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.