Incidental congenitally corrected transposition of the great arteries (ccTGA) in an adult with suspected coronary artery disease: review on radiological features and pathophysiology

Abstract

We report a case of a 46-year-old woman who has presented to a peripheral hospital with progressive exertional dyspnoea and chest discomfort. The resting ECG showed features of left-sided ventricular hypertrophy. The initial chest radiograph was reported as cardiomegaly. Initial echocardiography revealed left atrial dilatation and ‘left ventricular’ hypertrophy with normal ejection fraction. She was treated as possible coronary artery disease and was subsequently referred to our centre for CT coronary angiography. Findings from the CT scan were consistent with congenitally corrected transposition of the great arteries (ccTGA). This report describes the radiological features of ccTGA, its associated cardiovascular anomalies, pathophysiology and potential complications.

Background

Congenitally corrected transposition of the great arteries (ccTGA), also known as levotransposition of the great arteries, was initially reported by Rokitansky in 1875. Since then, it remains a rare cardiovascular anomaly comprising less than 1% of all congenital cardiac diseases.^{1 2} In this disease, the atria are at their normal location. However, there is atrioventricular (AV) and ventriculoarterial discordance whereby the right atrium is connected to the left ventricle while the left ventricle connects directly to the pulmonary artery. On the left side, the left atrium is connected to the right ventricle and the right ventricle connects to aorta allowing the oxygenated blood to enter the systemic circulation.³ This results in uninterrupted pulmonary and systemic blood flow, hence the term ‘congenitally corrected transposition’.^{3 4} The ventricular inversion and the associated aortopulmonary rotation also result in mirror-image coronary artery distribution.^{3 5}

In the absence of other associated anomalies, ccTGA causes no immediate haemodynamic complications and the patient will be asymptomatic in the early life.³ However, heart failure gradually develops usually by the fourth or fifth decade of life due to long-standing pressure and volume overload on the right ventricle trying to meet the systemic demand.^6–8

We present a case of undiagnosed ccTGA who presented with heart failure symptoms but was undetected on the initial echocardiography. We highlight the importance of recognising the abnormal cardiovascular anatomy on imaging even in the unsuspected cases, features of ccTGA, the associated anomalies and complications.

Case presentation

A 46-year-old woman presented to a peripheral hospital with a 1-year history of exertional dyspnoea and chest discomfort which progressively worsened for 2 weeks prior to admission. She also had orthopnoea requiring two pillows at night. She was a non-smoker. There was a family history of hypertension and diabetes mellitus, but no ischaemic heart disease. She has five children, all born via spontaneous vaginal delivery.

On arrival, she was pink with oxygen saturation of 98% on room air. Her heart rate was 94 bpm with a blood pressure of 146/77. There was pitting oedema of bilateral feet up to the ankle. The jugular venous pressure was not raised. Auscultation revealed pansystolic murmur and reduced breath sound at the left lung base. There was no sign of ascites.

Investigations

The serum cholesterol level was mildly elevated and the cardiac markers were within normal limit. Other blood investigations were unremarkable. Her resting ECG showed sinus rhythm with features of left-sided ventricular hypertrophy. There was no specific evidence of myocardial ischaemia (image not shown). Chest radiograph demonstrated levocardia, cardiomegaly, slightly prominent pulmonary hilar vessels, straightened upper left mediastinal border and opacity in the left costophrenic angle (figure 1). Echocardiography was performed by the treating general physician and showed dilated left atrium, ‘left ventricular’ hypertrophy with an ejection fraction of 68%. There was no other abnormality detected (images unavailable).

Figure 1.

Frontal chest radiograph shows levocardia, cardiomegaly, slightly prominent pulmonary hilar vessels and opaque left costophrenic angle. Note the leftward location of the thoracic aorta at the left upper mediastinum (arrows).

She has been treated for congestive cardiac failure and was referred to our centre for CT coronary angiography (CTCA) in order to look for coronary artery disease. On the limited non-contrast CT planning image, abnormal location of the great arteries was recognised raising the suspicion of congenital cardiovascular anomaly. The CTCA protocol was performed with ECG-gated technique and the superior field of view was extended to above the aortic arch.

The CTCA confirmed visceroatrial situs solitus and levocardia. Four heart chambers were visualised with AV and ventriculoarterial discordance. The left-sided ventricle has right ventricular morphology (mRV) which has hypertrabeculated wall involving the septum with presence of infundibulum separating the inflow valve plane from the outflow aortic valve. The mRV wall was thickened as compared with the opposite ventricle thus limits the differentiation between the moderator band and other trabeculae. There was also apical displacement of the septal leaflet of its AV valve, about 8 mm/m² below the septal annulus of the right-sided AV valve suggestive of Ebstein anomaly. On the contrary, despite the faint contrast enhancement the right-sided ventricle has a left ventricular morphology (mLV) characterised by relatively smooth septal wall and its AV valve lies in continuity with the outflow pulmonary valve. The mLV appeared to have normal wall thickness. There was no intraventricular or interatrial septal defect seen (figure 2). The left atrium was mildly dilated, 25 cm². The mRV ejection fraction was about 67%.

Figure 2.

Multiplanar reconstruction CT in four-chamber view of the heart in diastole (A) and systole (B) shows atrioventricular discordance. The mRV is hypertrophied and hypertrabeculated especially at mid to apical wall. The septal annulus of the tricuspid valve of mRV (black arrow) is apically displaced as compared with the posterior annulus of the mitral valve of mLV (curved arrow). Oblique sagittal views (C and D) demonstrate subaortic infundibulum (black arrowhead) separating the outflow aortic valve (red arrow) from the inflow tricuspid valve (yellow arrow), a characteristic feature of mRV. On the right side, the inflow mitral valve (white arrowhead) is in continuity with the outflow pulmonary valve (chevron arrow), a characteristic feature of mLV. AA, ascending aorta; LA, left atrium; mLV, morphologic left ventricle; MPA, main pulmonary artery; mRV, morphologic right ventricle; RA, right atrium.

There was abnormal relationship of the great arteries where the ascending aorta located anterior and slightly to the left of the main pulmonary artery (MPA). These great arteries also run in parallel fashion (figure 3). The aortic valve appeared trileaflet and located to the left of the pulmonary valve. The aortic arch was left sided with normal arch branches. This arrangement allows the aorta to form the left upper mediastinal border while the MPA does not form mediastinal outline on the frontal chest radiograph. Both MPA and aorta were normal in size. There was no evidence of patent ductus arteriosus.

Figure 3.

CT image in axial view (A) shows the AA is immediately anterior to the MPA. The coronal oblique view (B) shows the ventriculoarterial discordance and the parallel course of the great arteries which is a characteristic feature of transposition of the great arteries (TGA). AA, ascending aorta; mLV, morphologic left ventricle; MPA, main pulmonary artery; mRV, morphologic right ventricle.

The coronary arteries demonstrated an almost ‘mirror-image’ distribution (figure 4). The left-sided coronary artery (LSCA) originated from the anterior right coronary cusp and it bifurcates into anterior descending artery (AD) which runs within the anterior interventricular groove and a small circumflex artery (Cx) that runs within the right AV groove (between right atrium and mLV). Another artery was seen to arise separately from the anterior right coronary cusp and supplied the mRV free wall. The right-sided coronary artery (RSCA) originated from the posterior coronary cusp. It coursed to the left and inferiorly within the left AV groove (between left atrium and mRV) and it supplied the posterior descending artery (PDA). There was no evidence of atherosclerotic disease or stenosis of the coronary arteries. Minimal pericardial effusion and mild left pleural effusion were also present.

Figure 4.

Axial multiplanar reconstruction CT at the level of the coronary sinus (A) shows the aortic root located to the left and slight anterior to the MPA. The LSCA originates from the anterior right coronary cusp and bifurcates into AD and Cx. The mRV artery arises separately from the anterior right coronary cusp and supplies the mRV free wall. The RSCA originates from the posterior coronary cusp and gives rise to PDA (not shown). Volume rendered images (B and C) further illustrate the coronary artery anatomy. AD, anterior descending artery; Cx, circumflex artery; LSCA, left-sided coronary artery; AO, aorta; MPA, main pulmonary artery; mRV, morphologic right ventricle; PDA, posterior descending artery; RSCA, right-sided coronary artery.

Differential diagnosis

ccTGA with coronary artery and Ebstein anomalies complicated with mRV hypertrophy and possible myocardial ischaemia.

Treatment

The treating physician started the patient on antihypertensive (telmisartan) and diuretic (hydrochlorothiazide) to control the blood pressure and fluid overload. Dietary advice was given for hypercholesterolaemia. She was referred to the paediatric cardiologist for baseline echocardiography and further management of the ccTGA. At the time of writing this report, she was still waiting for the appointment with the paediatric cardiologists.

Outcome and follow-up

The patient had another admission to the same peripheral hospital for heart failure several weeks later. No new resting ECG changes were noted. She was treated medically and discharged home after a short hospital stay.

Discussion

In this report we highlight the importance of imaging in providing an alternative diagnosis in an unsuspected case. We also highlight the importance of recognising the abnormal cardiovascular anatomy which forms the basis of all the congenital heart diseases. In this patient, the systemic ventricle is the mRV evidenced by the hypertrabeculated mid and apical septal wall as opposed to the smooth septal wall within the right-sided mLV. Since AV valve almost always follows the corresponding ventricle, the septal leaflet of the systemic AV valve of our patient is apically positioned which is a characteristic of a tricuspid valve.³ Ebstein anomaly, a common association in ccTGA, was also identified in our case. It causes the atrialisation of mRV inlet which may explain the mildly dilated left atrium.

The description of coronary artery anomaly in ccTGA is important especially before surgical intervention. Several investigators who have studied the coronary anomalies in ccTGA concluded that the pattern of anomaly is influenced by the inverted ventricles, and a result of aortopulmonary rotation.^{5 9} There is a universal description of coronary artery anomaly in ccTGA as suggested by Sithamparanathan et al.¹⁰ However, we did not adopt the alphanumerical sequential classification in our report. Our patient has the coronary artery anatomy that is almost similar to the reported ccTGA cases.^{9 11} She also has an additional separate artery from the anterior right coronary cusp supplying the mRV free wall, likely due to absence of the marginal branch from the RSCA. If the proposed description above is followed, the LSCA should be called the right coronary artery which then gives rise to AD, whereas our RSCA is called the Cx which later forms the PDA.

Individuals diagnosed with ccTGA without associated cardiac anomaly may survive longer and symptoms usually occur in adulthood.¹² Apart from the coronary artery and Ebstein anomalies, our CT images did not show other associated findings, for example, ventricular septal defect (typically perimembranous) which occurs in about 70%–80% of ccTGA cases.¹³ Pulmonary stenosis (typically subvalvular) that occurs in 40%–50% of ccTGA cases was also not evident in our patient.¹³ Situs inversus with ccTGA has been reported, although an extremely rare finding especially in adulthood.¹⁴ Abnormal conducting system such as unusual location and course of the AV node and bundle of His may also occur in ccTGA but the pattern will be different between situs solitus and inversus.¹⁵ Our patient’s ECG did not demonstrate any significant abnormal conduction activity.

Despite the absence of many significant associated anomalies, our patient has developed congestive cardiac failure. On basic principle, the mRV anatomy is not designed to perform workload of systemic ventricle over a normal lifespan. The long-standing systemic pressure overload will lead to mRV hypertrophy which is a compensatory mechanism as seen in this case. This mechanism will eventually fail and lead to cardiac failure.^{6 16} The significantly thickened mRV wall will potentially interfere with the coronary artery supply making the myocardium vulnerable to ischaemia which may explain the exertional chest discomfort in our patient.

Echocardiography is traditionally used to diagnose ccTGA. However, this condition was missed in the initial echocardiographic assessment of our patient due to the lack of exposure to the congenital heart diseases among the non-paediatric doctors. Despite this problem, echocardiography is still the best baseline imaging assessment since it is more accessible, cheaper and radiation free. It also can identify the intracardiac anomalies and great vessels in most instances. It allows the assessment of myocardial wall motion, systolic and diastolic function. Given the detection of pansystolic murmur and dilated left atrium in this patient, echocardiography will be able to identify and grade the tricuspid valve regurgitation that usually occurs in Ebstein anomaly and pressure overload. This modality is also able to exclude functional aortic or pulmonary outflow obstruction which is difficult to assess on CT scan.

CT scan is an alternative imaging modality in ccTGA since it allows multiplanar image reconstruction in cases with poor echocardiographic window. It is also the imaging of choice to demonstrate coronary artery anomaly. Having adequate knowledge in congenital heart disease allowed us to describe detailed cardiovascular morphology in our patient. Although less desirable due to ionising radiation, CT is able to provide quantitative analysis of ventricular function.

MRI is considered the best imaging modality for morphological and functional evaluation in congenital heart diseases due to lack of ionising radiation. However, the cost and longer acquisition time have become the main limitations in our case. Since our CT images have been able to provide the detailed anatomy of ccTGA, we have suggested further evaluation of our patient with echocardiography by a trained paediatric cardiologist.

The intervention for ccTGA is usually a surgery which is to correct the associated cardiac lesion such as ventricular septal defect, pulmonary stenosis or atresia, and tricuspid insufficiency without addressing the double discordance anomaly. However, this approach will ultimately end up with dysfunctional mRV and heart failure. The double switch procedure was introduced as approach for anatomical repair where the mLV is incorporated as systemic ventricle instead of the mRV.^17–19 As for our patient, there is still no decision on intervention for the time being.

Patient’s perspective.

I was having shortness of breath for 2 weeks before I seek treatment from the hospital. During the admission, they decided to do CT scan for my heart vessels to look for causes for my current condition. I was worried because previously the doctor said I probably had a heart attack that caused my current condition. After the scan, another diagnosis came which also made me worried at first with the complex explanation given by my doctor. However, after being told that my condition is controllable with medication and change in lifestyle, I felt reassured. Now, by following the advice and compliant with the medications, I rarely had the symptom and I was feeling well since my last hospital admission. I was informed that in the future, operation might be an option for my disease. However, I would like to not to think of the possibility to be operated just yet. I was also worried the risk of the operation at that time since I am getting older. So, if there is a need for surgery, I will discuss this matter with my family first and decide from there.

Learning points.

• Congenitally corrected transposition of the great arteries (ccTGA) is a rare congenital disease in which most of the patients will present with symptomatic heart failure in their fourth or fifth decades if there are no other significant associated anomalies.

• The initial diagnosis of ccTGA could be missed on initial echocardiography, which is partially attributed to the inexperience of the operator in congenital heart diseases.

• It is important to recognise the radiological findings, associated features and coronary artery anatomy in ccTGA, which are crucial for prognostication and further management by the primary team.