Pacing failure of leadless pacemaker caused by fractured tines

Key Teaching Points.

• •The selection of leadless pacemaker (LLPM) or transvenous pacemaker (TVPM) for the treatment of bradycardia is an important issue. TVPM is still associated with a significant number of complications, mostly related to the transvenous lead or subcutaneous pocket, and LLPM has overcome these related concerns.
• •Although the use of the currently available LLPM systems appears to result in a lower rate of device dislodgement, the most common reason for dislodgement of LLPM is poor tine fixation.
• •Although it is extremely rare and the specific mechanism is unclear, dislodgement and pacing failure of the LLPM owing to tine fracture should also be noted.

Introduction

Leadless pacemakers (LLPM) have a low incidence of complications and good electrical performance. Although LLPM have a passive fixation mechanism using tines, the dislodgement issues remain a safety concern for patients. Here, we report the first case with pacing failure caused by tine fracture.

Case report

An 81-year-old man with a syncopal attack was referred to our hospital for the treatment of complete heart block. The echocardiography revealed normal left ventricular ejection fraction and no evidence of cardiac hypertrophy, atrial enlargement, intracardiac thrombus, or infiltrative disease. The chamber sizes were normal for body surface area, although there was a mild diastolic dysfunction with impaired relaxation pattern. The patient remained relatively active (height 160 cm, weight 60 kg, body mass index 23.4, frailty score 5) but had thrombocytopenia with a platelet count of 36,000/mL and diabetes mellitus. The LLPM (Micra AV^TM, Medtronic, Minneapolis, MN) was selected, with concerns over the possible difficulty in hemostasis. The tortuosity of the femoral veins and anatomical abnormalities of the heart were excluded by venography and right ventriculography (Figure 1A and 1B). LLPM was successfully implanted in the right ventricular mid septum on the first attempt, with a capture threshold of 1.00 V at 0.24 ms, R-wave amplitude of 5.5 mV, and pacing impedance of 480 ohms (Figure 1C and 1D). The engagement of the device was confirmed with the standard pull-and-hold test, showing at least 3 of the 4 tines were fixed. However, the pacing threshold, obtained by remote monitoring, increased gradually 2 months after the implantation. The device parameters did not change significantly between initial implantation and final measurement except for a capture threshold (capture threshold of 1.00 V at 0.24 ms to 4.63 V at 0.24 ms, pacing impedance of 480 ohms to 400 ohms, R-wave amplitude of 5.5 mV to 6.8 mV, A4 amplitude of 2.8 m/s² to 5.1 m/s², respectively). The patient presented to our hospital with fatigue at 6 months after implantation. Intermittent pacing failure was observed even at maximal pacing output (Figure 2A). Fluoroscopy showed that 2 of the tines were fractured, 1 of which was completely isolated from the Micra and buried in the myocardium (Figure 2B, red arrow; Supplemental Movie). Since the LLPM body was well fixed with the remaining 2 tines, device removal was avoided. As the platelet count recovered from 36,000/mL to 61,000/mL, reoperation with a transvenous pacemaker (TVPM) was performed with no complications.

Figure 1.

A, B: Anatomical abnormalities of the heart were excluded by right ventriculography in (A) right anterior oblique (RAO) and (B) left anterior oblique (LAO) view. C, D: The contrast from the device tip confirmed device engagement with and near tissue.

Figure 2.

A: The intermittent pacing failure was observed on 12-lead electrocardiogram even at maximal pacing output. B: Fluoroscopy showed that 2 of the tines were fractured, 1 of which was completely isolated from the Micra pacemaker and buried in the myocardium.

Discussion

To our knowledge, this is the first report of pacing failure caused by LLPM tine fracture. LLPM has been reported to have a low risk of complications and good electrical performance. In a systematic review and meta-analysis, the incidence of complications at 90 days was 0.46% (95% CI, 0.08%–1.05%) and at 1 year was 1.77% (95% CI, 0.76%–3.07%). At 1 year, 98.96% (95% CI, 97.26%–99.94%) of patients (N = 1376) had good pacing capture thresholds.¹ In an investigational device exemption study, the dislodgement of LLPM was observed in 0.13% of patients in 30 days after implantation, with no tine fracture observed at 1 year follow-up.²

The selection of LLPM or TVPM for the treatment of bradycardia is an important issue. Although numerous developments have augmented pacemaker design and functionality, TVPM is still associated with a significant number of complications (8%–12%), mostly related to the transvenous lead or subcutaneous pocket.³ The LLPM eliminates complications associated with transvenous leads and pockets and improves pacing therapy. The complication rate was significantly lower in LLPM than in TVPM (0.9% vs 4.7%) at 800 days of follow-up.⁴ The reasons for choosing LLPM at the initial procedure in this case were as follows: the patient was relatively elderly; the indication for pacemaker was complete heart block and the Micra AV is capable of atrioventricular synchronization; and the generator pocket hematomas of TVPM could lead to serious device infection, whereas femoral vein puncture site hematomas were less likely.

This case demonstrated an extremely rare phenomenon of pacing failure caused by LLPM tine fracture. Although the precise mechanism of tine fracture is unclear, electrophysiologists should be made aware of this phenomenon.

Appendix Supplementary Data

Supplemental Movie legend

Fluoroscopy showed that two of the tines were fractured, one of which was completely isolated from the Micra pacemaker and buried in the myocardium.