Y. Murakawa et al., EFFECTS OF A CLASS-III ANTIARRHYTHMIC DRUG AND BIPHASIC SHOCKS ON THEPOSTDEFIBRILLATION REFRACTORY PERIOD OF RELATIVELY REFRACTORY MYOCARDIUM, Journal of cardiovascular electrophysiology, 7(7), 1996, pp. 603-611
Introduction: This study was designed to test whether the refractory s
tate of nondepolarized myocardium is a major determinant of electrical
defibrillation.Methods and Results: Postshock recovery interval (PSRI
) was estimated by measuring the residual refractory period after an a
ppropriately timed field stimulus (1 to 16 V). The PSRI and transcardi
ac defibrillation threshold (DFT) were compared before and during the
administration of E-4031, a new Class III antiarrhythmic drug (group 1
, n = 10), or between monophasic and biphasic shocks (group 2, n = 14)
in anesthetized open chest dogs. Group 1: E-4031 reduced the DFT from
2.6 +/- 0.6 J to 1.8 +/- 0.6 J (P < 0.01). The PSRI increased with th
e increase of the applied voltage and was almost always greater during
E-4031 infusion than at baseline. There was an inverse correlation be
tween the changes of DFT and PSRI measured with a 14-V stimulus (r = -
0.80, P < 0.01) and a 16-V stimulus (r = -0.80, P < 0.01), Group 2: Me
an DFTs were not statistically different between the two waveforms (3.
3 +/- 1.0 J vs 2.9 +/- 1.4 J). However, there also was an inverse corr
elation between the differences in individual PSRIs and DFTs of the tw
o waveforms (10-V stimulus: r = -0.62, P < 0.05; 16-V stimulus: r = -0
.75, P < 0.01). Conclusions: Modulation of defibrillation efficiency b
y E-4031 infusion or by changes of the shock waveform was related to t
he effect of these interventions on PSRI. These results suggest an ind
ependent role for the refractoriness of nondepolarized myocardium in t
he mechanism of defibrillation.