Re: The atrioventricular delay of cardiac resynchronization can be optimized hemodynamically during exercise and predicted from resting measurements.

Document Type



Internal Medicine (East Africa)


We read with interest the excellent study by Whinnett et al 1 in the March 2008 issue of Heart Rhythm in which they evaluated the effect of exercise on optimal AV delay programming using acute noninvasive hemodynamics. The authors quote previous work by Scharf et al 2 that unexpectedly demonstrated that hemodynamically optimized AV/VV delay increases with increasing heart rates and with exercise. This finding was not replicated by the authors, who discovered that only 8 of the 20 patients had an exercise optimal AV delay that was longer than the rest-optimized AV delay. A shorter optimal AV delay with exercise was identified in 11 patients.

The authors excluded patients who were pacing dependent, and in doing so they may have eliminated patients with severe AV conduction disease and those with chronotropic incompetence.

The intrinsic AV delay in patients without AV conduction disease can be expected to shorten physiologically in exercise. For this reason, it would be important to evaluate the effect of maintaining or lengthening the AV delay on the percent biventricular capture in the population studied. It is conceivable that hemodynamic worsening with increasing AV delay in some of the 11 patients reflected the “switching off” of biventricular pacing.

Likewise, it previously has been demonstrated that programming a rate-adaptive AV delay (i.e., shortening AV delay with exercise) in patients with severe chronic incompetence (>70% atrial pacing) provides an incremental benefit to exercise capacity, whereas the same effect is not seen in patients with less severe chronotropic incompetence. 3 It would be interesting to see data on the relationship between optimal exercise AV delay and the severity of chronotropic incompetence.


Heart Rhythm