Acute or delayed lead perforation is a rare but serious complication of pacemaker implantation with numerous case reports and case series known . A perforation-resistant lead tip design requires detailed knowledge regarding the mechanical failure of the ventricular wall. Like many other soft biological tissues, ventricular tissue exhibits complex mechanical properties like incompressibility, finite deformability, inhomogeneity, material non-linearity, anisotropy, strain rate-dependency, and a constitutive model should reflect that to the required degree of completeness. Within this work we investigate the failure mechanisms of myocardial penetration by advancing a rigid punch, conditions thought to be related to pacemaker lead perforation. Specifically, the impact of constitutive parameters related to the bulk material and the failure zone is analyzed.
A single penetration site of our previous penetration experiment of biaxially-stretched myocardial tissue  was models by the non-linear Finite Element Method (ABAQUS,
Dassault Systèmes). To this end a visco-elastic description was applied and a previously reported anisotropic constitutive model for myocardial tissue  was implemented using the user material model interface. All failure related inelastic deformations were lumped into a fracture process zone and captured by a triangular cohesive traction separation law. To this end the cohesive strength of ventricular tissue was experimentally determined by tensile testing in cross-fiber direction of porcine myocardial tissue. Simulated results with different visco-elastic and failure properties, i.e. by varying the associated sets of constitutive parameters of the myocardial tissue were investigated.
Results and Conclusions
Results demonstrated that visco-elastic properties of the myocardial tissue strongly determine the failure of myocardial tissue due to deep penetration. This finding is in line with failure of rubber-like materials, where visco-elastic energy dissipation in front of the crack tip was found to be an important factor of energy dissipation . In contrast dissipative effects which are directly related to failure (i.e. captured by the cohesive zone model) had a minor impact on the simulated penetration force displacement characteristics. Likewise, non-linearity and anisotropy of the bulk material did not change the predicted peak penetration force and the simulations did not reveal elastic crack-tip blunting.
The proposed numerical model integrates experimental data from different studies and allows a detailed investigation of failure related to pacemaker lead perforation. Results from the study provided novel insights into ventricular failure due to deep penetration, which might also be related to other soft biological tissues and helpful to design penetration resistant pacemaker leads.
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WCB 2010 - 6th World Congress on Biomechanics, Singapore, Singapore, August 1-6, 2010