[Pre-ejection period controlled cardiac pacemaker].

Numerous investigations have been performed in search for suitable parameters for physiologic adaptation of the pacing rate. In case of chronotropic incompetence corporeal as well as cardiac control parameters permit open or closed loop control of the pacing rate. Criteria to be considered are the patient's condition, the response time of the system, the proportionality to the oxygen uptake and the susceptibility to interference. A high specificity of the rate response is particularly important for the patient with a low cardiac reserve. The use of a parameter relating to the central hemodynamics, such as the systolic time intervals, particularly the pre-ejection period (PEP), as input signal for rate control is, therefore, of special interest. The concept presented of a PEP-controlled rate adaptive pacemaker is based on the linear proportionality between PEP and the cardiac cycle length. Changing with the sympathetic tone, the PEP permits adaptation of the pacing rate in response to physical as well as emotional stress. The right ventricular PEP parallels the left ventricular one and is measured between the electrode tip and the pacemaker housing. Clinical results obtained confirm the high sensitivity and specificity of this control parameter with respect to the metabolic demand. Technical details of an implantable multiprogrammable device are dealt with.