Thoracotomy elevates the defibrillation threshold and modifies the defibrillation dose-response curve

Thoracotomy Elevates the Defibrillation Threshold. Introduction: Despite innovations in nonthoracotomy defibrillation systems, thoracotomies are still required in some clinical settings and are utilized in many animal-based research protocols. The effect of a thoracotomy on defibrillation energy, however, has not been well characterized. Methods and Results: Ten dogs in the immediate testing group underwent defibrillation testing immediately following a thoracotomy; another ten dogs in the delayed testing group were given 48 to 72 hours of recovery before defibrillation testing. A right ventricular endocardial coil to cutaneous thoracic patch biphasic system was used. At the time of defibrillation testing, the immediate testing group had a faster mean heart rate (144.7 ± 30.2 vs 105.8 ± 17.5 beats/min, P < 0.01), higher mean pulmonary artery pressures (systolic: 18.14 ± 9.48 vs 11.28 ± 6.46 mmHg, P = 0.1; diastolic: 6.59 ± 2.88 vs 3.89 ± 1.75 mmHg, P < 0.05), and higher mean defibrillation shock impedance (89.0 ± 11.6 vs 70.9 ± 7.3 Ω, P < 0.002) than the delayed group. The mean ED₅₀ (energy with a 50% success rate) was significantly higher in the immediate group than in the delayed group (26.9 ± 14.9 vs 14.2 ± 6.9 J, P < 0.05), and the slopes of the dose-response curves were significantly different (P = 0.03). Conclusion: In a right ventricular endocardial to cutaneous patch system, thoracotomy significantly and transiently increased the defibrillation threshold and modified the defibrillation dose-response curve.