INABILITY OF THE SIGNAL-AVERAGED ELECTROCARDIOGRAM TO DETERMINE RISK OF ARRHYTHMIA RECURRENCE IN PATIENTS WITH IMPLANTABLE CARDIOVERTER DEFIBRILLATORS

Signal-averaged electrocardiography has been used to identify patients at risk for arrhythmic death after myocardial infarction. Since patients with implantable cardioverter defibrillators (ICDs) are at high risk for arrhythmic events, they should also be expected to have a high incidence of abnormal signal-averaged electrocardiograms (SAECGs). However, whether the SAECG can discriminate patients who will have arrhythmia recurrence and receive appropriate ICD shocks from those who will have no recurrence and no shocks is unknown. This study examines the usefulness of the SAECG to separate appropriate users from non-users of the ICD. Fifty patients with ICDs participated in this study. Those who received a shock preceded by symptoms, a shock without preceding symptoms but with electrocardiographic documentation of ventricular fibrillation or ventricular tachycardia, or a shock while asleep were classified as ICD users. All other patients were classified as nonusers. The SAECG was classified as normal if the QRS duration on the standard electrocardiogram was less-than-or-equal-to 110 msec and if the total filtered QRS duration was < 120 msec, the root-mean square voltage of the terminal 40 msec was > 25-mu-V, and the terminal low amplitude signal duration measured < 38 msec. The SAECG was classified as abnormal if the QRS duration on the standard electrocardiogram was less-than-or-equal-to 110 msec and any one of these three criteria were outside the "normal range." The SAECG was classified as indeterminate if the QRS duration on the standard 12-lead electrocardiogram was > 110 msec. For the entire group of 50 patients, 8 (16%), 12 (24%), and 30 (60%) had normal, abnormal, and indeterminate SAECGs, respectively. Of the 22 ICD users, 1 (5%), 5 (23%), and 16 (73%) patients had normal, abnormal, and intermediate SAECGs, respectively. Of the 28 ICD nonusers, 7 (25%), 7 (25%), and 14 (50%) patients had normal, abnormal, and intermediate SAECGs, respectively. ICD users had lower left ventricular ejection fractions (P = 0.0002), a higher incidence of ventricular tachycardia (P = 0.04), prior exposure to a greater number of antiarrhythmic drugs (P = 0.04), and a lower likelihood for survival (P = 0.02) compared to the ICD nonusers. There was no statistically significant difference between the ICD users and nonusers as stratified by SAECG classification regardless of whether or not the indeterminate studies were included or excluded from the analysis. When the analysis was restricted to the 35 patients with coronary artery disease and monomorphic ventricular tachycardia, again there was no statistically significant difference between the ICD users and nonusers as stratified by the SAECG classification. In a Cox analysis no SAECG parameter entered the model to predict ICD use. Thus, appropriate ICD discharges occurred regardless of the outcome of signal-averaged electrocardiography. The data suggest that the SAECG should not be used in the decision analysis whether to implant or deny ICD implantation for patients who have demonstrated life-threatening ventricular arrhythmias.