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CLINICAL STUDIES

Exploiting rate-related hysteresis in repolarization alternans to improve risk stratification for ventricular tachycardia

^a Division of Cardiology/Electrophysiology, Washington University School of Medicine, St. Louis, Missouri, USA

Manuscript received March 19, 1999; revised manuscript received October 20, 1999, accepted January 20, 2000.

Reprint requests and correspondence: Dr. Sanjiv M. Narayan, Division of Cardiology/Electrophysiology, Washington University School of Medicine, Box 8086, 660 South Euclid Avenue, St. Louis, Missouri 63110
snarayan{at}im.wustl.edu

OBJECTIVES

We sought to study the effect of heart rate acceleration and deceleration on the ability of repolarization alternans (RPA) to stratify ventricular tachycardia (VT) risk.

BACKGROUND

Heart rate fluctuations alter arrhythmic propensity, yet it is unclear whether fluctuations, as well as absolute rate, dynamically increase VT risk. We hypothesized that repolarization heterogeneity reflected by RPA would exhibit hysteresis during rising and falling heart rate, which may reflect arrhythmic propensity.

METHODS

The RPA magnitude (absolute voltage of alternation [V_alt] and T-wave alternans ratio [TWAR]) and temporal distribution were determined from the electrocardiogram (ECG) in 60 patients during paced heart rate acceleration from 100 to 150 beats/min, then deceleration to 100 beats/min at electrophysiologic study (EPS). The V_alt and TWAR thresholds were varied prospectively to generate receiver-operating characteristics (ROC) for the prediction of inducible VT at EPS.

RESULTS

Thirty-six patients were induced into VT and 24 were not. Hysteresis of RPA was seen. The V_alt reached steady-state within 60 beats of each rate transition and was higher in deceleration than in acceleration at matched heart rates. In induced patients, V_alt rose then fell with heart rate. In noninduced patients, V_alt was insensitive to acceleration, but rose on initial deceleration. The RPA distributed later within repolarization in induced patients but, on deceleration, moved earlier in both groups. By ROC analysis, V_alt = 2.6 µV in late repolarization at 120 beats/min provided optimal sensitivity and specificity for VT in acceleration (87.5% and 88.7%, respectively) versus deceleration (80% and 62.5%, respectively; p = 0.004, chi-square test).

CONCLUSIONS

1) Physiologic fluctuations in heart rate may affect the clinical utility of RPA for VT risk stratification; and 2) repolarization dispersion measured by RPA is more exaggerated during deceleration than acceleration at matched heart rates (rate hysteresis).

Abbreviations and Acronyms   APD = action potential duration   CL = cycle length   DI = diastolic interval   EPS = electrophysiologic study   PES = programmed electrical stimulation (of the ventricle)   ROC = receiver-operating characteristics   RPA = repolarization alternans   TWAR = T-wave alternans ratio   VT = ventricular tachycardia   Valt = absolute voltage of alternation (in µV)

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