Quantitative analysis of Wenckebach behavior in DDD pacemakers

Wenckebach-type behavior in P-synchronous pacing modes allows a gradual transition into 2:1 block. As this behavior is dependent on precise timing intervals, it can be quantitated with mathematical equations. In this report, equations for quantitating the Wenckebach escape rate and the (N + 1)/N block points have been derived. These equations were then used to produce plots of Wenckebach escape rates for given AV intervals, atrial refractory periods, and atrial rates. These equations were validated utilizing a DDD pulse generator interfaced with a patient simulation device. The predicted values for the Wenckebach escape rate and ratio (n = 33) correlated highly with the observed values (r = 0.99, P less than 0.0001, and r = 0.97, P less than 0.0001, respectively) thereby validating the derived equations. This quantitative analysis has allowed a close look at the pacing behavior between the maximum tracking rate and the 2:1 block point. These equations may be clinically useful for assessing whether a nontriggering P wave resulted from Wenckebach type block or atrial undersensing and for the more complicated interval analysis in DDDR pacing with rate responsive AV delays and postventricular atrial refractory periods.