Do the effects of antiarrhythmic drugs on defibrillation efficacy vary among different shock waveforms?
This study was designed to extend our knowledge on how pharmacological modification of defibrillation efficacy is associated with shock waveform. In 35 anesthetized dogs, the baseline transcardiac DFT was determined using 12-ms monophasic and three biphasic waveforms (10 ms-2 ms, 8 ms-4 ms, and 6 ms-6 ms). Twenty-eight dogs were then treated with either lidocaine (n = 7), mexiletine (n = 7), dofetilide (n = 7), or MS-551 (n = 7), while 7 dogs were left untreated to confirm the reproducibility of DFT data. Subsequently, DFT measurements were repeated in all dogs. Waveform related differences of the baseline DFT were significant, and the monophasic DFT was higher than any of the biphasic DFTs. Lidocaine increased DFT by 11% +/- 12% (12-ms monophasic), 20% +/- 20% (10 ms-2 ms, P < 0.05), 13% +/- 20% (8 ms-4 ms), and 12% +/- 10% (6 ms-6 ms, P < 0.05). With infusion of mexiletine, the DFT increased by 17% +/- 16% (P < 0.05), 9% +/- 12%, 10% +/- 10% (P < 0.05), and 4% +/- 15%, respectively.
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