K. Hoeland

Sensor and control technology for cardiac pacing

Pacemakers are implanted on account of deficiencies in rhythm generation and excitation conduction in the heart. The aim of sensor-controlled pacemaker systems is, apart from the preservation of life, the greatest possible restoration of physiological adaptation to circulatory stress. If the intrinsic rhythm generator breaks down, this cannot be achieved ideally by a technical shunt, but approximately by sensing physical and/or physiological variables suited to heart rate control. The latter leads both to feedforward control systems and to feedback (closed) control loops. After an overview on existing sensors the authors offer two new sensor technologies for closed-loop systems which are optimally suited to restore the original physiological control loop to the utmost extent. One uses sensors measuring the atrio-ventricular delay in the heart (dromotropic pacemaker), and the other uses a fibre optic sensor measuring the contraction of the heart (inotropic pacemaker).

Sensorgesteuerte Herzschrittmacher-Systeme

Technische Herzschrittmacher werden bei Störungen der herzeigenen Rhythmusbildung und Erregungsleitung implantiert. Zielsetzung sensorgesteuerter Schrittmacher-Systeme ist über die Lebenserhaltung hinaus die möglichst weitgehende Wiederherstellung physischer und psychischer Belastbarkeit. Da diese bei Ausfall des herzeigenen Rhythmusgebers in idealer Weise (durch einen technischen „Shunt) nicht erreicht werden kann, wird die Messung physikalischer und/oder physiologischer Größen herangezogen, die zur technischen Steuerung der Herzschlagfrequenz geeignet sind. Dabei werden teils offene Systeme im Sinne einer Störgrößenaufschaltung und teils geschlossene Systeme im Sinne einer Regelung realisiert. Das Autorenteam arbeitet insbesondere an der Umsetzung des sog. dromotropen Schrittmacherkonzepts als Zwei-Sensor-System mit Störgrößenaufschaltung.

New sensor based on fibre optics for measurement of heart movement.

Innovative fibre-optic sensor technology for measuring the movement of the myocardial walls, and from this the heart chamber volumes, was developed. An optical fibre, with a mirror at its end, is inserted into a catheter located in the heart. An opto-electrical control unit positioned outside the heart contains both the light source and the signal receiver. It generates and couples the light into the fibre and transforms and analyses the reflected signal. With such a system, the movement of the cardiac wall can be continuously measured during each cycle, because the fibre moves synchronously with the heart, and this movement bends the fibre, changing the optical attenuation. Experiments where the fibres were wound around metal cylinders of different diameters revealed a maximum sensitivity of 4% mm−1 diameter. The noise signal corresponded to about 1% of the diameter. First tests in a working pig heart showed a high correspondence of the fibre signal with cardiac parameters. Although these tests are promising, further long-term, extensive experiments in preclinical test devices, and later in clinical tests, must be carried out before the new sensor is used in clinical practice. The fibre-optic technique could be used in monitoring devices, assist devices, pacemaker systems or cardioverter defibrillators.

Closed loop control of the heart by rate adaptive pacemakers

Abstract The goal of rate-adaptive heart pacemakers, apart from the preservation of life is the maximum possible restoration of physiological control including the adequate response to physical and emotional stress. From the control engineering viewpoint very different systems have become a reality. Whereas the system most frequently implanted (the activity-controlled) pacemaker obviously is an open-loop system, approaches have been proposed to close the control loop. The authors focus on the following developments: Technical pacemakers controlled by venous oxygen saturation and by cardiac signals, particularly by the atrio-ventricular delay. The latter comes very near to the ideal pacemaker for the patient with incompetence of the intrinsic physiological pacemaker.

A NEW INOTROPIC PACEMAKER SYSTEM

Abstract A new “inotropic” pacemaker system is introduced for patients unable to increase heart rate in accordance with cardiocirculatory strain. An inotropic pacemaker senses the increase of heart contraction (inotropy) and uses this information to adjust the pacing rate. The fiber optic sensor, the optoelectrical unit and the re-closing of the control-loop are explained. The device is tested successfully in first experiments, both in technical set-ups and in pig hearts.

In vitro Testung einer neuen faseroptischen Sensortechnologie für Schrittmacher- und Defibrillationssysteme

ZusammenfassungDas faseroptischen Signal verändert sich in Abhängigkeit der Biegung der Glasfaser, was wiederum von der Inotropie bestimmt wird. Diese Ergebnisse zeigen eine gute Korrelation mit der linksventrikulären Pumpfunktion. Dadurch haben wir ein zusätzliches Signal, welches für die Entwicklung eines faseroptisch gesteuerten „inotropen” Schrittmachers herangezogen werden kann. Weiterhin ist an einen Einsatz in antitachykarden Systemen, wie den implantierbaren Defibrillatoren zur verbesserten Tachykardiedetektion zu denken.