High Ouput Pacing: Effects on QRS Duration

D.F. Ortega, R. Chirife, L. D. Barja, G. Pellegrino, R. Laino, A. Giniger.

Abstract
Background: Several pacing methods have been proposed to improve biventricular resynchronization, aimed at enhancing cardiac performance or for prevention of tachyarrhythmia. Of these, multi-site cardiac pacing has been shown to reduce QRS duration. Also, pacing at standard output (4 to 5 v) appears to have some protective effect on induction of tachycardia as compared to pacing at twice threshold, during programmed ventricular stimulation. In the present study, the effect of a single-lead, large virtual electrode resulting from high output pacing (HOP) on QRS duration was explored. It was hypothesized that more synchronous myofibril recruitment from both right and left ventricle may be achieved, causing a narrowing of total QRS duration.
Methods Eleven consecutive patients (Pts) (45% females), undergoing routine EP testing were included in this feasibility study. Age ranged from 56 to 91 years (mean 74 years). A standard EP pacing lead (bipolar configuration) was placed at the apex of the RV. VVI pacing was switched from normal output pacing (NOP) of 4 volt, 0.5 ms to HOP (34 Volt, 1 ms) and vice-versa, at identical rates, for 20 to 50 beats each time. Two operators measured and averaged at least 20 beats for each output in every patient, using digitized waveforms and a commercial program.
Results HOP caused QRS narrowing in all Pts, with a mean shortening of 18 ms +/- 8 SD. QRS duration during NOP averaged 192 Ms +/- 24 SD, and HOP shortened it to 174 ms +/- 25 SD (P< 0.001). HOP caused important chest discomfort in 2 Pts, moderate in 2 and very mild or none in the rest.
Conclusions: Single-lead HOP decreased QRS duration in all Pts, suggesting improvement in biventricular synchronization. This may be the result of a large virtual electrode.

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