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CLINICAL RESEARCH: ELECTROPHYSIOLOGY

Patient alert in implantable cardioverter defibrillators: toy or tool?

^* University of Heidelberg/Cardiology, Heidelberg, Germany

Manuscript received November 10, 2003; revised manuscript received February 3, 2004, accepted March 16, 2004.

^* Reprint requests and correspondence: Dr. Ruediger Becker, University of Heidelberg/Cardiology, Bergheimer Strasse 58, 69115 Heidelberg, Germany.
ruediger_becker{at}med.uni-heidelberg.de

OBJECTIVES: The purpose of this study was to analyze the utility of patient-alert features in implantable cardioverter defibrillators (ICDs).

BACKGROUND: Various alert features producing acoustic warning signals have been implemented in newer generation ICDs, but their role in early detection of system-related complications has not been systematically evaluated.

METHODS: In 240 patients implanted with Medtronic ICD devices, the following alert features were routinely activated: pacing lead impedance <200 or >2,000 , high-voltage lead impedance <10 or >200 , low battery voltage (elective replacement indicator), long charge time (>18 s), >3 shocks delivered per episode, and all therapies in a zone delivered. Alert events occurring during follow-up were assessed in relation to actual findings (hospital charts, chest X-rays, ICD printouts including sensing/pacing/defibrillation threshold tests, episode data) to determine incidence, sensitivity, and specificity of the alert function.

RESULTS: During 12.2 ± 8.9 months, 24 alert events occurred in the 240 patients (pacing lead impedance, n = 4; high-voltage lead impedance, n = 7; low battery voltage, n = 1; >3 shocks, n = 6; all therapies, n = 6). A total of 22 serious complications (necessitating reprogramming or device/lead replacement) were observed, 14 of which were primarily identified through a patient alert (lead fracture, n = 11; connector defect, n = 1; T-wave oversensing, n = 1; battery depletion, n = 1). This reflects a sensitivity of 64% and a specificity of 96% of the alert function for serious complications. With 14 of 24 patient alerts being caused by serious complications, the positive predictive value reached 58%.

CONCLUSIONS: Patient-alert features are a useful additional tool facilitating early detection of serious ICD complications, but they do not substitute for regular ICD follow-up, because of their low sensitivity.

Abbreviations and Acronyms   ICD = implantable cardioverter defibrillator   RV = right ventricle/ventricular   SVC = superior vena cava   UPV = unplanned visit   VF = ventricular fibrillation

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