The first human pocket histology at an eight-week cardiac implantable electronic device with absorbable antibacterial envelope: case report

Background: The second-generation TYRX™ absorbable antibacterial envelope (Medtronic, Minneapolis, MN, USA) effectively reduces cardiac implantable electronic device (CIED) infections, as shown in the WRAP-IT trial. However, data on its degradation process and pocket histopathology in humans remain scarce, with most evidence derived from preclinical studies. Case summary: An 80-year-old woman with hypertension and hyperlipidaemia received a cardiac resynchronization therapy pacemaker for heart failure with reduced ejection fraction and left bundle branch block. The device was implanted with a TYRX envelope. Fifty-six days later, she presented with intermittent loss of left ventricular pacing due to atrial undersensing and underwent right atrial lead revision. Pocket exploration revealed a thin light amber capsule covering the device. Histopathology showed different stages of TYRX resorption and wound healing: residual envelope material with lymphocytes and multinucleated giant cells in the outer layer (chronic inflammation), collagen-rich granulation tissue with neovascularization in the middle layer (proliferation), and a dense acellular fibrous capsule adjacent to the device (remodelling). The maximum thickness of capsule measured 1210 μm. Discussion: This case provides rare human histopathological evidence of an eight-week-old TYRX envelope, illustrating ongoing degradation and distinct wound-healing phases. The findings bridge preclinical observations and human data, enhancing understanding of envelope absorption dynamics.