Chronotropic Response to Exercise in Patients with Atrial Fibrillation

The exercise chronotropic response of patients with chronic atrial fibrillation requiring pacemaker therapy for bradycardia was assessed to characterize the chronotropic response and identify patients who would potentially benefit from a rate adaptive pacemaker. The population consisted of all patients who received a VVI pacemaker between January 1980 and November 1987 who underwent exercise tolerance testing (n = 130) and were in atrial fibrillation (n = 19). There were 11 males and 8 females with a mean age of 62 +/- 14 years. Left ventricular function was normal in eight patients, mildly impaired in three, and severely impaired in two. Long-term medications were continued until the morning of the test; digoxin 73%, beta blockers 21%, calcium channel blockers 26%, and nitrates 21%. Maximal exercise tolerance tests were performed. Parameters assessed were: (a) heart rate at rest, the end of each stage, and at peak exercise; (b) percent heart rate reserve per stage; and (c) percent metabolic reserve per stage. Results were compared to 100 normal subjects on no medications and without evidence of medical illness or cardiac disease. Heart rates were depressed in 58% of the study patients (21% early, 53% late) and elevated in 74% (74% early, 32% late). All 19 (100%) patients had abnormal heart rate responses at some point during the exercise test. Only four patients (21%) had a response within one standard deviation from the mean of the normal population during either the early or late segment of the exercise test. Patients in chronic atrial fibrillation requiring pacemakers for bradycardiac support at rest have an abnormal chronotropic response to exercise.(ABSTRACT TRUNCATED AT 400 WORDS)