Inappropriate ICD Therapies and Changing Patient Population

The high proportion of primary prevention patients now receiving ICDs seems to be causing a relative increase in the prevalence of SVT versus VT in ICD patients, thus lowering the positive predictive value of VT/VF detection compared to earlier studies with secondary prevention patients. This has resulted in renewed concern for inappropriate therapy (especially shocks) in ICD patients, since the shift in patient population has resulted in a relative increase of inappropriate shocks compared to appropriate shocks. Despite improvements in the specificity of SVT discrimination algorithms, recent prospective studies with spontaneous tachycardias in ICD patients have reported positive predictive values for VT/VF detection of only 60-70% for modern, optimized ICD detection algorithms.114'119 Studies such as the Primary Prevention Parameters Evaluation (PREPARE) trial are being conducted in an attempt to reduce ICD morbidity caused by shocks through selecting optimal ICD detection and therapy parameters that reduce overtreatment of self-terminating tachycardias, improving discrimination of SVTs from VT/VF and maximizing the use of antitachycardia pacing therapy to terminate tachyarrhythmias.120

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