Background: Today, there is no manufacturer-supplied retrieval tool for the Micra TM pacemaker (Medtronic, Minneapolis, MN, USA); therefore, off-the-shelf catheters have been employed for retrievals. The proximal retrieval feature of the Micra TM can be snared and the device is then retracted from the myocardium, pulling the device through the tricuspid valve. This study characterizes the potential risks of Micra TM nitinol tine engagement with the tricuspid sub-valvular apparatus.Methods: Fresh human hearts nonviable for transplant (n = 10) were obtained from our regional organ procurement agency (LifeSource, Minneapolis, MN, USA). Micra TM fixation tines were affixed to a linear force transducer. Tines were then engaged in tricuspid chordae tendineae to conduct a constant velocity tensile test. Each test was run until tines disengaged from the chordae tendineae or until they released from the valve apparatus. Subsequently, biomechanical failure properties of the valve apparatus and isolated chordae tendineae were determined using a series of uniaxial tensile tests.Results: There were no chordal ruptures observed during our Micra TM tine extraction testing.Chordal failure required 15.0 times the force of extracting a single engaged tine, and 9.0 times the force of extracting two engaged tines. The uniaxial stresses required for isolated chordal failure averaged 17.4 N/mm 2 ; failure strains exceeded 150% resting chordal length. Conclusions:The forces required to rupture tricuspid chordae tendineae significantly exceeded the forces potentially imposed on the chordae during Micra TM device retrievals. We conclude that the fixation tines of the Micra TM device are unlikely to damage the tricuspid apparatus during either implant or retrieval. K E Y W O R D Sbiomechanical failure properties, cardiac anatomy, extraction, Micra pacemaker, retrieval, tricuspid valve device interactions

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Epicardial electrophysiological procedures rely on dependable interfacing with the myocardial tissue. For example, epicardial pacing systems must generate sustainable chronic pacing capture, while epicardial ablations must effectively deliver energy to the target hyper-excitable myocytes. The human heart has a significant adipose layer which may impede epicardial procedures. The objective of this study was to quantitatively assess the relative location of epicardial adipose on the human heart, to define locations where epicardial therapies might be performed successfully. We studied perfusion-fixed human hearts (n = 105) in multiple isolated planes including: left ventricular margin, diaphragmatic surface, and anterior right ventricle. Relative adipose distribution was quantitatively assessed via planar images, using a custom-generated image analysis algorithm. In these specimens, 76.7 ± 13.8% of the left ventricular margin, 72.7 ± 11.3% of the diaphragmatic surface, and 92.1 ± 8.7% of the anterior right margin were covered with superficial epicardial adipose layers. Percent adipose coverage significantly increased with age (P < 0.001) and history of coronary artery disease (P < 0.05). No significant relationships were identified between relative percent adipose coverage and gender, body weight or height, BMI, history of hypertension, and/or history of congestive heart failure. Additionally, we describe two-dimensional probability distributions of epicardial adipose coverage for each of the three analysis planes. In this study, we detail the quantitative assessment and probabilistic mapping of the distribution of superficial epicardial adipose on the adult human heart. These findings have implications relative to performing epicardial procedures and/or designing procedures or tools to successfully perform such treatments. Clin. Anat. 31:661-666, 2018. © 2018 Wiley Periodicals, Inc.

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