The effects of applied voltage and phase of respiration on impedance of pathways used by implantable cardioverter-defibrillators were investigated. Patients were studied at implantation of cardioverter-defibrillators using epicardial (n = 12) or transvenous and subcutaneous (SQ) (n = 30) electrodes. Transvenous-SQ pathways were right ventricular cathode to SQ anode and coronary sinus cathode to SQ anode. Transvenoustransvenous pathways were right ventricle to coronary sinus and right ventricle to superior vena cava. Patients with nonthoracotomy electrode systems were studied at end-expiration and end-Inspiration. Five shocks of 65 to 745 V (0.2 to 34 J) were given in random order in sinus rhythm. Over this range, end-expiratory impedance decreased monotonically for all pathways. This effect was greatest for transvenous-SQ pathways (13 ± 3% to 17 ± 4%, p <0.001), intennediate for transvenous-transvenous pathways (5 ± 4% to 8 ± 5%, p <0.001), and least for epicardial pathways (3 ± 3%, p = 0.006). Paired data in inspiration and expiration showed that inspiration increased impedance in transvenous-SQ pathways (p <0.001) but not in transvenous~transvenous pathways. Further, the effects of respiration and voltages on impedance in transvenous-SQ pathways were interactive (p <0.001): Inspiration increased voltage-dependence of impedance. The magnitude of the inverse relationship between voltage and impedance depends on type of defibrillation pathway. The effect of respiration on impedance suggests that voltage-dependence of impedance is greatest in the lungs. These findings have potential relevance for introoperative testing of cardioverter-defibrillators and selection of pathways for low-energy cardioversion.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine