Enhanced detection criteria in implantable defibrillators.

Introduction: Enhanced detection criteria in third-generation implantable defibrillators have been implemented to avoid inappropriate therapy of fast supraventricular arrhythmias. We prospectively analyzed the use of these criteria in patients with an implantable defibrillator with electrogram storing capability.
Methods and Results: In 82 consecutive patients with a Guidant-CPI implantable defibrillator, sudden onset > 9% and stability < 40 msec were systematically programmed in zone 1 of therapy together with a sustained rate duration security mechanism. All detected tachycardia episodes were analyzed. The study population consisted of 59 patients who had at least one episode of tachycardia detected in zone 1 during follow-up. The tachycardia rate in zone 1 never exceeded 210 beats/min. Twenty patients had no episodes during follow-up, and three patients had episodes detected exclusively in zone 2 of therapy. Supraventricular arrhythmias were detected frequently in the ventricular tachycardia zone (193 of 690 tachycardia episodes in 23 of 59 patients). Use of sudden onset was very effective in detecting sinus tachycardias (65 of 67 episodes), and stability was very useful in detecting atrial fibrillation (31 of 32 episodes). However, sensitivity in detecting ventricular tachycardia was only 90% (451 of 497 episodes). Application of the sustained rate duration criterion allowed appropriate treatment of all ventricular tachycardia episodes, increasing sensitivity to 100%; however, specificity in appropriate nontreatment of supraventricular decreased from 96% to 83%. Subsequent analysis of different algorithms applied to our data showed that sudden onset > 9% and stability < 40 msec was the algorithm with the best specificity and sensitivity.
Conclusion: Programming sudden onset and stability detection criteria with a sustained rate duration safety net for triggering tachycardia therapy results in appropriate device management in most patients with supraventricular and slow (< 210 beats/min) ventricular tachycardias.