INITIAL EXPERIENCE WITH A NEW ALGORITHM FOR AUTOMATIC-MODE SWITCHING FROM DDDR TO DDIR MODE

Implantation of dual chamber devices in patients with paroxysmal atria l tachyarrhythmias who require permanent pacemakers may lead to signif icant complications due to an inappropriately triggered ventricular re sponse. VVI/VVIR units cause loss of AV synchrony in the presence of S inus activity, A new DDDR device (THERA DR, model 7940), with an autom atic mode switching (AMS) algorithm, was evaluated. When the mean atri al rate is > 182 beats/min, atrial tachyarrhythmia is detected, and AM S is activated. Twenty-three patients (12 males, mean age 71 +/- 7 yea rs) underwent implantation of a THERA DDDR device with the AMS algorit hm. Seventeen patients had AV block and/ or sick sinus syndrome (SSS) and atrial arrhythmias, and 6 patients (2 with hypertrophic obstructiv e cardiomyopathy) had SSS and paroxysmal atrial fibrillation (PAF). Th e follow-up period was from 1-9 months. During follow-up, Holter monit oring and treadmill tests were performed. Results: Eighty-seven episod es of AMS were recorded. Telemetered AMS recordings demonstrated episo des in which the DDDR mode switched to the DDIR mode in the presence o f PAF, and reverted to DDDR when sinus rhythm returned. Paroxysmal sup raventricular arrhythmias with a heart rate < 182 beats/min did not ac tivate the mode switch. Conclusions: This early, short-term clinical e xperience with a DDDR device capable of AMS from DDDR to DDIR demonstr ated appropriate clinical function and response to PAF. These prelimin ary results suggest that DDDR pacemakers with AMS to DDIR may signific antly extend the current indications for dual chamber pacing.