MADIT II (Multicenter Automatic Defibrillator Implantation Trial II) Substudy Findings

The presentations at the NASPE Scientific Sessions refined and reinforced these guideline recommendations. One issue that has, in part, been responsible for the slow approval of prophylactic ICD reimbursement in patients with coronary artery disease and left ventricular ejection fractions </= 0.30 has been the difficulty in identifying subsets of this group who may derive special benefit.

Limitations of Electrophysiologic Studies

Dr. James P. Daubert (University of Rochester Medical Center, Rochester, New York) presented the electrophysiologic study results from patients in the MADIT II study,[1] with emphasis on their ability to predict subsequent ventricular tachycardia and fibrillation events.[2] Of 742 patients randomized to defibrillator therapy, 583 underwent electrophysiologic study. Ventricular arrhythmias were induced in 210 of these individuals (36%). The main findings of the study were that inducibility showed a trend to predict subsequent ICD therapy delivery, but only for patients with inducible ventricular tachycardia. Conversely, ventricular arrhythmia inducibility was inversely related to the occurrence of ventricular fibrillation. The implications of this study are that inducibility is not predictive of mortality and ICD use. Therefore, in patients post-MI with left ventricular ejection fractions </= 0.30, electrophysiologic study is not indicated to select those for prophylactic defibrillator implantation.

 

Further limitations of the clinical utility of electrophysiologic study were presented by Dr. Helmut U. Klein and colleagues (Otto-von-Guericke University, Magdeburg, Germany), who discussed the reproducibility of electrophysiologic study testing in a group of 56 patients enrolled in the MADIT II study from 2 centers.[3] Of these patients, 23% had an inducible ventricular arrhythmia at baseline. At a second electrophysiologic study, 27% of the inducible patients had become noninducible. Conversely, 18% of patients with an inducible arrhythmia had become noninducible at the second study. Similar reversals were seen at a third electrophysiologic study, when performed. Thus, neither inducibility nor noninducibility of ventricular tachycardia is a reliable marker for risk stratification, and further limits the clinical utility of electrophysiologic study testing.