Surgical intervention for bilateral coronary artery fistulas to the pulmonary artery

Abstract

INTRODUCTION

A coronary artery fistula is an infrequent coronary abnormality. Treatment is indicated for symptomatic patients as well as for asymptomatic patients who are at risk for future complications, including pulmonary hypertension, congestive heart failure or coronary steal phenomena. In this paper, we report a patient with coronary artery fistulas to the pulmonary artery (PA) along with a high-flow left-to-right shunt, who was successfully treated by surgical intervention.

CASE REPORT

A 60-year old female with an underlying diagnosis of coronary artery fistulas to the PA was referred to our institution by a primary care physician. The patient was asymptomatic, though a Levine III/VI continuous murmur was heard in the upper left parasternal area in a physical examination. Multidetector computed tomography (MDCT) imaging showed two tortuous vessels with multiple aneurysmal dilatations originating from the right coronary artery (RCA) and the proximal site of the left anterior descending artery (LAD), located anterior to the main PA (Fig. 1 A and B). MDCT also revealed aneurysm formation in the proximal part of the LAD connecting with the origin of the afferent vessel of the coronary fistula, whereas the arterial vessels in the distal part of the LAD were relatively tiny (Fig. 1 B). Although coronary angiogram results showed no significant coronary stenosis, they confirmed two abnormal vessels arising from the conus branch of the RCA and LAD, and subsequently draining into the main PA (Fig. 1 C and D). Cardiac catheterization before surgery demonstrated PA pressure of 19/9 (16) mmHg, whereas right ventricular systolic pressure was 26/4 mmHg, indicating modest pulmonary or right ventricular pressure overload. Also, oximetry revealed an oxygen step-up of 10% between the right ventricle and the PA, consistent with an estimated left-to-right shunt of 47.1% and pulmonary/systemic flow ratio of 1.9. Based on these findings and anatomical features, a definitive repair procedure was scheduled.

Figure 1:

( A ) Preoperative MDCT image showing two tortuous vessels with multiple aneurysmal dilatations originating from the RCA and LAD. ( B ) MDCT image showing aneurysm formation in the proximal part of the LAD, connecting with the origin of the afferent vessel of the coronary fistula (black arrow head). Relatively tiny arterial vessels were seen in the distal part of the LAD. ( C ) Left coronary artery angiogram image showing abnormal vessels arising from the LAD and subsequently draining into the main PA. ( D ) RCA angiogram image showing abnormal vessels arising from the conus branch and coursing towards the PA. MDCT: multidetector computed tomography, LAD: left anterior descending artery, LCX: left circumflex artery, RCA: right coronary artery, PA: pulmonary artery.

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Intraoperatively, the abnormal vessels were found to have multiple aneurysmal dilatations along their course (Fig. 2 A). After establishing a standard cardiopulmonary bypass, the two fistulas were looped at their proximal origins. We confirmed the absence of electrocardiographic and haemodynamic alterations by temporal clamping of the abnormal vessels. Under heart arrest, the main PA was longitudinally opened from the pulmonary trunk towards the bifurcation of the PA and antegrade infusion of blood cardioplegia into the aortic root confirmed a single efferent hole sized 10 mm in diameter, which was located in the anterior sinus of the pulmonary trunk. This efferent hole was directly closed with two pairs of pledgeted mattress sutures of 4-0 polypropylene. Additionally, a cardioplegic solution was perfused through the aortic root in an antegrade manner, which confirmed a lack of vessel connection between the coronary artery and the PA. A sample of the PA wall was taken from a longitudinally incised portion of the main PA at the time of its closure. Thereafter, the afferent vessel arising from the RCA was ligated and subsequently transected at which it was looped in advance. A sample of the malformed vessel arising from the conus branch was taken from its transected site. The fistula originating from LAD was just ligated in a similar fashion. After weaning from the cardiopulmonary bypass system, we also confirmed the absence of arterial pulse in the fistulas and the oxygen saturation in the PA was nearly equivalent to that in the right ventricle.

Figure 2:

( A ) Intraoperative image showing abnormal vessels with multiple aneurysmal dilatations located anterior to the main PA. ( B ) Postoperative MDCT image showing no evidence of abnormal vessel communication between the coronary arteries and the PA. Black arrow heads indicate the closure site of afferent vessels arising from the conus branch of the RCA and LAD. MDCT: multidetector computed tomography, LAD: left anterior descending artery, RCA: right coronary artery, PA: pulmonary artery.

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Postoperative MDCT demonstrated no evidence of abnormal vessel communication between the coronary arteries and the PA, as well as relative dilatation of the native coronary arteries when compared with the preoperative state (Fig. 2 B). Haematoxylin–eosin staining showed elastic fibres aligned in an inhomogeneous manner and a cleavage in the PA wall associated with myxoid change. Elastica van Gieson staining demonstrated that the wall of the malformed vessel (fistula) mainly consisted of collagenous fibres and smooth muscle, partly accompanied by the inhomogeneously aligned elastic fibres.

DISCUSSION

A coronary artery fistula is an uncommon abnormal vessel communication between the coronary artery and cardiac chamber, great vessel or other vascular structures, with an estimated incidence of 0.002% in the general population. Bilateral coronary artery fistulas are even rarer and account for 5% of all coronary artery fistulas [ 1 ]. Previous studies have reported that low-pressure chambers are the usual drainage sites and about half (56%) of reported bilateral coronary artery fistulas terminate in the PA, as observed in our patient [ 2 , 3 ]. In this case, MDCT imaging enabled us to correctly characterize the complex and unusual coronary anomaly, which was crucial for successful intervention and also provided a means for postoperative assessment in a non-invasive manner. Interestingly, serial assessments revealed that the calibre of the native coronary arteries returned to normal when compared with the preoperative state, indicating that the surgical procedure effectively eliminated the left-to-right shunt. To the best of our knowledge, this is the first report to confirm morphological response of coronary artery vessels following a surgical procedure for coronary artery fistulas to the PA.

Surgical intervention for asymptomatic cases remains controversial. Gowda et al. reported that it is indicated for asymptomatic cases with specific conditions, including aneurysmal formation or high-flow left-to-right shunting (i.e. >30%) [ 4 ]. In our case, the indication of surgery was mainly based on high-flow left-to-right shunt (47.1%), though the patient did not show clinically significant pulmonary hypertension. Interestingly, there was a discrepancy between our preoperative assessment of PA pressure overload and the profound histological alteration of the PA wall, which may have been caused by long-standing volume overload. This finding suggests that a high-flow left-to-right shunt (>30%) may cause profound histological alterations of the main PA wall regardless of the severity of pulmonary hypertension.

Surgical treatment for a coronary artery fistula can be performed either with or without the use of a cardiopulmonary bypass. We performed transpulmonary closure of the efferent site of the coronary artery fistula and subsequent ligation of the afferent vessels under a cardiopulmonary bypass in the present patient. Antegrade perfusion of cardioplegia through the aortic root was extremely useful to confirm the absence of residual vessel communication between the coronary artery and the PA. Although it can be presumed that the exclusion of malformed vessels associated with a coronary artery fistula enables treatment of other small coronary artery fistula connections, the absence of both arterial pulse in the fistulas and oxygen step-up between the right ventricle and the PA led us to leave the malformed vessels as they were.

Pre- and postoperative MDCT assessments confirmed successful elimination of abnormal vessel communication, while the latter also showed residual aneurysm formation in the proximal part of the LAD. The cause of a coronary aneurysm concomitant with a coronary artery fistula is considered to be atherosclerotic, traumatic or mycotic [ 5 ]. In our case, neither a theromatous plaque nor bacterial or fungal infection was found in the malformed vessel wall. It is possible that a profound alteration of the musculo-elastic elements of the vessel wall promoted aneurysm formation associated with a coronary fistula to the PA. Given that the residual diseased coronary vessel can further promote aneurysm formation, long-term follow-up examinations are mandatory even after successful intervention for a coronary artery fistula to the PA.

CONCLUSION

We report successful surgical intervention for a relatively rare case of bilateral coronary artery fistulas to the PA. MDCT imaging was extremely useful to correctly characterize this complex and unusual coronary anomaly, as well as establish a treatment strategy. It also provided a means for accurate non-invasive postoperative assessment. In our patient, the presence of residual diseased coronary vessel requires further follow-up examinations, as that can further promote aneurysm formation.

Conflict of interest: none declared.

REFERENCES