J. Ströbel

A FRACTALLY COATED, 1.3 MM2 HIGH IMPEDANCE PACING ELECTRODE

Minimizing the geometric surface area of pacing electrodes increases impedance and reduces the current drain during stimulation, provided that voltage (pulse‐width) thresholds remain unchanged. This may be feasible by coating the electrode surface to increase the capacity of the electrode tissue interface and to diminish polarization. Ten unipolar, tined leads with a surface area of 1.3 mm2 and a “fractal” coating of Iridium (Biotronik SD‐V137) were implanted in the ventricle, and electrogram amplitude (unfiltered), slew‐rate, pacing threshold (0.5 ms), and impedance (2.5 V; 0.5 ms) were measured by the 5311 PSA (Medtronic). On days 0, 2, 5, 10, 28, 90, 180, 360 postimplant, sensing threshold (up to 7.0 mV, measuring range 1–14 mV on day 360 only) and the strength duration curve (0.5–4.0 V; 0.03–1.5 ms; steps: 0.5 V; 0.01 ms, respectively) were determined, the minimum charge delivered per pulse (charge threshold), and the impedance were taken from pacemaker telemetry (Intermedics 294–03). Data were compared with those of an earlier series of 20 unipolar, tined TIR‐leads (Biotronik) with a surface area of 10 mm2 and a “fractal” coating of titanium nitride. With the model SD‐V137 versus TIR, intraoperative electrogram amplitudes were 15.1 ± 6.1 versus 14.4 ± 3.9 mV(NS), slew rates 3.45 ± 1.57 versus 1.94 ± 1.06 V/s (P < 0. 05), pacing thresholds 0.16 ± 0.05 versus 0.52 ± 0.15 V (P < 0.01) and impedance measurements 1,136 ±175 versus 441 ± 73 Ω (P < 0.0001), respectively. During follow‐up, sensing thresholds were the same with both leads. Differences in pulse width thresholds lost its significance on day 28 but resumed on day 360 (SD‐V137: 0.08 ± 0.04 ms; TIR: 0.16 ± 0.06 ms at 2.5 V; P < 0.01). With an electrode surface of 1.3 mm2, charge per pulse and impedance consistently differed from control, beingO.15 ± 0.15 versus 0. 66 ± 0. 20 μC (P < 0.001) and 1,344 ± 376 versus 538 ± 79 Ω, respectively, one year after implantation (P < 0.0001). In summary, “fractally” coated small surface electrodes do not compromise sensing; by more than doubling impedance against controls they offer pacing thresholds (mainly in terms of charge) that are significantly lower than with the reference electrode.

Optimizing the Geometry of Implantable Leads for Recording the Monophasic Action Potential with Fractally Coated Electrodes

This study investigates the influence of various lead geometry on intracardial signals like the monophasic action potential (MAP) to optimize the geometry of implantable MAP leads. The experimental results were compared with a field theoretical approach to the origin of MAP from the transmembrane potential (TAP). During the experiments several lead geometries (tip surface: 1.3 to 12 mm2; tip‐ring distance: 0.8 mm to 25 cm; ring surface: 1.8mm2 to 40 mm2) were investigated in endo‐ and epicardial positions in 12 dogs (17±9 kg). The electrodes were fixed passively (tines) or actively (screws). MAP was recorded during several interventions and correlated with MAP measured using an Ag‐AgCl MAP catheter. The experimental results showed that small tips provided high MAP amplitudes with less pressure. No difference was observed using active and passive fixations. A tip‐ring distance smaller than 5 mm with a ring surface smaller than the tip (<5 mm2) avoided artifacts in the repolarization course. For the theoretical approach the quasistatic, anisotropic bidomain model was calculated in smalt unity volumes Vi where the TAP φm was constant and represented by the current density J. Two solutions for electrode positions at and outside the heart were achieved. By superposition of each solution φei the summed potential at the electrode position was calculated. The theoretical findings show in good correlation with the experimental results that a larger distance than 10 mm leads to distortions in repolarization course by signals proportional to φout.

SIMULTANEOUS RECORDINGS OF THE MONOPHASIC ACTION POTENTIAL WITH SILVER CHLORIDE- AND IR-COATED ELECTRODES

Ag AgCI and Ir‐coated electrodes allow the recording of the monophasic action potential (MAP) due to their electrical properties like non‐polarisability. This study investigates the correlation of MAP recorded with both types of electrodes. In 20 mongrel dogs (18 ± 6 kg) an Ag/AgCI and an Ir‐coated catheter (Ir) were placed endo‐cardially in the apex of the right ventricle. The effects of isoproterenol and verapamil were investigated during spontaneous rhythm and stimulation simultaneously recorded with both types of electrodes in 10 dogs without AV‐node ablation. The correlation at different heart rates were investigated in 10 other dogs with complete AV‐block. The morphology and amplitudes of MAP were comparable (AgCl: 15±7 mV; Ir: 13±8 mV). Following an i.v. bolus of 2μg/kg isoproterenol the spontaneous rate increased (175±18 to 245±25 bpm). During stimulation with 250 ms cycle length the duration shortened (MAPd90: AgCl: 160 ± 11 to 130 ± 12 ms; Ir: 154 ± 18 to 128±15 ms). The alterations reversed after 20 mm. An i.v. bolus of 0.2 mg/kg verapamil decreased the spontaneous rate (167±11 to 104 ± 23 bpm) and lengthened the MAPd90 (AgCl: 182 ± 14 to 220±13 ms; Ir: 174 ± 16 to 216, 21 ms) at 300 ms stimulation. The correlation between the MAPd90 of both lead types was r=0.98 during all measurements. Under the effect of beta‐agonist and Ca2+ ‐antagonist medication MAP showed a strong correlation recorded with both types of electrodes. Thus, both leads allow the recording of MAP but only the Ir‐electrodes with their long‐term stability are implantable and allows us to control the effects of drugs with implantable devices.

Nichtinvasive Überwachung antiarrhythmischer Sotalol-Therapie durch Analyse intrakardialer Signale

EINLEITUNG Mit dem monophasischen Aktionspotential (MAP) und der ventrikulär evozierten Reizantwort (VER) stehen Signale zur Verfügung, mit denen sich in-vivo die Effekte verschiedener Interventionen auf das Transmembranpotential (TAP) messen lassen [1-6]. Da fraktal beschichtete Elektroden es erlauben, beide Signale langzeitstabil in der klinischen Praxis zu messen [7,8], öffnen sich neue Möglichkeiten der Überwachung antiarrhythmischer Therapie. In dieser experimentellen und klinischen Studie wurde die Wirkung von Sotalol auf beide Summenpotentiale des TAP untersucht, um die Möglichkeit einer nichtinvasiven Kontrolle einer Therapie mit Sotalol zu prüfen.

Das monophasische Aktionspotential im Langzeitverlauf

Das monophasische Aktionspotential (MAP) ist ein Summensignal des zellulären Aktionspotentials (AP) der Herzzellen in unmittelbarer Umgebung um die Elektrode. Ein Modell der Entstehung des MAP aus dem zellulären Aktionspotential wurde bereits vorgestellt und anhand akuter Messungen in-vitro und in-vivo erfolgreich validiert [1,2], Dieses Modell sagt voraus, daß bei stabilen geometrischen Positionen der differenten und indifferenten Elektrode MAP-Messungen im Langzeitverlauf möglich sind. Neben den zur Validierung des Modells verwendeten Akutversuchen von wenigen Stunden Meßdauer stehen nun neuere klinische Ergebnisse zur Verfügung, die das MAP im Langzeitverlauf untersuchen [3], Diese bieten die Datenbasis, Langzeiteffekte bei MAP-Messungen experimentell zu bestimmen und somit das Modell zu erweitern.

Estimulação DDD com eletrodo único usando estimulação atrial bifásica simultânea: primeiros resultados clínicos

Single lead, dual chamber (DDD) pacing with an atrial floating electrode is limited by high atrial capture thresholds. We evaluated a new atrial stimulation lead with two atrial ring electrodes on a single lead and overlapping unipolar square wave pulses of an opposite polarity. The first pulse is applied to the distal electrode and is positive, the second pulse is to the proximal electrode and is negative, both with respect to the pacemaker housing. The delay between the two pulses is programmable between 0.0 ms to 1.0 ms. The distance between the atrial electrode rings is 10 mm and the distance from the distal atrial ring to the unipolar ventricular electrode can be selected to be 11, 13 or 15 cm. The positioning of the atrial ring is selected according to the measured overlapping biphasic pulse thresholds, including respiratory maneuvers to confirm continuous capture/sensing. The pulse generator has a single lead connection and the capability of delivering the two atrial square wave opposite programmable pulses, with delays from 0.0 to 1.0 ms. The generator may be programmed to the single lead unipolar VDD mode. This system was implanted in 4 patients with complete AV block with normal sinus mode fuction. Atrial and diaphragmatic thresholds for various pulse configurations, widths and delays were measured intra and postoperatively. The midportion of RA was selected as the best location for the atrial rings with continuous capture during deep inspiration. The intra and postoperative (48hrs) measurements were: Threshold Intra-op POstop. (48hrs) Atrial unipolar 3.2 + 0.47 V not measurable Atrial (overlapping biphasic) 1.6 + 0.37 V 3.37 + 0.84 V Diaphragmatic above 7 V 5.21 + 0.3 V wave sensing 2.35 + 1.3 mV 1.27 + 0.8 mV The patients were discharged in the VDD mode. Evaluation thirty days after showed transient loss of atrial capture during inspiration in one patient in spite of absence of other threshold changes compared to the 48 hours evaluation. In conclusion, overlapping biphasic stimulation reduces the atrial pacing thresholds while maintaining adequate atrial sensing with a safe margin regarding diaphragmatic stimulation.

Optimierung der Elektrodengeometrie und der Pulskonfiguration zur Stimulation des Atriums mit flottierenden Elektrodenringen

EINLEITUNG: Die Entwicklung von Zweikammerschrittmachersystemen, die sich nur einer Elektrodensonde bedienen, wurde mit der erfolgreichen Wahrnehmung atrialer Signale über flottierende Ringelektroden eingeleitet. Die Realisierung einer Möglichkeit der Vorhofstimulation über Elektroden ohne direkten Kontakt zur Herzwand ist Gegenstand aktueller Untersuchungen. Hierzu wurde unter anderem die OLBl-Konfiguration (Overlapping Biphasic Impulse) entwickelt und in ein Schrittmachersystem implementiert. Bei dieser Stimulationsmethode werden über zwei flottierende Ringelektroden bezüglich des Gehäuses überlappende gegenpolige Stimulationspulse abgegeben. In dieser Arbeit wird die Optimierung der atrialen Stimulation über flottierende Elektroden anhand einer numerischen Analyse und klinischer Untersuchungen vorgestellt.

Untersuchung des Einflusses von Ischämie auf die Signalmorphologie von monophasischen Aktionspotentialen und evozierten Reizantworten

EINLEITUNG Der implantierbare Herzschrittmacher vollzieht derzeit einen Wandel vom reinen Therapiegerät hin zu einem implantierbaren elektrophysiologischen Labor, das neben der reinen Stimulation auch zunehmend die Diagnose unterstützt [1]. Hierbei hat vor allem die Messung der intrakardialen Signale MAP (Monophasisches AktionsPotential) und VER (Ventrikulär Evozierte Reizantwort) einen großen Stellenwert [2]. Gegenüber einer Analyse des Oberflächen-EKG im Hinblick auf durch Ischämien verursachte Veränderungen bietet eine Überwachung anhand von MAP und VER Vorteile durch eine kontinuierliche Meßbarkeit und eine sensitivere Erkennung ischämischer Reaktionen des Myokads. Ziel der Untersuchungen ist es, Veränderungen der intrakardialen Signale MAP und VER beim Vorliegen einer Ischämie zu messen und zu analysieren, um so geeignete Parameter für die Ischämie-Detektion zu finden.

Feldtheoretische Berechnung des monophasischen Aktionspotentials zur Optimierung von implantierbaren Elektroden

Das monophasische Aktionspotential (MAP) ist dem Transmembranpotential (TAP) der Myokardzellen morphologisch ähnlich und gilt als Standardsignal in der klinischen Diagnostik, um die Wirkung verschiedener therapeutischer Interventionen auf das TAP der Herzzellen zu bestimmen [1-3]. Die fraktale Beschichtung erlaubt aufgrund der elektrischen Eigenschaften der Oberflächenmodifikation die Langzeitmessung von MAP mit implantierbaren Sonden, doch muß die Geometrie der Elektroden weiter optimiert werden. Deswegen wird in diesem Beitrag eine Hypothese der Entstehung des bipolaren MAP aus dem TAP dargestellt, mit Hilfe derer eine geometrisch optimierte implantierbare MAP Elektrode entwickelt wurde.

Measurement of the complexity of the heart beat intervals

The complexity of the heart beat intervals of 7 patients with arrhythmia absoluta and 11 healthy control subjects was investigated using the box dimension D/sub B/ and the correlation dimension D/sub c/. Using a 2D embedding space, the box dimension assumed values greater than 1.40 (mean: 1.53/spl plusmn/0.010) in all arrhythmic patients whereas in all control subjects D/sub B/ was less than 1.31 (mean: 1.13/spl plusmn/0.012). D/sub c/ was computed in a 10D embedding space. The mean value of D/sub c/ was 7.26/spl plusmn/1.69 in the arrhythmia group and 5.70/spl plusmn/1.51 in the control group. Although this difference of the means is significant with 2.01/spl middot/10/sup -12/, a separation between arrhythmic and healthy persons was not possible.