EVALUATION OF OUTPATIENTS EXPERIENCING IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR SHOCKS ASSOCIATED WITH MINIMAL SYMPTOMS

Patients receiving minimally symptomatic shocks from their implantable cardioverter defibrillators were studied prospectively using transtel ephonic ECG loop monitoring. The time course to the first subsequent s hock was evaluated. Twenty-nine consecutive patients who received a sh ock preceded by mild palpitations or no symptoms were given a transtel ephonic ECG loop monitor and instructed to activate th e monitor if a subsequ ent shock occurred. Kaplan-Meier analysis was used to quantita te the time to first shock during the study period. The point estimate +/- standard error of patients receiving a shock during the study per iod was 31% +/- 9% at 30 days, 41% +/- 9% at 60 days, and 60% +/- 9% a t 120 days. The ECG was successfully transmitted in 7 of 13 patients w ho had shocks in the 60-day monitoring period, and demonstrated inappr opriate shocks in 6 of 7. Determination of the cause of shock led to a change in subsequent management in all 7 patients. We conclude that t he incidence of inappropriate shocks may be higher than estimated prev iously in patients with minimal symptoms prior to the shock. There are thousands of patients with implantable cardioverter defibrillators th at have no storage function for treated tachycardias; transtelephonic ECG loop monitoring can determine the cause of implantable cardioverte r defibrillator discharge in these patients, and the diagnosis is inva luable in their management.