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Ventricular fibrillation threshold: Influence of the type of electrical stimulus

Abstract:

The objective of this work was to reassess the possible influences of the type of stimuli employed to determine the ventricular fibrillatory threshold (VFT). Three types of stimulation modes were applied in 11 mongrel dogs: 1) A train of rectangular pulses (TP) for 1 s, at 50 Hz, with 2 ms pulse width, not synchronized to the ECG; 2) A 5 ms single pulse (SP), synchronized to the ECG R-wave; and 3) A 5 ms single pulse (S2) synchronized with a previous pacemaker train (S1) of 10 pulses. Two direct stimulating leads were applied: a bipolar internal (Ei) and two external hook electrodes (Ee). For either electrode lead, the differences between S2-TP (S2Ei = 21.8 mA, SD = 4.6, TPEi = 2.0 mA, SD = 0.8; S2Ee = 14.9 mA, SD = 5.8; TPEe = 0.9 mA, SD = 0.4) and SP-TP (SPEi = 17.1 mA, SD = 5.6, SPEe = 14.3 mA, SD = 3.5) were statistically significant (P < 0.001). In all three stimulation modes the mean values, using Ei arrangements, were higher than those obtained with Ee. These results show a higher vulnerability of the ventricles to an unsynchronized train of pulses than to single pulses, either with or without previous pacing. In conclusion, these stimulation modes (SP, TP, S2) can be used to evaluate the VFT. Single pulses, however, are more suitable for the research laboratory. © 1987, Quest Publishing Co.