Coronary artery fistulas are rare vascular anomalies characterized by abnormal communication between a coronary artery and a cardiac chamber or major vessel, with a reported prevalence of approximately 0.05%-0.25% on conventional coronary angiography and up to 0.9% on coronary computed tomography angiography^[1]. Depending on the fistula size, drainage site, and shunt volume, untreated medium or large fistulas may lead to coronary steal, chronic volume overload, chamber enlargement, myocardial ischemia, pulmonary hypertension, arrhythmia, and heart failure^[2]. Aneurysmal atrial septal artery is uncommon and may further complicate the anatomy when associated with coronary artery fistula. In this setting, long-standing left-to-right shunting and chamber remodeling may contribute to secondary mitral regurgitation even in the absence of primary mitral leaflet pathology^[3].

Surgical repair remains an established treatment option for complex coronary artery fistulas; however, with advances in transcatheter equipment and techniques, percutaneous closure has become an alternative in selected patients, particularly when surgical risk is high and the anatomy is suitable for device closure^[2]. In patients with concomitant severe mitral regurgitation, treatment sequencing requires careful assessment because mitral regurgitation may improve, persist, or worsen after correction of the primary shunt lesion. Here, we report a rare case of left coronary artery fistula associated with a giant aneurysmal atrial septal artery and severe mitral regurgitation, managed with sequential transcatheter fistula closure and transcatheter edge-to-edge repair supported by multimodality imaging and 3D printing.

A 72-year-old female patient presented with a 7-year history of chest distress and exertional dyspnea. Over the preceding 3 days, her symptoms had worsened, with orthopnea and mild bilateral pitting edema. On admission, her blood pressure was 104/64 mm Hg, heart rate was 105 beats per minute, respiratory rate was 22 breaths per minute, and oxygen saturation was 99%. Physical examination revealed a continuous grade IV/VI murmur at the left sternal border and moist rales over both lower lung fields, consistent with heart failure. The hepatojugular reflux sign was negative. Electrocardiography showed atrial fibrillation with a ventricular rate of 90-130 bpm. The N-terminal pro-B-type natriuretic peptide (NT-proBNP) level was elevated at 5,138 pg/mL.

Transthoracic echocardiography revealed enlargement of the left atrium, right atrium, and left ventricle, with a left atrial diameter of 77 × 94 mm, right atrial diameter of 43 × 76 mm, left ventricular end-diastolic diameter of 61 mm, left ventricular end-systolic diameter of 48 mm, and left ventricular ejection fraction of 54% measured by the modified Simpson’s biplane method. Severe mitral regurgitation was mainly related to poor leaflet coaptation, with an effective regurgitant orifice area of 0.56 cm² and a regurgitant volume of 89 mL. Moderate tricuspid regurgitation and mildly elevated pulmonary artery systolic pressure of 45 mm Hg were also noted.

Transesophageal echocardiography demonstrated an enlarged left main coronary artery with a 19 mm fistulous tract and a large interatrial lesion measuring 31 × 30 mm, which was identified as an aneurysmal atrial septal artery rather than an intracardiac tumor or thrombus. The aneurysm had a 5 mm outflow to the right atrium. No thrombus was detected in the left atrial appendage, and no pericardial effusion was observed. Three-dimensional reconstruction further confirmed the presence of a giant aneurysmal atrial septal artery [Figure 1].

Cardiac computed tomography confirmed a tortuous and markedly dilated coronary artery fistula communicating with the right atrium through the giant aneurysmal atrial septal artery, which was located on the right lateral aspect of the atrial septum [Figure 2]. Coronary angiography showed no significant obstructive coronary artery disease and confirmed a left main coronary artery-to-right atrium fistula [Figure 3].

This case illustrates the staged transcatheter management of a rare and complex condition involving a left main coronary artery-to-right atrium fistula, a giant aneurysmal atrial septal artery, and severe secondary mitral regurgitation. The main value of this case lies in the combination of unusual anatomy, aggravation of mitral regurgitation after fistula closure, and subsequent transcatheter edge-to-edge repair guided by multimodality imaging and 3D printing.

Medium or large coronary artery fistulas may cause chronic left-to-right shunting, coronary steal, chamber enlargement, pulmonary hypertension, arrhythmia, and heart failure^[2]. In the present case, long-standing left-to-right shunting was associated with marked enlargement of the left atrium, right atrium, and left ventricle, elevated pulmonary artery pressure, atrial fibrillation, elevated NT-proBNP, and severe mitral regurgitation due to poor leaflet coaptation. These findings supported a secondary mechanism of mitral regurgitation related to chronic chamber remodeling rather than isolated primary leaflet disease^[3]. Severe heart failure related to large coronary cameral fistulas has been described in previous reports, although coexistence with a giant aneurysmal atrial septal artery and dynamic worsening of secondary mitral regurgitation after fistula closure remains uncommon^[4,5].

The decision to adopt a staged strategy was based on both pathophysiological and procedural considerations. Because the mitral regurgitation was considered predominantly secondary to chronic volume overload and chamber remodeling, initial closure of the primary shunt lesion followed by guideline-directed medical therapy and reassessment was considered reasonable. In addition, simultaneous transcatheter edge-to-edge repair was not favored because the giant aneurysmal atrial septal artery increased the risk of transseptal puncture-related injury and acute left-to-right shunting. This rationale was particularly relevant in the present case, in which safe transseptal access was a major procedural concern.

The worsening of mitral regurgitation after fistula closure is an important observation in this case. One possible explanation is that elimination of the low-resistance shunt altered left-sided loading conditions and unmasked or aggravated pre-existing secondary mitral regurgitation. However, this interpretation remains inferential rather than definitive because right heart catheterization and Qp/Qs measurement were not performed. Therefore, the proposed mechanism was supported mainly by the temporal relationship, serial echocardiographic findings, and changes in clinical and biomarker status. This point is important because the case should be interpreted as an individualized treatment experience rather than definitive evidence of causality.

Precise imaging was essential for both stages of treatment. Echocardiography defined the severity and mechanism of mitral regurgitation, cardiac computed tomography delineated the fistula course and its relationship to the aneurysmal atrial septal artery, and coronary angiography guided device selection and closure. The 16 mm vascular plug was selected according to the 10.9 mm angiographic landing zone, with coil embolization used for residual small channels. Prior experience with device-based closure of giant high-flow vascular fistulas also supports the broader procedural principle that occluder selection should be individualized according to fistula anatomy and flow characteristics, although coronary fistulas require additional attention to preservation of distal coronary perfusion^[6].

The 3D-printed model provided information beyond routine two-dimensional imaging by allowing direct assessment of the spatial relationship between the aneurysmal atrial septal artery and the planned transseptal route. In this case, the model showed that the aneurysm was located posteriorly and superiorly along the atrial septum, supporting an anterior and mid-septal puncture trajectory to avoid the aneurysmal segment. This helped reduce procedural uncertainty before transcatheter edge-to-edge repair. Similar applications of CT-based 3D modeling have been reported in complex fistula closure and transcatheter structural heart interventions^[7-9].

Alternative strategies included surgical fistula ligation with aneurysm repair and mitral valve surgery, hybrid treatment, or simultaneous transcatheter intervention. Surgery may provide definitive anatomical correction in selected patients; however, it was not favored in this patient because of advanced age, heart failure, atrial fibrillation, recent clinical deterioration, and complex anatomy. Simultaneous transcatheter treatment was also avoided due to the anticipated risk of transseptal access in the presence of a giant aneurysmal atrial septal artery. The favorable 12-month clinical, echocardiographic, and biomarker outcomes suggest that sequential transcatheter treatment may be feasible in carefully selected high-risk patients.

This case has several limitations. First, it is a single case report and cannot establish generalizable treatment recommendations. Second, invasive hemodynamic assessment, including right heart catheterization and Qp/Qs measurement, was not performed. Finally, although 12-month follow-up showed sustained clinical improvement and reduced mitral regurgitation compared with the pre-TEER status, longer follow-up is needed to assess residual mitral regurgitation, residual fistula flow, and long-term cardiac remodeling.

In summary, this case demonstrates that sequential transcatheter treatment may be feasible for selected high-risk patients with coronary artery fistula, giant aneurysmal atrial septal artery, and severe secondary mitral regurgitation. Closure of the primary shunt lesion, followed by reassessment and transcatheter edge-to-edge repair, was associated with symptomatic, echocardiographic, and biomarker improvement at 12 months. Multimodality imaging and 3D printing were useful for defining complex anatomy, guiding device-based treatment, and reducing uncertainty during transseptal procedural planning.