Preserving normal ventricular activation versus atrioventricular delay optimization during pacing: The role of intrinsic atrioventricular conduction and pacing rate

The purpose of the study was to compare the effects of DDD pacing with opti mal AV delay and AAI pacing on the systolic and diastolic performance at re st in patients with prolonged intrinsic AV conduction (first-degree AV bloc k). We studied 17 patients (8 men, aged 69 +/- 9 years) with dual chamber p acemakers implanted for sick sinus syndrome in 15 patients and paroxysmal h igh degree AV block in 2 patients. Aortic flow and mitral flow were evaluat ed using Doppler echocardiography. Study protocol included the determinatio n of the optimal AV delay in the DDD mode and comparison between AAT and DD D with optimal AV delay for pacing rate 70/min and 90/min. Stimulus-R inter val during AAI (ARI) was 282 +/- 68 ms for rate 70/min and 330 +/- 98 ms fo r rate 90/min (P < 0.01). The optimal AV delay was 159 +/- 22 ms. AV delay optimization resulted in an increase of an aortic flow time velocity integr al (AFTVI) of 16% +/- 9 %. At rate 70/min the patients with ARI less than o r equal to 270 ms had higher AFTVI in AAI than in DDD ( 0.224 +/- 0.05 m vs 0.296 +/- 0.05 m, P < 0.01), while the patients with ARI > 270 ms demonstr ated greater AFTVI under DDD compared to AAI (0.192 +/- 0.03 m vs 0.166 +/- 0.02 m, P < 0.01). At rate 90/min AFTVI was higher during DDD than AAI (0. 183 +/- 0.03 m vs 0.162 +/- 0.03 m, P < 0.01). Mitral flow time velocity in tegral (MFTVI) at rate 70/min was higher in DDD than in AAI (0.189 +/- 0.05 m vs 0.173 +/- 0.05 m, P < 0.01), while at rate 90/min the difference was not significant in favor of DDD (0.149 +/- 0.05 m vs 0.258 +/- 0.04 m). The results suggest that in patients with first-degree AV block the relative i mpact of DDD and AAI pacing modes on the systolic performance depends on th e intrinsic AV conduction time and on pacing rate.