Ischemic preconditioning does not acutely improve load-insensitive parameters of contractility in in vivo stunned porcine myocardium

OBJECTIVE

Ischemic preconditioning has been shown to have no beneficial effect on segment shortening in in vivo regionally stunned myocardium. The purpose of this study was to determine whether ischemic preconditioning improves the recovery of postischemic ventricular function when contractility is assessed by load-insensitive measurements including end-systolic pressure length relations, preload recruitable stroke work, and preload recruitable stroke work area in in vivo regionally stunned porcine myocardium.

METHODS

Open chest, pentobarbital-anesthetized pigs were used. Regional ventricular function was monitored by measurements of segment shortening, stroke work, end systolic pressure length relations, preload recruitable stroke work, and preload recruitable stroke work area. The control group was submitted to 15 minutes of left anterior descending coronary artery occlusion and 3 hours of reperfusion. The preconditioned group underwent 2 cycles of 5-minute left anterior descending coronary artery occlusion and 10-minute reperfusion before 15 minutes of occlusion.

RESULTS

There was no infarct in either group. The preconditioning protocol significantly depressed preischemic segment shortening but not regional stroke work. Ischemic preconditioning had no significant beneficial effect on regional stroke work, end-systolic pressure length relations, preload recruitable stroke work, or preload recruitable stroke work area.

CONCLUSIONS

These results confirm that ischemic preconditioning does not ameliorate in vivo porcine myocardial stunning and indicate that ischemic preconditioning may have a limited cardioprotective role during cardiac operation.

Impact of University of Wisconsin solution on clinical heart transplantation. A comparison with Stanford solution for extended preservation

BACKGROUND

The University of Wisconsin Solution (UW) has extended preservation of abdominal organs but has not allowed equally extended preservation of the heart. Therefore, the impact of UW on clinical heart transplantation has remained unclear.

METHODS AND RESULTS

Between June 1986 and March 1994, 161 orthotopic heart transplants were performed at our center. Of these, 66 were preserved for > or = 3 hours. Of these, 17 hearts were preserved with Stanford solution (STNF), which was used before 1990, and 49 were preserved with UW. These groups were compared for indexes of ischemic injury, ventricular function, and survival. The UW group contained more status-1 recipients (57% versus 29%, P < 0.05) and a higher mean donor age (30.7 versus 22.1 years, P = 0.008). Mean ischemic time was slightly but not significantly higher with UW (228 versus 205 minutes for UW versus STNF, respectively; P = 0.085). The time to wean from bypass after cross-clamp removal was nearly twice as long with STNF than with UW (80.6 versus 44.3 minutes, P < 0.001). There was no difference in the incidence of primary graft failure (2% for UW versus 6% for STNF, P = 0.43). The average need for inotropic support over the first 8 posttransplant hours was significantly higher with STNF than UW. Neither hospital stay nor survival differed. Nevertheless, the ability to use donor organs from more distant sites was increased. Of all hearts preserved with STNF, 26% were stored for > or = 3 hours, whereas 51% of all hearts preserved in UW were stored for this length of time. Donor use of hearts increased from 20% in 1989 to 63% in 1993, largely because of greater use of more distant donors.

CONCLUSIONS

We conclude that heart preservation with UW limits ischemic damage from prolonged storage and improves myocardial function in the early posttransplant period, thus allowing greater use of available donors from distant sites to patients awaiting heart transplantation.

Dose-dependent effects of adenosine on interstitial fluid adenosine and postischemic function in the isolated rat heart

Exogenous adenosine produces numerous beneficial effects in ischemic myocardium, but pharmacological doses of adenosine are required to exert these effects. This is thought to be due to the rapid metabolism of adenosine by coronary endothelium, although there is no direct evidence supporting this hypothesis in the ischemic/reperfused heart. The purpose of this study was to determine the relationship between vascular and interstitial fluid (ISF) adenosine levels during adenosine-induced cardioprotection. Isolated perfused rat hearts were submitted to 30-min global normothermic ischemia and 30- min reperfusion. Left ventricular developed pressure (LVDP) was measured with a fluid-filled latex balloon, and ISF adenosine was estimated with cardiac microdialysis. Control hearts were compared with hearts treated with increasing doses of adenosine (1, 10 and 100 microM) for 10 min immediately preceding ischemia. Adenosine produced dose-dependent increases in coronary effluent adenosine levels, but only 10 and 100 microM adenosine increased dialysate adenosine concentrations. All adenosine doses increased coronary flow to the same extent, but only the two higher doses decreased spontaneous heart rate. Control and 1 microM adenosine-treated hearts recovered 60 +/- 3% and 46 +/- 7% of preischemic LVDP, respectively, whereas 10 and 100 microM adenosine improved recovery to 80 +/- 5% and 90 +/- 4% of preischemic LVDP, respectively, after 30-min reperfusion. Because ISF bathes the cardiac myocytes, these results are consistent with the hypothesis that adenosine protects the ischemic rat heart via the activation of cardiac myocyte adenosine receptors.

Adenosine attenuates in vivo myocardial stunning with minimal effects on cardiac energetics

Adenosine has been shown to modulate myocardial intermediary metabolism. The purpose of this study was to determine whether adenosine-mediated attenuation of in vivo myocardial stunning is associated with improved myocardial phosphorylation potential. Adult, open chest pigs were subjected to 10 minutes of regional myocardial ischemia and 90 minutes reperfusion. Regional ventricular function was assessed by measuring systolic wall thickening. Myocardial phosphorylation potential was estimated from the tissue (CrP/CrxPi) ratio determined in rapid-frozen tissue biopsy samples from normal and stunned myocardium. Control pigs were compared to animals treated prior to ischemia with intracoronary adenosine (50 micrograms/kg/min). Postischemic regional systolic wall thickening in adenosine treated pigs was significantly improved (40 +/- 3% of preischemic values) compared to control untreated pigs (26 +/- 3%). Myocardial stunning was associated with decreased ATP levels, but neither the total creatine pool (CrP + Cr) nor the (CrP/CrxPi) ratio was reduced. Adenosine pretreatment was associated with decreased Pi and Cr contents resulting in improved postischemic (CrP/CrxPi) ratio in the stunned bed compared to controls, but this effect occurred only after postischemic function had attained maximal improvement. These results suggest that adenosine attenuation of in vivo myocardial stunning is independent of elevated myocardial phosphorylation potential.

Comparison of interstitial fluid and coronary venous adenosine levels in in vivo porcine myocardium

There are numerous reports of interstitial fluid (ISF) and coronary venous adenosine measurements in isolated perfused hearts. This study was designed to simultaneously compare ISF and coronary venous adenosine concentrations during various interventions in in vivo porcine myocardium. In anesthetized, open-chest pigs, ISF adenosine, inosine, and hypoxanthine were sampled with cardiac microdialysis. Coronary sinus or venous purines were sampled with a metabolism-stop solution. During basal conditions, ISF adenosine was greater than coronary venous adenosine, but vascular inosine and hypoxanthine were greater than corresponding ISF levels. Dobutamine (20 micrograms/kg/min, i.v.) and systemic hypoxia produced three- and two-fold increases in ISF adenosine, but had no significant effect on coronary sinus adenosine concentration. Hypoxia, but not dobutamine, increased coronary sinus total purines 50%. In contrast to these interventions, intracoronary adenosine infusion (0.5-50 micrograms/kg/min) was associated with significantly greater coronary venous adenosine concentrations than ISF levels. Only during a coronary artery occlusion/reperfusion protocol were ISF and coronary venous adenosine concentrations comparable. The results of this study thus provide in vivo evidence of the powerful endothelial and red blood cell metabolic barriers to both exogenous and endogenous adenosine. These results also illustrate the differences in adenosine concentrations in the ISF and vascular spaces.

Adenosine A1 receptor stimulation antagonizes the negative inotropic effects of the PKC activator dioctanoylglycerol

It has been suggested that adenosine cardioprotection occurs via adenosine A1 receptor-mediated activation of protein kinase C (PKC). However, adenosine has well-known vasodilatory effects in the myocardium, whereas PKC is a vasoconstrictor. This study examined whether adenosine A1 receptor activation alters the effects of the PKC activator. 1,2-dioctanoyl-s,n-glycerol (DOG) in isolated perfused rat hearts (left-ventricular developed pressure) and rat ventricular myocytes ([Ca2+]i and cell shortening). Exposure to DOG decreased left-ventricular developed pressure by 30%, an effect that was completely reversible. Pretreatment of isolated hearts with either the PKC inhibitor chelerythrine or the adenosine A1 agonist 2-chloro-N6-cyclo-cyclo-isolated pentlyadenosine (CCPA) attenuated the negative inotropic effects of DOG. In the isolated myocytes, DOG decreased [Ca2+]i and cell shortening by 25 and 28%, respectively, effects that were attenuated by both chelerythrine and CCPA. The CCPA attenuation of the DOG-induced decrease in [Ca2+]i and cell shortening was blocked by pretreating the myocytes with the adenosine A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). These results indicate that in rat ventricular myocardium, adenosine A1 receptor activation attenuates the apparent PKC-dependent negative inotropic effects of DOG via preservation of [Ca2+]i levels.

Tacrolimus as a rescue immunosuppressant after heart and lung transplantation. The U.S. Multicenter FK506 Study Group

BACKGROUND

Organ transplant recipients with refractory rejection or intolerance to conventional immunosuppressants may respond to rescue therapy with tacrolimus.

METHODS

Tacrolimus was used as a rescue immunosuppressant for 16 heart and 15 lung recipients. Heart recipients were converted to tacrolimus therapy because of cyclosporine intolerance, acute rejection despite treatment with cyclosporine, or humoral rejection. Lung recipients were converted because of cyclosporine intolerance, chronic rejection, or acute rejection. All immunosuppressive medications except corticosteroids were discontinued before tacrolimus therapy was begun. Patients remained in the study until they were converted to commercial tacrolimus.

RESULTS

The duration of follow-up after conversion varied widely (heart recipients: 183+/-65 days; lung recipients: 169+/-86 days). For the heart recipients, patient and graft survivals were 100%. Twenty percent of recipients experienced no rejection episodes after conversion to tacrolimus; 60% experienced none or only one. For the lung recipients, patient survival was 67% and graft survival was 60%. Eighty percent of recipients experienced no rejections and 13% experienced one episode of rejection each. The remaining patient experienced two biopsy-confirmed episodes of rejection. Five lung patients died within the year and one patient required retransplantation. The most common adverse events were diarrhea, headache, abnormal kidney function, depression, dyspnea, nausea, and pneumonia.

CONCLUSIONS

Tacrolimus is an effective and safe immunosuppressant for the rescue of heart transplant patients. Lung transplant patients may receive more benefit if rescued earlier.

Pyruvate augments calcium transients and cell shortening in rat ventricular myocytes

Pyruvate has been shown to be a metabolic inotrope in the myocardium. In millimolar concentrations, it has been shown to increase both myocardial phosphorylation potential and the cytosolic [NAD+]-to-[NADH] ratio. To determine if changes in these parameters can alter intracellular Ca2+ concentration ([Ca2+]i) and hence contractile function, Ca2+ transients and cell shortening (CS) were measured in isolated rat ventricular myocytes superfused with a physiological N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer (11 mmol/l glucose) with and without additional pyruvate, L-lactate, acetate, or isoproterenol. The addition of 5 mmol/l pyruvate resulted in a 33% increase in CS and a 39% increase in systolic [Ca2+]i. These pyruvate effects were 70% of those observed with 100 nmol/l isoproterenol. The mitochondrial monocarboxylate transport inhibitor alpha-cyano-4-hydroxycinnamate (250 mumol/l) strongly inhibited pyruvate inotropy, suggesting a substantial obligatory coupling between pyruvate inotropism and its oxidation by the mitochondria. A possible role of the cytosolic [NAD+]-to-[NADH] ratio was assessed by comparing the effects of 20 mmol/l L-lactate to those of equimolar pyruvate. In contrast to 20 mmol/l pyruvate, excess L-lactate failed to appreciably increase CS or systolic [Ca2+]i. The findings imply that, at levels substantially above 5 mmol/l, a portion of pyruvate inotropism might be due to extreme cytosolic [NAD+]-to-[NADH] ratios. This study is the first evidence that augmented [Ca2+]i transients are most likely the mechanism of cardiac pyruvate inotropism.

Effects of protein kinase C inhibitors in in situ and isolated ischemic rabbit myocardium

We tested the effects of the protein kinase C (PKC) inhibitors bisindolylmaleimide (1 microM) and chelerythrine (2 microM) on myocardial ischemia-reperfusion injury in in situ and isolated perfused rabbit hearts. In non-ischemic isolated hearts, bisindolylmaleimide (1 microM) and chelerythrine (2 microM) blocked sn-1,2-dioctanoylglycerol (DOG)-induced coronary vasoconstriction by approximately 80%. Intact hearts were subjected to 45 min coronary artery occlusion and 2 h reperfusion. Infarct size, determined by triphenyltetrazolium chloride (TTC)-staining and expressed as percentage of risk area, was reduced approximately 50% by both bisindolylmaleimide (0.05 mg/kg, i.v.) and chelerythrine (0.1 mg/kg, i.v.) compared to vehicle treated controls. In contrast, a higher dose of chelerythrine (3.8 mg/kg, i.v.) did not significantly reduce infarct size. Isolated hearts were subjected to 45 min of global normothermic (37 degrees C) ischemia and 60 min reperfusion. Control hearts exhibited 45+/-2% recovery of pre-ischemic left ventricular developed pressure (LVDP) compared to bisindolylmaleimide- (73+/-7%) and chelerythrine-treated hearts (70+/-11%). Bisindolylmaleimide and cherythrine reduced infarct size from a control value of 24+/-4 to 8+/-2 and 9+/-3%, respectively. Preconditioning isolated hearts with 5 min ischemia and 10 min reperfusion prior to prolonged ischemia reduced infarct size to 10.4+/-2.3%, an effect which was blocked by chelerythrine (22.5+/-4.2% infarct size). These results suggest that although PKC may play a role in ischemic preconditioning, PKC inhibitors can be cardioprotective during prolonged ischemia.

Safety, tolerance, and efficacy of adenosine as an additive to blood cardioplegia in humans during coronary artery bypass surgery

Myocardial stunning after heart surgery is associated with increased morbidity and mortality in patients with severe multivessel disease and reduced myocardial function. The purpose of this study was to evaluate the safety, tolerance, and efficacy of adenosine as a cardioprotective agent when added to blood cardioplegia in patients undergoing coronary artery bypass surgery. Sixty-one patients were randomized to standard cold-blood cardioplegia, or cold-blood cardioplegia containing 1 of 5 adenosine doses (100 microM, 500 microM, 1 mM, 2 mM, and 2 mM with a preischemic infusion of 140 microg/kg/min of adenosine). Invasive and noninvasive measurements of ventricular performance and rhythm were obtained preoperatively, prebypass, and then at 1, 2, 4, 8, 16, and 24 hours postbypass. Use of inotropic agents and vasoactive drugs pastoperatively was recorded; blood samples were collected for measurement of nucleoside levels. High-dose adenosine treatment was associated with a 249-fold increase in the plasma adenosine concentration and a 69-fold increase in the combined levels of adenosine, inosine, and hypoxanthine (p <0.05). Increasing doses of the adenosine additive were also associated with lower requirements of dopamine (p = 0.003) and nitroglycerine (p = 0.001). The 24-hour average doses for dopamine and nitroglycerine in the placebo group were 28-fold and 2.6-fold greater than their respective high-dose adenosine treatment cohorts. Finally, the placebo- and 100 microM-adenosine group was associated with a lower ejection fraction when compared to patients receiving the intermediate dose or high-dose treatment. These findings are consistent with the hypothesis that adenosine is effective in attenuating myocardial stunning in humans.

Infarct size reduction with the nucleoside transport inhibitor R-75231 in swine

Adenosine (Ado) has been reported to be cardioprotective in several models of myocardial ischemia. The nucleoside transport inhibitor R-75231 (R-75) has been reported to enhance local Ado concentrations and postischemic recovery of function, but little is known regarding its effects on myocardial infarct size. The purpose of the present study was to determine the effects of R-75 on infarct size and to measure myocardial regional Ado concentrations. Studies were conducted in pentobarbital-anesthetized swine undergoing 60 min of coronary artery occlusion and 2 h of reperfusion. Control pigs (n = 8) were compared with those receiving R-75 (0.1 mg/kg i.v.) 15 min before either occlusion (Pre R-75, n = 8) or reperfusion (Rep R-75, n = 8). Interstitial fluid (ISF) Ado, coronary venous Ado, and infarct size (% of the region at risk) were measured. In the Pre R-75 group, ISF Ado concentrations were significantly increased before and during ischemia, reaching a peak value of 71.8 +/- 8.6 microM (vs. 16.8 +/- 0.8 microM in control). ISF inosine and hypoxanthine concentrations were significantly reduced during ischemia in Pre R-75 animals. Infarct size was smaller in Pre R-75 compared with control (21.6 +/- 1.9 vs. 38.4 +/- 2.6%, P < 0.05). The Rep R-75 group had significantly elevated coronary venous Ado concentrations but no increases in ISF Ado or reduction in infarct size (33.5 +/- 3.5%). These data indicate that R-75 increases myocardial Ado and reduces infarct size when administered before coronary occlusion. The R-75-induced reduction in infarct size appears to be related to the augmentation of ISF Ado before ischemia rather than to increased plasma Ado during reperfusion.

Adenosine reduces postbypass transfusion requirements in humans after heart surgery

OBJECTIVE

The objective of this study was to determine the effect, if any, of adenosine blood cardioplegia on blood component usage after heart surgery.

SUMMARY BACKGROUND DATA

The most common cause of nonsurgical postcardiopulmonary bypass bleeding is platelet dysfunction. For this reason, pharmacologic agents are under investigation in an effort to reduce the need for transfusion in this setting.

METHODS

A posthoc analysis of blood product usage was performed in data obtained from a Phase I, single center, open label, randomized study performed in 63 patients. The trial was designed to test the safety and tolerance of adenosine when added to blood cardioplegia in increasing doses to enhance myocardial protection. The database provided information regarding the effect of adenosine cardioplegia on venous plasma adenosine concentrations, the amount of platelets, fresh frozen plasma and packed erythrocytes used, and the association between the adenosine dose and postoperative thoracic drainage.

RESULTS

The postoperative thoracic drainage at 6 hours, 24 hours, and at the time of chest tube removal in the high-dose adenosine cardioplegia group was 68%, 76%, and 75% of the placebo and low-dose adenosine cardioplegia group (p < 0.05). The highest dose of adenosine studied increased baseline adenosine venous plasma levels 360-fold, from 0.17 +/- 0.09 mumol/L to 42.30 +/- 11.20 mumol/L (p < 0.05). This marked increase was associated with a 68%, 56%, and 58% reduction in platelet, fresh frozen plasma, and packed erythrocyte usage, respectively (p < 0.05).

CONCLUSIONS

In addition to enhancing the heart's tolerance to ischemia, adenosine-supplemented cardioplegic solution also may reduce bleeding after cardiopulmonary bypass.

Donor-derived human leukocyte antigen class I proteins in the serum of heart transplant recipients

BACKGROUND

Human leukocyte antigen class I proteins are expressed on most cell types in all organ allografts but are constitutively secreted only by certain organs, for example, the liver. We hypothesized that detectable levels of donor-derived human leukocyte antigen proteins would be released from transplanted cardiac allografts only when the allograft was immunologically stimulated, that is, during rejection and perhaps during viral infection. If so, then the release of donor human leukocyte antigen might be a noninvasive monitor of these events.

METHODS

We used an enzyme-linked immunosorbent assay to detect donor-derived human leukocyte antigen-A2 in the serum of 21 human leukocyte antigen-A2 negative recipients of human leukocyte antigen-A2-positive heart transplants. The level of donor human leukocyte antigen-A2 during the first 100 days after transplantation was correlated with the clinical status of the patient.

RESULTS

We found little or no donor human leukocyte antigen in the serum of heart transplant recipients whose postoperative clinical course was unremarkable for infection or rejection. We did find donor-derived human leukocyte antigen in the serum of heart transplant recipients transiently in the week immediately after transplantation, continuously from patients in whom chronic rejection was developing, during cytomegalovirus infection, and during some, but not all, acute rejection episodes as determined by endomyocardial biopsy.

CONCLUSIONS

These findings are consistent with the hypothesis that the donor human leukocyte antigen serum level reflects vascular diseases, rather than myocardial disease in the transplanted heart. Therefore, the serum level of donor human leukocyte antigen cannot be used as a monitor of cellular infiltration and myocyte damage as currently assessed by endomyocardial biopsy but may be an early indicator of the development of vascular disease such as chronic rejection.

Myofibrillar calcium sensitivity of isometric tension is increased in human dilated cardiomyopathies: role of altered beta-adrenergically mediated protein phosphorylation

To examine the role of alterations in myofibrillar function in human dilated cardiomyopathies, we determined isometric tension-calcium relations in permeabilized myocytesized myofibrillar preparations (n = 16) obtained from left ventricular biopsies from nine patients with dilated cardiomyopathy (DCM) during cardiac transplantation or left ventricular assist device implantation. Similar preparations (n = 10) were obtained from six normal hearts used for cardiac transplantation. Passive and maximal Ca2+-activated tensions were similar for the two groups. However, the calcium sensitivity of isometric tension was increased in DCM compared to nonfailing preparations ([Ca2+]50=2.46+/-0.49 microM vs 3.24+/-0.51 microM, P < 0.001). In vitro treatment with the catalytic subunit of protein kinase A (PKA) decreased calcium sensitivity of tension to a greater degree in failing than in normal preparations. Further, isometric tension-calcium relations in failing and normal myofibrillar preparations were similar after PKA treatment. These findings suggest that the increased calcium sensitivity of isometric tension in DCM may be due at least in part to a reduction of the beta-adrenergically mediated (PKA-dependent) phosphorylation of myofibrillar regulatory proteins such as troponin I and/or C-protein.

Efficacy of a partnership in enhancing Veterans Affairs cardiac transplantation activity

BACKGROUND

Despite a nationwide surplus of cardiac transplantation programs, the number of United States armed forces veterans who receive heart transplants has declined over the past several years. This study reviews the efficacy of a partnership between a Veterans Affairs hospital and a university hospital in maximizing the access of veterans to the limited donor heart supply.

METHODS

As part of a contract-based sharing agreement between the University of Wisconsin Hospital and the William S. Middleton Memorial Veterans Affairs Hospital, 25 veterans underwent orthotopic heart transplantation between October 1993 and April 1995. Care of the patients was provided at the Veterans Affairs Hospital. The transplantation operations were performed at the University of Wisconsin Hospital, and all patients were transferred back to the Veterans Affairs Hospital 5 to 7 days afterward. All patients were men (mean age, 52.1 +/- 2.1 years) and were referred from Veterans Affairs hospitals in nine different states.

RESULTS

During the 19-month period, the average length of hospital stay for pretransplantation evaluation was 7.0 +/- 0.7 days (range, 2 to 15 days). Average status I waiting time was 26.9 +/- 3.3 days (range, 5 to 54 days); the average waiting time for status II was 115.1 +/- 16 days (range, 15 to 242 days). Posttransplantation length of stay at the Veterans Affairs Hospital was 22 +/- 1.8 days (range, 11 to 41 days). Only 1 patient (4%) experienced a lethal postoperative complication. Ten patients (40%) exhibited graft rejection within the first month after transplantation, requiring treatment with augmented immunosuppressive therapy (steroids, orally in 2 patients and intravenously in 8). The overall 30-day mortality rate was 4% (1 patient). The cause of death was acute grade 4 graft rejection 3 weeks after transplantation. Overall patient survival was 96%.

CONCLUSIONS

A partnership between a Veterans Affairs hospital and a university hospital committed to transplantation can increase Veterans Affairs cardiac transplantation activity, with excellent 30-day mortality and early survival results.

Different effects of an adenosine A1 analogue and ischemic preconditioning in isolated rabbit hearts

BACKGROUND

Ischemic preconditioning reduces infarct size, but its effects on postischemic function are variable. Adenosine, which is thought to play a role in ischemic preconditioning, reduces both infarct size and postischemic dysfunction. The purpose of this study was to compare the cardioprotective effects of ischemic preconditioning and an adenosine A1 receptor agonist on recovery of function and infarct size in isolated rabbit hearts.

METHODS

Krebs buffer-perfused hearts (at least 7 per group) were subjected to 60 minutes of global ischemia (37 degrees C) and 60 minutes of reperfusion. Ventricular function was assessed by measuring left ventricular developed pressure, and infarct size (percentage of the left ventricle) was determined by tetrazolium staining.

RESULTS

Control hearts exhibited 34% +/- 6% infarct size and 56% +/- 4% recovery of preischemic left ventricular developed pressure. Ischemic preconditioning reduced infarct size to 13% +/- 1% but had no effect on recovery of function (65% +/- 5%). Hearts treated with the adenosine A1 agonist R-phenylisopropyladenosine for 5 minutes immediately before ischemia exhibited both reduced infarct size (10% +/- 2%) and enhanced postischemic recovery of left ventricular developed pressure (86% +/- 3%). Termination of the R-phenylisopropyladenosine treatment before ischemia eliminated its beneficial effects. The adenosine A1 receptor antagonist DPCPX blocked both of the effects of R-phenylisopropyladenosine but did not block ischemic preconditioning.

CONCLUSIONS

These results demonstrate fundamental differences between the cardioprotective effects of adenosine A1 receptor activation and ischemic preconditioning.

Myocardial stunning: a therapeutic conundrum

Dobutamine and pyruvate are two inotropic agents with different mechanisms of action. Although both agents alter postischemic myocardial dysfunction, their potential metabolic effects in the setting of in vivo myocardial stunning have not been addressed. In this study, the effects of dobutamine and pyruvate on systolic wall thickening, myocardial phosphorylation potential index, interstitial fluid adenosine level, and myocardial oxygen consumption in in vivo stunned porcine myocardium were assessed. Stunning was induced with a 10-minute occlusion of the left anterior descending coronary artery. After 30 minutes of reperfusion, pigs were treated with either intravenous dobutamine (10 micrograms/kg per minute) or intracoronary pyruvate (1 ml/min, 150 mmol/L solution, pH 7.4). Infusion of both agents resulted in a marked improvement in regional systolic wall thickening. The dobutamine effect, however, produced a marked increase in myocardial oxygen consumption and was associated with an increase in interstitial adenosine caused by myocardial de-energization, because the myocardial phosphorylation potential index ratio decreased from 0.17 +/- 0.02 to 0.09 +/- 0.02 (p < 0.05). In contrast, pyruvate enhanced myocardial energy status, because the myocardial phosphorylation potential index ratio increased from 0.20 +/- 0.03 to 0.55 +/- 0.08 (p < 0.01). These experimental findings suggest that under certain circumstances the use of beta-receptor agonists to treat myocardial stunning may be suboptimal, if not undesirable. Further investigation is warranted to determine the optimum therapy for the stunned heart.

The effects of intraoperative autologous whole blood sequestration on the need for transfusion of allogenic blood and blood products in coronary bypass operations

We investigated the effect of intraoperative autologous blood sequestration (IABS), an old blood conservation method, on transfusion requirements for homologous packed red blood cells (PRBC), platelets, and fresh frozen plasma (FFP) for patients undergoing coronary bypass surgery. This non-randomized retrospective study involved 204 patients who underwent isolated primary coronary artery bypass grafting (CABG). In 140 patients (IABS Group), autologous heparinized whole blood was removed intraoperatively via aortic cannula before bypass and retransfused at the conclusion of extracorporeal circulation. In 64 control patients, no IABS was performed. Demographic characteristics and operative and perioperative variables for both groups were similar (p > 0.05). In 140 patients, the mean sequestered blood volume was 1430 ml (range = 700-2100 ml). The banked PRBC requirement during hospitalization was 1.91 units in the No IABS Group and 2.25 units for the IABS Group (p = 0.2957). The need for platelet transfusion was 3.06 units in the No IABS Group and 1.09 units in the IABS Group (p = 0.0003). In the No IABS Group, 1.31 units of FFP was transfused and in the IABS Group, 0.49 units was transfused (p = 0.0004). To identify possible confounding factors, we performed a multivariate Poisson regression analysis for the 22 patient variables by a forward stepwise procedure. Regression analysis indicated that IABS did not alter the need for PRBC transfusion (p = 0.6194) but adjusted differences did confirm that IABS was associated with decreased need for transfusion of platelets and FFP (p = 0.0001 and p = 0.0002, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ischemic and adenosine preconditioning on interstitial fluid adenosine and myocardial infarct size

The accumulation of adenosine during a brief coronary occlusion has been proposed to mediate the infarct size-limiting effect of ischemic preconditioning. The purpose of this study was to compare the effects of ischemic preconditioning and a transient adenosine infusion on myocardial interstitial fluid (ISF) adenosine levels and infarct size. Microdialysis fibers (10.0 mm length) were placed in the left ventricular myocardium of pentobarbital sodium-anesthetized rabbits to estimate ISF adenosine. Ischemic preconditioning was induced by 5 min of coronary artery occlusion and 10 min of reperfusion before 45 min of occlusion. Adenosine preconditioning was induced with 5 min of intravenous adenosine infusion (140 micrograms.kg-1.min-1) followed by a 10-min washout before the prolonged occlusion. Myocardial infarct size was determined by triphenyltetrazolium chloride staining after 3 h of reperfusion. Five minutes of ischemia and 5 min of adenosine infusion produced comparable increases in dialysate adenosine levels (from 0.19 +/- 0.02 to 0.69 +/0- 0.11 and 0.28 +/- 0.10 to 0.71 +/- 0.18 microM, respectively) that decreased to baseline before the prolonged ischemia; however, ischemic-preconditioned hearts exhibited elevated dialysate adenosine levels for the first 5 min of reperfusion. Ischemic-preconditioned hearts exhibited significantly reduced dialysate adenosine concentrations for the first 20 min of the prolonged occlusion (P < 0.05 vs. control), and infarct size was reduced from 41 +/- 6 to 10 +/- 4% of risk area. Adenosine preconditioning had no effect on dialysate adenosine levels during prolonged ischemia but did reduce infarct size to 25 +/- 5% of risk area. These results indicate that a transient increase in ISF adenosine can reduce myocardial infarct size, but adenosine alone does not fully replicate the protective effects of ischemic preconditioning.

Protective effects of adenosine in the reversibly injured heart

BACKGROUND

There is substantial evidence that the nucleoside adenosine reduces postischemic ventricular dysfunction (ie, myocardial stunning). Studies performed in our laboratory have attempted to address the mechanism of adenosine-mediated protection of the reversibly injured heart.

METHODS

Experiments were performed in isolated perfused rat and rabbit hearts and in in situ canine and porcine preparations. The role of adenosine A1 receptors was assessed by using adenosine A1 receptor agonists and antagonists, and by measuring interstitial fluid purine levels with the cardiac microdialysis technique.

RESULTS

In isolated perfused hearts, treatment immediately before ischemia with adenosine and adenosine A1 receptor analogues significantly improved postischemic ventricular function, effects that were blocked by a selective adenosine A1 receptor antagonist. In in situ canine and porcine preparations, pretreatment with adenosine and an adenosine deaminase inhibitor increased preischemic interstitial fluid adenosine levels and attenuated regional myocardial stunning. Adenosine treatment was also associated with improved myocardial phosphorylation potential in isolated guinea pig hearts and in the in situ porcine preparation.

CONCLUSIONS

These results suggest that adenosine-induced attenuation of myocardial stunning is mediated via adenosine A1 receptor activation and enhancement of postischemic myocardial phosphorylation potential.