Ventricular tachycardias above the initially programmed tachycardia detection interval in patients with implantable cardioverter-defibrillators - Incidence, prediction and significance

OBJECTIVES This retrospective study was performed to provide data on ventri cular tachycardias (VT) with a cycle length longer than the initially progr ammed tachycardia detection interval (TDI) in patients with implantable car dioverter defibrillators (ICDs). BACKGROUND It has been clinical practice to program a safety margin of 30 t o 60 ms between the slowest spontaneous or inducible VT and the TDI. METHODS Baseline characteristics of 659 consecutive patients with ICDs were prospectively; follow-up information was retrospectively collected. RESULTS During a mean follow-up of 31 +/- 23 months, 377 patients (57.2%) h ad at least one recurrent VT or ventricular fibrillation; 47 patients (7.1% ) suffered 61 VTs above the TDI. The risk of a VT above the TDI ranged betw een 2.7% and 3.5% per year during the first four years after ICD implantati on. The difference between the cycle length of the slowest VT before ICD im plantation, spontaneous or induced, and the first VT above TDI was 108 +/- 58 ms. Fifty-four VTs (88.5%) above the TDI were associated with significan t clinical symptoms (angina or palpitation 63.9%, heart failure 6.6% and sy ncope 8.2%). Six patients (9.8%) had to be resuscitated. Kaplan-Meyer analy sis identified New York Heart Association class II or III (p = 0.021), ejec tion fraction < 0.40 (p = 0.027), spontaneous (p < 0.001) or inducible (p < 0.001) monomorphic VTs and the use of class III antiarrhythmic drugs (amio darone, p < 0.001; sotalol, p = 0.004) as risk predictors of VTs above the TDI. The risk of recurrent VTs above TDI was 11.8%, 12.5% and 26.6% during the first, second and third year after first VT above TDI, respectively. CONCLUSIONS The risk of VTs above the TDI is significantly increased in som e patients, and many VTs above TDI cause significant clinical symptoms. A l arger safety margin between spontaneous or inducible VTs and the TDI seems to be necessary in selected patients. This is in conflict with an increased risk of inadequate episodes and demands highly specific and sensitive dete ction algorithms in these patients. (C) 2000 by the American College of Car diology.