On the 12th day of life, coronary buds appear after the truncus arteriosus begin to divide by spiral septum forming the aorta and pulmonary artery. Mal-positioning of coronary buds or malrotation of the spiral septum can lead to coronary artery anomalies . In a study on a series of 38,000 patients undergoing cardiac catheterization, coronary artery anomalies were detected in 1.6%. Congenital coronary artery anomalies are divided into 4 groups, anomalous origin of a coronary artery from the pulmonary artery, the ectopic origin of a coronary artery from the aortic sinus, absence of a coronary artery, and coronary artery fistula . The most common type of anomalous coronary artery with connection to the pulmonary artery is the anomalous origin of a left coronary artery from the pulmonary artery (ALCAPA) with an incidence of 0.008% followed by ARCAPA (0.002%). Due to the higher oxygen demand of the left ventricle and bigger territory fed by the left coronary artery (LCA) symptoms appear early in life leading to early diagnosis, Myocardial ischemia and sudden cardiac death are also more common in ALCAPA for the same reason [29, 31].
Since 1882 when John Brooks described the first case of ARCAPA, more than 100 cases of ARCAPA are identified. Patients with ARCAPA are usually asymptomatic and usually detected incidentally when the patient is undergoing cardiac evaluation for other problems. But when symptomatic, although uncommon, can include dyspnea, fatigue, congestive heart failure, angina, MI, and even sudden cardiac death . ARCAPA symptoms onset has two peaks, one early after birth and another between 40 and 60 years. Early in life, high pulmonary pressure feeds RCA territory with deoxygenated blood, leading to the formation of collateral vessels. When pulmonary pressure drops, these collaterals result in the backflow of oxygenated blood from the LCA system to the pulmonary artery which is called “coronary steal”. If this phenomenon happens, symptoms of ischemia appear in the early years. As for later onset symptoms, because the single functioning coronary system is more prone to atherosclerosis, ARCAPA patients develop ischemia around 40–60 .
Before 1965 all ARCAPA cases were diagnosed during surgery or at autopsy but due to cardiac imaging advancement coronary angiography and echocardiography are the most popular methods nowadays . Cardiac angiography is still the gold standard method for coronary artery anomalies, despite being invasive it can establish a complete map of coronary vasculature which can also be helpful for the treatment of anomalies. Retrograde flow through the RCA, increased flow with dilation of the LCA/RCA, direct flow between the pulmonary artery and the RCA, and collateralization between the left and RCA systems are features suggestive of ARCAPA in angiography .
Transthoracic echocardiography (TTE) is a safe, non-invasive, inexpensive, and portable method to examine the origin of coronary arteries . Echocardiography also has the chance of finding synchronous cardiac lesions, which was seen in 23.8% of ARCAPA patients. knowledge of these lesions can improve myocardial protection strategies when performing cardiopulmonary bypass, reducing post-operative complications .
One of the best views to visualize the origins of coronary arteries is the parasternal short-axis. In patients with ALCAPA, there are usually signs of myocardial ischemia. Endocardium and papillary muscles look “shiny”. Reverse flow from the myocardium to the pulmonary trunk is one of the most important findings suggesting the diagnosis. in addition, as the lesion is a fistula, and due to increased collateral flow from the right to the left coronary system, there is an increase in flow across minor coronary arteries which is detected by lowering the Nyquist limit. It is essential to perform color flow mapping because isolated cross-sectional imaging may find LCA a normal aortic origin. After all, sometimes LCA takes an intramural course through the aortic wall in ALCAPA. In the younger patient, the most striking features are dilation of the RCA and collateral arterial flow in the ventricular septum which can be misdiagnosed as multiple muscular ventricular septal defects (VSD). To distinct these two, pulse-wave interrogation should be performed. ALCAPA has continuous flow in collateral arteries, whereas in VSD cases the major finding is systolic color flow entering the right ventricle [28, 33].
ARCAPA is easier to find in echocardiography compared to ALCAPA. Main findings in adult patients with ARCAPA include intraseptal coronary collaterals in using color flow Doppler mapping, dilation of coronary arteries, increased flow in the LCA, and flow between the RCA and the pulmonary artery. Sometimes even the ostium of RCA can be seen entering the pulmonary artery trunk. The left coronary artery is usually enlarged and tortuous and collateral arteries are present in the ventricular septum as seen in ALCAPA. Wall motion abnormalities in ventricles can also be seen in TTE [4, 6, 10,11,12,13,14, 28, 32]. When there is a dilated LCA and continuous or diastolic retrograde flow from an anomalous vessel to the pulmonary artery, ARCAPA can be mistaken for a coronary fistula. It is usually the case when the origin of ARCAPA is not visualized. In a real coronary fistula, the origin of RCA can be traced back to the right sinus of Valsalva. Atresia of RCA is also a differential diagnosis when dilated LCA is present with inter-coronary collaterals in the ventricular septum. In this case, the origin of RCA from pulmonary should not be visible .
Transesophageal echocardiography also further distinguishes the tortuous anomalous coronary arteries and characterizes their flow patterns. It has the advantage of the proximity of the probe to the interest area, in addition to better spatial resolution due to a higher frequency transducer. This method also has some limitations because vessels have a curvilinear path along the epicardial surface, and it is very difficult and time-consuming to visualize their entire course .
It is crucial to mention that even with a detailed echocardiographic examination the diagnosis can be easily missed because there are inherent limitations in ultrasound resolution which can lead to difficulty distinguishing the origin of coronary arteries, especially because there can be an ultrasonic dropout in the wall of the aorta near transverse sinus and left coronary artery. Therefore, TTE can only be used to rule in the diagnosis not ruling out. Albeit Doppler color flow improved this diagnosis significantly. It is recommended that when the coronary artery appears to originate from the aorta in echocardiography but all the facts point to anomalous origin from the pulmonary trunk, a different modality should be used . CTA and MRA can provide a 3-dimensional representation of cardiac anatomy, helping confirm the suspected diagnoses of echocardiography. MRA has the advantage of determining blood flow direction and velocity as well as not requiring ionizing radiation or intravenous contrast . The main disadvantage of these methods is their high price, which highlights echocardiography's role as a quick first step when ARCAPA is suspected .
Although most cases of ARCAPA have isolated lesions, approximately 40% of patients have concomitant congenital cardiac defects. Aortopulmonary window is the most common associated congenital lesion with ARCAPA accounting for one-fourth of cases [1, 3, 6, 14, 34]. Other associated lesions include VSD, atrial septal defect (ASD), tetralogy of Fallot, patent ductus arteriosus, aberrant right subclavian artery, and bicuspid aortic valve [32, 34]. The aortopulmonary window is characterized by abnormal communication between the pulmonary artery and ascending aorta with two separate semilunar valves. When it is associated with ARCAPA, the pulmonary artery pressure is kept high therefore the flow in the anomalous coronary artery is maintained and myocardial ischemia usually doesn’t develop. Moreover, there is no sign of dilation or tortuosity in coronary arteries and collateral circulation in contrast to isolated ARCAPA in echocardiography [35, 36].
Nearly all studies suggest surgical treatment as soon as ARCAPA is diagnosed due to the chance of myocardial ischemia and cardiac failure. Patients who were not surgically treated had shorter life spans, and besides surgical correction have low postoperative mortality of 2–3%. Surgical treatment of ARCAPA has 2 purposes, elimination of left to right shunt or “coronary steal” and establishment of dual coronary circulation from the aorta [3, 6]. Formerly, ligation of the anomalous coronary artery was often used, and oxygenation of RCA territory was dependent on the collateral vessels, but this method was associated with high early and late mortality . Now there are 3 surgical options for ARCAPA treatment, reimplantation of the anomalous coronary artery to the ascending aorta, ligation of ARCAPA, and CABG using saphenous vein graft, and single ligation. Reimplantation is the ideal one because it can achieve both treatment goals. CABG is selected when ARCAPA originates from the posterior wall of the pulmonary artery and reimplantation cannot be done. Ligation should be the last option when CABG and reimplantation are not possible .
There are several limitations to our study. First, we only included published ARCAPA cases, and thus unreported cases were not analyzed. Second, echocardiographic findings are highly operator dependent and we were confined by what the authors report in their examinations. Third, comprised cases were gathered over nearly 40 years and echocardiographic devices and diagnostic criteria have highly evolved, leading to disparity in findings. Albeit, we used recent suggested echocardiographic findings in ARCAPA for comparison and removed those cases that did not match our criteria.