We thank Drs Selvaraj and Chauhan for their interest in our work1 and discussion of the possible impact of white noise and respiration. We do not feel that white noise is a significant problem, although respiration (along with other physiological factors) may play a role, as emphasized in our report.

We used the “surrogate” analysis (ie, test of baseline stability) to control for white noise, respiration, movement, and other sources of artifacts. In addition, we removed noisy segments of data and used sectional (T-wave) averaging to …

Response to Letter Regarding Article, “Upsurge in T-Wave Alternans and Nonalternating Repolarization Instability Precedes Spontaneous Initiation of Ventricular Tachyarrhythmias in Humans”

Evaluation of beat-to-beat ventricular repolarization lability from standard 12‐lead ECG during acute myocardial ischemia

Measurement of T wave variability in body surface ECG

Nonalternans repolarization variability and arrhythmia – the calcium connection

BACKROUND T-wave alternans (TWA) is associated with ventricular tachycardia (VT). Nonalternans repolarization variability (NARV) precedes VT in certain experimental models, but its link to clinical arrhythmia is unproven. This study was conducted to determine if NARV increases prior to VT in patients with implantable cardioverter defibrillators (ICDs). METHODS TWA and NARV were calculated from shock-channel electrograms preceding onset of VT or non-VT events in patients with an ICD. In each patient, presence of both a VT and a non-VT event with the same QRS morphology before the event was required. Mixed linear model was used for data analysis, using heart rate (HR) and the number of analyzed beats as covariates. RESULTS Five hundred and sixty-eight events from 64 patients (males/females 51/13, 67 ± 13 years) were analyzed. HR preceding non-VT events was higher than before VT events (RR interval 595 ± 159 vs 706 ± 111 ms; P < 0.0001). Both TWA and NARV increased with increasing HR (P < 0.001). TWA decreased with increasing number of analyzed beats. When controlled for number of analyzed beats and HR, both TWA and NARV were higher before VT than before non-VT events (P < 0.002 and P < 0.0005, respectively). CONCLUSIONS NARV is elevated prior to spontaneous VT onset. Both NARV and TWA increase with HR. The decrease of TWA with increasing number of analyzed beats may indicate contamination with NARV or noise when only a small number of beats is available for analysis. NARV might be useful for VT prediction in the future.

Yuliya Krokhaleva

Papers

Increased Nonalternans Repolarization Variability Precedes Ventricular Tachycardia Onset in Patients with Implantable Defibrillators.