Bradycardia Pacing-Induced Short-Long-Short Sequences at the Onset of Ventricular TachyarrhythmiasA Possible Mechanism of Proarrhythmia?
Michael O. Sweeney, MD, FACC*,*,
Linda L. Ruetz, MS ,
Paul Belk, PhD,
Thomas J. Mullen, PhD,
James W. Johnson, MS and
Todd Sheldon, MS
* Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts
Medtronic, Inc., Minneapolis, Minnesota
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Figure 1 VVI/R
For pacing facilitated short-long-short (S-L-S), sinus rhythm is interrupted by a single ventricular premature depolarization (VPD) (coupling interval 700 ms, asterisk) ("short"). A 1,500-ms pause (bracket) ("long") is terminated by a single ventricular paced beat (VP) at the lower rate limit (40 beats/min). A VPD (coupling interval 440 ms) ("short") after the VP anticipates ventricular tachycardia (VT) that degenerated to ventricular fibrillation (VF) (not shown).
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Figure 2 DDD/R
For pacing facilitated S-L-S, the pacing rate approximates the lower programmed rate (1,000 ms). Intermittent far-field R-wave oversensing (AR) occurs after VPs. An atrial premature beat 250 ms after far-field R-wave (asterisk) is tracked, and a synchronized VP occurs at the upper limit of 500 ms ("short"). A 1,060-ms pause (bracket) ("long") follows, due to normal lower rate behavior. A VPD (610 ms) ("short") after the final VP anticipates VF onset. Abbreviations as in Figure 1.
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Figure 3 Managed Ventricular Pacing
For pacing facilitated S-L-S, a VPD (600-ms interval, asterisk) ("short") occurs almost simultaneously with an atrial pace (AP) (800-ms interval). The VPD is marked as a sensed event but, because it falls in the 80-ms cross-talk window, is not considered a true ventricular event. The next AP (800 ms) fulfills the criteria for an A-A interval without an intervening ventricular sense (VS) event, and a single VP is delivered ("long"). The pause (bracket) is only 830 ms, because of rate modulation. An early-coupled VPD (390 ms) ("short") anticipates VF onset. Abbreviations as in Figure 1.
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