Session S93.3

Potential Confounding Effect of Heart Rate on T-Wave Morphology Can Affect the Measurement of Ventricular Instability

JP Couderc*

University of Rochester
Rochester, NY, USA

Background: An increasing number of clinical investigations have revealed enhanced risk for ventricular arrhythmias and sudden cardiac death in cardiac patients with increased repolarization variability. Current ECG technologies measuring repolarization instability rely on T-wave morphology rather than QT interval because of the latter’s lack of robustness to noise. While autonomic nervous system regulation (ANS) plays a predominant contributing role to beat-to-beat variability, it is expected that repolarization instability is dependent on heart rate too, yet there is limited description of the effect of the heart rate on the cardiac ventricular repolarization morphology.
Method: We evaluated the heart rate dependency of QT interval and T-amplitude in Holter recordings from 37 healthy individuals (29% females, 28±8 yrs). Based on an algorithm developed for automatic measurement of the repolarization signal, we implemented a RR-bin analysis to estimate the level of changes of repolarization morphology across normal ambulatory heart ranges.
Results: In these healthy individuals, T-wave amplitude was 0.41±0.15 mV, RR=784±72 msec and QTc=399±16msec. As expected, we found a significant relationship between QT and RR intervals (0.12±0.04, p<0.05) but also observed a statistically significant relationship between T-wave amplitude and heart rate (0.55±0.29 µV/ms, p<0.05) emphasizing the need for designing repolarization variability method independent of T-wave amplitude.
Conclusion: The challenges associated with the measurements of repolarization variability when measured from the surface electrocardiogram requires control for the effect of heart rate on both ventricular repolarization duration (QT) and its amplitude.

(Abstract Control Number: 9)