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(Circulation. 1999;100:1887-1893.)
© 1999 American Heart Association, Inc.

Clinical Investigation and Reports

Demonstration of the Proarrhythmic Preconditioning of Single Premature Extrastimuli by Use of the Magnitude, Phase, and Distribution of Repolarization Alternans

Presented in part in the Samuel A. Levine Young Investigator Award Competition of the 71st Scientific Sessions of the American Heart Association, Dallas, Tex, November 8, 1998, and published in abstract form (Circulation. 1998;98[suppl I]:I-M, I-27).

Sanjiv M. Narayan, MB, CHB, MD, MS, MRCP; Bruce D. Lindsay, MD; Joseph M. Smith, MD, PhD

From the Division of Cardiology/Electrophysiology, Washington University School of Medicine, St. Louis, Mo.

Correspondence to Dr Sanjiv M. Narayan, Division of Cardiology/Electrophysiology, Campus Box 8086, Washington University School of Medicine, 660 S Euclid Ave, St. Louis, MO 63110. E-mail snarayan{at}im.wustl.edu

Background—We hypothesized that single premature extrastimuli (S₂) insufficient to induce reentry produce proarrhythmic effects (proarrhythmic preconditioning) that are measurable by use of the magnitude, phase, and temporal distribution of repolarization alternans (RPA; alternate-beat fluctuations in ECG repolarization).

Methods and Results—Before programmed electrical stimulation (PES), surface ECG leads I, aVF, and V₁ were recorded in 30 patients during simultaneous atrial and ventricular pacing at 500 ms with S₂ coupling intervals (CIs) decreasing from 400 to 240 ms in 20-ms steps. We determined RPA magnitude (V_alt) as the 0.5-cycle/beat peak after spectral decomposition of consecutive STU intervals over 64 beats immediately preceding and following each S₂, RPA phase reversals as discontinuities in the even/odd phase of STU alternation, and RPA distribution as the time point of median RPA magnitude within repolarization. Eighteen patients were induced into ventricular tachycardia (VT), whereas 12 were not. Extrastimuli dynamically modulated each characteristic of RPA. S₂ augmented V_alt in inducible (8.2±2.3 versus 6.2±1.6 µV; P=0.003) but not noninducible patients. S₂ reversed RPA phase more in inducible than in noninducible patients (56.7% versus 45.3%; P=0.02 by ²), particularly when CI was 300 ms (66.3% versus 46.5%; P=0.006). Finally, S₂ redistributed RPA significantly later within repolarization in inducible patients. Each effect was more marked for CI 300 ms.

Conclusions—A single S₂ increases RPA magnitude, reverses its phase, and redistributes it later in repolarization in patients with the substrates for VT. These effects become more pronounced with shorter coupling intervals. These results suggest that it is possible to track the dynamic proarrhythmic preconditioning of single premature depolarizations.

Key Words: tachyarrhythmias • pacing • computers • waves • depolarizing • death, sudden

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