken to measure blood pH and levels of lactate, creatine kinase, and troponin T.

RESULTS

In the control group of 9 dogs, tissue pH averaged 6.4 +/- 0.1, 6.5 +/- 0.1, and 6.8 +/- 0.1 after the end of global ischemia, cardioplegia, and reperfusion, respectively. Tissue pH averaged 6.4 +/- 0.1, 6.6 +/- 0.1, and 6.9 +/- 0.1, respectively, in the experimental group of 9 animals with 2 mmol/L of L-arginine added to the cardioplegic solution. Tissue pH averaged 6.2 +/- 0.1, 6.7 +/- 0.1, 7.1 +/- 0.1, respectively, in the third group of 9 animals that received an additional infusion of L-arginine (10 mg.kg-1.min-1) during reperfusion. Tissue pH recovered faster in groups with L-arginine (p = 0.00001). A hyperemic response of coronary blood flow was shown at reperfusion in animals in the control group only. In 6 dogs, L-NAME (N-nitroarginine methyl ester), an inhibitor of nitric oxide synthesis, was injected and resulted in a slower pH recovery on reperfusion compared with that of animals that received L-arginine.

CONCLUSIONS

The addition of L-arginine to the cardioplegic solution and the systemic circulation during reperfusion resulted in a significant increase in coronary blood flow during cardioplegia infusion and in a faster recovery of myocardial tissue pH, possibly by increasing coronary blood flow through the release of nitric oxide.

Constitutive nitric oxide release is impaired after ischemia and reperfusion

Myocardial ischemia and reperfusion may result in endothelial dysfunction and reduced release of nitric oxide. With the use of an amperometric sensor, the first direct measurements of constitutive nitric oxide release from a beating heart were measured from the coronary effluent of isolated working rat hearts subjected to ischemia and reperfusion. Rats, six to eight per group, were randomly studied as follows: control (no pretreatment) and pretreatment with the nitric oxide donor L-arginine (3 mmol/L), its enantiomer D-arginine (3 mmol/L), nitric oxide inhibitor N omega-nitro-L-arginine methyl ester (100 mumol/L), and combined N omega-nitro-L-arginine methyl ester/L-arginine. Isolated hearts were pretreated for 10 minutes before 30 minutes of global ischemia and 30 minutes of reperfusion. A nonischemic control group (n = 4) was continuously perfused with oxygenated unsupplemented buffer. After ischemia/reperfusion, hearts supplemented with L-arginine recovered significantly (p < 0.05) increased developed pressure, first derivative of the aortic pressure (dP/dtmax), and aortic flow compared with all other hearts that underwent ischemia/reperfusion. In addition, nitric oxide release was significantly (p < 0.05) increased during reperfusion in the L-arginine group. During reperfusion, the recovery of aortic flow correlated with nitric oxide release (r = 0.81, p < 0.0001). We conclude that after ischemia/reperfusion, endothelial dysfunction results in decreased nitric oxide release, which can be ameliorated with L-arginine pretreatment. The direct cytoprotective properties of nitric oxide may contribute to improved functional recovery in hearts pretreated with L-arginine. Augmentation of the L-arginine/nitric oxide pathway may provide a new approach for improved recovery after cardiovascular operations.

Reduction in surgical ischemic-reperfusion injury with adenosine and nitric oxide therapy

Ischemia and reperfusion impair the inherent capacity of the heart to protect itself from related pathophysiologic events by reducing endogenous oxygen radical scavengers and inhibitors. However, other endogenously produced agents, notably adenosine and nitric oxide, are produced during ischemia, reperfusion, or both. These autacoids have several cardioprotection actions in common, particularly antineutrophil effects and inhibition of endothelial-neutrophil interactions, which are key initial steps in ischemic-reperfusion injury. Studies have shown that nitric oxide exerts cardioprotection primarily during reperfusion. Adenosine, on the other hand, protects the myocardium to some extent during both ischemia and reperfusion, thereby covering both periods during which myocardial injury may be sustained during a cardiac operation. Native adenosine or active analogues, or donors of nitric oxide, may be given before or in conjunction with cardioplegia solutions. However, these endogenous agents can also be pharmacologically recruited to provide a new potent therapeutic approach against surgical ischemic-reperfusion injury. This article reviews the cardioprotective effects of primarily endogenous nitric oxide and adenosine in both nonsurgical and surgical models of ischemia-reperfusion injury. Both adenosine and nitric oxide provide potent cardioprotection in surgical and nonsurgical models of ischemia-reperfusion. An important mechanism in this cardioprotection is attenuation of neutrophil-mediated damage.

Role of selectins in myocardial ischemia-reperfusion injury

During reperfusion of ischemic myocardium, there is a well-orchestrated interplay between the coronary vascular endothelium and the circulating neutrophils. This interplay involves the initial slowing or "rolling" of neutrophils along the endothelium during the early moments of reperfusion, followed by firm attachment and amplification of the neutrophil response, and culminating with the diapedesis of neutrophils into the myocardial parenchyma where neutrophil-myocyte interaction contributes to the necrotic process. The selectins are glycoproteins that play a key role in the early phases of neutrophil adherence and activation. There are three members of the selectin family: P-selectin on endothelial cells and platelets, L-selectin on neutrophils, and E-selectin on endothelium. Monoclonal antibodies directed specifically toward these selectins and their associated ligands (eg, Sialyl Lewisx) not only substantiate their role in the dynamic process of neutrophil-mediated reperfusion injury but also offer a unique therapeutic opportunity to interfere with this cascade of inflammatory events.

Supplemental L-arginine during cardioplegic arrest and reperfusion avoids regional postischemic injury

Unenhanced hypothermic cardioplegia does not prevent postischemic endothelial and contractile dysfunction in hearts subjected to antecedent regional or global ischemia. This study tested the hypothesis that supplementing blood cardioplegic solution and reperfusion with the nitric oxide precursor L-arginine would preserve endothelial function, reduce infarct size, and reverse postcardioplegia regional contractile dysfunction by the L-arginine-nitric oxide pathway. In 23 anesthetized dogs, the left anterior descending coronary artery was ligated for 90 minutes, after which total bypass was established for surgical "revascularization." In 10 dogs, unsupplemented multidose hypothermic blood cardioplegic solution was administered for a total of 60 minutes of cardioplegic arrest. In eight dogs, L-arginine was given intravenously (4 mg/kg per minute) and in blood cardioplegic solution (10 mmol) during arrest. In five dogs, the nitric oxide synthesis blocker N omega-nitro-L-arginine (1 mmol) was used to block the L-arginine-nitric oxide pathway during cardioplegia and reperfusion. Infarct size (triphenyltetrazolium chloride) as percent of the area at risk was significantly reduced by L-arginine compared with blood cardioplegic solution (28.2% +/- 4.1% versus 40.5% +/- 3.5%) and was reversed by N omega-nitro-L-arginine to 68.9% +/- 3.0% (p < 0.05). Postischemic regional segmental work in millimeters of mercury per millimeter (sonomicrometry) was significantly better with L-arginine (92 +/- 15) versus blood cardioplegic solution (28 +/- 3) and N omega-nitro-L-arginine (26 +/- 6). Segmental diastolic stiffness was significantly lower with L-arginine (0.46 +/- 0.06) compared with blood cardioplegic solution (1.10 +/- 0.11) and was significantly greater with N omega-nitro-L-arginine (2.70 +/- 0.43). In ischemic-reperfused left anterior descending coronary arterial vascular rings, maximum relaxation responses to acetylcholine, the stimulator of endothelial nitric oxide, was depressed in the blood cardioplegic solution group (77% +/- 4%) and was significantly reversed by L-arginine (92% +/- 3%). Smooth muscle function was unaffected in all groups. We conclude that cardioplegic solution supplemented with L-arginine reduces infarct size, preserves postischemic systolic and diastolic regional function, and prevents arterial endothelial dysfunction via the L-arginine-nitric oxide pathway.

The role of nitric oxide and NO-donor agents in myocardial protection from surgical ischemic-reperfusion injury

The coronary vascular endothelium is injured by ischemia-reperfusion, which may facilitate the pathophysiological role played by neutrophils. Hearts undergoing coronary artery bypass surgery or other surgical procedures requiring cardiopulmonary bypass and elective cardioplegia undergo repetitive episodes of ischemia and reperfusion, which leads to endothelial injury as well as contractile dysfunction and morphological injury, despite the use of cardioprotective cardioplegic solutions and other strategies of myocardial protection. In cardiac surgery, as in coronary occlusion, endothelial injury seems to occur upon reperfusion with unmodified blood. Blood cardioplegia does not prevent this surgical 'reperfusion injury', but does prevent extension of endothelial injury during the period of hypothermic cardioplegic arrest ('protected ischemia'). It is not known whether global cardioplegic ischemia in preoperatively injured hearts impairs the basal release of nitric oxide (NO) and hence obtunds this endogenous protective mechanism. However, enhancement of blood cardioplegia with the NO precursor, L-arginine, reduces postsurgical myocardial injury, suggesting that endogenous or basal release of NO participates in the modulation of ischemic-reperfusion injury. In addition, an NO-donor agent also protects the myocardium from surgical ischemic-reperfusion injury. Both cardioprotective strategies involve inhibition of neutrophil accumulation, consistent with the known inhibitory effects of NO on neutrophil adherence and neutrophil-mediated damage to the coronary endothelium. Therefore, NO-related therapy offers a new strategy to protect the myocardium, including the coronary endothelium, from surgically imposed ischemic-reperfusion injury.

Augmentation of microvascular nitric oxide improves myocardial performance following global ischemia

Hearts exposed to global myocardial ischemia associated with cardiac surgery often suffer postischemic endothelial and contractile dysfunction related to antecedent regional or global ischemia. Our studies tested the hypothesis that supplementing blood cardioplegia and reperfusion with the nitric oxide (NO) precursor L-arginine or the NO donor SPM-5185 would preserve endothelial function, reduce infarct size, and reverse postcardioplegia regional contractile dysfunction or global dysfunction. In the first study involving 23 anesthetized dogs undergoing regional ischemia, supplementation of blood cardioplegia with L-arginine: (1) reduced infarct size; (2) improved postischemic regional segmental work and diastolic stiffness; (3) attenuated neutrophil accumulation in the area at risk; and (4) improved postischemic depressed coronary artery endothelial function. The NO synthase inhibitor N-nitro-L-arginine (L-NA) reversed these protective effects. In another experiment involving 18 anesthetized dogs undergoing normothermic global ischemia, hearts treated with blood cardioplegia supplemented with the NO donor SPM-5185 demonstrated better postischemic coronary artery endothelial function, lowered myeloperoxidase activity in the ischemic-reperfused myocardium, and significantly improved global ventricular function in the group receiving high-dose SPM-5185. We conclude that the inclusion of L-arginine or high-dose NO donor SPM-5185 in blood cardioplegia improves postischemic ventricular performance and endothelial function in ischemically injured hearts, possibly by inhibition of neutrophil-mediated damage via the L-arginine-NO pathway.

Effects of intracoronary calcium chloride on the postischemic heart in pigs

Whether calcium chloride (CaCl2) should be used to reverse myocardial dysfunction during cardiac operations remains a controversial issue. Calcium chloride may reduce, rather than increase, myocardial contractility and may produce exaggerated vasoconstriction in postischemic vessels in which the endothelium has been damaged. These possibilities were investigated in an open-chest porcine model that allowed control of systemic hemodynamics. Incremental doses of CaCl2 (1, 3, and 10 mg/min) were infused directly into a coronary artery before and after 10 or 15 minutes of ischemia followed by 15 minutes of reperfusion. Calcium chloride increased regional contraction, coronary blood flow, and oxygen consumption before ischemia, whereas oxygen and lactate extraction were unchanged. After ischemia and reperfusion, contraction was impaired and lactate extraction was reduced, but a similar response to CaCl2 was observed. Contraction returned to baseline values promptly after CaCl2. Thus, CaCl2 exerts a positive inotropic effect both in normal and in postischemic myocardium. Calcium chloride does not cause direct coronary constriction nor does it worsen myocardial stunning after a short period of normothermic myocardial ischemia.

Blood cardioplegia enhanced with nitric oxide donor SPM-5185 counteracts postischemic endothelial and ventricular dysfunction

This study tested the hypothesis that enhancement of blood cardioplegia with the nitric oxide donor agent SPM-5185 inhibits postischemic left ventricular and coronary endothelial dysfunction. Eighteen anesthetized dogs supported by total vented bypass were subjected to 30 minutes of normothermic ischemia followed by 4 degrees C multidose blood cardioplegia. Hearts received either standard blood cardioplegia (vehicle group; n = 6), blood cardioplegia with 1 mumol/L SPM-5185 (low-dose group; n = 6), or 10 mumol/L SPM-5185 (high-dose group; n = 6). After 60 minutes of cardioplegic arrest, the heart was reperfused for a total of 60 minutes, first in the beating empty state for 30 minutes and then after discontinuation of bypass for 30 minutes. Baseline and postischemic left ventricular function was assessed by the slope of the end-systolic pressure-volume (impedance catheter) relation. Postischemic end-systolic pressure-volume relation was depressed by 53.7% of preischemic values in the vehicle group (from 8.2 +/- 1.0 to 3.8 +/- 0.3 mm Hg/ml) and by 33.7% (from 9.2 +/- 1.1 to 6.1 +/- 0.5 mm Hg/ml) in the low-dose group. In contrast, there was complete postischemic functional recovery in the high-dose group (from 7.6 +/- 1.1 to 7.2 +/- 1.2 mm Hg/ml). In coronary arteries isolated from these hearts, endothelium-dependent maximal relaxation to acetylcholine was impaired by 27% in the vehicle group and by 18% in the low-dose group, whereas the high-dose group showed complete endothelium-dependent relaxation. Myeloperoxidase activity, an index of neutrophil accumulation in postischemic myocardium, was elevated in the vehicle and low-dose groups (3.36 +/- 0.58 and 2.56 +/- 0.68 U/100 mg tissue) but was significantly reduced in the high-dose group to 1.27 +/- 0.45 U/100 mg tissue. We conclude that inclusion of 10 mumol/L nitric oxide donor SPM-5185 in blood cardioplegia improves postischemic ventricular performance and endothelial function in ischemically injured hearts, possibly via inhibition of neutrophil-mediated damage.