CLINICAL EFFICACY OF SHOCK WAVE-FORMS AND LEAD CONFIGURATIONS FOR DEFIBRILLATION

A randomized, prospective comparison of the defibrillation efficacy of various shock waveforms and nonthoracotomy lead configurations was pe rformed in five distinct patient groups undergoing implantation of a c ardioverter defibrillator. In the first group using a bidirectional le ad configuration, there was no significant difference in the mean defi brillation threshold (DFT) between simultaneous and sequential monopha sic shocks (17.8 +/- 5.8 joules versus 17.3 +/- 2.7 joules). In the se cond group using a bidirectional lead configuration, the mean DFT was 21.9 +/- 7.3 joules with monophasic shocks and 14.9 +/- 5.0 joules wit h biphasic shocks (p < 0.001). In the third group using a unidirection al lead configuration, the mean DFT was significantly higher (p < 0.00 1) with monophasic shocks (22.1 +/- 4.2 joules) compared with biphasic shocks (15.0 +/- 5.4 joules). In the fourth group, an intraindividual comparison with monophasic shock waveforms showed no significant diff erences in DFT using either a bidirectional (21.3 +/- 5.8 joules) or a unidirectional (21.7 +/- 2.6 joules) lead configuration. In the fifth group, a simplified unipolar transvenous defibrillation lead system ( ''active can'') demonstrated significant lower DFTs (9.7 +/- 3.8 joule s) compared with a standardized unidirectional lead configuration (18. 0 +/- 6.8 joules). It is concluded that: (1) there seems to be no sign ificant difference in the DFT between simultaneous and sequential mono phasic shocks; (2) biphasic waveforms require significantly less energ y for defibrillation than their corresponding monophasic waveforms; an d (3) the unipolar single-electrode defibrillation system is easy to i mplant and provides DFTs at energies comparable with epicardial lead s ystems.