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Monomorphic ventricular tachycardia and ventricular extrasystoles have a specific exit site that can be localized using the multichannel surface electrocardiogram (ECG) and a database of paced ECG recordings. An algorithm is presented that improves on previous methods by providing a continuous estimate of the coordinates of the exit site instead of selecting one out of 25 predetermined segments. The accuracy improvement is greatest, and most useful, when adjacent pacing sites in individual patients are localized relative to each other. Important advantages of the new method are the objectivity and reproducibility of the localization results.

A QRS onset and offset detection algorithm has been developed for use in body surface QRS integral mapping of ventricular tachycardia. To determine QRS intervals, the algorithm uses two computed signals: the sum of the absolute values of the first derivatives of all leads and the sum of the absolute values of all leads. The second order derivative of the latter parameter is used to detect the time instants of QRS onset and offset. Using the algorithm, QRS integral maps are subsequently computed, which are correlated with a database of QRS integral maps in order to localize the site of origin of ventricular tachycardia. Comparison of the performance of the algorithm with visual evaluation by a human expert in this procedure revealed, in 95% of the cases, an identical or adjacent localization of the site of origin.

A design for patient isolation in 64-channel ECG recordings is presented. Small dimensions of the isolated section and the use of an optical fiber as the only connection between the isolated section and the grounded section of the measurement system ensured a minimal capacitance between the patient and the environment. The consistent low-power design of the isolated section resulted in a power consumption of 210 mW, which enabled a 10 h continuous operating time of the battery powered isolated section. The system handles 64 signals with a dynamic range of 75 dB. Analog to digital conversion is performed in the isolated section with a sample rate of 1 kHz per channel. The receiver interfaces to a commercially available DMA board for a standard personal computer.