AUTOMATIC ADAPTATION OF THE BASIC PACING RATE IN RESPONSE TO MINUTE VENTILATION

Rate responsive pacing based on minute ventilation (VE) correlates hig hly with metabolic demand. This type of sensing also recognizes extend ed periods of rest. The Chorum pacemaker includes a rate responsive al gorithm that modulates the basic rate according to phases of activity Versus sleep. Forty-six patients (mean age 78 +/- 15), received a Chor um pacemaker for atrioventricular block in 17 cases, sick sin us syndr ome in 25, and mixed disorders in 4. Holter monitoring was performed t o analyze heart rate and to examine the circadian adaptation of the mi nimal pacing rate. The mean basic rate was programmed at 63 +/- 5 beat s/min, and the sleep rate at 52 +/- 4 beats/min. Seventeen patients ha d spontaneous heart rates consistently above the programmed basic rate , and 6 had sustained supraventricular tachyarrhythmias, One-half of t he patients had periods of pacing at the programmed sleep rate. The me an diurnal pacing rate was 68 +/- 5 beats/min compared to a mean noctu rnal rate of 60 +/- 4 beats/min (P < 0.0001). The average time spent a t the basic rate was 37 +/- 30 min (0-110) during daytime (4%), versus 242 +/- 253 min (20-477) at night (45%, P < 0.0001). No adverse effec t was observed in this patient population. VE allows a reliable detect ion of the sleeping periods as well as an adjustment of the basic rate in accordance. Caution is advised in cases of bradycardia dependent t achyarrhythmias.