Internal Chdioverter-Defibrilla’ior Jo20 Sousa, MD, William Kou, MD, Hugh Calkins, MD, Shimon Rosenheck, MD, Alan Kadish, MD, and Fred Morady, MD To evaluate the effect of sympathetic activation on the efficacy of the implantable cardioverter-defi- brillator (ICD) in converting ventricular tachycar- dia (VT) or ventricular fibrillation (VF), 32 pa- tients who received an ICD because of life-threat- ening VT/VF underwent 1 week postimplant ICD testing both before and after infusion of 25 (16 patients) or 50 (16 patients) ng/kg/min of epi- nephrine for L: 12 minutes. These infusion rates are known to result in plasma epinephrine concen- trations comparable to mild-moderate stress. The patients’ mean age was 63 f 10 years; 26 had coronary artery disease, 2 had dilated cardiomy- opathy and 4 had no evidence of structural heart disease. VT and VF were induced in 16 patients each by programmed stimulation or alternating current. Among the 16 patients with VT, the first ICD discharge (26 to 30 1) was effective in 15 pa- tients in the baseline state and in all 16 patients during epinephrine infusion. Among patients with VF, the first ICD discharge (26 to 30 J) terminated VF in all patients in the baseline state, compared with 12 of 16 patients during epinephrine infusion (p <0.05). In 4 patients, VF was terminated dur- ing epinephrine infusion only by the second or third ICD discharge (30 J). In conclusion, physio- logic increases in the plasma epinephrine concen- tration may increase the number and energy of shocks needed to terminate VF. (Am J Cardiol 1992;69:509-512) From the Department of Internal Medicine, Division of Cardiology, University of Michigan Medical Center, Ann Arbor, Michigan. Manu- script received June 17,199 1; revised manuscript received and accepted October 11.1991. Address for reprints: Fred Morady, MD, University of Michigan Medical Center, 1500 E. Medical Drive, BI F245, Ann Arbor, Michi- gan 48109. T wo recent reports described degeneration of si- nus tachycardia to ventricular tachycardia (VT) when shocksfrom an internal cardioverter-defi- brillator (ICD) occurred during physical exercise.‘,* This suggested that the sympathetic activation that ac- companies exercisemay have adverse effects on the re- sponseto ICD discharges.However, no prior studies have systematically examined the effect of exercise or sympathetic activation on the response to ICD shocks. Therefore, the purposeof this study was to evaluate the influence of sympathetic activation on the efficacy of the ICD in converting VT and ventricular fibrillation (VF). Sympathetic activation was induced with intrave- nous infusions of epinephrine at dosespreviously dem- onstrated to achieve plasma concentrations similar to those observed during mild to moderate physical exer- cise.3 METHODS Patients: This study consisted of 32 consecutive pa- tients (24 men and 8 women, mean age f SD 63 f 10 years) who underwent implantation of an ICD because of life-threatening VT or VF and who underwent testing to evaluate ICD function 1 week later. Twenty-six pa- tients had coronary artery disease, 2 had a dilated car- diomyopathy and 4 had no evidence of structural heart disease. The mean left ventricular ejection fraction as determined by contrast ventriculography was 0.35 f 0.15. The clinical presentation was aborted sudden death in 21 patients and sustained VT accompanied by synco- pe or near-syncope in 11 patients. Among the patients with aborted sudden death, baseline electrophysiologic testing demonstratedinducible sustained monomorphic VT in 8 patients, sustained polymorphic VT in 4 pa- tients and no inducible arrhythmias in 9 patients. Sus- tained monomorphic VT was inducible in all of the pa- tients in whom the clinical presentation was sustained VT. Patients with inducible monomorphic VT failed se- rial electropharmacologic testing before ICD implanta- tion. ICD implantation: The ICD pulse generators and leads were manufactured by Cardiac Pacemakers, Inc. (St. Paul, Minnesota). A median sternotomy approach was used,with rate-sensing screw-in leadspositionedon the anterior surface or outflow tract of the right ventri- cle and defibrillator patch electrodes on the lateral left ventricle and right atrium. Thirty-one patients received a Ventak (model 1550) ICD and 1 patient received a Ventak-P (model 1600). An external cardioverter-defibrillator (Cardiac Pacemakers, Inc.) wasusedfor intraoperative defibrilla- EPINEPHRINE AND THE INTERNAL CARDIOVERTER-DEFIBRILIATOR 509