Left Main Coronary Artery Fistula Presenting as Heart Failure: A Case Report

Introduction

Coronary artery fistulas (CAFs) are rare, with an incidence of 0.002% in the general population [1]. CAFs are most commonly due to congenital abnormalities but can also be acquired due to trauma, iatrogenic factors, post-myocardial infarction, Kawasaki disease, intracardiac device implantation, cardiac surgery, or ruptured coronary artery aneurysm.

CAFs occur when a coronary artery communicates with a cardiac chamber or a great vessel, bypassing the capillary circulation and usually creating a left-to-right shunt [2]. CAFs rarely drain into the left cardiac chambers [3].

Most CAFs are asymptomatic for decades and are often found incidentally by cardiac imaging unless they are very large or hemodynamically significant [4]. Symptoms resulting from complications such as ischemia, arrhythmias, or heart failure may manifest with increasing age, requiring treatment. Management can be tailored based on CAF dimensions. Small CAFs typically close on their own over time, while larger ones may require intervention [5,6].

We report a rare case of a symptomatic left-main-coronary-artery-to-left-atrium fistula in a patient with suspected Kawasaki disease during childhood.

Case Report

A 44-year-old woman presented with a 3-week history of dyspnea on exertion, orthopnea, paroxysmal nocturnal dyspnea, and bilateral lower extremity edema. She denied chest pain, gastric disturbance, or hemoptysis. At age 22, there was concern for childhood Kawasaki disease with an aneurysmal left main coronary artery (LMCA), and she underwent repair and coronary artery bypass grafting of the left internal mammary artery (LIMA) to the left anterior descending coronary artery (LAD), with concomitant mechanical mitral valve replacement (after failed mitral valve annuloplasty) for severe mitral valve prolapse.

For several years, the patient was closely followed up for persistent atrial fibrillation status post-multiple pharmacological and electrical cardioversions. Catheter-based or surgical ablative therapy for atrial fibrillation could not be performed due to severe biatrial dilation with the transseptal sheath unable to reach the interatrial septum, distorted anatomy, and previous open-heart surgery. She began developing mild heart failure symptoms with dyspnea on exertion about 2 years prior to presentation. Transthoracic echocardiogram (TTE) at that time showed normal left ventricular size and function and a severely dilated left atrium (LA).

She had been compliant with warfarin, maintaining a therapeutic International Normalized Ratio (INR) range of 2.5–3.5 since the valve replacement. She denied alcohol, tobacco, or substance use and was fully vaccinated with BNT162b2 (Pfizer-BioNTech) against SARS-CoV-2 (COVID-19). Her family history was noncontributory.

Vital signs upon arrival revealed blood pressure of 115/64 mmHg, heart rate of 73 beats per minute, and oxygen saturation of 95% on room air. An irregular heart rate and rhythm, bilateral rales, and lower extremity pitting edema were appreciated. Auscultation of her heart revealed a prominent holosystolic murmur over the precordium and an S3. No neck vein distension was noted. Complete blood count and comprehensive metabolic panels were unremarkable. B-type natriuretic peptide was elevated at 871 pg/mL (reference range 0–100 pg/mL), and serial high-sensitivity troponins were negative. Electrocardiogram (EKG) showed atrial fibrillation with controlled ventricular response. Chest radiography showed vascular congestion and cardiomegaly.

TTE revealed a newly severely dilated left ventricle with a markedly reduced ejection fraction of 20–24%, massive left atrial enlargement, left atrial end-systolic volume index of 249.2 mL/m2) (normal <34 mL/m2), mechanical mitral valve mean gradient of 10 mmHg (normal <5 mmHg), prosthetic mitral valve-left ventricle outflow tract dimensionless valve index of 4.07 (normal >2.2), indexed mitral valve area of 0.85 cm2/m2 (normal >1 cmv/m2), and pressure half-time of 110 ms (normal <130 ms). These measurements suggest significant prosthetic mitral valve dysfunction.

Ischemic cardiomyopathy was suspected due to left ventricle dysfunction. Left heart catheterization showed a dilated LMCA and patent LIMA-to-LAD graft with non-obstructive disease and no fistulous connection was appreciated at the time. Right heart catheterization after 4 days of intravenous diuresis showed a pulmonary artery pressure (PAP) of 50/15 mmHg (mean of 30 mmHg) (normal mean PAP, 12–16 mmHg), pulmonary capillary wedge pressure of 14 mmHg (normal, 4–12 mmHg), left ventricle end-diastolic pressure (LVEDP) of 7 mmHg (normal <12 mmHg), and cardiac output of 4.34 L/min (normal, 5–6 L/min).

The transesophageal echocardiogram showed aberrant flow in the LA originating from the LMCA into the posterolateral LA with fistula opening shown in Figure 1, marked with an asterisk (at the end of the white arrow; Figure 1). This was not consistent with central or paravalvular prosthetic regurgitation. The continuous flow jet was seen in the basal postero-lateral LA, in proximity to the left atrial appendage and aortic root at the left main trunk. The jet was associated with the turbulent flow of the LMCA (Figure 2; white arrow), consistent with an LMCA-LA fistula from a ruptured large LMCA aneurysm measuring 6.0 cm by 3.3 cm in maximum diameter. The fistulous flow extended deep into the LA towards the lateral annulus of the prosthetic mechanical mitral valve.

Surgical repair planning was facilitated by coronary computed tomography (CT) angiography (Figure 3) which showed a large calcified LMCA (circle) and its relation with the ascending aorta and left ventricle. She underwent redo sternotomy, resection of the LMCA aneurysm and replacement with an 8 mm ringed Gore-Tex graft, closure of the LMCA-to-LA fistula, and bovine pericardial patch exclusion of the left atrial appendage. The prosthetic mitral valve was otherwise functioning well, with its measured high transvalvular gradient most likely due to increased flow from the LMCA-LA fistula; therefore, no mitral valve interventions were required.

Two months following successful CAF repair, the patient’s functional status improved from New York Heart Association class III to class I (asymptomatic). Left ventricle ejection fraction improved from 20–24% to 45–49%. LA volume decreased from 481 mL (235 mL/m2) to 274 mL (134 mL/m2) (Figure 4). At 1 year post-operatively, further LA remodeling occurred with an LA volume index of 80 mL/m2 and an unchanged left ventricle function.

Discussion

Coronary-cameral fistulas are abnormal connections between a cardiac chamber and the coronary artery. They are very rare and require a high index of suspicion for diagnosis since symptoms may be nonspecific and slowly progressive, with overt manifestation only seen decades after their development [7]. Imaging findings may be subtle and easily missed. The present report describes a complex case of a middle-aged woman who presented with overt heart failure 2 decades after LMCA aneurysm repair and prosthetic mechanical mitral valve replacement, who was found to have a highly symptomatic LMCA-to-LA fistula. It was first suspected by observing an aberrant high-velocity color Doppler jet during transesophageal echocardiography. The disorder was confirmed with multimodality cardiac imaging, and she had an excellent outcome following team-guided surgical heart repair.

Blood flow follows the path of least resistance. Therefore, CAFs typically drain into the right atrium with left-to-right shunting [7]. However, our case depicts an extremely rare connection of the LMCA to the LA. CAFs with left-sided coronary artery to left-sided heart chamber have rarely been described [8–10]. Nakagawa et al reported a similar case involving a 49-year-old woman with an aneurysmal LMCA and an LMCA-to-LA fistula, who presented with overt heart failure and demonstrated an excellent outcome 3 years after surgical closure [11]. Renew et al described a comparable case of a 72-year-old woman with an LMCA-to-LA fistula, identified through abnormal left atrial flow following mitral valve replacement [12].

Other etiologies of fistulas draining into the LA have been described, such as drainage from a left circumflex artery due to an aberrant vessel [2], an aneurysmal left circumflex artery [13], and severe coronary artery disease [14]. Wolking et al discovered a left circumflex artery-to-LA CAF after TEE was indicated for interrogation of high bioprosthetic mitral valve gradients [15]. Iatrogenic left circumflex artery injury and subsequent CAF were attributed to mitral valve surgery. This adverse effect can occur in up to 2% of mitral valve surgeries due to the close proximity of the left circumflex artery to the mitral annulus [16]. Interestingly, in that case, and similarly in our patient, overt symptoms only manifested more than a decade after mitral valve replacement.

The patient’s presenting symptoms were initially attributed to prosthetic mitral valve dysfunction, which would have misguided the treatment approach. Several opportunities for diagnosis of this complex case were retrospectively recognized upon review of her care continuum and serial echocardiograms. Her LA had progressively dilated with increasing pulmonary artery systolic pressure estimates from mild to moderate pulmonary hypertension. The presence of an abnormally, massively dilated LA decades after mitral valve prosthesis implantation should raise suspicion for important differential diagnoses of prosthetic mitral valve dysfunction due to pannus formation, valve thrombosis, or endocarditis, as well as CAF formation after mitral valve surgery. Additionally, the development of new-onset atrial fibrillation should prompt an exhaustive workup for an etiology, despite the presence of a mechanical mitral valve prosthesis, particularly in patients with complex anatomy.

Her echocardiographic Doppler parameters were initially erroneously attributed to significant prosthetic mitral valve stenosis despite a normal pressure half-time of 110 ms, which would be suggestive of significant prosthetic mitral regurgitation. Nonetheless, the high peak mitral velocity (≥1.9 m/s), mean gradient, and high prosthetic mitral valve flow can be explained by increased flow across the mitral valve due to the LMCA-LA fistula. Atrial fibrillation may have resulted in beat-to-beat variation and possible underestimation of left ventricle stroke volume, explaining the abnormally high (≥2.5) prosthetic mitral valve-left ventricle outflow tract dimensionless valve index [17].

In addition to echocardiographic findings, catheter-derived increased pulmonary capillary wedge pressure (PCWP), more so than LVEDP, can be seen in mitral stenosis, pulmonary venous obstruction, cor triatriatum sinister, tachycardia, or atrial fibrillation [18]. Although the PCWP/LVEDP discrepancy in our patient was initially thought to be due to mitral valve dysfunction, it was most likely due to high transmitral flow in the setting of atrial fibrillation.

The differential diagnosis for an aberrant Doppler jet in the LA is broad, usually related to abnormal connections into the LA [12]. Rare cases have been described of anomalous vena cava return to the LA from both superior and inferior vena cavae after cardiac surgery [19]. Although more than 70% of the population have a normal pulmonary venous return, where all 4 pulmonary veins drain into the LA, pulmonary venous anatomical variants are common, with resultant supernumerary pulmonary veins or conjoined ostia. Right-sided accessory pulmonary veins draining from the right middle or right lower lung lobes are most frequently encountered, whereas accessory left-sided pulmonary veins draining from the lingula, a superior segment of the left lung lobe, or apical-posterior segment of the left upper lobe are less common [20]. An un-roofed coronary sinus resulting in right-to-left shunting can also present similarly [21]. Our patient’s CAF flow was seen in the posterolateral aspect of the LA. The continuous nature of the regurgitant jet suggested arterial flow, most consistent with coronary arterial flow, and ruled out variant pulmonary vein or vena caval venous return.

Multimodality imaging for CAF detection with echocardiography, cardiac CT, and coronary angiography was paramount for the diagnosis and treatment of our patient. The role of echocardiography is key in CAF detection and assessment of hemodynamic significance, as demonstrated in our case. TEE is widely available, and can be used for follow-up, comparison, determining lesion extension, corroboration of hemodynamic impact, assessment of relationships with other structures such as valves, coronary arteries, and venous structures, and help with procedural planning. In our case, coronary CT was used to confirm the presence of the LMCA-LA fistula. CT could have also been used to assess prosthetic mitral valve dysfunction initially, by observing leaflet motion and the presence of pannus or thrombi. Although cardiovascular magnetic resonance may have helped determine peak velocities through the valve and better estimate mitral regurgitation volume, the possibility of susceptibility artifact largely limits its use for mechanical valves and was hence not employed in our case.

CAF treatment is indicated when its presence results in any of the following: evidence of ischemia, arrhythmia, endarteritis, vessel rupture, cardiac chamber enlargement, and/or ventricular dysfunction [6]. High-quality evidence for managing CAFs is lacking, with only a small case series available, and is primarily based on expert opinion. The 2018 American College of Cardiology/ American Heart Association Guideline for the Management of Adults With Congenital Heart Disease emphasizes the importance of a heart team approach to determine the feasibility and suitability of CAF closure [5]. The decision to proceed with transcatheter percutaneous vs surgical closure is defined by anatomic feasibility for the catheter approach, ability to safely access the lesion with a wire, surgical risk, and CAF size. Surgical treatment is preferred for large coronary aneurysms proximal to the CAF, given the higher risk of myocardial infarction following closure of the CAF due to stagnant flow and subsequent vessel thrombosis [7]. Consideration is also given to the myocardium at risk. Smaller asymptomatic CAFs may be monitored closely, with serial imaging, as most may spontaneously close over time, although it should be noted that it is difficult to predict which smaller fistulae will enlarge over time [5,6].

Our patient met several criteria for CAF repair, including cardiac chamber enlargement, volume overload, ventricular dysfunction, and heart failure symptoms. Since the patient’s LIMA-to-LAD graft was intact and the LMCA aneurysm extended up until the bifurcation of the LMCA into the LAD and left circumflex artery, only surgical aneurysmectomy and repair were required without additional bypass grafting.

Following successful surgical intervention, the patient showed significant improvement in functional class, left ventricle function, and LA enlargement. The improvement was sustained after 1 year.

Conclusions

CAFs are infrequent and rarely symptomatic but can lead to unexplained cardiac chamber enlargement and marked symptoms. A high degree of clinical suspicion should prompt consideration of coronary-cameral fistulas, particularly in patients with antecedent coronary artery aneurysms. Our patient’s case was complex, considering her history of open-heart surgery for an aneurysmal LMCA and concomitant mechanical mitral valve replacement after failed mitral valve annuloplasty for severe mitral valve prolapse. She was treated with an LMCA aneurysm resection, left coronary artery reimplantation, Gore-Tex graft, fistula closure, and left atrial appendage closure with a pericardial patch, and remained asymptomatic at 2 months. Correction through intervention can lead to a favorable and sustained outcome.