Haemodynamic advantage with single chamber rate responsive pacemakers over dual chamber pacemakers during exercise in chronotropic incompetence.

ABSTRACT

Sequential cardiac chamber activation and chronotropic response are amongst the important determinants of cardiac performance. This study compared VVIR mode with DDD and VVI mode to assess the contribution of these two factors in the determination of cardiac performance during exercise. Ten patients with a mean age of 68 +/- 5 years were studied during 1988-90, who had complete heart block and sinus node dysfunction with a mean LV ejection fraction of 51.5 +/- 6.25%. Five patients had DDD pacemakers and the rest had VVIR pacemakers. Patients were exercised first in VVI mode followed by either DDD or VVIR mode. Exercise duration, maximum rate pressure product, exercise capacity and cardiac output were measured with graded treadmill test in Bruce protocol. There was remarkable increase in the exercise duration (P < 0.001) and the maximum rate pressure product (P < 0.001) in patients with VVIR as compared to DDD and VVI mode. In DDD mode, as compared to VVI mode, this increase was less remarkable, though statistically significant (P < 0.005). Therefore, it is concluded that patients with chronotropic incompetence as well as complete heart block do better during dynamic exercise when they have VVIR mode compared to VVI or DDD mode.