Use of automatic mode change between DDD and AAI to facilitate native atrioventricular conduction in patients with sick sinus syndrome or transient atrioventricular block.

The benefits of the automatic DDD (DDD/AMC) mode in the Chorus II pacemaker (Chorus 6234; Ela Medical Inc.), which automatically switches the modes between DDD and AAI to respect spontaneous AV conduction as much as possible in AAI while preserving safety pacing in DDD during paroxysmal AV block (AVB) only, remain unproven. This study examined the functions of the DDD/AMC mode in 12 patients with sick sinus syndrome (SSS; n = 10) or paroxysmal complete AVB (n = 2). A short-term (24 hours) comparative study between simple DDD mode and the DDD/AMC mode was performed in 8 of the 12 patients, and a medium-term (55.2 +/- 54.6 days) follow-up of the DDD/AMC mode was completed in all 12 patients. A comparative pair of 24-hour surface Holter ECGs was obtained in 6 of the 8 patients in the short-term study. Telemetry and built-in Holter histograms were collected in the outpatient clinic in all 12 patients. Although the percentage atrial pacing of the telemetry increased from 59.2 +/- 35.4 in DDD to 70.4 +/- 31.8 in DDD/AMC (P < 0.009; n = 8), the percentage ventricular pacing decreased from 64.6 +/- 37.7 in DDD to 36.2 +/- 43.1 in DDD/AMC (P < 0.027) in the short-term study. In particular, the reduction of percentage ventricular pacing to < 10% was observed in four patients with SSS not associated with > or = first-degree (1 degree) AVB on preoperative ECGs. Between the two modes a significant difference in arrhythmic events was not observed by the 24-hour surface Holter ECGS taken from the six patients in the short-term study. AAI-DDD switching associated with automatic modulation of AV delay and AV hysteresis occurred in all patients in the medium-term study. From the medium-term study, the total AV delay (AV delay plus AV hysteresis) exceeded 300 ms in 6 of the 12 patients in DDD/AMC, and usually became longest during nighttime. From the short- or medium-term study in the 12 patients, two patients preferred the DDD/AMC mode while one preferred the DDD mode. These results suggest that the DDD/AMC mode is useful, at least in SSS patients without > or = 1 degree AVB, by reducing the percentage ventricular pacing.