PREDICTORS OF LOSS OF ATRIOVENTRICULAR SYNCHRONY IN SINGLE-LEAD VDD PACING

Objective-To evaluate maintenance of proper VDD function, defined as p ersistence of sinus rhythm with atrial synchronous ventricular pacing, and to define factors predicting failure of the VDD mode in patients with atrioventricular (AV) block and normal sinus function. Design-Obs ervational study in 86 consecutive patients (mean (SD) age 74 (12) yea rs; 38 women, 48 men) with single lead VDD pacing systems (Intermedics Unity, n = 66, Medtronic Thera VDD, n = 20), implanted for high degre e AV block with documented normal sinus node. Pacemaker function was a ssessed by event counters, telemetric measurements, and Holter recordi ngs. Demographic, radiological, and pacing variables were correlated w ith loss of proper VDD function. Results-During a mean (SD) follow up of 10 (10) months (range 1-37), sinus rhythm and atrial triggered vent ricular pacing were maintained in 70 of 86 patients (81%). Atrial unde rsensing was observed in nine patients, lead migration in two, atrial fibrillation in three, and symptomatic sinus bradycardia in two. Univa riate predictors of loss of groper VDD function were: low position of the atrial dipole relative to the carina (greater than or equal to 6 c m; p < 0.01) during fluoroscopy; and maximum programmable atrial sensi tivity of the pacemaker (p = 0.03). Hn a multivariate analysis, only d ipole position remained predictive of outcome (p < 0.02). Not predicti ve: were sex, ape, symptoms before pacemaker implantation, cardiothora cic ratio or dilation of individual heart chambers on chest x ray, sid e of device implant, and P wave amplitude at implant. Conclusions-To m aintain proper VDD function ifs the long term, a low anatomical dipole position relative to the carina should be avoided. Electrical. guidan ce of dipole positioning does not seem to influence long term outcome.