Pacing failure of leadless pacemaker caused by fractured tines

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, BMI 23.4, frailty score 5), but had thrombocytopenia with a platelet count of 36,000/$\mu$ L and diabetes mellitus. The LLPM (Micra AV^TM) was selected with concerns over the possible difficulty in hemostasis. The femoral veins tortuousity and anatomical abnormalities of the heart were excluded by venography and right ventriculography. (Figure 1-A, 1-B) 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 1-C, 1-D) The engagement of the device was confirmed with the standard pull and hold test, showing at least three of the four tines were fixed. However, pacing threshold obtained by remote monitoring increased gradually two months after the implantation. The device parameters did not change significantly between initial implantation and final measurement except for a capture threshold. (a capture threshold of 1.00V at 0.24 ms to 4.63V at 0.24 ms, pacing impedance of 480ohms to 400 ohms, R wave amplitude of 5.5mV to 6.8mV, A4 amplitude of 2.8m/s² to 5.1m/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 2-A) Fluoroscopy showed that two of tines were fractured, one of which was completely isolated from Micra and buried in myocardium. (Figure 2-B, red arrow, Supplementary Movie) Since the LLPM body was well fixed with the remaining two tines, device removal was avoided. As the platelet count was recovered from 36,000/$\mu$ L to 61,000/$\mu$ L, the reoperation with a transvenous pacemaker (TVPM) was performed with no complications.