Leadless pacemaker in heart transplantation: a case report and literature review

Discussion

During the first 24 hours post-transplant, most patients require chronotropic support or temporary pacing due to sinus node dysfunction.1 Early sinus node dysfunction is due to sympathetic denervation, surgical trauma and prolonged graft ischaemic time.1 2 AV block is less common in cardiac transplant patients, but the risk increases with time. After 30 days post-transplant, AV conduction disease is as prevalent an indication for pacemaker placement as sinus node dysfunction.2 AV block is thought to be a sequela of chronic rejection, cardiac allograft vasculopathy and injury from recurrent endomyocardial biopsies.2 Most patients eventually regain normal sinus or AV node function. For patients with persistent bradycardia, theophylline is used off-label to increase heart rate.1 Patients with bradycardia that persists after theophylline use may need a pacemaker.1

Pacemaker implantation in cardiac transplant patients is complicated by a higher risk of infection due to immunosuppression required to prevent allograft rejection. Infection is a leading cause of death in this population. About one in four cardiac transplant patients with pacemakers die of infection within 5 years.3 Time of pacemaker implantation from time of transplantation has unclear prognostic implications. One study showed no difference in mortality rates between patients with early pacemaker requirement (defined as ≤30 days post-transplant), late pacemaker requirement or no pacemaker requirement.4 Another study found that early pacemaker requirement (defined as ≤1 year post-transplant) was associated with increased mortality due to chest infection.3 This is likely due to the higher levels of immunosuppression required more immediately post-transplant.

LPMs are a newer technology designed to address infections associated with traditional pacemakers. The major advantage of LPMs over traditional pacemakers is the absence of a subcutaneous pocket and transvenous leads. The pulse generator of a traditional pacemaker is implanted under the skin, allowing potential contamination of the pocket and leads from bacterial skin flora.5 On the other hand, LPMs are implanted directly into the myocardium and endothelialise over time. Endothelialisation reduces the already smaller surface area of the device exposed to the bloodstream and potential bacteria.5 The rate of traditional pacemaker-related infection is estimated to be 385 per 50 000 cases, whereas that of LPMs is 1 per 50 000 cases.5 Thus, cardiac transplant patients may be ideal candidates for LPMs. Another important benefit of LPMs is their ability to be implanted in patients with challenging upper extremity venous access, such as our patient who had prior transvenous lead extraction with a retained fragment. Traditional pacemakers require a lead to be placed through a large superior vein leading to the heart. LPMs are implanted using a femoral approach, bypassing the need for superior venous access. Conversely, LPMs can also be advantageous to preserve superior venous access, such as in patients with chronic kidney disease who may eventually require haemodialysis.

The major advantage of traditional pacemakers over LPMs was the ability to use dual chamber pacing. However, this may no longer be the case as a recent prospective study demonstrated the safety and efficacy of dual chamber LPMs at 90 days post-implantation.6 Dual-chamber LPMs may be an excellent option for cardiac transplant patients who require a high level of pacing to preserve atrial-ventricular synchrony and optimise cardiac output.

Complications of LPMs include device dislodgement, cardiac perforation, cardiac tamponade, infection and vascular injury. However, the incidence of these complications from Micra implantation is extremely low at 0.46% at 90 days and 1.77% at 1 year.7 In comparison, the incidence of serious complications after traditional pacemaker implantation is 7.8% at 90 days8 and 16% at 3 years.9

Safe LPM implantation has been described in four prior case reports or case series of heart transplant recipients (table 1).10–13 Biatrial transplant technique was used in seven patients and bicaval technique in three patients. The more common pacemaker indication was high-grade AV block. Most patients were paced for ≤2% of the time, but two patients with sinus dysfunction were paced 50% and 100% of the time.10 11 Our patient aligned with the majority and had biatrial transplant technique, paroxysmal complete AV block and pacing ≤0.1% of the time. Our patient appears to have had the longest follow-up time at 5 years. Like our patient, no subsequent adverse events, infectious or otherwise, occurred. LPM implantation was effective in 10 of 11 cases, including our patient. One patient had a traditional pacemaker implanted after LPM implantation due to loss of capture, but there were no associated adverse events.10

In conclusion, our case demonstrates the safe and effective use of an LPM in a heart transplant recipient with 5 years follow-up. When permanent pacing is required, implantation of an LPM should be considered in heart transplant recipients given their immunocompromised state and increased risk for infection.