Rate responsive cardiac pacing using a minute ventilation sensor

A minute ventilation sensing rate responsive pacemaker was implanted in 15 patients (8 males and 7 females) with bradycardia. The mean age was 72.8 +/- 8.7 years. The single chamber system measures transthoracic impedance between the tip electrode of a standard bipolar lead and the pulse generator case. In the adaptive mode the pulse generator calculates a rate responsive factor or slope during maximal exercise but functions as in the VVI mode. The patients exercised maximally on an upright cycle ergometer with the pacemaker programmed to VVI mode, adaptive mode, and rate responsive mode. Exercise and gas exchange data were collected continuously and analyzed using an automated breath-by-breath system. The slope, heart rate, and ventilation were measured every 20 seconds. Heart rate in pacemaker dependent patients correlated well 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.