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 AVTM, 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.