A Novel Ex Vivo Heart Model for the Assessment of Cardiac Pacing Systems

[+] Author and Article Information
Timothy G. Laske, Nicholas D. Skadsberg

 Medtronic, Inc., 7000 Central Avenue NE, Minneapolis, Minnesota 55432

Paul A. Iaizzo

Departments of Biomedical Engineering, Physiology, and Surgery, University of Minnesota, 420 Delaware St SE, Minneapolis, Minnesota 55455iaizz001@umn.edu

J Biomech Eng 127(6), 894-898 (Jun 28, 2005) (5 pages) doi:10.1115/1.2049312 History: Received March 04, 2005; Revised June 28, 2005

Background: Advances in endocardial device design have been limited by the inability to visualize the device-tissue interface. The purpose of this study was to assess the validity of an isolated heart approach, which allows direct ex vivo intracardiac visualization, as a research tool for studying endocardial pacing systems. Method of approach: Endocardial pacing leads were implanted in the right atria and ventricles of intact swine (n=8) under fluoroscopic guidance. After collection of pacing and sensing performance parameters, the hearts were excised with the leads intact and reanimated on the isolated heart apparatus, and parameters again recorded. Results: Atrial ex vivo parameters significantly decreased compared with in vivo measurements: P-wave amplitudes by 39%, slew rates by 61%, and pacing impedances by 42% (p<0.05 for each). Similarly, several ventricular ex vivo parameters decreased: R-wave amplitudes by 39%, slew rates by 62%, and pacing impedances by 31%. In contrast, both atrial (4.4±2.8 vs 3.3±2.8V; p=ns) and ventricular thresholds increased (1.2±0.7 vs 0.6±0.1V; p<0.05 for all). Three distinct phenomena were observed at the lead-tissue interface. Normal implants (70%) demonstrated minimal tissue distortion and resulted in elevated impedance and threshold values. Three implants (13%) resulted in severe tissue distortion and/or tissue wrapping and were associated with highly elevated pacing parameters. Tissue coring occurred in four implants (17%) where the lead would spin freely in the tissue after overtorquing of the lead. Conclusions: The utility of the isolated heart approach was demonstrated as a tool for the design and assessment of the performance of endocardial pacing systems. Specifically, the ability to visualize device-heart interactions allows new insights into the impact of product design and clinical factors on lead performance and successful implantation.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

(Color) Representative images of Medtronic 5076 right atrial (A) and right ventricular (B) lead implants under fluoroscopic visualization (arrows point to the site of implant). Representative images of direct ex vivo visualization of right atrial (C) and right ventricular (D) implants.

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Figure 2

(Color) (A) Example of a “normal” lead implantation in the right atrium without any distortion of the endocardial tissue. (B) Example of a lead that “cored” the tissue at the implant site (arrows). (C) Example of an overtorqued lead implantation in the right atrium that resulted in the endocardial tissue to “wrap” around the distal end of the lead thereby significantly increasing pacing impedance and threshold values.

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Figure 3

Equivalent circuit schematic of the resistance network for a bipolar pacing system (top). Representative resistance circuit at the lead-tissue interface (bottom). A=Anode, AT=Anode-tissue interface, B=Blood, C=Cathode, CT=Cathode-tissue interface, M=Myocardium, and T=Tissue.

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Figure 4

(Color) Images showing a lead implantation on the low free wall of the right ventricular outflow tract: (A) Fluoroscopic image of the implant site demonstrating the inability to appreciate the fixation of the lead in the endocardial tissue, (B) superior endoscopic view shown from the pulmonary valve of the lead secured on the free wall of the outflow tract, and (C) inferior view of the implant shown from an endoscopic camera that is placed past the tricuspid valve.



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