Background

Mitral valve prolapse (MVP) is an etiologically heterogeneous disorder [1, 2]. Early diagnosis and prompt treatment of the underlying disease are critical. Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) is a rare and potentially life-threatening congenital coronary artery anomaly with an incidence of 1 in 300,000 live births, accounting for 0.25–0.5% of all congenital heart diseases [3]. Rarely, it is associated with other cardiac anomalies such as atrial septal defect, ventricular septal defect, aortic coarctation, tetralogy of Fallot or bicuspid aortic valve [5]. Our patient, who was also a young mother, had never experienced any discomforts in her life and her left ventricular function was preserved. This may have been attributed to her well-developed collateral vessels.

ALCAPA is most prevalent in infants, children and young adults. Therefore, this rare disorder may go unnoticed. Transthoracic echocardiogram, which is widely accessible, allows for a rapid and noninvasive assessment of structural and functional cardiac abnormalities at relatively low cost and is, therefore, the preferred imaging modality for these patients [8, 9]. In the present case, the extremely dilated coronary arteries and retrograde blood flow from the LCA shown by echocardiogram prompted us to search for the underlying cause of MVP. While coronary angiography allows for good visualization of the course of the anomalous coronary artery and collateral vessels, it is invasive and has some complications. Coronary computed tomography angiography, which has an excellent spatial and temporal resolution, can noninvasively show the origin and course of the anomalous coronary artery and it is regarded as the mainstay diagnostic technique for ALCAPA [10]. In addition, cardiac magnetic resonance imaging is a highly valuable imaging modality because of its unique tissue characterization, which enables the accurate assessment of myocardial ischemia and fibrosis [11, 12].

Prompt surgical intervention is critical for patients with ALCAPA, as it allows for gradual and even complete myocardial recovery [6, 13]. The recommended treatment for ALCAPA is direct reimplantation of LCA into the aorta to reestablish two-coronary circulation. In cases where direct reimplantation of LCA is not technically feasible (eg. LCA originating far from the aorta, abundant collaterals or noncompliant tissues around the ostium of ALCAPA), intrapulmonary tunnel repair (Takeuchi operation) or coronary artery bypass grafting (CABG) with LCA ligation should be considered [6, 14].

Mitral insufficiency (MR), a common complication of ALCAPA, is predominantly caused by ischemic dysfunction of the papillary muscles and adjacent myocardium, as well as annular dilation due to left ventricular remodeling [3, 15]. In these situations, the majority of mitral insufficiencies are reversible and may improve following ALCAPA repair, with only a small percentage deteriorating and requiring mitral valve reintervention [16]. Therefore, performing mitral valve intervention at the time of ALCAPA repair is still contentious. Nonetheless, structural abnormalities of the mitral apparatus including MVP, chordae tendineae rupture, mitral valve cleft and papillary muscle infarction/fibrosis, which occur in about 20% of ALCAPA patients, can’t recover from revascularization and concomitant mitral valve repair should be considered [3, 13, 16].

The mechanisms of MVP in ALCAPA may be similar to those in coronary artery disease, which include ischemic impairment of the papillary muscles and adjacent myocardium as well as chordae tendineae rupture [7, 17, 18]. Different from coronary artery disease, a recent study found that anterior leaflet prolapses occur more often in ALCAPA patients than posterior ones [16]. This may be explained by the difference in blood supply. For ALCAPA patients, the left ventricle is entirely supplied by the low-pressure collateral vessels. Additionally, the blood from collateral vessels preferentially flows into the low-pressure pulmonary circulation rather than into the high-resistance myocardial circulation, resulting in a longstanding “coronary steal” phenomenon. Lastly, the anterior papillary muscle is exclusively supplied by the remote branch of LCA [19]. In this case, the arterial supply of the anterior papillary muscle is severely compromised and the chordae tendineae connecting the anterior papillary muscle is highly vulnerable. Therefore, the ruptured chordae tendineae (A2) in our patient was probably caused by previously severe ischemic impairment. Furthermore, her anterolateral papillary muscle on the enhanced CT was much smaller than the posteromedial papillary muscle (Fig. 4), also indicating longstanding ischemic atrophy of the anterolateral papillary muscle.

Fig. 4
figure 4

Enhanced computed tomography of the small anterolateral papillary muscle (a) and the normal posteromedial papillary muscle (b)

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In conclusion, ALCAPA is a rare and potentially life-threatening congenital coronary artery anomaly that may cause mitral valve prolapse. Echocardiogram is an important screening tool for this disorder.