Duan, Xiaomin MM^*; Yu, Tong MD^†; Wang, Fangyun MM^‡; Liu, Hui BA^§; Sun, Jihang MM^†; Zhai, Renyou MD^∥

Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) is a rare congenital cardiovascular malformation. Approximately 90% of patients with coronary artery anomalies originating from the pulmonary trunk presented with ALCAPA,¹ which is a malignant form that can cause myocardial ischemia, resulting in left ventricular dysfunction, mitral insufficiency, congestive heart failure, arrhythmia, or sudden death. It occurs in approximately 1 in 300,000 live births or 0.25% to 0.5% of children with congenital heart disease.² It usually manifests as an isolated defect; but in 5% of cases, it may be associated with other cardiac anomalies, such as atrial septal defect, ventricular septal defect, and aortic coarctation.³ ALCAPA was first reported by Bland, White and Garland in 1933. Thus, this malformation was therefore named the Bland-White-Garland syndrome.⁴ An embryological defect during fetal cardiac development results in the left coronary artery (LCA) arising from the pulmonary artery instead of the aorta.^5,6 In fetal life, this anomaly most likely has no harmful effect: pressure and oxygen saturations are similar in the aorta and pulmonary artery. Myocardial perfusion is presumably normal.⁷ At birth, newborns are rarely symptomatic, as they have a relatively higher pulmonary artery resistance, which enables anterograde flow into the anomalous LCA. However, as the child approaches 1 to 2 months of age, the pulmonary pressure decreases gradually and there is retrograde flow from the high-pressure coronary arteries to the pulmonary trunk.⁴ This phenomenon is known as pulmonary-coronary steal, which results in myocardial ischemia and infarction. At this period, if the collateral vessels between the normal right and abnormal left coronary are well established, then it is the adult type of the disease, and if there are no or few collateral vessels established, then it is the infant type. Both types of the disease have different manifestations and outcomes.

MATERIALS AND METHODS

Patients Clinical Data

Between 2007 and 2014, 9 patients (4 males and 5 females) were diagnosed with ALCAPA. Diagnosis was made on the basis of imaging studies by cardiac CT and was confirmed by cardiac surgery in our hospital. The age at presentation ranged from 2 to 17 months, with a median age of 10 months, the weight ranged from 3.0 to 9.2 kg, with an average of 6.2 kg. Five patients were referred for the evaluation of heart failure and 4 patients complained of cough and dyspnea. Chest x-rays, electrocardiogram (ECG), 2-dimensional, and color Doppler echocardiograms were performed on all patients. Coronary angiography was performed on 1 patient. The institutional review board approved this retrospective study, and the requirement for informed consent was waived.

Cardiac CT Scans Protocol

The acquisition was strictly limited to the heart, and ECG-synchronized cardiac CT (Lightspeed VCT; GE Healthcare, Waukesha, WI) scan was performed in all 9 patients using a body size adapted low-dose protocol. The scanning range covered 5 to 10 cm, from 1 cm below the tracheal carina to 1 cm under the margin of the cardiac apex, working from head to foot.

The effective absorbed dose estimates of cardiac CT based on International Commission on Radiological Protection (publication 103) ranged from 0.68 to 2.54 mSv. Raw data sets were reconstructed from 5% to 95% using the snapshot segment plus method, at every 5% of the RR interval; the reconstructed slice thickness was 0.625 mm. All data were transferred to a workstation (Deep-Blue Advantage Workstation 4.3, GE Medical Systems). Three-dimensional coronary tree, multiplane reconstruction (MPR), and maximum intensity projection (MIP) for each coronary artery were performed to select the best image for qualitative analysis. During the 5%, 45%, 55%, or 95% phase of the RR interval, the images were the best, and clear visualization of the connection of the coronary artery and pulmonary artery was observed.

Contrast Administration

In all patients, an iodinated contrast medium, iopromide at 300 mg/mL (Ultravist 300; Bayer Schering Pharma, Berlin, Germany) was bolus injected intravenously at a dose of 1.6 to 2.0 mL/kg with a double-head power injector (EZEM, New York). The contrast medium was administered via the antecubital vein using a 22- to 24-gauge needle in all patients. The delay time of scanning was fixed within 20 to 21 seconds, which included a single stage of contrast medium injection within 12 to 13 seconds, which was then followed by a flush of 6 to 12 mL saline within 5 to 6 seconds and waiting time of 2 seconds. All delay times were based on the 0.33-second rotation time of the scanner.

Image Review

The image analysis included 36 coronary arterial original positions and diameters including the right coronary artery (RCA), the LCA, the left anterior descending artery (LAD), the left circumflex artery (LCX), and the coronary collateral vessels. Two experienced pediatric radiologists independently assessed the image quality. They were aware of the diagnosis of ALCAPA and any disagreements between these 2 observers were solved by consensus.

RESULTS

Imaging Manifestations

In all patients referred after the chest x-ray film, standard 12-lead ECG, 2-dimensional, and color Doppler echocardiograms and MDCT were performed (Table 1). One of the 9 patients was referred to cardiac catheterization.

Table 1

Anteroposterior chest films of all patients exhibited marked cardiomegaly, predominantly affecting the left atrium and ventricle. The cardiothoracic ratio was 0.56 to 0.76, with an average of 0.64. Five patients experienced mild pulmonary edema. Two patients had normal pulmonary markings.

ECG: All patients showed normal sinus rhythm without abnormalities in atrioventricular conduction. Five patients exhibited an abnormal Q wave with inverted T-wave. In 4 patients, ST segment depression was found in leads I, aVL, and V5. Ventricular extrasystole was found in 4 patients, atrial extrasystole in 1 patient, and A-V block in 2 patients.

Echocardiography (ECHO): In this group, ECHO demonstrated the existence of anomalous origin of the vessel in 6 patients. In one of these, the anomalous vessel arose from the posterior aspect of the pulmonary artery trunk, in 3 patients from the lateral aspect and 2 patients from the pulmonary left sinus. There was retrograde blood flow in the LCA in these 6 patients, in 4 of whom intercollateral vessels could be seen between the LCA and RCA on the surface of the diaphragm. In the other 3 patients, the precise origin of the LCA was uncertain (Fig. 1), retrograde blood flow too fine to be seen. They were diagnosed as endocardial fibroelastosis (EFE).

Figure 1

In all patients, the endocardium was thickened at the anterior and lateral walls and there was enhanced echogenicity involving the anterolateral papillary muscle and its chordae tendineae, with various degrees of mitral regurgitation. The left ventricular ejection fraction (LVEF) was impaired (below 50%) in 5 patients, and normal (beyond 51%) in 4. In 2 of patients, a ventricular aneurysm had formed (Table 2).

Table 2

Cardiac CT: A total of 10 anomalous coronary arteries were found in 9 patients. Nine LCAs arose from the pulmonary artery and 1 right coronary from a left cusp of aorta (Fig. 2). Two of these 9 patients had anomalous LCAs arising from the posterior aspect of the pulmonary artery (Figs. 3 and 4C), which passed between the aorta and the main pulmonary artery, extending from the inferior pulmonary trunk to reach the interventricular groove, then branching into the LAD and LCX. In 2 patients, anomalous LCAs arose from the inner aspect of the pulmonary artery (Figs. 4A, B). Three of these 9 patients had anomalous coronary arteries originating from the left lateral aspect of the pulmonary trunk, separating into LAD and LCX. In the remaining 2 patients, the LCA originated from the pulmonary valve sinus extending into the interventricular groove (Fig. 5).

Figure 2

Figure 3

Figure 4

Figure 5

Concentration of contrast medium in the LCAs and pulmonary artery in 4 patients indicated a blood steal phenomenon (Fig. 3). The LCA appeared normal in size with no coronary collateral development in 4 patients, who had obvious symptoms of heart failure (LVEF below 50%) and myocardial infarction. Ventricular aneurysms were found in 2 of these patients. The other 6 patients exhibited no distinct thinning of the myocardia, with abundant collateral vessels and a tortuous RCA (Fig. 6).

Figure 6

DISCUSSION

According to the pathophysiology, ALPACA classified the primary and secondary 2 findings. Primary findings were anomalies of origins and/or the reverse blood flow. Secondary findings included left ventricular enlargement, functional failure, ventricular aneurysm formation, mitral regurgitation, endocardial thickening, papillary muscle degeneration, the formation of collateral vessels, and left-to-right shunt.

Diagnostic Imaging Modalities

Various imaging modalities including ECHO, cardiac CT, cardiac MRI, and catheter cardiac angiography have been used to evaluate cardiac abnormalities seen in infants.

Echocardiography is the initial routine diagnostic modality for patients with cardiomegaly. Echocardiography is not only convenient, economical, and requires no radiation, but it also can provide more important information for the clinical doctor, such as left-to-right shunts in the interventricular septum, increased echogenicity of endocardium and papillary muscles, mitral regurgitation, and obvious reversal blood flow. Although ECHO is the initial diagnostic modality, there are inherent limitations to the resolution of ultrasound, which can reduce the ability to distinguish the origin of the coronary artery with confidence, specifically because there can be an ultrasonic dropout of the wall of the aorta adjacent to the transverse sinus and the wall of the LCA.⁸ In addition, for very fine retrograde flow, some cases are poorly resolved. Thus, the anomaly can be ruled in, but never be ruled out, by ECHO. Also, some ultrasound physicians find it challenging to diagnose ALCAPA using noninvasive measures, as their little experiences with this rare anomaly may be limited.

Currently, cardiac CT and cardiac MR are valuable noninvasive modalities that can be used to help diagnose ALCAPA. Both of them have the advantages and disadvantages of diagnosing ALCAPA. Cardiac CT has been recently recognized as the imaging modality of choice fairly suitable for fast and accurate diagnosis of coronary abnormalities in these unstable and fragile patients.⁹ Cardiac CT not only enables the detection of coronary artery anomalies but also allow the discrimination of variants of the original site of the anomalous LCA. Depending on variations of the original site (inner wall, lateral wall, and posterior wall of the pulmonary trunk), surgical strategies for coronary reimplantation were different.¹⁰

Although Gerald and colleagues¹¹ recently reported MR assessment of the origin and the course of the coronary arteries in infants and young children, they proposed that the origin and course of the coronary arteries were usually not imaged well in patients younger than 4 months, and these results improved with age or slower heart rates. MR has no obvious advantages over cardiac CT in assessing small vessels such as the coronary artery in infants and young children for MR examinations.³ We used the advantages of MR to assess intracardiac anatomy, myocardial viability, and mitral valvular function preoperatively. To the best of our knowledge, MR application in infants with coronary diseases has only been reported in a few articles. Cardiac MR is not more widely used than cardiac CT in clinical settings for the evaluation of coronary arteries in infants.

The main disadvantages of MR imaging in comparison with CT are its relatively long examination times, its low spatial resolution, and it also requires general anesthesia. And the main limitations of ECHO are that not all features are directly related to the visualization of the coronary arterial origin. In addition, because of the high risk of cardiac catheterization, at present, coronary angiography is not routine examination of ALCAPA.^9,12

Coronary Artery CT Angiography Reconstruction Technique

Cardiac CT can be performed on patients who are suspected of having coronary artery anomalies by ECHO. Interpretation of cardiac CT should always include a review of the MPR, MIP, and 3-dimensional coronary tree images, which better display their origins and course. In addition, the well-timed scan steal phenomenon can also be observed (Fig. 3).

Cardiac CT can distinguish the site of origin of the anomalous LCA and variants: inner, left-sided, posterior wall of the pulmonary trunk, and sinus of the pulmonary root. At the same time, the origin of the RCA position and status can be clearly shown.

Multiplane reconstruction might permit the visualization of the junction point of the coronary arteries and pulmonary artery, as well as ventricular aneurysms. Anomalous LCAs arising from the inner or posterior aspect of the pulmonary artery can be shown using coronal MPR (Fig. 4). In addition, if it arose from the left-sided aspect of the pulmonary trunk, then an axial MPR can better display it. Multiplane reconstruction can also observe whether the postoperative anastomotic blood flow is smooth (Fig. 7). Maximum intensity projection images are most important for depicting the coronary artery and collateral vessel course (Fig. 6).

Figure 7

By measuring the main pulmonary artery diameter and calculating the mPAD/ascending aorta diameter ratio, we can estimate the pulmonary artery pressure and screen for pulmonary hypertension¹³ and recommend that physicians protect the lung and respiratory tract before and after surgery.

Finally, we should note whether other malformations exist, such as patent ductus arteriosus, ventricular septal defect, among other factors, so that surgeons can take the necessary actions if required.

Surgical Strategies

Once confirmed, surgery should be performed on patients with critical conditions. Reconstructing a 2-artery coronary system is the main method to correct ALCAPA in infants. Using cardiac CT, we can determine each of the ALCAPA variations, which is the distance between an empty left aortic sinus and the site of the anomalously connected coronary artery. It is important to determine the surgical strategies, which can include coronary button transfer, extending the coronary artery, or tunnel operation (Takeuchi repair).¹⁴ The surgeon should have carefully studied the preoperative imaging to have a clear idea of the precise location of the anomalous ostium relative to the pulmonary artery.

If the LCA connects to the posterior or right-sided (inner) aspect of the pulmonary trunk near the aorta, then the LCA translocation with button from the pulmonary artery wall is the most commonly used procedure and will result in the best anatomical correction. The LCA can be directly mobilized for a short distance (Fig. 8).

Figure 8

If the LCA connects to the left side of the pulmonary trunk wall far away from the aorta, another technique to extend the coronary artery is usually performed (Fig. 9). A wide range of pulmonary artery walls will be cut to recreate a proximal tubular LCA. The coronary artery can be extended by autologous flaps of the pulmonary artery with no mobilization of the LCA to reach the aorta and anastomosed within the aortic lumen; thus, there is no danger of kinking or excessively stretching the left main coronary artery.¹⁵

Figure 9

Takeuchi repair on late severe supravalvular pulmonary stenosis limits the wide application of surgical techniques.

There are still some cases where, before surgery, it is necessary not only to define the different origins of the LCA abnormalities but also to clear the origin of the RCA position, thereby avoiding damage to the RCA during the operation.¹⁴ In addition, if there is RCA dysplasia or narrow openings, then it cannot serve as a source of supply to the left ventricle of collateral blood flow, such that not only must reconstruction of the dual coronary blood supply system occur but also myocardial protection strategies must be considered.

Follow-up Evaluations

All patients underwent left coronary reimplantation to correct ALCAPA. Four patients underwent a coronary button transfer, and an extended coronary artery was performed on the other patients. Two of the patients with infant type experienced acute heart failure, with sudden death 2 days after the operation. Another 2 patients with infant type and all 5 patients with adult type survived the operation. All discharged patients were followed up for a mean period of 18 months using ECHO after surgical repair to assess the recovery of the left ventricular performance, as well as the LVEF and mitral regurgitation. The LVEF of 4 patients was increased and mitral regurgitation decreased. The left ventricular performance was not worse compared to the previous condition in 3 patients. A cardiac CT scan was performed on 1 of the 7 patients 1 month after surgery, and it showed the coronary located aortic roots, smooth blood flow, and no anastomotic stenosis.

Differentiation With Idiopathic EFE and Dilated Cardiomyopathy

It is important that patients with ALCAPA be treated by operation, whereas idiopathic EFE and dilated cardiomyopathy do not need surgery, except cardiac transplantation. Due to the lack of specificity in clinical manifestations, Zheng et al¹⁶ reported that 47.4% of the patients with ALCAPA had a misdiagnosis of EFE, 15.8% had a misdiagnosis of dilated cardiomyopathy, and most of ALCAPA patients had a false initial diagnosis. All patients, particularly infant patients, with a suspicion of idiopathic EFE or isolated severe mitral regurgitation must be routinely ruled out for ALCAPA.¹⁷ Moreover, a series of imaging studies can confirm that patients with idiopathic EFE have normal coronary origins and diameter and the lack of collateral vessel formation.

Coronary-Pulmonary Fistulas

Normal coronary arteries terminate in broom-like arborizations, which penetrate the myocardium and originate from the aorta sinus of Valsalva. Coronary-pulmonary fistulas are anomalously terminated coronary arteries but with a normal origin. Terminations of coronary-pulmonary fistulas are often directed into cardiac cavities or great vessels close to the heart. Use of multiplanar reformation may demonstrate sites of origin and termination of abnormal blood vessels.¹⁸

CONCLUSIONS

ALCAPA is a rare congenital anomaly in which the LCA originates from the main pulmonary artery. Its clinical signs are difficult to distinguish from those of idiopathic EFE or cardiomyopathy. Cardiac CT can provide fast and accurate depiction of complex coronary arteries, particularly in unstable and fragile patients with ALCAPA, and according to cardiac CT, surgical strategies can be decided. Currently, cardiac CT has become an important diagnostic tool combined with ECHO and MR in this patient population.

REFERENCES