THE EFFECT OF ATRIAL-FIBRILLATION AND THE VENTRICULAR RATE CONTROL ONEXERCISE CAPACITY

Background: Atrial fibrillation (AF) is a common cardiac arrhythmia, a ffecting approximately 1.5 million patients in the United States. Hypo thesis: This study was designed to determine the effect of AF and the ventricular rate control during AF on cardiovascular performance as me asured by exercise endurance on a standard Bruce protocol. Methods: Si xty-three patients with AF who underwent exercise stress testing durin g both sinus rhythm and AF were analyzed. Heart rate, blood pressure, heart rate acceleration, exercise duration, and left ventricular (LV) systolic function were measured. Results: Atrial fibrillation resulted in a small but statistically significant decrease in exercise enduran ce (426 +/- 180 vs. 402 +/- 168 s, p<0.05). The drop in exercise toler ance was consistent regardless of the underlying heart condition or ad equate ventricular rate control during AF. Heart rate in AF was consis tently faster than in sinus rhythm, at rest, and at peak exercise (63 vs. 79 beats/min and 125 vs. 149 beats/min, respectively, p<0.001). Co nclusion: Our analyses indicated that (1) the loss of atrioventricular synchrony had minimal effect on cardiovascular performance in patient s with preserved LV function, (2) the decrease in cardiovascular perfo rmance was related to loss of atrioventricular synchrony but not to un derlying heart disease or ventricular rate control, and (3) compensati on for the loss of the atrial contribution was provided by consistentl y faster heart rate during AF.