Primary Graft Failure and Ca2+ Sensitizers After Heart Transplantation

Compromised right ventricular contractility in an ovine model of heart transplantation following 24 h donor brain stem death

BACKGROUND

Heart failure is an inexorably progressive disease with a high mortality, for which heart transplantation (HTx) remains the gold standard treatment. Currently, donor hearts are primarily derived from patients following brain stem death (BSD). BSD causes activation of the sympathetic nervous system, increases endothelin levels, and triggers significant inflammation that together with potential myocardial injury associated with the transplant procedure, may affect contractility of the donor heart. We examined peri-transplant myocardial catecholamine sensitivity and cardiac contractility post-BSD and transplantation in a clinically relevant ovine model.

METHODS

Donor sheep underwent BSD (BSD, n = 5) or sham (no BSD) procedures (SHAM, n = 4) and were monitored for 24h prior to heart procurement. Orthotopic HTx was performed on a separate group of donor animals following 24h of BSD (BSD-Tx, n = 6) or SHAM injury (SH-Tx, n = 5). The healthy recipient heart was used as a control (HC, n = 11). A cumulative concentration-effect curve to (-)-noradrenaline (NA) was established using left (LV) and right ventricular (RV) trabeculae to determine β₁-adrenoceptor mediated potency (-logEC₅₀ [(-)-noradrenaline] M) and maximal contractility (Emax).

RESULTS

Our data showed reduced basal and maximal (-)-noradrenaline induced contractility of the RV (but not LV) following BSD as well as HTx, regardless of whether the donor heart was exposed to BSD or SHAM. The potency of (-)-noradrenaline was lower in left and right ventricles for BSD-Tx and SH-Tx compared to HC.

CONCLUSION

These studies show that the combination of BSD and transplantation are likely to impair contractility of the donor heart, particularly for the RV. For the donor heart, this contractile dysfunction appears to be independent of changes to β₁-adrenoceptor sensitivity. However, altered β₁-adrenoceptor signalling is likely to be involved in post-HTx contractile dysfunction.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Levosimendan as rescue therapy in low output syndrome after cardiac surgery: effects and predictors of outcome

Objectives

Calcium sensitizers have been shown to improve outcomes in patients with low cardiac output syndrome (LCOS) after cardiac surgery. We assessed the effects of levosimendan on LCOS in cardiac surgical patients to identify outcome predictors.

Methods

A total of 106 patients in whom LCOS persisted despite conventional therapy additionally received 0.1 µg/kg/min of levosimendan for 24 hours according to a defined treatment algorithm. Baseline and treatment data as well as hemodynamic and outcome parameters were compared between survivors and nonsurvivors, and a multivariate correlation and regression tree analysis was implemented.

Results

The ejection fraction significantly increased from 27% ± 4% to 38% ± 8% within 24 hours and to 45% ± 10% within 48 hours of starting levosimendan. These changes were accompanied by a significant increase in cardiac output from 5.2 ± 0.6 to 6.2 ± 0.7 L/min within 24 hours and significant dose reductions in vasopressors and inotropes. In contrast to nonsurvivors, survivors’ need for inotropic support decreased after the addition of levosimendan to the therapy.

Conclusion

In our patients, all of whom were treated according to the same algorithm, the response to levosimendan in terms of the post-levosimendan need for inotropes and vasopressors predicted survival.

Levosimendan protects human hepatocytes from ischemia-reperfusion injury

Background

Ischemia-reperfusion injury (IRI) is a major challenge in liver transplantation. The mitochondrial pathway plays a pivotal role in hepatic IRI. Levosimendan, a calcium channel sensitizer, was shown to attenuate apoptosis after IRI in animal livers. The aim of this study was to investigate the effect of levosimendan on apoptosis in human hepatocytes.

Methods

Primary human hepatocytes were either exposed to hypoxia or cultured under normoxic conditions. After the hypoxic phase, reoxygenation was implemented and cells were treated with different concentrations of levosimendan (10ng/ml, 100ng/ml, 1000ng/ml). The overall metabolic activity of the cells was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and aspartate aminotransferase (AST) levels were determined in order to quantify hepatic injury. Fluorescence-activated cell sorting (FACS) analysis was applied to measure necrosis and apoptosis. Finally, Western blotting was performed to analyze apoptotic pathway proteins.

Results

Administration of levosimendan during reperfusion increases the metabolic activity of human hepatocytes and decreases AST levels. Moreover, apoptosis after IRI is reduced in treated vs. untreated hepatocytes, and levosimendan prevents down-regulation of the anti-apoptotic protein Bcl-2 as well as up-regulation of the pro-apoptotic protein BAX.

Conclusion

The present study suggests a protective effect of levosimendan on human hepatocytes. Our findings suggest that treatment with levosimendan during reperfusion attenuates apoptosis of human hepatocytes by influencing BAX and Bcl-2 levels.