Analytical Modeling for Computing Lead Stress in a Novel Epicardial Micropacemaker.

Implantation and maintenance of a permanent cardiac pacing system in children remains challenging due to small patient size, congenital heart defects and somatic growth. We are developing a novel epicardial micropacemaker for children that can be implanted on the epicardium within the pericardial space via a minimally-invasive technique. The key design configurations include a novel open-coiled lead in which living tissue replaces the usual polymeric support for the coiled conductor. To better understand and be able to predict the behavior of the implanted lead, we performed a radiographic image-based modeling study on a chronic animal test. We report a pilot study in which two mechanical dummy pacemakers with epicardial leads were implanted into an adult pig model via a minimally invasive approach. Fluoroscopy was obtained on the animal on Post-Operative Days #9, #35 and #56 (necropsy). We then constructed an analytic model to estimate the in vivo stress conditions on the open-coil lead based on the analysis of orthogonal biplane radiographic images. We obtained geometric deformation data of the implanted lead including elongation magnitudes and bending radii from sequenced films of cardiac motion cycles. The lead stress distribution was investigated on each film frame and the point of maximum stress (Mean Stress = 531.4 MPa; Alternating Stress = ± 216.4 MPa) was consistently where one of the leads exited the pericardial space, a deployment that we expected to be unfavorable. These results suggest the modeling approach can provide a basis for further design optimization. More animal tests and modeling will be needed to validate whether the novel lead design could meet the requirements to withstand ~200 million cardiac motion cycles over 5 years.