Crystalloid cardioplegia and hypothermia do not impair endothelium-dependent relaxation or damage vascular smooth muscle of epicardial coronary arteries

Hyperkalemia: Major but still understudied complication among heart transplant recipients

Hyperkalemia is a recognized and potentially life-threatening complication of heart transplantation. In the complex biosystem created by transplantation, recipients are susceptible to multiple mechanisms for hyperkalemia which are discussed in detail in this manuscript. Hyperkalemia in heart transplantation could occur pre-transplant, during the transplant period, or post-transplant. Pre-transplant causes of hyperkalemia include hypothermia, donor heart preservation solutions, conventional cardioplegia, normokalemic cardioplegia, continuous warm reperfusion technique, and ex-vivo heart perfusion. Intra-transplant causes of hyperkalemia include anesthetic medications used during the procedure, heparinization, blood transfusions, and a low output state. Finally, post-transplant causes of hyperkalemia include hemostasis and drug-induced hyperkalemia. Hyperkalemia has been studied in kidney and liver transplant recipients, but there is limited data on the incidence, causes, management, and prevention in heart transplant recipients. Hyperkalemia is associated with an increased risk of hospital mortality and readmission in these patients. This review describes the current literature pertaining to the causes, pathophysiology, and treatment of hyperkalemia in patients undergoing heart transplantation and focuses primarily on post-heart transplantation.

Validation of using cardioplegic solutions for preserving cardiac function in isolated rabbit heart assays

INTRODUCTION

Cardioplegic solutions were first developed to preserve heart function during cardiac surgeries and heart transplants but have application in the nonclinical setting. Due to lack of lab space in the vivarium, cardioplegic solution was used to conserve cardiac function for ex-vivo studies performed in a separate building. All studies in this report were conducted with isolated female rabbit hearts (IRHs) via retrograde perfusion using the Langendorff apparatus to investigate if cardioplegia usage affects cardiac function.

METHODS

Cardioplegia was achieved with a hyperkalemia (27 mM KCL) solution kept at 4 °C. Cardiac function was assessed by measuring ECG parameters, left ventricular contractility, and coronary flow under constant perfusion pressure. IRHs were cannulated with Krebs Henseleit buffer (KH) either fresh or after cardioplegic solution storage (C-IRH). Three comparisons were performed with and without cardioplegia; (i) direct side-by side studies of cardiac function; (ii) pharmacological responses to typical ion channels blockers, dofetilide, flecainide, and diltiazem; (iii) retrospective evaluation of cardiac functions in a large sample of hearts.

RESULTS

In the side-by-side comparisons, cardioplegia-stored IRHs (C-IRH; storage time 90 min) had similar electrocardiographic (ECG) and hemodynamic parameters to fresh-cannulated hearts with KH buffer (KH-IRH). In addition, responses to dofetilide, flecainide, and diltiazem, were similar for C-IRH and KH-IRH hearts. Over the years (2006-2011), baseline data was collected from 79 hearts without cardioplegia and 100 hearts with cardioplegia (C-IRH; storage time 15 min), which showed no meaningful differences in a retrospective analysis.

DISCUSSION

Cardiac function was preserved after cardioplegic treatment, however, coronary flow rates were decreased (-19.3%) in C-IRH hearts which indicated an altered coronary vascular tone. In conclusion, storage in cardioplegic solution preserves rabbit cardiac function, a practice that enables heart tissues to be collected at one site (e.g., vivarium) and transported to a laboratory in a separate location.

Protection of coronary endothelial function during cardiac surgery: potential of targeting endothelial ion channels in cardioprotection

Vascular endothelium plays a critical role in the control of blood flow by producing vasoactive factors to regulate vascular tone. Ion channels, in particular, K⁺ channels and Ca²⁺-permeable channels in endothelial cells, are essential to the production and function of endothelium-derived vasoactive factors. Impairment of coronary endothelial function occurs in open heart surgery that may result in reduction of coronary blood flow and thus in an inadequate myocardial perfusion. Hyperkalemic exposure and concurrent ischemia-reperfusion during cardioplegic intervention compromise NO and EDHF-mediated function and the impairment involves alterations of K⁺ channels, that is, K_ATP and K_Ca, and Ca²⁺-permeable TRP channels in endothelial cells. Pharmacological modulation of these channels during ischemia-reperfusion and hyperkalemic exposure show promising results on the preservation of NO and EDHF-mediated endothelial function, which suggests the potential of targeting endothelial K⁺ and TRP channels for myocardial protection during cardiac surgery.

Nitric oxide and prostacyclin-dependent pathways involvement on in vitro induced hypothermia

Nitric oxide and prostacyclin are endogenous endothelium-derived vasodilators, but little information is available on their release during hypothermia. This study was carried out to test the hypothesis that endothelium may modulate vascular reactivity to decreased temperature changes. Segments of contracted (prostaglandin F(2alpha), 2x10(-6)M) canine coronary, femoral, and renal arteries, with and without endothelium, were in vitro ("organ chambers") exposed to progressive hypothermia (from 37 to 10 degrees C) in graded steps. The study is limited to physiological measurements of vascular tone, in the presence or absence of PGI(2) and/or NOS inhibitors, which show correlation with the relaxation. Hypothermia induced vasodilatation of vessels with intact endothelium, which became endothelium-independent below 20 degrees C. This vasodilatation began at 35 degrees C and, in the presence of indomethacin (2x10(-6)M), at 30 degrees C. Endothelium-dependent vasodilatation to hypothermia was blocked by L-NMMA or L-NOARG (10(-5)M), two competitive inhibitors of nitric oxide synthase (n=5 each, P<0.05). Oxyhemoglobin (2x10(-6)M) also inhibited vasodilatation induced by hypothermia (n=6, P<0.05). Pretreatment with either atropine or pirenzepine (10(-6)M) inhibited hypothermia-mediated vasodilatation (n=5 each, P<0.05). The present in vitro study concluded that the endothelium is sensitive to temperature variations and indicated that PGI(2) and NO-dependent pathways may be involved endothelium-dependent relaxation to hypothermia. The endothelium-dependent vasodilatation to hypothermia, in systemic and coronary arteries, is mediated by the M1 muscarinic receptor.

Effect of cardioplegic and organ preservation solutions and their components on coronary endothelium-derived relaxing factors

Cardioplegic (and organ preservation) solutions were initially designed to protect the myocardium (cardiac myocytes) during cardiac operation (and heart transplantation). Because of differences between cardiac myocytes and vascular (endothelial and smooth muscle) cells in structure and function, the solutions may have an adverse effect on coronary vascular cells. However, such effect is often complicated by many other factors such as ischemia-reperfusion injury, temperature, and perfusion pressure or duration. To evaluate the effect of a solution on the coronary endothelial function, a number of points should be taken into consideration. First, the overall effect on endothelium should be identified. Second, the effect of the solution on the individual endothelium-derived relaxing factors (nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor) must be distinguished. Third, the effect of each major component of the solution should be investigated. Lastly, the effect of a variety of new additives in the solution may be studied. Based on available literature these issues are reviewed to provide information for further development of cardioplegic or organ preservation solutions.

Calcium channel blocker and renal mitochondrial function in warm renal ischemia

OBJECTIVE

Ions, particularly calcium ions, play an important role in ischemia-reperfusion cell injury. In this study, we investigated the action of verapamil on the mitochondrial function of kidneys submitted to ischemia without blood reperfusion in order to study isolated early and late ischemic effects.

MATERIALS AND METHODS

44 rats were submitted to bilateral warm renal ischemia for 30 minutes. The kidneys were then immediately reperfused with saline or Euro-Collins (EC) solution, with and without previous administration of 0.35 mg/kg of verapamil. Mitochondrial function was assessed at the end of renal perfusion and after 24 hours of cold preservation.

RESULTS

In kidneys perfused with saline, verapamil allowed a significant early preservation of state III mitochondrial respiration, a result that was no longer evident after 24 hours. In kidneys perfused with EC solution, verapamil did not change state III for either early or late evaluations. Comparison of the groups showed that the results obtained for kidneys perfused with EC were always superior to those obtained for the saline group, except for the initial analysis of kidneys treated with saline and verapamil, which showed results similar to those obtained with EC perfusion alone.

CONCLUSION

Administration of verapamil before warm ischemia provides partial and short-lasting functional protection of the mitochondrial function in kidneys perfused with sodium rich saline. With Euro-Collins solution, verapamil did not show any additional beneficial effect. This fact permits us to conclude that protective action is effective only under conditions that facilitate increased sodium uptake and/or potassium loss.

Endothelial Function Related to Vascular Tone in Cardiac Surgery

Vascular endothelium has multiple functions including regulating of vascular tone, preventing platelet aggregation, anti-proliferation, etc. An intact endothelial function is essential to the maintenance of an adequate vascular tone, to prevent platelet aggregation in the intimal surface of blood vessels, to prevent smooth muscle proliferation, and to prevent atherosclerosis. This review focuses on endothelial function related to the vascular tone in cardiac surgery. The review is composed by three sections. In the first section, normal endothelial function related to vascular tone is described. In the second section, coronary endothelial function related to cardiac arrest and cardioplegic exposure is reviewed. In the third section, the endothelial function in the coronary bypass grafts is summarised. It is particularly important to understand that coronary endothelial dysfunction may be one of the major causes of low perfusion of the myocardium after cardiac arrest or donor heart preservation. Further, endothelium plays a major role in the maintenance of vascular tone and in the long-term patency of CABG grafts. The characteristics of endothelium in arterial and venous grafts and the correlation to the long-term patency are now more understood. A number of methods have been suggested to protect endothelial function in either coronary circulation or in coronary artery bypass grafts during cardiac surgery but further investigations in this field are warranted.

Endothelium-dependent vasodilation during acute rejection in dogs

BACKGROUND

Acute rejection, which is a major cause of death after cardiac transplantation, is associated with increased coronary artery resistance and decreased coronary blood flow, leading to congestive heart failure.

MATERIALS AND METHODS

To examine the contribution of endothelium-derived vasoactive factors on coronary artery tone during acute rejection, dogs underwent orthotopic heart transplantation without immunosuppression. Plasma levels of endothelin, a potent endogenous vasoconstrictor peptide, and atrial natriuretic peptide, an endogenous coronary vasodilator of cardiac origin, were measured daily by radioimmunoassay until sacrifice.

RESULTS

Over 7 days, all animals developed acute rejection accompanied by progressive increases in plasma endothelin (10 +/- 3 to 25 +/- 4 pg/ml, n = 6, P < 0.05) and atrial natriuretic peptide (57 +/- 10 to 188 +/- 42 pg/ml, n = 6, P < 0.05). However, in organ chamber experiments, coronary artery segments from rejecting hearts exhibited normal endothelium-dependent vasodilation to acetylcholine, adenosine diphosphate, and the calcium ionophore A23187. In addition, coronary arteries exhibited normal relaxation to sodium nitroprusside (cyclic guanosine monophosphate-dependent) and isoproterenol (cyclic adenosine monophosphate-dependent).

CONCLUSIONS

In early, untreated acute rejection after orthotopic heart transplantation, graft dysfunction is not associated with impaired endothelium-dependent coronary artery vasodilation but may result from enhanced production of endothelin, a potent vasoconstrictor.

Impaired endothelium-derived hyperpolarizing factor-mediated relaxation in porcine pulmonary microarteries after cold storage with Euro-Collins and University of Wisconsin solutions

BACKGROUND

Endothelium plays an important role in mediating the function of transplanted organs. The widely used University of Wisconsin solution impairs the endothelium-derived hyperpolarizing factor-mediated relaxation in coronary arteries, but little is known about effects of lung preservation on endothelium-derived hyperpolarizing factor-mediated endothelial function. This study examined the effect of organ preservation solutions on the endothelium-derived hyperpolarizing factor-mediated relaxation in the pulmonary microarteries (diameter 200 to 450 microm).

METHODS

Two segments (1 as control) from the same microartery were allocated in 2 chambers of a myograph. After incubation with hyperkalemia (potassium 115 mmol/L), University of Wisconsin, or Euro-Collins solution (at 4 degrees C for 4 hours), the endothelium-derived hyperpolarizing factor-mediated relaxation was induced by bradykinin (-10 to -6.5 log M, n = 8) or calcium ionophore (A(23187), -9 to -5.5 log M, n = 7) in U(46619) (-7.5 log M) precontracted rings in the presence of indomethacin (7 micromol/L), N(G)-nitro-L-arginine (300 micromol/L), and oxyhemoglobin (20 micromol/L).

RESULTS

Exposure to hyperkalemia and storage with Euro-Collins or University of Wisconsin solution significantly decreased the relaxation to bradykinin (51.9 +/- 8.4% vs 60.3 +/- 6.1%, P =.02 or 49.3 +/- 7.3% vs 65.2 +/- 3.5%, P =.04) or A(23187) (12.5 +/- 0.02% vs 33.8 +/- 0.07%, P =.02 or 13.2 +/- 0.03% vs 31.0 +/- 0.05%, P =.03%).

CONCLUSIONS

Endothelium-derived hyperpolarizing factor plays an important role in porcine pulmonary microarteries, and the endothelium-derived hyperpolarizing factor-mediated relaxation is impaired when the lung is preserved with University of Wisconsin or Euro-Collins solution. This impairment may affect the lung function during the reperfusion period after lung transplantation.

Protective effect of magnesium on the endothelial function mediated by endothelium-derived hyperpolarizing factor in coronary arteries during cardioplegic arrest in a porcine model

OBJECTIVES

Hyperkalemia in cardioplegia impairs the function mediated by endothelium-derived hyperpolarizing factor. This study examined the effect and mechanism of magnesium ion on the relaxation mediated by endothelium-derived hyperpolarizing factor.

METHODS

In the isometric force study, porcine coronary microarteries in a myograph (diameter 200-450 microm) were incubated in Krebs solution (subgroups Ia, IIa, and IIIa), potassium ion (20 mmol/L, subgroups Ib, IIb, and IIIb), magnesium ion (16 mmol/L, subgroups Ic, IIc, and IIIc), or potassium ion plus magnesium ion (subgroups Id, IId, and IIId) for 1 hour at 37 degrees C in group I or II, followed by washout for 45 minutes in group III (n = 8). Relaxation to bradykinin (groups I and III) or sodium nitroprusside (group II) in U(46619)-stimulated contraction was established. In the electrophysiologic study, the membrane potentials of single smooth muscle cells of arteries were measured by microelectrode after superfusion with the previously described solutions (subgroups IVa-IVc).

RESULTS

In group I, 20-mmol/L potassium ion greatly reduced the bradykinin-induced relaxation (35.0% +/- 4.9% vs 86.0% +/- 5.3%, P <.001), which was significantly restored by magnesium ion (51.9% +/- 4.0%, P =.017). In groups II and III, the bradykinin- or nitroprusside-induced relaxation had no significant differences. In group IV, potassium ion depolarized the smooth muscle and decreased the bradykinin-induced hyperpolarization (-72.0 +/- 1.5 vs -61.7 +/- 0.7 mV, n = 7, P <.001), which was significantly restored by magnesium ion (-68.0 +/- 2.5 mV vs -72.5 +/- 1.5 mV, n = 6, P =.029).

CONCLUSIONS

Magnesium ion, either alone or added to hyperkalemic solutions, preserves or helps to restore the endothelial function mediated by endothelium-derived hyperpolarizing factor. The mechanism is related to preservation of the membrane hyperpolarization and reversal of the potassium-induced membrane depolarization of the smooth muscle cell.

Endothelial damage during myocardial preservation and storage

Preservation and storage techniques represent two major issues in routine cardiac surgery and heart transplantation. Historically, these methods were conceived to prevent ischemic injury to myocardium after cardiac arrest during heart operations. Evidence shows that endothelium plays a critical role in the maintenance of normal heart function after cardiac operation, mainly by controlling the coronary circulation. Methods for preservation and storage, developed initially to protect cardiomyocyte function, may be deleterious for vascular endothelium and compromise myocardial protection. In this review article the present knowledge about endothelial injury secondary to preservation and storage techniques is discussed.

Vasorelaxant response to isoprenaline, nitric oxide donor, calcitonin gene-related peptide and vasoactive intestinal peptide in aortic rings of adult C57BL/6J mice

The mouse and tissues from this species are increasingly used as experimental models because of the wide variety of gene deletions and overexpressions available in this species. Yet, very little is known about normal vascular responses in the mouse. We investigated the vasorelaxant responses on thoracic aortic rings from the adult male C57BL/6J mouse. Isoprenaline, acetylcholine, calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and sodium nitroprusside all caused concentration-dependent relaxations in aortic rings possessing healthy endothelium and precontracted with phenylephrine. Maximum relaxations were 64.9+/-2.6%, 66.8+/-2.9%, 114.3+/-4.6%, 65.1+/-4.2% and 116.2+/-5.1% with -logEC(50) values of 6.76+/-0.14, 7.04+/-0.11, 8.53+/-0.14, 8.29+/-0.26 and 8.10+/-0.20 for isoprenaline, acetylcholine, CGRP, VIP and sodium nitroprusside, respectively. There were significantly smaller responses to isoprenaline, acetylcholine, CGRP and VIP when the endothelium was denuded. The maximum relaxations for isoprenaline, CGRP and acetylcholine were 48.3+/-5.1%, 99.6+/-4.4% and 5.7+/-1.6% with -logEC(50) values of 6.44+/-0.40 and 8.23+/-0.192, respectively, following endothelium removal. The response to VIP was completely dependent to endothelium. Without precontraction, isoprenaline, at the higher doses, caused small contractions. These experiments provide new information about vascular responses of five vasodilators in aortic rings of adult male C57BL/6J mice.

Improved preservation of coronary endothelial function with Celsior compared with blood and crystalloid solutions in heart transplantation

BACKGROUND

Endothelial injury from preservation solutions has been implicated in acute coronary vasospasm and pathologic activation of the endothelium, which can contribute to the development of graft coronary vasculopathy after heart transplantation. Preservation solutions with a powerful antioxidant capacity may decrease the occurrence of these complications.

MATERIALS AND METHODS

This study was designed to evaluate the effect of Celsior (an anti-oxidant solution specifically designed for cardiac preservation) in a model of heart preservation (4 hours at 4 degrees C to reproduce the situation encountered in clinical heart transplantation) compared two commonly used cardioplegic and preservation strategies on coronary endothelial function. Endothelium-dependent relaxation of normal porcine epicardial coronary arteries to serotonin (5-HT, an agonist that activates 5-HT(1d) receptors coupled to Gi proteins) and bradykinin (BK, which activates B2 receptors coupled to Gq proteins) was studied in standard organ chamber experiments in the following groups: a control group was submitted to immediate excision without cardioplegia and preserved in saline solution (0.9% NaCl) for 4 hours (Group 1); two groups had cardioplegia induced with a crystalloid solution and were stored for 4 hours in saline (Group 2) or 4 hours in Celsior solution (Group 3); and two groups had cardioplegia induced with normothermic blood cardioplegia and were stored for 4 hours in the saline (Group 4), or 4 hours in Celsior solution (Group 5). Finally, two groups underwent cardioplegia with Celsior and were stored for 4 hours in saline (Group 6), or 4 hours in the Celsior solution (Group 7). All cardioplegia solutions were at 4 degrees C (except blood cardioplegia at 37 degrees C) and all preservations solutions were at 4 degrees C.

RESULTS

Endothelium-dependent relaxations to serotonin were significantly decreased in all groups except the Celsior + Celsior group compared with the control group. There were no significant differences in relaxation to bradykinin except in one group. Use of the Celsior solution for induction of cardioplegia and storage better preserved endothelium-dependent G-protein-mediated relaxation compared with the other arrest and preservation strategies.

CONCLUSIONS

The observed effect may be associated with an improvement in both short- and long-term outcome in heart transplantation, especially because these alterations may be further compounded by reperfusion.

Morphometric identification of luminal narrowing of myocardial capillaries after cardioplegic arrest

BACKGROUND

Because there is no smooth muscle cell surrounding the capillary endothelial cells, the effect of coronary microcirculation at the capillary level following cardioplegic arrest and reperfusion would be much different from that of resistant arterioles. We therefore studied the effect of hypothermic blood cardioplegic arrest and subsequent reperfusion on the myocardial capillaries in cardiac operation patients.

METHODS

Twenty-seven patients who underwent cardiac operations were included in this study. Three sequential biopsies (preischemia, ischemia, and reperfusion) were obtained from the right atrium. This study was restricted to blood vessels with a diameter of less than 8 microns. Ten randomly selected capillaries from each biopsy were measured for luminal surface area, endothelial cytoplasmic surface area, and total cross-sectional surface area of capillaries.

RESULTS

From stereologic morphometric studies, the serial changes in total cross-sectional surface area were not statistically significant (p = 0.152). However, there was a significant swelling of endothelial cytoplasm following ischemia and reperfusion (p = 0.0007). Meanwhile, changes in luminal surface area of capillaries following ischemia and reperfusion were also remarkable (p = 0.0008).

CONCLUSIONS

The most striking finding of this study was the progressive decrease in capillary lumen during ischemia and after reperfusion. The swelling of endothelial cells is a major determinant of luminal narrowing of capillaries in patients receiving cardioplegic arrest.

Myocardial protection during cardiac surgery from the viewpoint of coronary endothelial function

1. During cardiac surgery, the heart is arrested and subject to ischaemia-reperfusion injury. 2. To protect the heart, cardioplegia is usually used to initially stop and then maintain the still condition of the heart, which not only facilitates the precise operation but, more importantly, minimizes the energy consumption of the heart during this period. 3. The ischaemia-reperfusion injury may involve both myocytes and coronary endothelium-smooth muscle and, therefore, the protection of the heart should also involve these two aspects. 4. Injury to the heart involves: (i) ischaemia-reperfusion injury to the myocytes and coronary circulation; and (ii) possible injury to the coronary circulation by cardioplegia due to its hyperkalaemic components. 5. Injury to the coronary circulation may involve both endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) mechanisms. The EDNO mechanism is susceptible to ischaemia-reperfusion, whereas the EDHF mechanism may be altered by hyperkalaemic cardioplegia. 6. To further protect the heart, supplemental therapy for EDNO and optimizing the components of cardioplegia to restore the EDHF mechanism may be important.

Potassium-channel opener in cardioplegia may restore coronary endothelial function

BACKGROUND

Depolarizing (hyperkalemic) solutions impair the coronary endothelial function through an endothelium-derived hyperpolarizing factor mechanism. I examined the hypothesis that potassium-channel openers may restore the impaired endothelium-derived hyperpolarizing factor-mediated coronary vasorelaxation when added to hyperkalemic cardioplegia.

METHODS

The porcine coronary arteries were exposed to hyperkalemia (potassium, 20 or 50 mmol/L) or hyperkalemia plus the potassium-channel opener aprikalim at 0.1 mmol/L for 1 hour. Endothelium-derived hyperpolarizing factor-mediated relaxation (percentage of 30 nmol/L U46619 precontraction) was induced by calcium ionophore A23187 and bradykinin in the presence of indomethacin (7 micromol/L) and Nomega-nitro-L-arginine (300 micromol/L).

RESULTS

The endothelium-derived hyperpolarizing factor-mediated relaxation was significantly impaired by exposure to hyperkalemia (20 mmol/L: 24.9%+/-14.1% versus 88.0%+/-3.3% in control, p = 0.002 for A23187; 50 mmol/L: 40.5%+/-12.3% versus 76.5%+/-3.8%, p = 0.003 for bradykinin). This reduced relaxation was significantly recovered by addition of aprikalim into the hyperkalemic (20 mmol/L) solution in A23187 experiments (81.2%+/-4.8%, p = 0.002) but only slightly recovered when added into the higher concentration of potassium (50 mmol/L) in bradykinin experiments (56.1%+/-4.7%, p = 0.2).

CONCLUSIONS

Potassium-channel openers may preserve endothelium-derived hyperpolarizing factor-mediated coronary relaxation when added to traditional hyperkalemic cardioplegia. This effect is significant when the potassium concentration is 20 mmol/L but partially lost when it reaches 50 mmol/L. This study may provide new insights into cardioprotection during open heart operations.

Impaired endothelium-derived hyperpolarizing factor-mediated relaxation in coronary arteries by cold storage with University of Wisconsin solution

OBJECTIVES

University of Wisconsin solution is widely used to preserve organs for transplantation, but its effect on the individual endothelium-derived relaxing factors has not been studied. This study was designed to examine the effect of cold storage of the heart with University of Wisconsin solution on relaxation mediated by the endothelium-derived hyperpolarizing factor (EDHF).

METHODS

Porcine coronary artery rings were studied in organ chambers. Relaxation in response to the EDHFs stimuli bradykinin and A23187 in U46619 (30 nmol/L)-induced precontraction after incubation with University of Wisconsin solution (either at 37 degrees C in the oxygenated organ chamber or at 4 degrees C in a refrigerator for 4 hours) was compared with the control.

RESULTS

During the incubation, the coronary tone initially increased transiently (4.8 +/- 0.8 gm) and was subsequently reduced by 10.9 +/- 1.2 gm. Under both normothermia and hypothermia, after the incubation, the relaxation mediated by EDHF significantly decreased (under normothermia: from 68.7% +/- 10.2% to 32.1% +/- 8%, n = 7, p = 0.001, for bradykinin and from 79.9% +/- 8.4% to 56.9% +/- 8.5%, n = 7, p = 0.01, for A23187; under hypothermia and hypoxia: to 18.9% +/- 5.6%, n = 9, p = 0.0005, for bradykinin and 52.7% +/- 7.5%, n = 9, p = 0.03, for A23187). The incubation at normothermia also impaired the coronary smooth muscle contractility to U46619, but this contractility was preserved by cold storage.

CONCLUSIONS

During cold storage, University of Wisconsin solution impairs the endothelium-dependent relaxation mediated by EDHF in the coronary circulation. This effect exists after the storage for at least 1 hour.

Platelet and neutrophil activation during cardiac surgical procedures: impact of cardiopulmonary bypass

BACKGROUND

Platelet and neutrophil activation plays a crucial role in reperfusion injury. To determine whether platelet and neutrophil activation occurs in the coronary circulation after cold cardioplegic arrest and reperfusion, we studied 22 patients undergoing coronary artery bypass or valve procedures, or both procedures.

METHODS

Blood was sampled from the coronary sinus and the radial artery (A) before bypass; (B) immediately after cross-clamp release; and (C) 5 minutes after cross-clamp release; and was analyzed for surface markers of platelet (CD62P) and neutrophil (CD11b) activation.

RESULTS

During bypass, platelet activation increased significantly (p < 0.01) over prebypass values, but no difference was seen between arterial and coronary sinus samples. Neutrophil activation also increased significantly (p < 0.001) during bypass, but there was no difference between arterial and coronary sinus samples.

CONCLUSIONS

Cellular activation occurs locally in the coronary circulation during bypass, but no more so after cold cardioplegic arrest and reperfusion.

Assessment of left ventricular compliance during heart preservation

There is critical need for a greater number of donor hearts for transplantation. The demand can be relieved, in part, by an extension of preservation time. This necessitates new methods of preservation and development of means to assess the functional condition of the preserved heart. We report a heart-preservation system designed for long-term preservation support and discuss issues specifically related to extended heart preservation. This article presents methodology to assess ventricular compliance and to quantify coronary flow distribution during the use of microperfusion preservation. Ventricular adenosine triphosphate (ATP) concentrations are directly related to the immediate post-preservation function: however, direct measurement of ATP is not clinically available. Based on the premise that ventricular compliance relates directly to the ventricular ATP concentrations, we performed sequential ventricular compliance measurements using a simple left ventricular balloon during a 24 h preservation period. A porcine heart model was employed using a continuous, hypothermic, antegrade, microperfusion system for 24 h and measurements were made at specific intervals during the preservation time. The compliance measurements were ascertained by pressure-volume curves using a flaccid balloon inserted into the left ventricle through the mitral valve. In addition, to assess microvascular function during the preservation interval, regional coronary flow measurements were performed using a microsphere technique. We report that after 12 h of preservation there was a twofold reduction in ventricular compliance which decreased further by fivefold at 18 h. In contrast, there was a time-dependent decrease in left ventricular coronary flow, especially with the left-ventricular subendocardial region significantly decreasing by 50% at 12 h. In conclusion, a simple ventricular-compliance balloon provided a direct measurement of ventricular compliance of the preserved heart which may provide an indirect estimate of the ventricular high-energy phosphates of the preserved heart prior to transplantation.

Time dependence of endothelium-mediated vasodilation by intermittent antegrade warm blood cardioplegia

BACKGROUND

The technique of intermittent antegrade warm blood cardioplegia (IAWBC) exposes the heart to brief periods of normothermic ischemia. This may impair endothelial function in coronary arteries.

METHODS

Three cardioplegic technique were tested in porcine hearts arrested for 32 to 36 minutes and reperfused for 30 minutes: IAWBC, antegrade cold blood cardioplegia (ACBC), and antegrade cold crystalloid cardioplegia (ACCC). In the hearts arrested with IAWBC, three different intervals of ischemia were used: three 10-minute intervals (IAWBC1), two 15-minute intervals (IAWBC2), and one 30-minute interval (IAWBC3). Rings from the coronary arteries were used to evaluate in vitro the contractile responses to U46619 and the relaxant responses to bradykinin, A23187, and sodium nitroprusside.

RESULTS

All six groups (treatment groups and control group) displayed similar responses to U46619 (30 nmol/L) and nitroprusside. In the IAWBC1, IAWBC2, AND ACBC groups, endothelium-dependent relaxations to bradykinin and A23187 were preserved compared with controls, whereas those of the ACCC and IAWBC3 groups were significantly impaired (bradykinin: control, 8.72 +/- 0.07; IAWBC1, 8.73 +/- 0.03; IAWBC2, 8.65 +/- 0.05; IAWBC3, 8.30 +/- 0.07 [p < 0.05]; ACBC, 8.50 +/- 0.03; ACCC, 8.25 +/- 0.09 [p < 0.05]; A23187: control, 7.07 +/- 0.08; IAWBC1, 7.07 +/- 0.06; IAWBC2, 7.04 +/- 0.03; IAWBC3, 6.64 +/- 0.01 [p < 0.05]; ACBC, 6.80 +/- 0.05; ACCC, 6.60 +/- 0.08 [p < 0.05]; nitroprusside: control, 6.19 +/- 0.1; IAWBC1, 6.19 +/- 0.07; IAWBC2, 6.03 +/- 0.03; IAWBC3, 6.08 +/- 0.05; ACBC, 6.04 +/- 0.2; ACCC, 6.05 +/- 0.03; all values are expressed as the negative logarithm of the concentration producing 50% of the maximal response).

CONCLUSIONS

Myocardial preservation with IAWBC with ischemic intervals of 15 minutes or shorter does not alter the endothelium-dependent relaxation to bradykinin or A23187 in porcine coronary arteries, but these responses are significantly impaired by ACCC and IAWBC with an ischemic interval of 30 minutes.

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.

Functional and morphological evaluation of canine veins following preservation in different storage media

Injuries of endothelial and smooth muscle cells of autologous vein due to preservation in standard storage media may be responsible for graft failure. The effects of vein preservation with University of Wisconsin solution (UWs) on endothelial and smooth muscle cell function and morphology were compared to the effects of preservation with autologous whole blood (AWB) and normal saline (NS), which are frequently used in cardiovascular surgery. Canine external jugular and common femoral vein segments were preserved in the different solutions at 4 degrees C for 45 min and 24 hr. Rings (4-5 mm in length) from control and preserved veins were evaluated by isometric tension studies at 37 degrees C and by scanning and transmission electron microscopy. Differences between groups were evaluated by Student's t test or Mann-Whitney U test and by analysis of the variance, and considered to be significant at P < 0.05. Sensitivities to norepinephrine (NE) showed that a 45-min vein storage in AWB (5.7 +/- 0.2 mumol/L) but not in NS (5.8 +/- 0.2 mumol/L) or UWs (6.5 +/- 0.2 mumol/L) had a deleterious effect on function of smooth muscle (P < 0.05) when compared to control veins (6.6 +/- 0.2 mumol/L). Maximum contractile responses and sensitivities to NE were significantly altered (P < 0.05) after 24-hr vein storage in AWB (0.09 +/- 0.02 g/mm2 and 5.4 +/- 0.07 mumol/L) and NS (0.12 +/- 0.03 g/mm2 and 5.6 +/- 0.08 mumol/L) but not in UWs (0.36 +/- 0.06 g/mm2 and 6.4 +/- 0.07 mumol/L). With both storage times, acetylcholine-induced endothelium-dependent maximum relaxations and sensitivities were significantly reduced (P < 0.05) in veins stored in AWB and NS, but not in UWs, compared with controls. Similarly, transmission electron microscopy revealed marked neutrophil migration beneath the intimal surface of vessels and extensive separation and desquamation of endothelial cells with exposure of subendothelial structures in veins stored in AWB and NS. The results suggest that UWs is a suitable storage medium when compared to AWB and NS.

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.

Myocardial protection for cardiac surgery: the nursing perspective

The advancement of myocardial protection techniques is considered to be the most instrumental in achieving successful cardiac surgical outcomes. Although many issues complicate the efficacy of myocardial protection, warm cardioplegia is instituted more often as a better myocardial protection method for patients undergoing cardiac surgery. Understanding differences in patient response between warm and cold cardioplegia is essential for development of appropriate nursing intervention strategies and prevention of postoperative complications. Advanced practice nurses in cardiac surgical settings must continue to evaluate metabolic, functional, and hemodynamic variations of patients with different cardioplegia for positive patient outcomes.

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.

Hyperkalemia exposure impairs EDHF-mediated endothelial function in the human coronary artery

BACKGROUND

My colleagues and I have found in the porcine coronary artery that the pathway other than the nitric oxide (NG-nitro-L-arginine [L-NNA]-sensitive) and cyclooxygenase (indomethacin-sensitive) pathways of endothelium-dependent relaxation, related to the endothelium-derived hyperpolarizing factor (K+ channel-related), are altered after exposure to hyperkalemia. The present study was designed to examine whether this effect exists in the human coronary artery.

METHODS

Coronary artery rings obtained from explanted fresh human hearts were studied in organ chambers under physiologic pressure. The endothelium-dependent relaxation in response to calcium ionophore A23187 was studied in U46619 (30 nmol/L)-induced precontraction in the presence of the cyclooxygenase inhibitor indomethacin (7 mumol/L) and the nitric oxide biosynthesis inhibitor L-NNA (300 mumol/L). The effect of incubation with 20 mmol/L K+ for 1 hour on the relaxation was examined in other coronary rings.

RESULTS

In control rings, A23187 induced a maximal relaxation of 50.7% +/- 3.2% (n = 6). After 1 hour of exposure to 20 mmol/L K+, the relaxation was reduced to 30.4% +/- 4.6% (n = 6; p = 0.005). Incubation with hyperkalemia also significantly reduced the sensitivity (increased effective concentration that caused 50% of maximal relaxation) of the indomethacin- and L-NNA-resistant relaxation (-7.37 +/- 0.17 versus -8.28 +/- 0.27 log mol/L; p = 0.019).

CONCLUSIONS

Exposure to hyperkalemia reduces the indomethacin- and L-NNA-resistant, endothelium-dependent (endothelium-derived hyperpolarizing factor-related) relaxation in the human coronary artery. This suggests that the previously proposed mechanism of coronary dysfunction after exposure to cardioplegic and organ preservation solutions in animal vessels is also valid in the human heart.

Effect of cardioplegic arrest and reperfusion on coronary reserve and autoregulation

BACKGROUND

The effects of cardioplegic arrest and reperfusion on the coronary vasculature remain to be characterized. This study was designed to investigate changes in coronary reserve and autoregulation after hypothermic cardioplegic arrest and reperfusion.

METHODS

Isolated rabbit hearts were perfused in a retrograde manner with Krebs-Henseleit bicarbonate buffer solution at a pressure of 80 cm H2O. Baseline measurements were performed for (1) coronary flow; (2) vasodilatory response to 5-hydroxytryptamine (10(-7) mol/L) and nitroglycerin (10(-4) mol/L); (3) autoregulatory capacity, quantified as closed-loop gains; and (4) isovolemic left ventricular function. Hearts were then subjected to cardioplegic arrest for 90 minutes. Twenty minutes after reperfusion, measurements were repeated.

RESULTS

Coronary flow decreased significantly after reperfusion (6.2 +/- 1.1 versus 5.3 +/- 1.1 mL.min-1.g-1; p < 0.01). The response to 5-hydroxytryptamine as percentage increase of flow decreased significantly after reperfusion (134.0% +/- 12.0% versus 109.1% +/- 6.8%; p < 0.01). However, there was no significant change in the response to nitroglycerin after reperfusion (121.3% +/- 17.6% versus 136.6% +/- 13.3%). The closed-loop gain demonstrated negative values before arrest but became positive after reperfusion, indicating loss of autoregulation after reperfusion. There was no significant change in left ventricular function.

CONCLUSIONS

The coronary flow reserve in response to 5-hydroxytryptamine and autoregulation were impaired after cardioplegic arrest and reperfusion, whereas nitroglycerin-induced vasodilatory response and left ventricular function were preserved.

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.

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.

Hyperkalemia alters endothelium-dependent relaxation through non-nitric oxide and noncyclooxygenase pathway: a mechanism for coronary dysfunction due to cardioplegia

BACKGROUND

Reported results of hyperkalemia (cardioplegia or organ preservation solutions) on endothelial function are contradictory. The endothelium-dependent relaxation is related to three major mechanisms: cyclooxygenase, nitric oxide, and endothelium-derived hyperpolarizing factor (K+ channel related). The present study was designed to test the hypothesis that hyperkalemia may alter endothelial function through non-nitric oxide and noncyclooxygenase pathways.

METHODS

Porcine coronary artery rings (5 to 10 in each group) were studied in organ chambers under physiologic pressure. After incubation with 20 or 50 mmol/L K+ for 1 hour, the response to substance P, an endothelium-dependent vasorelaxant peptide, in K+ (25 mmol/L)-induced contraction was studied in the presence of the cyclooxygenase inhibitor indomethacin (7 mumol/L), the nitric oxide biosynthesis inhibitor NG-nitro-L-arginine (L-NNA) (300 mumol/L), or the adenosine triphosphate-sensitive K(+)-channel blocker glybenclamide (3 mumol/L) in comparison with control arteries (69.8 +/- 4.6% of K+ contraction).

RESULTS

Without exposure to hyperkalemia, indomethacin (with or without glybenclamide) did not alter but L-NNA significantly reduced the relaxation (39.7% +/- 3.7%, p < 0.001). After exposure to K+, the indomethacin- and L-NNA-resistant relaxation was further reduced (7.4% +/- 3.2% for 20 mmol/L K+, p < 0.0001; or 13.5% +/- 8.4% for 50 mmol/L K+, p < 0.05, compared with rings without exposure), whereas the indomethacin- and glybenclamide-resistant relaxation was not altered. Incubation with hyperkalemia (50 mmol/L) also significantly reduced the sensitivity (increased EC50) of the indomethacin- and L-NNA-resistant relaxation (-9.75 +/- 0.06 versus -9.33 +/- 0.04 log M, p < 0.01).

CONCLUSIONS

Exposure to hyperkalemia reduces the indomethacin- and L-NNA-resistant, endothelium-dependent (endothelium-derived hyperpolarizing factor-related) relaxation. Our study may suggest a new mechanism of coronary dysfunction after exposure to hyperkalemia and open a new area for protection of coronary endothelium in cardiac surgery and for organ preservation in transplantation surgery.

Effects of cardioplegia on vascular function and the "no-reflow" phenomenon after ischemia and reperfusion: studies in the isolated blood-perfused rat heart

The ability of cardioplegia to protect against cardiac contractile dysfunction caused by ischemia and reperfusion is well established. The effects of cardioplegia on vascular injury and the no-reflow phenomenon, however, remain controversial. We used the blood-perfused rat heart to study the effect of St. Thomas' Hospital cardioplegic solution on postischemic endothelium-dependent and endothelium-independent vascular function, the extent of the no-reflow phenomenon, and the temporal relationship between postischemic vascular and contractile function. Isolated rat hearts (16 per group) perfused with blood from a support rat at 60 mm Hg were subjected to 10, 20, 30 or 40 minutes of global ischemia and 40 minutes of reperfusion at 37 degrees C. Eight hearts in each group also received cardioplegia (45 mm Hg for 2 minutes) before ischemia. Left ventricular developed pressure was measured with an intraventricular balloon. At the end of reperfusion, a bolus of 250 micrograms nitro-L-arginine methyl ester was infused to assess endothelium dependent vascular function. After a 20-minute washout, 25 micrograms sodium nitroprusside was infused to assess endothelium-independent vascular function. Fluorescein (1 ml, 1% weight/volume) was then infused to assess no-reflow; this involved freezing the hearts, cutting them into transverse sections (10 x 1 mm), video recording the sections under ultraviolet light, digitizing the images, and analyzing density of fluorescence. No-reflow was defined as a flow of less than 5%. Compared with nonischemic control responses, endothelium-independent vascular function was significantly decreased only after 30 and 40 minutes of ischemia (48.1% +/- 3.8% and 24.3% +/- 7.4%, p < 0.05), but it was significantly protected by cardioplegia (66.6% +/- 3.9% and 64.5% +/- 5.2%, p < 0.05). A significant reduction in endothelium-dependent vascular function was observed after 40 minutes of ischemia (-31.8% +/- 6.6% vs -50.4% +/- 1.6% in control hearts, p < 0.05), and again this was improved by cardioplegia (-45.0% +/- 3.4%, p < 0.05 vs ischemic group). Areas of no reflow were present after 30 and 40 minutes of ischemia (11.9% +/- 6.8% and 33.4% +/- 14.1% of left ventricular mass), and at each time period they were significantly decreased by cardioplegia (0.7% +/- 0.4% and 3.8% +/- 1.6%, p < 0.05). Postischemic contractile dysfunction was observed before any vascular alteration was apparent. After only 20 minutes of ischemia, the postischemic recovery of left ventricular developed pressure fell to 56.7% +/- 4.0%, but both endothelium-dependent vascular function and endothelium-independent vascular function were unaffected. In conclusion, vascular alterations are apparent only after prolonged periods of ischemia, longer than those required to observe contractile dysfunction, and cardioplegia protects against postischemic endothelium-dependent and endothelium-independent vascular dysfunction and reduces the extent of the no-reflow phenomenon.

Ischemia--a coagulation problem?

The causes of perioperative ischemia and myocardial infarction (MI) in coronary artery bypass graft (CABG) patients are almost certainly multifactorial, although not well understood. Ultimately, outcome after CABG is dependent on myocardial preservation and prevention of further myocardial ischemia. The largest number of ST-T-wave events come immediately after protamine is given, suggesting that re-establishment of coagulation function after cardiopulmonary bypass (CPB) may be an important event. CPB induces an inflammatory state that involves platelet-endothelial-cell interactions and vasospastic responses that result in low flow states in the coronary vasculature. The fibrinolytic system is activated during CPB, with raised tissue plasminogen activator (tPA) levels and related falls in plasminogen activator inhibitor (PAI-1). PAI-1 levels rise during the postoperative period. There is a huge variability in human response. However, the patients with the highest tPA surge are not the same patients who have the highest PAI surge. It could be postulated that patients with high PAI-1 levels are at highest risk for early ischemia. New data just being evaluated from the Multicenter Study of Perioperative Ischemia (McSPI) Research Groups' database in San Francisco may support the hypothesis that coagulation influences perioperative ischemia. The study of approximately 2,400 patients undergoing CABG surgery at 24 major institutions in the United States revealed that intensive care unit (ICU) entry hematocrit was significantly related to the risk for postoperative MI. Patients entering the ICU with hematocrits below 24% had the lowest MI rate (3.7%), whereas those with hematocrits greater than 34% had the highest rate (8.1%). Patients with ICU entry hematocrits below 18% had a zero incidence of perioperative MI. One possible explanation for these findings is that platelets are involved. As red cells stream down vessels, they marginate the smaller formed elements of the blood. As hematocrit is increased, the number of platelets moved to the outer sides of the vessels increases. Therefore, the number of endothelial-platelet interactions would increase over time with higher hematocrits.

Hypothermia reversibly inhibits endothelial cell expression of E-selectin and tissue factor

Hypothermia frequently accompanies cardiopulmonary bypass (CPB) and myocardial protection strategies during cardiac surgery. With CPB, the blood/artificial surface interface activates components of the humoral and cellular inflammatory cascades and may contribute to postoperative end organ dysfunction including the heart or multiple other organ systems. The endothelial cell (EC) monolayer normally mediates components of solute transport, vasomotor function, coagulation, cell differentiation/growth, and immune/inflammatory processes. E-selectin is a vascular adhesion molecule that mediates neutrophil adherence and that is inducible in ECs by inflammatory mediators such as cytokines. Tissue factor (TF) is similarly an inducible procoagulant factor in ECs that contributes to thrombosis. The induction, transcription, and expression of both molecules were studied in cultured human umbilical vein cells at normothermic (37 degrees), hypothermic (25 degrees), and rewarmed (37 degrees) conditions after stimulation with the cytokines tumor necrosis factor alpha and interleukin-1. Hypothermia reversibly inhibits the transcription and expression but not the induction of both E-selectin and TF.

Protection of the chronic hypoxic immature rat heart during global ischemia

The benefit of cardioplegic cardiac arrest for the protection of immature myocardium is controversial. We therefore investigated the efficacy of (1) topical hypothermia alone, (2) slow cooling by coronary perfusion hypothermia, and (3) cardioplegic cardiac arrest for the protection of isolated immature rats hearts (28 days) during 8 hours of global ischemia at 10 degrees C. The study was conducted in hearts from rats that were kept hypoxemic by lifelong exposure to simulated high altitude. Left ventricular function, endothelial function, the metabolic status, and the extent of myocardial injury were all assessed. Topical hypothermia provided superior protection in hypoxic hearts, with recovery of the maximum developed left ventricular pressure by 70.6% +/- 18.0% (mean +/- standard deviation) of its preischemic value (p < 0.01 versus slow cooling and versus cardioplegic protection). The same pattern of recovery was observed among control hearts. The degree of recovery of endothelial function after sole topical hypothermia measured 54% +/- 36% in hypoxic hearts and 62% +/- 37% in control hearts, but was not recordable in any of the other groups. Creatine kinase leakage and the myocardial high-energy content did not differ significantly among any of the groups. Rapid cooling by topical hypothermia alone provides superior protection in chronic hypoxic, immature rat hearts versus the protection conferred by slow cooling. St. Thomas' Hospital cardioplegic solution II does not afford additional protection. Endothelial injury caused by cold asanguineous perfusates, including cardioplegia, interferes with the recovery of vascular function, which, in turn, may limit mechanical function.

Endothelium-dependent contraction of canine coronary artery is enhanced by crystalloid cardioplegic solution

Experiments were designed to determine whether hyperkalemic crystalloid cardioplegic solution enhances endothelium-dependent contraction of coronary arteries. Segments of canine coronary arteries (n = 8 in each group) were preserved in cold (4 degrees C) crystalloid cardioplegic solution (group 1) and physiologic solution (group 2) for 60 minutes. Segments of preserved and control (group 3) coronary arteries with or without endothelium were suspended in organ chambers to measure isometric force. Perfusate hypoxia (oxygen tension 35 +/- 5 mm Hg) caused endothelium-dependent contraction in the arteries of all three groups. However, vascular segments with endothelium of group 1 exhibited hypoxic contraction (68.5% +/- 15.3% of the initial tension contracted by prostaglandin F2 alpha 2 x 10(-6) mol/L, p < 0.05) that was significantly greater than contraction of the group 2 and group 3 segments with endothelium (26.6% +/- 5.6% and 20.6 +/- 4.4%). The hypoxic contraction in arteries of group 1 could be attenuated by NG-monomethyl-L-arginine, the blocker of endothelial cell synthesis of the nitric oxide from L-arginine. The action of NG-monomethyl-L-arginine could be reversed by L-arginine but not D-arginine. Thus after preservation with cardioplegic solution, augmented endothelium-dependent contraction, occurs by L-arginine-dependent pathway, would favor coronary vasospasm after cardiac operation.

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

This study tests the hypothesis that blood cardioplegia (BCP) attenuates endothelial dysfunction related to nitric oxide after global normothermic ischemia, cardioplegic arrest, and reperfusion in anesthetized open-chest dogs placed on cardiopulmonary bypass. The dogs were divided into five groups to identify the time when endothelial injury occurred: group 1 = control without ischemia; group 2 = 45 minutes of normothermic ischemia only; group 3 = 45 minutes of normothermic ischemia plus unmodified reperfusion; group 4 = 45 minutes of ischemia plus intermittent BCP without reperfusion; and group 5 = ischemia plus BCP and reperfusion. In vitro coronary vascular relaxation responses to the nitric oxide stimulator acetylcholine (endothelium-dependent, receptor-dependent), the calcium ionophore A23187 (endothelium-dependent, receptor-independent), and acidified NaNO2 (endothelium-independent) were measured at the end of the protocol. Maximum in vitro coronary vascular responses to acetylcholine were similar among groups 1, 2, and 4, indicating an absence of endothelial injury. In contrast, significantly impaired relaxations to acetylcholine were demonstrated in the two reperfused groups (groups 3 and 5). Relaxation responses to A23187 and NaNO2 were not altered markedly in any group. Electron microscopy showed intact endothelium in groups 1, 2, and 4. However, moderately severe endothelium damage was seen in groups 3 and 5. We conclude that morphologic and functional endothelial damage occurs after blood reperfusion with or without BCP, and 1-hour hypothermic BCP arrest after normothermic ischemia is not associated with extension of endothelial damage.

Mechanisms of coronary vasomotor dysfunction in the transplanted heart

The transplanted heart sustains both cold ischemic and reperfusion injuries. These can produce coronary vascular endothelial or smooth muscle injury or both, which, in turn, can produce coronary vasomotor dysfunction. Using a canine model of autologous heart transplantation, we examined the following coronary vasomotor control mechanisms in isolated coronary artery rings: (1) endothelial-dependent cyclic guanosine monophosphate (cGMP)-mediated vasorelaxation (response to acetylcholine); (2) endothelial-independent cGMP-mediated vasorelaxation (response to sodium nitroprusside); and (3) beta-adrenergic cyclic adenosine monophosphate (cAMP)-mediated vasorelaxation (response to isoproterenol hydrochloride). Further, these mechanisms were related to 3 hours of cold ischemia alone and to 3 hours of cold ischemia plus 1 hour of reperfusion. Autologous heart transplantation was performed in dogs, and isolated distal left anterior descending coronary artery rings were studied in individual organ chambers. Cold ischemia alone produced significant dysfunction of beta-adrenergic cAMP-mediated vasorelaxation, which was exacerbated after reperfusion. Neither endothelial-dependent nor endothelial-independent cGMP-mediated vasorelaxation was dysfunctional after cold ischemia alone, but both were significantly impaired after reperfusion. We conclude that cold ischemia and reperfusion each produce coronary vasomotor dysfunction in the transplanted heart. Cumulatively, such coronary vasomotor dysfunction can acutely impair coronary vasodilatation and potentially jeopardize myocardial blood flow in the transplanted heart.

Tolerance of epicardial coronary endothelium and smooth muscle to hyperkalemia

Results of previous studies have suggested that high K+ concentrations in cardioplegic solutions may be detrimental to coronary endothelium in perfused hearts, as determined from changes in the coronary flow rate, but the direct functional changes in endothelium secondary to hyperkalemia have not been fully studied. To determine the effect of the K+ concentration in a physiologic solution (Krebs') and in St. Thomas' cardioplegic solution, and the effect of exposure time on endothelium and smooth muscle, porcine coronary artery rings were set up in organ baths under a physiologic pressure. The effect of exposure to Krebs' solution containing 5.9 or 50 mmol/L K+ or to St. Thomas' solution containing 16 or 50 mmol/L K+, for either 2 hours (group I) or 4 hours (group II), was examined. The solutions were continuously aerated with 95% oxygen and 5% carbon dioxide to exclude the effects of ischemia and hypoxia. The rings were then washed and contracted with K+ (25 mmol/L). The ability to release endothelium-derived relaxing factor (EDRF) in response to an EDRF stimulus (substance P) was used as an index of endothelial function. Smooth muscle function was evaluated in terms of the K(+)-induced contraction force and the relaxation induced with glyceryl trinitrate, in addition to the maximal substance P-induced relaxation. The maximal relaxation induced by substance P did not decrease by incubation with 50 mmol/L K+ in any group (p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)