EFFECTS OF VOLTAGE AND RESPIRATION ON IMPEDANCE IN NONTHORACOTOMY DEFIBRILLATION PATHWAYS

The effects of applied voltage and phase of respiration on impedance o f pathways used by implantable cardioverter-defibrillators were invest igated. Patients were studied at implantation of cardioverter-defibril lators using epicardial (n = 12) or transvenous and subcutaneous (SQ) (n = 30) electrodes. Transvenous-SQ pathways were right ventricular ca thode to SQ anode and coronary sinus cathode to SQ anode. Transvenous- transvenous pathways were right ventricle to coronary sinus and right ventricle to superior vena cava. Patients with nonthoracotomy electrod e systems were studied at end-expiration and end-inspiration. Five sho cks of 65 to 745 V (0.2 to 34 J) were given in random order in sinus r hythm. Over this range, end-expiratory impedance decreased monotonical ly for all pathways. This effect was greatest for transvenous-SQ pathw ays (13 +/- 3% to 17 +/- 4%, p <0.001), intermediate for transvenous-t ransvenous pathways (5 +/- 4% to 8 +/- 5%, p <0.001), and least for ep icardial pathways (3 +/- 3%, p = 0.006). Paired data in inspiration an d expiration showed that inspiration increased impedance in transvenou s-SQ pathways (p <0.001) but not in transvenous-transvenous pathways. Further, the effects of respiration and voltage on impedance in transv enous-SQ pathways were interactive (p <0.001): Inspiration increased v oltage-dependence of impedance. The magnitude of the inverse relations hip between voltage and impedance depends on type of defibrillation pa thway. The effect of respiration on impedance suggests that voltage-de pendence of impedance is greatest in the lungs. These findings have po tential relevance for intraoperative testing of cardioverter-defibrill ators and selection of pathways for low-energy cardioversion.