Ventricular Response In Atrial Fibrillation: Effects of AV Nodal Refractory Periods, Atrioventricular Block, and Preexcitation Syndromes

Abstract

Aerial fibrillation (AF) is a rapid (400–600 cycles/min) and irregular activation of the atria [161M, 31S]. Successive activation fronts separated by variable time intervals pass through different pathways in the thin atrial myocardial wall [120C, 52S]. These irregularities explain the continually changing appearance of the atrial activity in the surface ECG. The temporal and spatial irregularities cause fascicular atrial movements resulting in ineffective atrial contractility. When the disorganized electrical activity reaches the atrioventricular (AV) node of Aschoff and Tawara, only a fraction of the atrial impulses conduct to the ventricles, and ventricular rhythm is irregular but the rate is slower than that of atrial fibrillation [31C]. The fraction of transmitted atrial impulses depends on several factors which are discussed below.