Novel Quantitative Evaluation of Beat-To-Beat Variability of Ventricular Repolarization Using Poincaré Plot Method

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Background: Although it is well known about the beat-to-beat variability of ventricular repolarization, the quantitative evaluation method has not been still established. To assess the beat-to-beat variability of ventricular repolarization, we investigated the beat-to-beat variability of QT interval (BVR). Methods: An electrocardiography at rest was obtained in 26 normal subjects and 25 patients with any heart diseases such as paroxysmal atrial fibrillation, hypertension, ischemic heart disease, or heart failure. The QT interval was measured automatically using wavelet transformation method, and the Poincare plot graph was constructed using QTn and QTn+1 during consecutive 50 normal sinus beats. The BVR was expressed as a long-term variability (LTV) and a short-term variability (STV) in the Poincare plot graph. Results: The Poincare plot graph could be constructed clearly in all cases. Both LTV and STV were significantly longer in patients with any heart diseases compared with normal subjects (LTV; 6.7±5.0 vs 3.8±1.9 msec, STV; 6.4±5.3 vs 2.8±1.3 msec). Conclusion: This study demonstrates that patients with heart diseases have a large BVR compared with normal subjects, since LTV and STV were significantly longer in those patients. This shows that the BVR using the Poincare plot graph may be useful to evaluate beat-to-beat variability of ventricular repolarization abnormality quantitatively.