title: Effects of voltage and respiration on impedance in nonthoracotomy defibrillation pathways.
abstract: 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. Transvenous-transvenous 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), intermediate 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 voltage 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 intraoperative testing of cardioverter-defibrillators and selection of pathways for low-energy cardioversion.
authors.affiliation: Division of Cardiology, Cedars-Sinai Medical Center, Los Angeles, California.
authors.forename: C D
authors.initials: CD
authors.lastname: Swerdlow
authors.forename: R M
authors.initials: RM
authors.lastname: Kass
authors.forename: C
authors.initials: C
authors.lastname: Hwang
authors.forename: E
authors.initials: E
authors.lastname: Gang
authors.forename: P S
authors.initials: PS
authors.lastname: Chen
authors.forename: C T
authors.initials: CT
authors.lastname: Peter
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D017147:Defibrillators, Implantable; D004554:Electric Countershock; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D012119:Respiration / Q000502:physiology*; D013908:Thoracotomy