R. Hardt

Sputter-deposited TiN electrode coatings for superior sensing and pacing performance.

SCHALDACH, M., ET AL.: Sputter‐Deposited TiN Electrode Coatings for Superior Sensing and Pacing Performance. The sensing and pacing performance of pacemaker electrodes is characterized by the electrochemical properties of the electrode/tissue interface affecting tissue reactions and the kinetics of the ionic exchange. The usually smooth metallic electrode surface results in a high pass filter characteristic. To better match the electrodes filter characteristic to the spectral content of the depolarization signal, various combinations of electrode shape, material and surface structure have been researched. The electrode with sputter‐deposited TiN coating presented in this report has been designed to meet the demand for low acute as well as chronic thresholds and superior sensing performance not only with respect to spontaneous activity but also regarding the detection of the evoked response. The clinical results obtained with this electrode prove the excellent pacing and sensing properties resulting from minimized polarization losses and optimized filtering of the signal to be detected, respectively. The acute and chronic clinical advantages over previous concepts are attributed mainly to the biocompatibility of the material used and the microcrystalline surface structure achieved by the coating process. The design concept of the new electrode is presented together with the clinical results obtained. While the advancements in microelectronics and battery technology have certainly formed the basis for the development of pulse generators featuring an ever increasing versatility of functions at the same or even smaller pacemaker dimensions, from a point of view of pacing system performance the development of improved electrode concepts as the one presented must be regarded as equally indispensable.

Titannitrid-Herzschrittmacher-Elektroden - Pacemaker Electrodes Made of Titanium Nitride

The sensing and pacing performance of pacemaker electrodes is characterized by the electrochemical properties of the electrodes/tissue layer; the usually smooth metallic electrode surface results in a high pass filter characteristic. Consequently, the detected intracardiac signals, which control the implantable systems, are not optimally matched to the spectral contents of the depolarisation signal. To avoid interference caused by noise (EMI, muscle potentials, etc.) a shift of the frequency of the band pass towards the lower frequency spectrum is required. As previously reported, the electrochemical properties of sintered and surface-treated electrodes prove the predicted improvement of sensing performance if titanium-nitride coated electrodes are used. Our results demonstrate their superiority above all the other electrodes presently known. The advantages can be referred to the micro-crystalline surface structure achieved by sputter-deposited electrode coatings and the kinetics of the ionic exchange. Furthermore, the acute thresholds achieved with the TiN-systems were significantly better than those of the smooth metallic surface. These results were also confirmed for chronic implants and are attributable to the known biocompatibility of titanium and its alloys.

Bewegungsenergie als Steuergröße für die Anpassung der Stimulationsfrequenz - Motion Energy as a Control Variable for Sensor-Driven Rate Adaptation

: An activity sensing rate-responsive pacing system is presented which adaptively controls heart rate to adjust cardiac output in response to increased metabolic demand, and more optimally restore homeostasis of the intact cardiovascular system. The current use of ventricular demand and DDD universal pacing systems, although rate and multi-parameter and multi-function programmable, are fixed at these programmed settings. These devices are adequate for patients at rest or during moderate exertion, but are suboptimal for physically active patients whose physiology requires increased oxygen supply to meet an increased cardiac demand. In the past, these patients may have experienced fatigue or dyspnea out of proportion to their cardiovascular disease. The Ergos rate-adaptive single- and dual-chamber pacing system is a second generation pulse generator which is rate responsive to a patients increased physiologic demand by sensing a motion signal which reflects increased work load and the need for a compensating increase in heart rate. Ergos offers increased assistance to patients with sinus bradycardia who may require the rate-responsiveness with the additional advantage of AV synchrony. Clinical results show the effectiveness of the presented sensor control by motion energy for rate adaptive pacing therapy.

Analyse evozierter Myokardpotentiale in Abhängigkeit von ergometrischer Belastung und Schlagfrequenz für die Anwendung in frequenzadaptiven Schrittmachern

EINLEITUNG: Die zuverlässige Messung ventrikulär evozierter Myokardpotentiale wird seit mehr als zwei Jahrzehnten im Rahmen der Herzschrittmacherentwicklung angestrebt, da die mittels Schrittmacherimpuls evozierten Myokardpotentiale Träger zahlreicher Informationen über den elektrophysiologischen Status der Herzmuskelzellen sind. Bei der Signalanalyse steht die Gewinnung von Informationen im Vordergrund, die einerseits eine Erfolgskontrolle der Stimulation und andererseits eine Anpassung der Schlagfrequenz an die Belastung erlauben. Die störungfreie Erfassung evozierter Myokardpotentiale setzt eine effektive Unterdrückung des Stimulationsartefakts voraus, der anderenfalls das Nutzsignal überlagert. Mittels zweier getrennter Elektroden wurde dieses Ziel bereits erfolgreich umgesetzt [1]. Für die vorliegenden Untersuchungen wurde jedoch ein neuartiges Konzept angewendet, das es erstmalig erlaubt, evozierte Myokardpotentiale mittels unipolarer Schrittmacherelektroden artefaktfrei zu messen.

Das Detektions- und Reizschwellenverhalten von Titannitrid-Herzschrittmacher-Elektroden

Die Vorgänge der künstlichen Reizung lassen sich aus dem Potentialund Stromdichteverlauf im Nahund Fernfeld der Elektrode verstehen, wobei die physikalische Erklärung der Reizauslösung auf der Annahme eines geeigneten Feldverlaufes im Myokard beruht, der zu einer Erniedrigung des Membranpotentials führt und durch die nachfolgende Depolarisation der Zellen die Kontraktion des Herzens zur Folge hat. Die für die Synchronisation des Schrittmachers notwendige Detektion intrakardialer Signale beruht auf der Notwendigkeit der Frequenzselektion; das im Vorhof gemessene Signal ist hochfrequenter (70 Hz) als das im Ventrikel (30 Hz). Die Erkennung einer Herzaktion beinhaltet also das meßtechnische Problem der selektiven Verstärkung und Detektion der Depolarisation bei hohem Nutzsignal-Störspannungs-Verhältnis. Wesentliche Verbesserungen hinsichtlich der Optimierung der Reizauslösung und der Reizerkennung lassen sich durch Anpassung der elektrochemischen und physikalischen Parameter der Phasengrenze an die biologischen Gleichgewichtsbedingungen erreichen.