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.
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.