Changes in the QT interval and its adaptation to rate, assessed with continuous electrocardiographic recordings in patients with ventricular fibrillation, as compared to normal individuals without arrhythmias

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Abstract
Various QT interval variables and heart rate variability parameters were studied in six patients with ventricular fibrillation but without heart disease and compared with findings in 21 normal persons. QT and QT dispersion (QTd) were measured from conventional 12 lead ECGs; for dynamic QT analysis, QT intervals were automatically measured to the end of the T wave (QTe) on a 24 h ECG recording. The adaptation of the QT interval to changes in heart rate was expressed as the slope of the linear regression lines relating QTe to the RR interval (Se). The complete 24 h ECG recording and four 6 h segments were studied (morning, day, evening, and night). Ventricular fibrillation patients had slightly prolonged QTmax intervals on the 12 lead ECG, QT dispersion was longer in ventricular fibrillation patients than in normal persons (88±29 ms vs 59±26 ms, pp<0·05). In conclusion, patients with ventricular fibrillation but without underlying structural heart disease have normal heart rate variability parameters. However, abnormal re-polarization behaviour, characterized by an increased QTd and a depressed adaptation of QT to variations in RR (especially during the night and the morning), is present. These findings may help to understand and treat arrhythmias in this patient group.

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