Search PubMed⌕ Search

Biomedical subjects

M Schaldach

Publications and source records attributed to M Schaldach.

At least 73 records · Page 4Linked to original sources
PubMed1996

Evoked epimyocardial electrogram for rejection diagnosis after heart transplantation.

An endomyocardial electrogram (ECG) was reported to be a sensitive and practicable method for rejection monitoring after heart transplantation. Long-term follow up was limited, however, by variations of signals. The repolarization part of ECG signals vary with changes of heart rate. Both can be avoided by using pacemaker-induced signals. For stimulation and sensing of the ventricular-evoked response, a new type of electrode with fractal surface structure was used. Twenty patients undergoing heart transplantation were evaluated. Amplitudes of the depolarization and repolarization part of the ventricular-evoked response signals were analyzed and related to the degree of acute rejection according to histological findings from endomyocardial biopsy. Signals were transferred by Internet and analyzed automatically. In the case of focal moderate rejection (grade 2, International Society for Heart Transplantation grading) and higher degrees of rejection, a significant amplitude decrease was found. This sensitive non-invasive method for rejection monitoring with a high level of reliability provides the possibility of reducing the number of endomyocardial biopsies.

Adult↗
PubMed1996

[Technology and algorithms for implantable dual chamber defibrillators].

The next generation of implantable cardioverter/defibrillators (ICDs) will have the capability for sensing and defibrillating in both chambers of the heart. These devices, which are presently being developed, will thus be able to differentiate between ventricular and supraventricular tachycardias, and to respond accordingly. The burden of stress on the patient will therefore also be further reduced by avoiding unnecessary shock treatment of supraventricular tachycardias. In addition, the new generation of ICDs can also be used for the treatment of chronic atrial tachyarrhythmias. With the dual-chamber IEGM-recording capability, these ICDs will also provide the physician with an important diagnostic tool. The present article describes such an ICD.

Algorithms↗
PubMed1996

Coating of cardiovascular stents with a semiconductor to improve their hemocompatibility.

Thrombogenesis on artificial surfaces can be described as an electron transfer reaction. To inhibit this oxidation process and thereby achieve high hemocompatibility, a surface requires semiconducting properties. However, because all known solid semiconductors are extremely brittle, the requirements for high hemocompatibility and mechanical stability cannot be met by any single material. Therefore, a hybrid design is introduced as a new approach to improve the hemocompatibility of cardiovascular stents.

Angiography↗
PubMed1996

Paced epimyocardial electrograms for noninvasive rejection monitoring after heart transplantation.

BACKGROUND: Diagnosis of acute heart rejection after transplantation with the help of epimyocardial electrograms has been reported as a sensitive and practicable method. Long-term follow-up has been limited, however, by variations o signal, which can be avoided by using pacemaker-induced signals. METHODS: For stimulation and detection of the ventricular evoked response, a new type of electrode with fractal surface structure was used. Seventeen patients undergoing heart transplantation were included in the study. Amplitudes of the depolarization and repolarization parts of ventricular evoked response signals were analyzed and related to the degree of acute rejection according to histologic findings from endomyocardial biopsy. RESULTS: In cases of focal moderate rejection (grade 2, International Society for Heart and Lung Transplantation grading) and higher degrees of rejection, significant amplitude decreases were found. CONCLUSION: This sensitive noninvasive method for rejection monitoring with a high level of reliability provides the possibility of reducing the number of endomyocardial biopsies.

Biopsy↗
PubMed1995

[Simulation of myocardial action potentials of various cell types in relation to neural parameters].

Action potentials of various myocardial cell types were simulated in a computer model based on current knowledge of the electrical properties of ionic channels and pumps in the ventricular cell membrane and the sarcoplasmic reticulum. The transport mechanisms of sodium, potassium, calcium and chlorine ions through the cell membrane are described mathematically, as is the exchange of calcium between the myoplasm and sarcoplasmic reticulum. Ten ionic channels and three pumps of the cell membrane are taken into account, while three channels and one pump of the sarcoplasmic reticulum are considered in the computations. For the first time, the transient outward potassium current IK,to was simulated, the effect of which on the early repolarisation phase of the action potential was reproducible in the model. Calcium buffers in the myoplasm and the sarcoplasmic reticulum are also considered. From the resulting ionic currents through the channels and pumps, the membrane potential is computed using an equivalent circuit diagram of the cell membrane. In particular the influence of neural activity on channel conductance and the probability of channel patency were taken into account. By means of this model, different shapes of ventricular action potentials were simulated. The action potentials of epicardial cells, M-cells, endocardial cells and Purkinje fibres were accurately simulated. In addition, the effects of sympathetic drive and various drugs were demonstrated in the model as well as the shortening of the action potential duration with increasing stimulation frequency.

Calcium↗
PubMed1995

[Measurement and analysis of monophasic action potentials using fractally coated electrodes--I].

The monophasic action potential (MAP) contains a wealth of information about the stat of the myocardium, which makes it very useful for numerous diagnostic and therapeutic applications in patients with heart disease. The silver-silver chloride electrodes which are currently used for the measurement of MAP have poor long-term stability in contact with biological tissue. This study was therefore undertaken with the aim of investigating the electrochemical behaviour of fractally coated leads in terms of their signal-detection performance. Experience gained with these leads in cardiac pacemakers has already demonstrated the long-term stability and biocompatibility of the fractally coated leads. Present results show that, due to their large electrochemically active surface area, fractally coated leads have a very low impedance over a wide frequency range. The negligible polarization artifact of these leads permits the measurement of cardiac potentials immediately after a stimulus. Fractally coated leads are thus highly suitable for the measurement of MAP, and have clear advantages over Ag/AgCl electrodes. The second part of this study reports on the results of MAP measurements using fractally coated leads.

Electrocardiography↗
PubMed1995

[Measurement and analysis of monophasic action potentials using fractally coated electrodes--II].

The monophasic action potential (MAP) represents a summed signal formed by overlapping action potentials of myocardial cells close to the tip of the lead. Analysis of the MAP therefore provides detailed information about the electrophysiological effects of autonomous nervous and pharmacological influences on the myocardium, for example adrenergic or cholinergic stimulation of the heart. All known MAP recordings were obtained with Ag/AgCl electrodes, which, thanks to their low polarization properties, ensure reliable MAP measurement. Owing to their toxicity and inadequate long-term stability, however, Ag/AgCl electrodes cannot be implanted. With the aim of making MAP measurement available for implantable devices, fractally coated leads were therefore developed. The aim of the present study was to evaluate the in vivo measurement of fractally coated leads which are characterized by negligible polarization, low impedance over a wide frequency range, high biocompatibility and good long-term stability. In addition, as a result of their extremely high Helmholtz capacities (up to 50 mF/cm2), fractally coated leads permit stimulation and virtually undisturbed recording of MAP with the same pair of electrodes. For the evaluation of MAP measurements with fractally coated leads, a quadrupolar catheter enabling simultaneous MAP recordings with 2 Ag/AgCl electrodes and 2 fractally coated leads was devised. The stimulation pulses were always applied via the fractally coated leads. With both types of electrode, with spontaneous excitation and stimulation, the well-known MAP morphology, with amplitudes of between 10 and 25 mV in the ventricle, and between 5 and 10 mV in the atrium, was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Atropine↗
PubMed1995

New aspects in electrostimulation of the heart.

The interaction of the autonomic nervous system (ANS) and the heart is characterized by a new interdisciplinary field known as neurocardiology which presents the newest strategy for electro-cardiostimulation. In this context, the reestablishment of chronotropy with physiological, closed-loop pacing, as well as the prevention and treatment of a malignant arrhythmia by ANS modulation, is of the highest priority. The main objective toward this goal consists of appropriate monitoring of the autonomic balance and stimulation, respectively, so that neuromodulation of the cardiac efferents can be established. The electrode, as a sensor and an actuator, with its interface on the cellular level becomes of essential importance. The electrode-myocardium interface is determined by the structure of the Helmholtz double layer with regard to its physical, electrochemical, and physiological behavior. The transportation of electrons across the boundary, as well as the electro-chemical reactions determining the biocompatibility of the interface, can be improved by the microstructure of the solid component by creating a fractal surface coating with titanium-nitride or iridium. Experimental and clinical results have demonstrated that the fractal structure ensures negligible polarization as well as improved detection performance, thus, detecting the evoked response of the myocardial cells makes it possible to monitor the neural response of the myocardium as a consequence of a superimposed chronotropic disturbance. The stimulation electrode also monitors the sympathetic activity extracted from intracardiac impedance measurements, thereby providing a new principle of rate adaptation in which the pacemaker is an integral part of the ANS, reestablishing normal chronotropy. Further advantages of the improved electrode interface performance open new aspects in the treatment and prevention of tachyarrhythmia, and in the follow-up of transplanted hearts for the prevention of the rejection processes.

Arrhythmias, Cardiac↗