What is the minimum ECG length to quantify beat-to-beat variability of repolarization morphology?

Beat-to-beat changes in ventricular repolarization are associated with increased vulnerability to ventricular arrhythmias. Beat-to-beat repolarization variability (RV) is usually measured by computing consecutive QT or RT intervals, which strongly depend on the definition of the T-wave endpoints. In this study we describe our new method for measuring RV based on the morphological analysis of the repolarization segment and determine the minimal ECG length needed to quantify RV. RV was analyzed in 42 ischemic cardiomyopathy patients. For each one, we analyzed ECGs of 8, 16, 32, 64, 96 and 128 consecutive beats from Holter ECG recordings. We found that our method provides a new approach to quantify RV without the need to identify T- wave endpoints. In addition, both long-term and short-term ECGs can be used to defect RV, but only long-term ECGs provide information about time changes of the RV signal.