Studies on malignant ventricular tachyarrhythmias and their treatment with an implantable defibrillator

Abstract

Aims: To investigate the hemodynamic, metabolic and autonomic effects of ventricular fibrillation per se during maintained circulation. To study the defibrillation threshold (DFT) and efficacy of a new and thinner ICD lead (DSP) compared with the standard lead (C). To study the effects of pectoral or abdominal generator positioning on bidirectional and biphasic defibrillation. To study if the results of perioperative induction testing data would make postoperative ICD induction testing unnecessary. The evaluate the effects of time, exercise and amiodarone on an electrogram morphology discriminator. Methods: The coronary sinus flow (CSF), systemic and left ventricular pressure, myocardial oxygen consumption, metabolic products and catecholamine were analyzed in patients with aortic stenosis during induction of ventricular fibrillation (VF) with ongoing cardiopulmonary bypass. DSP and C leads DFT and pacing data from implantation and during follow-up were compared. The effect on DFT was studied by an alternating step-down protocol with an ICD in abdominal and a pectoral position in the same patient. Peroperative and postoperative ICD induction tests were performed and the relative and absolute defibrillation energy efficacy was analyzed. The effects of time, exercise and amiodarone therapy on the algorithm function were studied.Results: Myocardial ischemia, acidosis and a temporary noradrenalin net release developed during 4 min of VF despite an unchanged CSF and global myocardial oxygen consumption. The aortic and left ventricular pressure equilibrated rapidly after start of VF start. In the DSP both performed equally well. Abdominal or pectoral position did not affect the DFT. A relative energy of d 10J and an absolute defibrillation energy of T 20J at implantation could have made 89% of the predischarge tests unnecessary. The mean long-term MD function was not changed over time, at exercise or treatment of amiodarone. Transient miss-classification of electrograms occurred over time and during tachycardias.Conclusions: VF, per se, rapidly induced signs of myocardial ischemia, acidosis and a transient increase in noradrenaline release as well as an equilibration of the left ventricular and aortic pressures. Both the DSP and the C electrode were safe and effective in the treatment of ventricular tachyarrhythmias. No difference was found between the abdominal and pectoral positions in the same patient. The combined criteria of a relative defibrillation margin of 10 J and an absolute energy of 20 J at ICD implantation could be used without risk to reduce the need of postoperative induction testing to 11%. The morphological electrogram discrimination function showed stable mean values over time, during an exercise test and during amiodarone treatment. Single, transient, false low morphology discrimination scores were found during follow-up. The morphology discrimination must be frequently automatically updated and combined with other detection enhancements.