First Diagonal to Left Ventricle Fistula With LAD Collateral Flow: An Unusual Coronary Detour

Coronary artery fistulas are rare vascular anomalies connecting a coronary artery to a cardiac chamber or vessel. While typically associated with ischemia via coronary steal, they can paradoxically serve a protective role.

We present a 57-year-old Asian male with 2 weeks of effort angina who was found to have an elevated high-sensitivity troponin. Urgent coronary angiography revealed a 100% mid left anterior descending artery (LAD) occlusion with collateral flow supplied predominantly by a fistulizing first diagonal artery (D1) communicating with the left ventricle.

The D1 fistula branches provided critical left-to-left collateral perfusion to the occluded LAD territory, likely limiting ischemic burden and preserving ventricular function. The LAD was successfully recanalized with drug-eluting stent placement, and percutaneous transluminal coronary angioplasty of the D1 was performed.

This case demonstrates that coronary artery fistulas are not inherently pathological and highlights the importance of individualized anatomical assessment when planning coronary interventions.