Title : Complete heart block and persistent left SVC: A pacing challenge after AV canal repair
Abstract:
Case presentation
A 30-year-old woman with Down syndrome, who had open-heart surgery for AVSD in early childhood (undocumented), presented to the emergency department with symptomatic bradycardia. She was alert and normotensive (BP 100/60 mmHg) with a heart rate of 30 bpm and SpO2 of 99% on room air. There were no signs of heart failure and no murmurs. The ECG showed complete atrioventricular block.
Work up:
Transthoracic echocardiography showed normal biventricular size and systolic function. There was no residual atrial or ventricular septal defect and no left AV valve regurgitation, and estimated RVSP was 29 mmHg. The CS was dilated, and a modified suprasternal view confirmed a PLSVC. A bubble study with agitated saline showed contrast appearing first in the CS, before the right ventricle. A temporary pacing wire was placed via the right femoral vein for stabilization. Left-sided venography showed that the left subclavian vein drained into the PLSVC. There was no bridging (left innominate) vein, and no contrast reached the right SVC.
Management
A dual-chamber permanent pacemaker was implanted through the left subclavian vein and PLSVC. The leads passed through the PLSVC and CS into the right atrium and right ventricle, and were positioned under fluoroscopic guidance. Pacing and sensing parameters were satisfactory, and the postprocedure chest X-ray confirmed the lead course through the PLSVC and CS. The patient recovered without complications.
Discussion
About half of patients with Down syndrome have congenital heart disease, and AVSD is the most common lesion. Because the triangle of Koch is absent in AVSD, the conduction axis runs more inferiorly, which makes conduction vulnerable to disease. Late AV block can also follow surgical repair. A dilated CS due to PLSVC may also compress adjacent conduction tissue, and this may have contributed here. When no bridging vein is present, the lead course is unusual and implantation is harder, so planning ahead with venography is important. Echo clues such as an unexplained dilated CS, along with bubble studies, can identify the anomaly before the procedure.
Learning points
1. In adults with Down syndrome and repaired AVSD, conduction disease can be presented late and needs a high index of suspicion.
2. An unexplained dilated CS on echo should prompt a search for PLSVC, which can be confirmed with a bubble study or CT.
3. When PLSVC is present, a venogram before device implantation helps define the venous anatomy,including the absence of a bridging vein.
4. Device implantation through a PLSVC is feasible and safe in experienced hands
