Comparison of various measures of optimum atrial timing in patients with dual chamber pacemakers: Superiority of mechanical compared to electrical intervals

Background: in patients with dual chamber pacemakers, the optimal AV delay is highly variable. This study examines the alternative measures of optimum atrial timing and the factors responsible for the marked variability in the optimal AV delay. Methods and results: Twelve patients with dual chamber pacemakers were studied. The AV delay was varied from 25 to 250 ms in 25-ms increments and at each stage, mitral, tricuspid, and aortic flows were recorded using the Doppler technique. The optimum AV delay varied from 75 to 175 ms (146 ± 37 ms). At optimum AV delay, both the E and A waves of the transmitral flow were partially fused, eliminating diastasis with a fusion velocity of 27 ± 14 cm/s. The stroke distance was lower when the E and A waves were not fused at shorter AVD, despite a longer diastolic filling period, or fully fused at a longer AVD, which also the shortened diastolic filling period. At optimum AV delay, the E/A velocity ratio was 0.74 ± 0.15, reflecting slight atrial predominance of LV filling. The optimum timing of atrial contraction was better defined in terms of its relation to LV ejection (175 ± 31 ms before LV ejection), and this had a smaller coefficient of variation than optimum AV delay. This interval, unlike the AV delay, was not affected by interatrial and interventricular conduction times. Conclusions: In this older population of patients with dual chamber pacemakers without significant valvular heart disease, the effective LA contraction in relation to LV ejection is a better measure of atrial timing than the programmed AV delay which is affected by atrial and ventricular conduction times.