New-Onset Atrial Flutter Revealing a Large Right Coronary Artery to Superior Vena Cava Fistula

BACKGROUND: Coronary artery fistulas are rare anomalous communications between a coronary artery and a cardiac chamber or great vessel. Large fistulas can cause chamber dilation, myocardial ischemia, heart failure, and arrhythmias. CASE SUMMARY: A 63-year-old man presented with palpitations, hypotension, and atrial flutter with rapid ventricular response requiring urgent cardioversion. Multimodality imaging with coronary computed tomography angiography and cardiac magnetic resonance revealed a large right coronary artery-to-superior vena cava fistula with right-sided chamber dilation. Cardiac catheterization confirmed the diagnosis, and the patient underwent successful transcatheter coil embolization. DISCUSSION: Coronary artery fistulas may present with atrial arrhythmias due to chronic left-to-right shunting and atrial remodeling. This case highlights atrial flutter as an uncommon presentation and underscores the importance of multimodality imaging for diagnosis and procedural planning. TAKE-HOME MESSAGES: Coronary artery fistulas should be considered in patients with unexplained atrial arrhythmias and cardiac chamber enlargement. Early recognition enables definitive treatment with transcatheter closure.