Effect of Phosphodiesterase-5 Inhibition With Tadalafil on SystEmic Right VEntricular Size and Function

Currently, there are an estimated 300-600 adults living in Switzerland with congenital heart disease (CHD) and a right ventricle (RV) in subaortic (systemic) position. This includes adults with prior atrial switch operations for complete transposition of the great arteries (D-TGA) and adults with congenitally corrected transposition of the great arteries (ccTGA). Although midterm survival is favourable, late outcome is compromised by ventricular dysfunction of the systemic RV, end-stage heart failure, and premature death. Medical heart failure therapy (ACE-inhibitors, beta-blockers, aldosterone antagonists) has been shown to improve ventricular function and survival in patients with left heart failure from acquired heart disease. Unfortunately, case-reports and studies failed to show similar clinical benefits of these drugs in adults with a failing systemic RV. Currently, the only established end-stage therapy for a failing systemic RV is heart transplantation. Given the ubiquitous shortage of donor organs and the number of adults at risk, medical options to improve the fate of patients with a systemic RV are urgently needed. The RV and left ventricle (LV) have different embryological origins, myocardial architecture and contractile properties. In response to increased afterload, as in an RV in systemic position, the RV expresses a fetal gene pattern, with an increase in phosphodiesterase (PDE)-5 expression. PDE-5 is not expressed in the normal RV, but is up-regulated in the hypertrophied RV. PDE-5 inhibition increases contractility in experimental models of RV hypertrophy, but not in the normal RV. In clinical practice, the effects of PDE-5 inhibition on systemic RV function and exercise capacity in adults with TGA have not been tested. This study assesses in a double-blind, randomized, placebo-controlled multi-center pilot trial the effect of PDE-5 inhibition with Tadalafil on RV size and function, exercise capacity and neurohumoral activation in adults with a systemic RV over a 3-year follow-up period.