Atrial synchronized ventricular pacing: contribution of the chronotropic response to improved exercise performance

In contrast to asynchronous ventricular pacing (VOO, VVI), atrial synchronized ventricular pacing (VAT, VDD, DDD) maintains the normal sequence of cardiac chamber activation and permits a chronotropic response to exercise, thereby improving exercise performance. To assess the separate contributions of these two factors to improved work capacity, 14 patients with implanted programmable VAT pacemakers were exercised according to the Bruce protocol, in three different pacing modes, selected in a random order and on a double blind basis: (a) VAT; (b) chest wall stimulation triggered ventricular (V-CWS-T) pacing, during which the pacemaker was programmed to VAT mode but driven externally using chest wall stimulation at rates fractionally above the patients' atrial rate, thereby providing a chronotropic response to exercise without atrioventricular synchronization; and (c) VOO mode at 70 beats per minute. There was a significant improvement in exercise performance in all patients during both VAT and V-CWS-T pacing as compared to VOO mode; the average increase in work capacity being similar: VAT: 44 +/- 31, (range, 12 to 140) percent and V-CWS-T; 40 +/- 24 (range, 5 to 85) percent. It is concluded that in patients with adaptive pacing systems, the chronotropic response is the major determinant of any improvement in exercise performance.