Novel role of phosphodiesterase inhibitors in the management of end-stage heart failure

cGMP signalling in cardiomyocyte microdomains

3',5'-Cyclic guanosine monophosphate (cGMP) is one of the major second messengers critically involved in the regulation of cardiac electrophysiology, hypertrophy, and contractility. Recent molecular and cellular studies have significantly advanced our understanding of the cGMP signalling cascade, its local microdomain-specific regulation and its role in protecting the heart from pathological stress. Here, we summarise recent findings on cardiac cGMP microdomain regulation and discuss their potential clinical significance.

Effects of milrinone on inflammatory response-related gene expressions in cultured rat cardiomyocytes

Congestive heart failure (CHF) is defined as a cardiac dysfunction leading to low cardiac output and inadequate tissue perfusion. Intravenous positive inotropes are used to increase myocardial contractility in hospitalized patients with advanced heart failure. Milrinone is a phosphodiesterase Ⅲ inhibitor and used most commonly for inotropic effect. The well-known PROMISE study investigated the effects of milrinone on mortality in patients with severe CHF, and concluded that long-term therapy with milrinone increased morbidity and mortality among patients with advanced CHF. Previous studies have suggested that phosphodiesterase inhibitors can have potential effects on inflammatory pathways. Hence, we hypothesized that milrinone may alter inflammatory gene expressions in cardiomyocytes, thus leading to adverse clinical outcomes. We used rat cardiomyocyte cell line H9C2 and studied the impact of exposing cardiomyocytes to milrinone (10 μmol/L) for 24 hours on inflammatory gene expressions. RNA extracted from cultured cardiomyocytes was used for whole rat genome gene expression assay (41,000 genes). The following changes in inflammatory response-related gene expressions were discovered. Genes with increased expressions included: THBS2 (+9.98), MMP2 (+3.47), DDIT3 (+2.39), and ADORA3 (+3.5). Genes with decreased expressions were: SPP1 (-5.28) and CD14 (-2.05). We found that the above mentioned gene expression changes seem to indicate that milrinone may hinder the inflammatory process which may potentially lead to adverse clinical outcomes. However, further in vivo and clinical investigations will be needed to illustrate the clinical relevance of these gene expression changes induced by milrinone.

Milrinone-Associated Cardiomyopathy and Arrhythmia in Cerebral Vasospasm

BACKGROUND

Milrinone is an inotropic and vasodilatory drug proven safe for use in treatment of cerebral vasospasm. Despite its reported safety profile, its use is not free of side effects. Milrinone-associated cardiomyopathy and arrhythmia can occur in patients with cerebral vasospasm.

CASE DESCRIPTION

This is a retrospective chart review of a patient who presented with aneurysmal subarachnoid hemorrhage and developed clinical vasospasm twice over a period of 2 weeks. Sustained intravenous milrinone infusion was used in association with norepinephrine infusion during this period. The patient developed R-on-T triggered torsades de pointes and cardiogenic shock requiring resuscitation. Follow-up echocardiogram showed decreased ejection fraction from 64% to 43% consistent with cardiac remodeling. Systemic complications such as cardiotoxicity and arrhythmias with the use of intravenous milrinone can be seen particularly when used in combination with catecholamines.

CONCLUSIONS

With increased combined milrinone and catecholamine use for the treatment of cerebral vasospasm, physicians should be aware of the potential cardiac complications of these agents. Close monitoring with daily electrocardiograms may be helpful to detect changes that suggest cardiotoxicity. If changes are noted, an echocardiogram and cardiology consultation may be warranted.