HEMODYNAMIC-EFFECTS OF AN IRREGULAR SEQUENCE OF VENTRICULAR CYCLE LENGTHS DURING ATRIAL-FIBRILLATION

Objectives. The aim of this study was to determine the independent hem odynamic effects of an irregular sequence of ventricular cycle lengths in patients with atrial fibrillation (AF). Background. Atrial fibrill ation may reduce cardiac output by several possible mechanisms, includ ing loss of the atrial contribution to left ventricular filling, valvu lar regurgitation, increased ventricular rate or irregular RR interval s. This study was designed to evaluate the effects of an irregular RR interval, independent of the average ventricular rate, on cardiac hemo dynamic data during AF. Methods. Sixteen patients with AF were studied invasively. During intrinsically conducted AF (mean rate 102 +/- 22 b eats/min), the right ventricular apex electrogram was recorded onto fr equency-modulated (FM) tape. After atrioventricular node ablation, the right ventricular apex was stimulated in three pacing modes in random ized sequence: 1) VVI at 60 beats/min; 2) VVI at the same average rate as during intrinsically conducted AF (102 +/- 22 beats/min); and 3) d uring VVT pacing in which the pacemaker was triggered by playback of t he FM tape recording of the right ventricular apex electrogram previou sly recorded during intrinsically conducted AF (VVT 102 +/- 22 beats/m in). Results. Compared with VVI pacing at the same average rate, an ir regular sequence of RR intervals decreased cardiac output (4.4 +/- 1.6 vs. 5.2 +/- 2.4 liters/min, p < 0.01), increased pulmonary capillary wedge pressure (17 +/- 7 vs. 14 +/- 6 mm Hg, p < 0.002) and increased right atrial pressure (10 +/- 6 vs. 8 +/- 4 mm Hg, p < 0.05). Conclusi ons. An irregular sequence of RR intervals produces adverse hemodynami c consequences that are independent of heart rate. (C) 1997 by the Ame rican College of Cardiology.