Abstract Body (Do not enter title and authors here): Background: Internal mammary artery (IMA) side branch flow diversion post- coronary artery bypass grafting (CABG) and its role in coronary steal syndrome remains controversial. However, evident association persists when substantial side branches stem from the IMA, possibly due to relatively lower peripheral resistance as compared to higher coronary resistance. Intervention has shown promise in ameliorating reversible ischemia in these cases. Recanalization of previously occluded side branch is rare and has only been reported within a 6 month period. We report a case of recanalization of a previously occluded side-branch after 4 years with recurrence of symptoms.

Case: A 63-year-old male underwent CABG with LIMA-LAD in 2020 and coil embolization of LIMA side branch for symptomatic coronary steal syndrome (figure 1). Angina recurred 3 years later, leading to right coronary artery stent placement. He now presents with palpitations and dyspnea on exertion. Vital signs and physical exam was unremarkable. ECG showed a normal sinus rhythm with no signs of ischemia. A 24-hour Holter showed significant polymorphic ventricular ectopy and episodes of sustained ventricular tachycardia (arrhythmic burden 12.4%). Transthoracic echocardiogram showed an ejection fraction of 71% and slightly decreased left ventricular global longitudinal strain (-16.6%).

Decision-making: A diagnostic cardiac catheterization was performed which showed patency of bypass and stent with no signs of occlusion or restenosis, rather revealing a permeable, previously occluded side-branch (figure 2A) and resurgent coronary steal phenomenon. Repeat coiling was performed, achieving complete cessation of flow (figure 2B) and evident increased flow to the LAD. Resolution of symptoms was observed and post-procedure Holter showed normal sinus rhythm with no arrhythmic changes.

Conclusion: Recanalization of an IMA side branch after complete occlusion with multiple coils is rare, particularly beyond 6 months. This appears to be the first reported case of the phenomenon, occurring after 4 years. Administration of heparin for recent stent placement, continuation of oral antiplatelet therapy and distal coil location may have contributed to restoration of flow, despite the presence of intraluminal coils. Repeat coiling proved successful in relieving symptoms.