Antiarrhythmic effects of losartan and enalapril in canine pulmonary vein sleeve preparations

Introduction: Angiotensin-converting Enzyme (ACE) inhibitors and angiotensin II-receptor blockers (ARBs) are prototypes of "upstream" therapy for the management of atrial fibrillation (AF). Ectopic activity arising from the PV sleeves plays a prominent role in the development of AF.

Methods: Transmembrane action potentials were recorded from canine superfused left superior or inferior PV sleeves using standard microelectrode techniques. Acetylcholine (ACh, 1 μM), isoproterenol (1 μM), high calcium ([CA(2+)](o) = 5.4 mM) or a combination was used to induce early or delayed afterdepolarizations (EADs or DADs) and triggered activity.

Results: The ARB losartan (1 μM, n = 5) and the ACE Inhibitor enalapril (10 μM, n = 5) produced no significant change in action potential duration, maximum rate of rise of action potential upstroke (V(max)), action potential amplitude or take-off potential at basic cycle lengths of 200 to 2000 ms. Losartan (1 μM) and enalapril (10-20 μM) markedly attenuated or suppressed EADs and DAD-induced triggered activity elicited by exposure of the PV sleeves to ACh, isoproterenol or high calcium following rapid pacing in 6 of 6 (losartan) and 4 of 5 (enalapril) PV sleeve preparations. Neither losartan nor enalapril altered CA(2+) or K(+) channel currents in enzymatically-dissociated atrial myocytes at these concentrations.

Conclusions: Our data suggest that in addition to their "upstream" effects to reduce atrial structural remodeling, ACE inhibitors and ARBs exert a "direct" antiarrhythmic effect by suppressing triggers responsible for the genesis of AF and other atrial arrhythmias.