| Popis: |
The efficacy and safety of a new defibrillating current waveform, consisting of a low-tilt 5 ms trapezoidal pulse followed closely by a second identical pulse of opposite polarity, was tested m seven isolated, perfused, working canine hearts suspended in an isoresistive, isosmotic shock bath at 37 oC. The efficacy and safety of the reciprocal pulse was compared with a single 5 ms pulse, a single 10 ms pulse, and a dual (unidirectional) 5 ms pulse waveform. The mean threshold average current densities for the 5 ms single pulse, 10 ms single pulse, dual 5 ms pulse, and reciprocal pulse (absolute values) were 50, 38, 36, and 37 mA/cm2, respectively. The corresponding mean threshold energy densities in the shock bath were 2.8, 2.9, 2.9, and 3.1 mJ/cm3. Despite the differences in threshold current density among the waveforms, no differences in safety factor (shock strength for 50 per cent post-shock depression, divided by threshold shock strength) were found among the waveforms. The current safety factors were 5.4, 5.4, 5.6, and 5.5 for the 5 ms single pulse, 10 ms single pulse, dual unidirectional pulse and reciprocal pulse, respectively. The corresponding energy density safety factors were 25, 27, 29, and 27. Thus the use of this reciprocal pulse waveform provides no advantage in efficacy or safety over waveforms of the same total duration. |
