Morphology and anatomy

Corrected transposition of the great arteries is the result of atrioventricular and ventriculoarterial discordance. Left atrium is connected to the morphologically right ventricle on the left side and right atrium connected to the morphologically left ventricle on the right side. Furthermore, morphologically left ventricle drainage to the pulmonary artery. A study conducted by Arribard et al. ^{Reference Arribard, Kara, Hascoët, Bessières, Bonnet and Houyel1} mentioned the discordant nature of the atrioventricular connections and not the nature of the ventriculoarterial connections as the major element of this condition; they also suggest the term “double discordance” as a better term for describing this situation.

Most patients with corrected transposition of the great arteries have one or more associated malformations. Ventricular septal defect (occurs in 70% of the cases, and its usually peri-membranous), PS (present in almost 40% of the cases, and most of them are sub-valvular), abnormalities of the left-sided atrioventricular valve, and the conduction system disturbance are the most common associated anomalies. Some of the left-sided atrioventricular valve abnormalities happens up to 90% of the patients, and the apical displacement of the septal and mural leaflets is the most common form of these abnormalities; the extent of regurgitation across this valve is the most important factor related to clinical symptoms. The unusual position and route of the atrioventricular node and its bundle and susceptibility of the long penetrating bundle to fibrosis make the patients vulnerable to complete heart block (occurring at almost 2% per year). Another likely anomaly is secundum-type atrial septal defect that can be isolated, but it is rare. ^{Reference Munaf, Farooqui, Kazmi and Ul-Haque2,Reference Warnes8,Reference Wallis, Debich-Spicer and Anderson9} Few studies have mentioned other rare associations like Criss cross heart ^{Reference Quintana, González and Muñoz10} and aortic coarctation. ^{Reference Brandão, Magalhães and Correia11}

Clinical presentation

Clinical presentation can range from being asymptomatic to sudden cardiac arrest. Most clinical manifestations are related to associated anomalies. Pulmonary stenosis and ventricular septal defect can cause cyanosis. Furthermore, we can see manifestations of heart failure caused by a haemodynamically significant ventricular septal defect. Patients can also be diagnosed by presenting manifestations of complete heart block. Complaining from dyspnoea and palpitations is also common. Being asymptomatic is another possibility that mainly happens to patients with isolated corrected transposition of the great arteries, which is rare. Some of these patients are diagnosed by incidental chest radiography or ECG. Even in some cases, patients experience a full life without any problem and are diagnosed after the autopsy. ^{Reference Wallis, Debich-Spicer and Anderson9,Reference Agarwal, Samad, Kalvin, Bush and Tajik12,Reference Amaral, Valente and Manso13}

On physical examination, bradycardia caused by high-degree atrioventricular block and a single loud second heart sound which is palpable on the left sternal border are the most common findings. Associated ventricular septal defect, pulmonary stenosis, or atrioventricular valve regurgitation can cause murmur. ^{Reference Wallis, Debich-Spicer and Anderson9}

Diagnosis

One of the simple ways to diagnose this disease is a chest X-ray, that in some cases, leads to disease diagnosis for the first time. On a chest X-ray, the heart can be levocardia, mesocardia, or dextrocardia. With levocardia and mesocardia, there are hints to guide us towards corrected transposition of the great arteries: the aorta and the pulmonary trunk form the upper part of cardiac silhouette. These elements will appear abnormally straight because of the loss of normal relationships between the great arteries; the ascending aorta is not visible on the right side, and there is no sign of the convexities of aortic knob and the pulmonary artery on the left side; the left ventricular border tend to appear more vertical than usual, which is called humped appearance. Due to the association of dextrocardia and corrected transposition of the great arteries, getting suspicious of corrected transposition of the great arteries when dextrocardia happens is important. ^{Reference Warnes8}

Another diagnostic tool is echocardiography and findings of an echocardiography can be the first clues for diagnosis. The common finding is the presence of Q waves in the right precordial leads and the absence of Q waves in the left precordial leads; unfortunately, this is sometimes misinterpreted as inferior myocardial infarction. Varying degrees of atrioventricular block can also be present. ^{Reference Warnes8,Reference Amaral, Valente and Manso13}

Another inexpensive and available diagnostic tool is echocardiography, which can provide us with valuable findings such as confirming the diagnosis and determining the presence of any associated anomalies. The anatomical approach should be detailed and sequential, starting from the visceral atrial situs and continuing to the great arteries. Due to the structural complexities, assessing the right ventricle and tricuspid valve can be challenging, but it is an essential part of the diagnosis. Using reliable parameters can be valuable: tricuspid annular plane systolic excursion, fractional area changing, tricuspid ring tissue doppler S’ wave, myocardial performance Tei index, and global longitudinal strain by the speckle tracking method. ^{Reference Wallis, Debich-Spicer and Anderson9,Reference Amaral, Valente and Manso13–Reference Rudski, Lai and Afilalo15} Considering that it is not possible to examine the right ventricle by echocardiography even in normal patients, it is recommended to use a cardiac MRI to accurately examine the size and function of the systemic right ventricle.

Another diagnostic tool is cardiac MRI which is not available everywhere, but its role has increased over the past few years. Defining ventricular function and volumes is the main function. Because of the complex shape of the right ventricle and the multiple coarse trabeculations in the context of right ventricle hypertrophy. It can be challenging and expertise in CHD imaging can be helpful. Hornung and Calder ^{Reference Hornung and Calder14} declared cardiac MRI as their primary method for tracking RV size and function in patients without pacemakers; and echocardiography as their primary method for patients with pacemakers. Radionuclide angiography is another mentioned ^{Reference Benson, Burns and Schwaiger16} modality for this application. ^{Reference Warnes8,Reference Amaral, Valente and Manso13}

Nowadays, with the advancement of non-invasive methods such as echocardiography and cardiac MRI, the indications for cardiac catheterisation have been limited, but the measurement of left and right heart pressures and pulmonary resistance, evaluation of the coronary arteries or the aortic arch, complex pulmonary atresia, and pulmonary venous abnormalities are still potential indications. It is also an essential part of any pre-operative assessment in older patients. ^{Reference Warnes8,Reference Wallis, Debich-Spicer and Anderson9}

Management

Medical management covers several issues including prevention from right-sided right ventricle failure; managing of failing systemic right ventricle; conduction abnormalities; and endocarditis. Conventional systemic left ventricle protection strategies are usually used in settings with symptomatic heart failure or severe systemic right ventricle dysfunction. Although the evidence is limited, diuretics, inhibitors of angiotensin-converting enzyme, angiotensin receptor blockers, and digoxin are prescribed routinely for this population. Beta-blockers are also used, but precaution should be taken regarding possible complete heart block in patients with known conduction system disturbance. ^{Reference Wallis, Debich-Spicer and Anderson9,Reference Agarwal, Samad, Kalvin, Bush and Tajik12,Reference Connolly, Miranda, Egbe and Warnes17} The presence of an advanced second- or third-degree AV block, having symptoms or ventricular dysfunction are the indications of pacemaker implantation. ^{Reference Amaral, Valente and Manso13} In a study conducted by Connelly et al. ^{Reference Connelly, Liu, Williams, Webb, Robertson and McLaughlin18} on 52 patients with corrected transposition of the great arteries, six patients (∼11%) developed endocarditis; this implies the importance of antibiotic prophylaxis according to the American Heart Association guideline. ^{Reference Baddour, Wilson and Bayer19}

Surgical management: Diagnosis of corrected transposition of the great arteries does not always imply the need for surgery. Furthermore, there is not much consensus about the preferred surgical approach; the reasons for that can be summarised into three words: complexity, variability, and rarity; consequently, most of the repairs are individually tailored. In general, two main surgical approaches are used in these patients, including physiological and anatomical repair.

Physiological approach is the classic method of repairing. The main aim of this method is to fix associated anomalies, and the common trait among all these methods is leaving the morphologically right ventricle at systemic pressure. This approach is straightforward, but the fact that morphologically right ventricle will likely fail over time results in poor prognosis. ^{Reference Wallis, Debich-Spicer and Anderson9,Reference Amaral, Valente and Manso13} Also, if complete heart block happens during the procedure, a pacemaker must be planted. ^{Reference Wallis, Debich-Spicer and Anderson9}

The most common physiologic surgery is tricuspid valve replacement. Valve repair is not encouraged and a mechanical or a bioprosthetic valve is the preferred option. It is usually performed either as an isolated procedure or at the time of intracardiac repair of other lesions. The causal relation between morphologically right ventricle dysfunction and TR is not clear yet. Having a better morphologically right ventricular function (ejection fraction >40%) leads to lower mortality during this surgery; hence, early operation can be beneficial. We generally expect satisfactory results, but systemic right ventricle ejection fraction <40%, atrial fibrillation, and non-systemic ventricular systolic pressure >50 mm/Hg at the time of operation are the risk factors for mortality or transplantation late after valve replacement. ^{Reference Amaral, Valente and Manso13,Reference Koolbergen, Ahmed and Bouma20,Reference Mongeon, Connolly, Dearani, Li and Warnes21}

Ventricular septal defect has a protective effect on TR. Haemodynamic impact and specific morphology of defect dictate the need for operation. This repair is usually done during the same operation for pulmonary stenosis; asymptomatic patients with the stable situation and not severe lesions are not good candidates for these combined procedures. The situation can become very challenging in very cyanotic patients. Heart block is an important complication of ventricular septal defect closure that should be considered after surgery and during follow-up. ^{Reference Amaral, Valente and Manso13,Reference de Leval, Bastos and Stark22,Reference Bogers, Head, de Jong, Witsenburg and Kappetein23}

When there is pulmonary stenosis, the severity of obstruction and the degree of cyanosis, hypoxaemia, and polycythaemia caused by the right-to-left shunt and the decreased flow of blood to the lungs will determine the indication for surgery. ^{Reference Wallis, Debich-Spicer and Anderson9}

Atrial septal defect is rare in congenitally corrected transposition of the great arteries, ^{Reference Munaf, Farooqui, Kazmi and Ul-Haque2} and information around it is scarce. Repairment of a large atrial septal defect, isolated or simultaneously with another defect, may be necessary. ^{Reference Amaral, Valente and Manso13}

Anatomic approach: The anatomic approach is comprised of surgical methods that try to return the morphologically left ventricle to systemic circulation and achieve better long-term prognosis. ^{Reference Hornung and Calder14} This is reached through the rerouting of the pulmonary venous return to the morphologically left ventricle and aorta, and the systemic venous return to the morphologically right ventricle and pulmonary arteries. ^{Reference Wallis, Debich-Spicer and Anderson9}

Double switch operation is the mixture of two previously used procedures: the Senning atrial baffle procedure which redirects blood flow at the atrial level and the arterial switch procedure where the great arteries are transected and reversed. ^{Reference Amaral, Valente and Manso13} Almost four decades after the introduction ^{Reference Nikaidoh24} of double switch operation, there is still not much consensus about it.

Relative contraindications of double switch operation are extensive and include straddling of the tricuspid valve, anomalous coronary arterial anatomy, hypoplasia of the morphologically left ventricle, and anomalies of the mitral valve. ^{Reference Wallis, Debich-Spicer and Anderson9}

This approach has been investigated in children. The studies ^{Reference Marathe, Chávez and Schulz25,Reference Hiramatsu, Matsumura, Konuma, Yamazaki, Kurosawa and Imai26} have shown that it is practical and promising in children, and even mentioned younger age at the time of operation as a favourable factor for better prognosis. In contrast, long-term complications including neo-aortic valve deterioration and reinterventions, Senning pathway obstruction, right ventricle-pulmonary artery conduit obstructions, and left ventricle dysfunction are also reported. ^{Reference Marathe, Chávez and Schulz25,Reference Murtuza, Barron and Stumper27}

The situation in adults is different: the reports of this operation in adults are scarce, and the criteria for a safe patient selection are not defined yet; consequently, this procedure should be performed with caution. Amaral et al. ^{Reference Amaral, Valente and Manso13} investigated 16 studies related to surgical experience in children and adults, published between 1995 and 2018 and concluded that, although the number of cases is small and cannot be used as strong evidence for decision-making, these cases can be instances of the feasibility of this method for adults; they also emphasised the importance of case-by-case decision making.

Complications of anatomical approach vary based on the method used. The atrial switch can cause sinus nodal dysfunction, supraventricular arrhythmias, and problems with the atrial baffle. The ventricular switch is related to aortic obstruction, aortic regurgitation, or conduit obstruction and regurgitation. Sometimes, arterial switch is performed as a part of the double switch which can result in coronary arterial obstruction or stenosis, aortic valvar regurgitation, and pulmonary arterial stenosis. When using a homograft conduit to restore circulation to the pulmonary arteries, deterioration of the homograft valve will require replacement. Complete heart block is another complication that arose during surgery in one-quarter of patients. Termignon et al. ^{Reference Termignon, Leca and Vouhé28} suggest implanting a pacemaker to resolve this problem. ^{Reference Wallis, Debich-Spicer and Anderson9}

Catheter-based interventions

Catheter-based interventions are well-established methods for the treatment of cardiac pathologies including corrected transposition of the great arteries patients. Catheter ablation for the treatment of arrhythmias ^{Reference Baral, Veldtman, Yue, Duke and Morgan29} and percutaneous TR repairment ^{Reference Franzen, von Samson, Dodge-Khatami, Geffert and Baldus30} are the most common applications. It is also used for atrial septal defect closure. Isolated atrial septal defect is rare in corrected transposition of the great arteries, and the studies regarding the application of percutaneous transcatheter closure in atrial septal defect are infrequent. Herein, we reviewed the literature for the reports of this intervention (Table 2).

Table 2. Previous studies on CC-TGA patients with percutaneous ASD closure.

CC-TGA, congenitally corrected transposition of the great arteries; ASD, atrial septal defect; F, female; M, male; T2DM, type 2 diabetes mellitus; HLP, hyperlipidaemia; PSVT, paroxysmal supraventricular tachycardia, AVRT, atrioventricular reentrant tachycardia; N.M, not mentioned; TTE, transthoracic echocardiography; TEE, transesophageal echocardiography; RFA, radiofrequency ablation.

We found five cases. All of these patients were young children except for a 62-year-old lady. Symptoms related to heart failure like dyspnoea and decreased exercise capacity were the most common. Having an intracardiac shunt was the most common characteristic related to corrected transposition of the great arteries. Echocardiography and heart catheterisation were the most diagnostic methods used. Four of these patients recovered from the procedure without any complication and remained free of their main complaint in the follow-up. Only a 12-year-old patient had palpitations during the first 24 hours of the procedure and abnormality in echocardiography and 24-hour Holter monitoring; these abnormalities resolved by 3 years.

Cardiac transplantation

For individuals with refractory heart failure, orthotopic transplantation seems to be the only option. Despite the higher early mortality in patients with CHD, including corrected transposition of the great arteries, long-term survival is higher in this group than that of non-CHD patients. ^{Reference Doumouras, Alba, Foroutan, Burchill, Dipchand and Ross31} They also had better early and long-term outcomes among all recipients of donor hearts in the United States of America between 2000 and 2018 who were older than 17 years of age. ^{Reference Riggs, Zafar, Radzi, Yu, Bryant and Morales32}

Follow-up

Annual or biannual clinical evaluation is necessary for all corrected transposition of the great arteries patients regardless of the type of their previous surgical repair; patients with complicating factors such as severe systemic right ventricular dysfunction may benefit from more frequent visits. Doing these follow-ups in a centre run by a paediatric cardiologist or adult cardiologist with specific expertise in CHD is the ideal scenario. Patients should be advised to maintain a healthy lifestyle and avoid smoking. Although many cardiologists advise against doing strenuous or endurance exercise, doing regular moderate exercise is encouraged. Due to the increased risk of heart block, echocardiography should be performed at each visit; considering 24-hour Holter monitoring is also beneficial. Regular cardiopulmonary exercise testing can be profitable because it can assess functional capacity and possible arrhythmias. Echocardiography and cardiac MRI can evaluate the anatomy and haemodynamics of the heart and are two essential parts of the follow-up. Hornung and Calder ^{Reference Hornung and Calder14} encourage performing cardiac MRI at least every 3 years. ^{Reference Warnes8,Reference Wallis, Debich-Spicer and Anderson9,Reference Hornung and Calder14} In case of atrial septal defect device closure, 1, 3, and 6 months and then annual evaluation for the detection of likely complications such as cardiac erosion or endocarditis is recommended.