Case Report
A 4-year-old male (16.1 kg, 0.67 m2) infant heart transplant recipient presented with unexplained syncope. Historically, despite aggressive immunosuppression, he experienced chronic antibody-mediated rejection and markedly elevated panel reactive antibodies precluded re-transplantation candidacy. Long-term treatment has prioritized palliative care and maximization of quality of life.
Inpatient telemetry captured episodes of second-degree, Mobitz type II AV block with symptoms of tiredness and dizziness (Fig 1). Episodes lasted for several minutes with spontaneous resolution. Heart block was considered the mechanism for syncope and a sequela of chronic graft rejection. Permanent pacing was indicated and traditional and non-traditional pacing options were considered. Implications of each approach including potential impact on vascular access, relative ease of future endomyocardial biopsies, and post-procedure recovery were discussed. Collective agreement between the parents, transplant team, cardiac surgeons, and electrophysiologist was reached to pursue leadless pacemaker implantation. With the recent availability of the FDA-approved MicraTM AV pacemaker at our institution, this was selected for its potential benefit in addressing the patient’s specific pacing indication (ie. heart block).
Conventional right femoral venous implantation was performed under general anesthesia. Ultrasound-guided venous access was obtained and a 6-French (Fr) sheath was inserted. Contrast injection through the sheath was performed to assess femoral and iliac vein caliber. Given the vessels’ capacity for distension, slow and serial dilation was performed over an exchange length stiff wire with a series of dilators culminating in the dilator of the Micra introducer sheath (IS), followed by insertion of the complete IS set (27-Fr outer diameter). Insertion of the IS proceeded smoothly without resistance.
The Micra delivery catheter (DC) was prepped and advanced through the IS. To cross the tricuspid valve (TV), active flexion of the DC was applied with counterclockwise torque. Mid-septal implantation was initially attempted, however adequate septal orientation of the delivery cup could not be achieved. Furthermore, given the dimensions of the chamber at this location, mid-septal deployment was felt to potentially obstruct the TV apparatus proximally and the RV outflow and pulmonary valve superiorly (Fig 2A). Therefore, an apical septal location was pursued. The TV was crossed again more inferiorly. Clockwise torque was applied after crossing the valve to direct the DC tip toward the apical septum (Fig 2B). The device was deployed with at least 2 splines exhibiting appropriate fixation. Testing demonstrated acceptable functional values (R waves >10 mV, pacing threshold 0.63 V at 0.24 ms, impedance 570 ohms). Transesophageal imaging confirmed the implant location and showed no pericardial effusion or significant tricuspid interference. The anchoring tether was removed with preservation of device position (Fig 2C). Following DC withdrawal and before IS removal, an 0-Ethibond pursestring suture was placed around the skin entry site for closure and hemostasis. The site was covered with a pressure dressing. Post-implant interrogation showed preserved functional values and reasonable accelerometer-derived signals corresponding to atrial contraction (Fig 3).
Right lower extremity (LE) vascular ultrasound performed 2 days post-implant showed a near-occlusive thrombus in the common femoral vein (CFV). The pressure dressing and skin suture were removed on post-implant day #4 without any evidence of bleeding or hematoma. Given the luminal thrombus, subcutaneous heparin was initiated without bleeding recurrence. Follow-up assessment at 6 weeks post-implant showed normal device function and interval reduction in thrombus size with normal vessel flow pattern on follow-up LE scanning. The patient had returned to normal activities without syncope recurrence.