RELIABILITY OF A NEW ALGORITHM FOR AUTOMATIC-MODE SWITCHING FROM DDDRTO DDIR PACING MODE IN SINUS NODE DISEASE PATIENTS WITH CHRONOTROPIC INCOMPETENCE AND RECURRENT PAROXYSMAL ATRIAL-FIBRILLATION

To evaluate the safety and efficacy of a new algorithm for automatic m ode switching (AMS) from DDD-DDDR to DDIR, 26 patients, 16 females and 10 males, mean age 73 +/- 6 years of age, affected by sinus node dise ase, chronotropic incompetence, and recurrent paroxysmal atrial fibril lation (PAF) received the Medtronic Thera DR pacemaker. The device con tinuously calculates, in ms, the running average of the intrinsic atri al rate (MAR) and compares the current atrial interval (CAI) with the stored MAR. When the CAI is greater than the MAR it increases by 8 ms, and when the CAI is less than the MAR, it decreases by 23 ms. When MA R less than or equal to 330 ms (182 beats/min), tachycardia is detecte d and AMS is activated. All patients had clinical evaluation, 12-lead EGG, Holter monitoring, and exercise testing after implantation and ev ery 3 months for I year. The results were compared with the data store d in the pacemaker memory: AMS episodes number; the histogram of the l ast 14 episodes; and atrial electrogram recording. Twenty-two Holter r ecordings in 13 patients showed PAF and in all of them RMS occurred si multaneously. AMS lasted between 10 seconds and 20 hours, and MAR rang ed from 195-400 beats/min. No episode of PAF and no RMS were recorded in 39 Holter recordings in 22 patients. Appropriate AMS was confirmed in five patients by stored atrial electrogram and in nine by 22-lead E CG and pacemaker event markers. Mean atrial sensing was 2.23 +/- 1.04 mV during PAF and 3.18 +/- 1.46 mV during sinus rhythm. No PAF episode and no AMS were recorded during exercise testing. In conclusion, this new algorithm was very reliable, sensitive, and specific.