Image Number 3 for United States Patent #4467807.
An implantable pacer having an effective stimulation rate which varies in response to a measured physiological parameter. Changes in the parameter to be measured must be related to physiologically required changes in heart rate. The level of oxygen within intracardiac or pulmonary artery venous blood is the preferred parameter. This parameter is measured by an oxygen sensor located on a transvenously implanted lead. As with normal demand pacers, a sensing electrode, also located on the lead, provides the pacer with an indication of whether a pacing pulse must be generated. The measured physiological parameter determines the escape interval for demand pacing. As such, a given minimum rate is determined for a given level of molecular oxygen in the intracardiac or pulmonary artery venous blood. The technique is readily employed in both ventricular and atrial-ventricular sequential modes.