EFFECTS OF HIGH AND LOW SHOCK ENERGIES ON SINUS ELECTROGRAMS RECORDEDVIA INTEGRATED AND TRUE BIPOLAR NONTHORACOTOMY LEAD SYSTEMS

Introduction: The purpose of this investigation was to prospectively e valuate the voltage- and time-dependent characteristics of a biphasic defibrillator discharge on the amplitude of the rate sensing electrogr am recorded from two ''integrated'' and one true bipolar nonthoracotom y lead system. Prolongation of redetection time has been noted after a failed first shock with nonthoracotomy lead systems. However, a prosp ective evaluation of the time- and voltage-dependent effects of biphas ic shocks on electrogram amplitude with clinically utilized lead syste ms has not been systematically performed. Methods and Results: Five- t hen 30-J R wave synchronous biphasic discharges were delivered during the supraventricular rhythm through three nonthoracotomy lead systems (Medtronic Transvene, Ventritex TVL, and CPI Endotak C 60 Series). The R wave amplitude was measured immediately postshock and for up to 1 m inute. Amplitude changes were compared with preshock baseline value. A 5-J discharge had minimal effect on the R wave amplitude recorded fro m the three lead systems; however, 30 J resulted in significant diminu tion in R wave amplitude recorded from the integrated bipolar leads (i n the Endotak lead to a greater extent than the TVL lead) with minimal effects on the Transvene lead. Following a 30-J discharge, the time c onstant for R wave recovery was 4.2, 14.9, and 153 seconds for Transve ne, TVL, and Endotak 60 leads, respectively. Conclusion: There are vol tage- and time-dependent reductions in postshock R wave amplitude. Int egrated bipolar systems appear more affected than the ''true'' bipolar lead evaluated. This may be due, in part, to lead design, distance of distal defibrillating surface from rate sensing cathode, and the inco rporation of the defibrillating surface as the rate sensing anode. The influence of postshock R wave diminution on subsequent redetection re mains speculative but may have implications for subsequent lead develo pment.