RESUMO
Various concepts for measuring (by means of biosensors incorporated into pacemakers) biologic parameters to determine the appropriate pacing rate are reviewed. They are pH, stimulus-to-T-wave interval, blood temperature, intercardiac blood pressure change, venous oxygen saturation, intercardiac impedance (stroke volume, ejection rate, preejection interval), thoracic impedance (respiratory rate, minute volume), R-wave area, and body vibration. Those which have been incorporated in an implantable pacemaker and studied in a significant number of patients include intracardiac blood temperature, respiratory rate, respiratory minute volume, stimulus-to-T-wave interval, and body vibration. Studies of intracardiac impedance, QRS complex area, venous oxygen saturation, and right ventricular pressure are in early stages. Because no single parameter has yet proved to be an ideal indicator of metabolic need, dual-chamber pacemakers, which use atrial rate and body vibration to control pacing rate, and multisensor pacemakers are under development.
