Quantification of Ventricular Repolarization Fluctuations in Patients With Myocardial Infarction

The objective of this study was to quantify ventricular repolarization fluctuations in patients with myocardial infarction (MI) by a novel ECG waveform morphology based QT interval variability (QTV) measure. We analyzed recordings of 79 MI patients and 69 healthy control subjects included in the Physikalisch-Technische Bunde-sanstalt diagnostic ECG database. To characterize the QT interval waveform, we employed two-dimensional signal warping (2DSW). Based on the two-dimensional template adaptation to every beat, a novel parameter QTfluc has been developed to take into account complex QT interval's waveform fluctuations in time and amplitude. To demonstrate the power of QTfluc we (1) compared MI patients and healthy subjects and (2) examined the stability of various QTV measures including QTfluc in relation to QT interval boundary shifts. A comparison of QTfluc with standard QTV measures showed a significant improvement (ef-fect size increased up to 60 %) in discriminating between MI patients and healthy subjects. QT interval boundary shifts showed significant less impact (by factor 10) on the stability of QTfluc in comparison to standard QTV measures. The proposed measure showed significant improved characterization of ventricular repolarization lability in MI patients. Moreover, QTfluc showed more stable characteristics and is less dependent on QT interval boarders.