Biomedical subjects

A M Pichlmaier

Publications and source records attributed to A M Pichlmaier.

5 recordsLinked to original sources

PubMed2001

Cell seeded decellularised allogeneic matrix grafts and biodegradable polydioxanone-prostheses compared with arterial autografts in a porcine model.

BACKGROUND: small diameter vascular grafts are limited by their restricted availability, early thrombosis, and requirement for anticoagulants. OBJECTIVE: to evaluate different approaches to biocompatible vascular grafts. METHODS: sixteen allogeneic acellularised arteries seeded with autologous endothelial cells were implanted to replace a segment of the common carotid artery (group I). Other animals received polydioxanone prostheses (group II: inner diameter, i.d. 4 mm, n=18; group III, i.d. 5 mm, n=20) or arterial autografts (group IV, n=8). Graft patency was evaluated by means of ultrasound duplex scanning, angiography and histology. RESULTS: patency was 54% (71%), 17% (0%), 50% (50%), and 100% (100%) in group I, II, III, and IV after 1 week (4 months), respectively. Significant differences (p<0.05) were found for group IV versus all other groups at 1 week, as well as for group IV versus groups II and III, for group II versus III, and group I versus II at 4 months. CONCLUSION: small diameter vascular grafts can be engineered from an acellular allogeneic matrix seeded with autologous cells. Patency is superior to polydioxanone prostheses but inferior to the arterial autograft.

Animals↗

PubMed1998

Prediction of the onset of atrial fibrillation after cardiac surgery using the monophasic action potential.

OBJECTIVE: To show that the monophasic action potential (MAP) recorded continuously from human epicardium may be used to predict the imminent onset of atrial fibrillation or flutter (AF) following surgery, thus allowing prophylactic treatment to be started. PATIENTS: 22 patients (14 male, 8 female; mean (SD) age 64 (12) years) undergoing aortic valve replacement. SETTING: Tertiary referral centre. METHODS: Over a mean observation period of 8 (2.7) days (range 4 to 14), nine episodes of AF were seen in six patients. Before AF, specific and significant alterations of the MAP morphology were observed. In seven of nine episodes the MAP shortened (25 (4)% 60 minutes before AF), developed a triangular shape, and the plateau amplitude decreased from 5.3 (1.2) to 2 (0.2) mV. In the two remaining episodes the beat to beat variability of cycle length and MAP duration at 90% repolarisation (MAPd90) increased significantly from 24 (7) ms and 12 (8) ms (24 hours before AF) to 137 (27) ms and 56 (11) ms (30 minutes before AF) respectively. AF was successfully treated by the administration of sotalol in three cases and by a combination of verapamil and digoxin in a further four. Previously observed changes of MAPd90 and MAP morphology regressed after conversion to sinus rhythm. CONCLUSIONS: The continuous and intermediate term recording of the MAP from atrial epicardium appears to be a valid tool for detecting imminent AF after cardiac surgery with a high sensitivity (99%) and specificity (88%). Optimised antiarrhythmic treatment may thus be given selectively for prophylaxis.

Action Potentials↗

PubMed1992

Autonomic nervous system controlled closed loop cardiac pacing.

A multicenter clinical study is presented, which focuses on the reestablishment of closed loop cardiac control in patients with chronotropic insufficiency. Using the information about sympathetic tone contained in the myocardial contractility, it is possible to reconnect the heart rate to the physiological control mechanisms. Intracardiac impedance is measured with the ventricular electrode and the ventricular inotropic parameter (VIP) is derived from that. The VIP serves directly as input to the control of heart rate by the pacemaker. Over 200 patients have received autonomic nervous system (ANS) controlled pacemakers. The patient-pacemaker system was investigated in different ways. This included standard exercise tests, long-term studies of every day activities over 24 hours, psychological, and pharmacological challenges. To prove the validity of the approach we specifically looked at (1) the appropriateness of changes in paced heart rate with sympathetic tone during exercise, (2) the correlation between heart rate and sinus rate, if detectable, and (3) the correlation between the echocardiographically determined preejection period (PEP) and the VIP controlled heart rate.

Autonomic Nervous System↗

PubMed1992

[Measuring intracardiac impedance for the determination of sympathetic nerve activity in frequency-adapted electrostimulation--Part 2: Clinical results].

The results of a multicenter clinical study involving patients receiving the first ANS controlled rate adaptive pacemaker are presented. In the patients with primary or secondary chronotropic insufficiency, it is possible to reestablish the closed loop control system that includes the baroreceptors, the medulla oblongata, the cardiac output and the mean arterial blood pressure. This system serves to keep the blood pressure constant in the face of changing demands on the circulation. Utilizing intracardiac impedance measurements, the myocardial contractility can be determined, which contains information about the current sympathetic tone, and thus represents an excellent physiological input for a rate adaptive mechanism. The results presented are taken from a study population of over 200 patients. The objective evaluation of this new approach was performed echocardiographically, by ergometry and 24-hour Holter monitoring.

Adult↗

PubMedDate not supplied

[Measuring intracardiac impedance for determining sympathetic nerve activity in frequency-adjustment electrostimulation--1: Biomedical technical principles].

Modern Pacemaker technology makes it possible to adapt the pacing rate to hemodynamic requirements. The most ambitious approach aims at restoring the physiological closed-loop system by utilizing the information supplied by the Autonomic Nervous System and extracted from myocardial contractile performance. Measurement is accomplished by the impedance method using the stimulating electrode as the measuring electrode. The Ventricular Inotropic Parameter (VIP) has been identified as an ANS-dependent parameter. A special detection algorithm, the Regional Effective Slope Quantity (RQ), with a high ANS sensitivity has been developed specially for the purpose. Rate adaptation is achieved by using an individually-adjustable Inotropic Index (II). The concept has been evaluated in a multicenter study employing a standardized exercise protocol. The clinical results will be presented in Part 2 of this paper.

Algorithms↗