Pacing thresholds for cathodal and anodal high-frequency monophasic pulses
Introduction: The purpose of this study was to investigate ventricular pacing with bursts of high-frequency monophasic pulses using mathematical modeling and animal experiments. The study concentrated on the dependence of anodal and cathodal thresholds on the frequency of the stimulus. Methods and Results: The stimulus had the form of a 2-msec burst of rectangular, constant-current pulses, with 50% duty cycle and frequency from 0.5 to 10 kHz. The thresholds were determined for bursts of both polarities, and strength-frequency curves were drawn. Computer simulations were initially performed with a one-dimensional model of the cardiac strand in which cells were coupled by a pure resistivity. The model predicted that the cathodal curve should rise and then level off for frequencies higher than 2-4 kHz; in contrast, the anodal curve, after initially rising with frequency, should end at 3 kHz. Above this frequency the strand could not be stimulated. Animal experiments performed to verify these predictions only partially agreed with the model. For both polarities, the myocardium responded to pacing up to 10 kHz, and both cathodal and anodal thresholds leveled off for frequencies higher than 2-4 kHz. To account for the experimental results, the model was modified by introducing capacitive coupling between cells. The junctional capacitance that gave the best agreement of modeling and experimental data was 130-160 pF (74-91 μF/cm2). Conclusion: The study suggests that pacing with bursts of high-frequency monophasic pulses relies on the capacitive path between cells and that theoretical studies of this type of stimulation should account for the junctional capacitance.
Krassowska, W; Rollins, DL; Wolf, PD; Dixon, EG; Pilkington, TC; Ideker, RE
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