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CLINICAL RESEARCH: HEART RHYTHM DISORDER

Bradycardia Pacing-Induced Short-Long-Short Sequences at the Onset of Ventricular Tachyarrhythmias

A Possible Mechanism of Proarrhythmia?

Michael O. Sweeney, MD, FACC^_*,1,_*, 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.

Manuscript received January 11, 2007; revised manuscript received February 5, 2007, accepted February 5, 2007.

^_* Reprint requests and correspondence: Dr. Michael O. Sweeney, Cardiac Arrhythmia Service Brigham and Women’s Hospital, 75 Francis Street, Boston, Massachusetts 02115. (Email: mosweeney{at}partners.org).

Objectives: The purpose of this study was to characterize interactions between normal pacing system operation and the initiating sequence of ventricular tachycardia (VT)/ventricular fibrillation (VF).

Background: Abrupt changes in ventricular cycle lengths (short-long-short, S-L-S) might initiate VT/VF. The S-L-S sequences might be passively permitted or actively facilitated by bradycardia pacing.

Methods: Initiating sequences of 1,356 VT/VF episodes in the PainFree Rx II (n = 634) and EnTrust Trial (n = 421) were analyzed with stored electrograms and by pacing mode (DDD/R, VVI/R, and Managed Ventricular Pacing [MVP]). Interactions between pacing and VT/VF initiation were classified as: non-pacing associated, pacing associated, pacing permitted, and pacing facilitated.

Results: Non-pacing associated (no pacing, no S-L-S) and pacing associated (ventricular pacing without S-L-S) onset accounted for 44.0% and 29.8% of all VT/VF, respectively. Pacing permitted (S-L-S sequences without ventricular pacing) episodes accounted for 6.4% (DDD/R), 20.0% (MVP), and 25.6% (VVI/R) of 1,356 VT/VF episodes. Pacing facilitated onset (S-L-S sequences actively facilitated by ventricular pacing including the terminal beat after a pause) accounted for 8.2% (MVP), 9.4% (VVI/R), and 14.8% (DDD/R) of 1,356 VT/VF episodes. Pacing facilitated S-L-S VT/VF occurred in 2.6% (MVP), 3.3% (VVI/R), and 5.2% (DDD/R) of patients with episodes and was the sole initiating sequence in approximately 1% of patients. Pause durations during pacing facilitated S-L-S differed between modes (DDD/R 793 ± 172 ms vs. MVP 865 ± 278 ms vs. VVI/R 1180 ± 414 ms, p = 0.002). The majority of these episodes were monomorphic VT.

Conclusions: Ventricular tachycardia/VF in some implantable cardioverter-defibrillator patients might be initiated by S-L-S sequences that are actively facilitated by bradycardia pacing operation and might constitute an important mechanism of ventricular proarrhythmia.

Abbreviations and Acronyms   AP = atrial pace   APD = atrial premature depolarization   AV = atrioventricular   CL = cycle length   EGM = electrogram   ICD = implantable cardioverter-defibrillator   MMVT = monomorphic ventricular tachycardia   MVP = Managed Ventricular Pacing   RVA = right ventricular apical   S-L-S = short-long-short   VF = ventricular fibrillation   VP = ventricular paced beat   VPD = ventricular premature depolarization   VT = ventricular tachycardia

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