Visual observation of extraction of a Micra leadless pacemaker from a human cadaver.

INTRODUCTION: In this article we present the extraction of a Micra from a human cadaver implanted 3 years previously with both visual and X-ray imaging taken during the removal. METHODS: A Micra pacemaker was extracted from a human cadaver with endoscopy and fluoroscopy using a Micra delivery tool. Histological analysis was performed on slices from the tissue surrounding the Micra. RESULTS: The fully encapsulated Micra was easily retrieved with a maximum force of 1.9 pounds. CONCLUSIONS: Even though the Micra was implanted almost 3 years previously, the snaring and extraction of the Micra was performed relatively easily and with minimal force required.

Implant, performance, and retrieval of an atrial leadless pacemaker in sheep.

BACKGROUND: Medtronic is developing an atrial Micra Transcatheter Pacing System (Medtronic, Minneapolis, Minnesota) and associated retrieval system. OBJECTIVE: The purpose of this study was to evaluate chronic atrial Micra retrieval, reimplantation, and chronic pacing performance. METHODS: Sheep were implanted in 2 groups: group 1 (n = 6) for 6 months, a second device implanted, and first retrieved and studied for an additional 6 months; group 2 (n = 6) for 6 months, devices were retrieved, and a second device implanted and observed acutely. Both groups underwent histopathological evaluation. Pacing capture thresholds (PCTs), p wave amplitude, and pacing impedances were measured chronically. Device retrieval times were recorded, and intracardiac echocardiography was used. RESULTS: At 24 weeks, PCTs for group 1 were low and stable for both the first device (0.55 ± 0.14 V) and the second device (0.57 ± 0.09 V), in which the average retrieval time was 17:35 minutes. For group 2, the average retrieval time was 6:12 minutes, chronic PCTs in the first device were 0.53 ± 0.11 V, and acute PCTs for the second device were 0.71 ± 0.19 V. Pathological findings were within an expected range of tissue responses for similar Micra acute and chronic implants and device retrievals. p waves and impedances were stable and within an expected range for implant site and electrode design. Complications included 1 early dislodgment and 1 death attributed to a prototype retrieval tool. CONCLUSION: In an animal model, an atrial Micra can be easily implanted with excellent chronic pacing performance and is easily retrievable at 6 months. A second device can successfully be implanted with low, chronic stable thresholds. A developed prototype retrieval tool was easy to use and, with modifications, complication free.

Electrical parameters for physiological His-Purkinje pacing vary by implant location in an ex vivo canine model.

BACKGROUND: Permanent His-bundle pacing (HBP) is an attractive, perhaps more physiological, alternative to traditional right ventricular pacing. OBJECTIVE: The purpose of this study was to utilize direct visualization to more comprehensively understand the anatomy central to HBP, correlating electrical lead performance to implant locations along the His-bundle (HB) pathway. METHODS: Canine hearts (n = 5) were isolated and reanimated using Visible Heart methodologies. Medtronic 3830 SelectSecure leads were fixated where His potentials were present. The location of each implant was mapped/binned into 4 regions approximately analogous to the proximal, penetrating, and distal HB. Locational differences in HBP capture and resultant QRS morphology were assessed. RESULTS: Average HBP capture thresholds did not significantly vary with respect to implant location (1.0-ms pulse width; P = .48). The resulting QRS morphologies from HB-paced beats varied in relation to implant location. As leads were placed further distally along the HB, the ratio of paced to native QRS complex duration increased (ΔQRSpaced/ΔQRSnative ratios-region 2: 0.84 ± 0.16; region 3: 1.04 ± 0.42; region 4: 1.74 ± 0.86). CONCLUSION: We demonstrated correlation between the anatomic locations of HBP lead placement and resultant QRS morphologies in a reanimated canine heart model. Proximal placement along the HB pathway resulted in more favorable QRS morphologies, suggesting improved selective HBP capture, with no significant increase in HBP capture thresholds. Pacing the HB in more proximal pathway locations improved the selectivity of HBP and may confer electrical and anatomic benefits relative to distal HBP.