RATE-RESPONSIVE CARDIAC PACING USING A MINUTE VENTILATION SENSOR

A minute ventilation sensing rate responsive pacemaker was implanted i n 15 patients (8 males and 7 females) with bradycardia. The mean age w as 72.8 +/- 8.7 years. The single chamber system measures transthoraci c impedance between the tip electrode of a standard bipolar lead and t he pulse generator case. In the adaptive mode the pulse generator calc ulates a rate responsive factor or slope during maximal exercise but f unctions as in the VVI mode. The patients exercised maximally on an up right cycle ergometer with the pacemaker programmed to VVI mode, adapt ive mode, and rate responsive mode. Exercise and gas exchange data wer e collected continuously and analyzed using an automated breath-by-bre ath system. The slope, heart rate, and ventilation were measured every 20 seconds. Heart rate in pacemaker dependent patients correlated wel l to minute ventilation (correlation coefficient ranging from 0. 72-0. 95, P < 0.0001). This study demonstrates that minute ventilation is a good metabolic sensor in rate responsive pacing.