Tony W. Simmons

Automatic implantable cardioverter-defibrillator implantation without thoracotomy using an endocardial and submuscular patch system

The automatic cardioverter-defibrillator lead system is implanted by a thoracotomy procedure that may result in atelectasis, pleural effusion, cardiac tamponade and lengthy convalescence. A new defibrillator lead system that allows selection of different defibrillating current pathways is implanted without a thoracotomy. Ten patients requiring a cardioverter-defibrillator for recurrent sustained ventricular tachycardia (five patients) or aborted sudden cardiac death (five patients) were evaluated for implantation of this lead system. A lead configuration with a bidirectional defibrillating current pathway was implanted in nine patients. The defibrillation threshold with this lead configuration was 15 J in five patients, 20 J in three and 30 to 35 J in one patient. In the remaining patient the lead system had a 40 J defibrillation threshold and was not implanted. No perioperative complications occurred. Induced ventricular fibrillation was successfully terminated at the predischarge and intermediate follow-up (8 to 12 weeks) electrophysiologic studies. During the follow-up period, there were three deaths (one sudden, two due to heart failure) and two lead system failures (oversensing with inappropriate shocks in one patient and patch lead fracture in another). Implantation of the cardioverter-defibrillator lead system by a nonthoracotomy approach is feasible, has no significant perioperative complications and is well tolerated by patients. Effective defibrillation was demonstrated immediately as well as at intermediate follow-up study. The occurrence of patch lead fracture and oversensing requires improvement in the present (nonthoracotomy) lead system technology.

Continuous Right Ventricular Volume Assessment by Catheter Measurement of Impedance for Antitachycardia System Control

KHOURY, D., et al.: Continuous Right Ventricular Volume Assessment by Catheter Measurement of Impedance for Antitachycardia System Control Current implantable defibrillators are unable to differentiate between hemodynamically stable and unstable arrhythmias. This may result in unnecessary high energy shocks during arrhythmias that are better managed with other interventions. This study assessed the efficacy of the impedance catheter in sensing relative volumetric changes in the right ventricle as a measure of the hemodynamic status during an arrhythmia, During electrophysiological testing, 37 arrhythmias were induced in 12 patients aged 28–74 years. Rhythms recorded were: (A) hemodynomically stable tachyarrhythmias (supraventricular tachycardia and sustained monomorphic ventricular tachycardia)—21 episodes; and (B) hemodynamically unstable ventricular arrhythmias causing syncope (hypotensive ventricular tachycardia and ventricular fibrillation)—16 episodes. During unstable arrhythmias, stroke impedance (32 ± 17%), arterial systolic pressure (40 ± 11%), end right ventricular pulse pressure (15 ± 20%), expressed as percentages of corresponding sinus rhythm values, were significantly lower than in stable arrhythmias (84 ± 26%, 72 ± 8%, and 111 ± 37%, respectively); P < 0.001. There was a good correlation befween stroke impedance and mean arterial pressure during arrhythmia (r = 0.84). Impedance sensing is a practical method for distinguishing between hemodynamically stable and unstable arrhythmias. Implementation of hemodynamic sensing into the algorithm of future antitachycardia systems may improve the management of arrhythmias by adding options for selective pace termination or cardioversion.

The impedance catheter: potential for differentiation between hemodynamically stable and unstable arrhythmias

An assessment is made of the efficacy of the impedance catheter in sensing relative volumetric changes in the right ventricle as a means of monitoring the hemodynamic status during an arrhythmia. During electrophysiologic testing, 37 arrhythmias were induced in 12 patients. Stroke impedance (peak value minus minimum value) was significantly lower in hemodynamically unstable ventricular arrhythmias (ventricular tachycardia and ventricular fibrillation) than in stable tachyarrhythmias (supraventricular tachycardia and stable monomorphic ventricular tachycardia). Implementation of hemodynamic sensing can improve arrhythmia specificity of the sensing algorithm of future implantable defibrillators and may add options for selective pace termination or cardioversion.<<ETX>>