Enhanced detection criteria in implantable cardioverter defibrillators: Sensitivity and specificity of the stability algorithm at different heart rates

The lack of specificity in the detection of ventricular tachyarrhythmias re mains a major clinical problem in the therapy with ICDs. The stability crit erion has been shown to be useful in discriminating ventricular tachyarrhyt hmias characterized by a small variation in cycle lengths from AF with rapi d ventricular response presenting a higher degree of variability of RR inte rvals. But RR variability decreases with increasing heart rate during AF. T herefore, the aim of the study was to determine if the sensitivity and spec ificity of the STABILITY algorithm for spontaneous tachyarrhythmias is rela ted to ventricular rate, Forty-two patients who had received an ICD (CPI Ve ntak Mini I, II, III or Ventak AV) were enrolled in the study. Two hundred ninety-eight episodes of AF with rapid ventricular response and 817 episode s of ventricular tachyarrhythmias were analyzed. Sensitivity and specificit y in the detection of ventricular tachyarrhythmias were calculated at diffe rent heart rates. When a stability value of 30 ms was programmed the result was a sensitivity of 82.7% and a specificity of 91.4% in the detection of slow ventricular tachyarrhythmias (heart rate < 150 beats/min). When faster ventricular tachyarrhythmias with rates between 150 and 169 beats/min (170 -189 beats/min) were analyzed, a stability value of 30 ms provided a sensit ivity of 94.5% (94.7%) and a specificity of 76.5% (54.0%). For arrhythmia e pisodes greater than or equal to 190 beats/min, the same stability value re sulted in a sensitivity of 78.2% and a specificity of 41.0%. Even when othe r stability values were taken into consideration, no acceptable sensitivity /specificity values could be obtained in this subgroup. RR variability decr eases with increasing heart rate during AF while RR variability remains alm ost constant at different cycle lengths during ventricular tachyarrhythmias . Thus, acceptable performance of the STABILITY algorithm appears to be lim ited to ventricular rate zones < 170 beats/min.