Role of a catheter lead system for transvenous countershock and pacing during electrophysiologic tests: An assessment of the usefulness of catheter shocks for terminating ventricular tachyarrhythmias

The practicality and safety of using a single catheter system for transvenous countershock, programmed stimulation and ventricular pacing during electrophysiologic tests were evaluated in 13 patients with inducible sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). The efficacy and patient toleration of transvenous countershock were compared with other methods of arrhythmia termination. The same lead was used for programmed stimulation at the right ventricular apex and for VT termination by pacing methods during serial testing (20 ± 15 days [mean ± standard deviation]). Synchronized countershock using energies that patients found tolerable (0.01 to 5 J) terminated 31 of 50 episodes (62%) of induced VT. Episodes of VT cardioverted with these low energies were distinguished from other episodes by a longer cycle length (352 ± 62 ms versus 297 ± 50 ms, p < 0.004). Among paired episodes of VT matched for patient, date of induction, morphologic characteristics, cycle length and drugs administered, pacing methods (single extrastimuli and bursts of rapid pacing) were just as effective as low-energy countershock for VT termination (25 of 25 versus 21 of 25, difference not significant). Transvenous countershock was uniformly effective for termination of ventricular flutter and VF when sufficient energy was used (range 5 to 30 J, mean 20.4 ± 7.7). This required interfacing leads to a defibrillation unit. VT acceleration occurred during 7 of 50 synchronized low-energy cardioversion attempts (14%). There was no evidence of myocardial injury as a result of shocks as high as 30 J, but patients required increasing sedation when energy exceeded 0.5 J. Thus, a single catheter system can be used for programmed stimulation, ventricular pacing and countershock during electrophysiologic tests. Low-energy countershock (0.01 to 5 J) is no more effective than pacing methods for VT termination and is tolerated less well. The most practical use of this catheter system, including any implantable unit, may be for slightly higher energy (5 to 30 J) countershock termination of repeated episodes of very rapid VT or VF, in which pacing techniques are ineffective. This method may be safer and less traumatic than conventional transthoracic countershock.