Direct pro-arrhythmogenic effects of angiotensin II can be suppressed by AT1 receptor blockade in human atrial myocardium

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice. Indirect evidence from clinical trials demonstrates that chronic inhibition of the renin-angiotensin-system (RAS) significantly reduces the incidence of AF. Since mechanisms of this protective effect of RAS-blockade are poorly understood, we directly tested proarrhythmic effects of angiotensin II (Ang II) in human atrial myocardium. Methods: Isolated trabeculae from human atrial appendages (n = 80) were electrically stimulated. We assessed isometric force and incidence of arrhythmic extra contractions (AECs) with and without increasing concentrations of Ang II (1-1000 nmol/L) in the absence or presence of receptor-blockade by saralasin (non-specific ATR-antagonist), irbesartan (AT1R-antagonist) or PD123319 (AT2R-antagonist). Results: Twitch force and AECs concentration-dependently increased with Ang II. Effects became significant at concentrations > 1 nmol/L Ang II and were maximal at 1000 nmol/L (increase in twitch force to 157 +/- 14% and AECs from 0 to 80%) saralasin and irbesartan partially prevented the inotropic effect of 100 nmol/L Ang II (by 45 +/- 12% and 68 +/- 6%; p < 0.05), and completely prevented the occurrence of AECs. Conclusion: Ang II exerts direct pro-arrhythmic effects in human atrial myocardium. These effects are mediated by AT I-receptors and can be prevented by AT1R-blockade. This mechanism may contribute to the beneficial effects of RAS-blockade on AF in clinical trials. (C) 2008 Published by Elsevier B.V. on behalf of European Society of Cardiology.