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Patients with the transposition of great arteries (TGA) who undergo atrial switch operation and congenitally corrected TGA (ccTGA) patients have the right ventricle as their systemic ventricle. Function of the systemic right ventricle (SRV) could deteriorate which is associated with impaired prognosis. It is of paramount importance to understand the course and fate of these patients during a long-term follow-up to identify the determinants of adverse outcomes.
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In the year 2000, the prevalence of congenital heart diseases (CHD) patients with transposition of great arteries (TGA) was 0.027% in living children and 0.004% in living adults (1). Considering a complete transition to arterial switch operation in the 1990s, it is expected that the number of patients with systemic right ventricle (SRV) decrease over time (2). However, considering the existing number of patients with the TGA who have not undergone arterial switch surgery, SRV remains a challenging issue in the practice of adult congenital heart disease (ACHD) specialists.
TGA is characterized by AV concordance and ventriculo-arterial discordance and is called simple without the presence of associated congenital anomalies. However, complex TGA is when other anomalies are present including VSD (∼45%), LVOTO (∼25%), and CoA (∼5%). TGA's pathogenesis is controversial and there is rare familial occurrence. Male are two times more affected than females. The prognosis of TGA patients without surgery is poor and only exceptional cases survive to adulthood (3).
Heart failure and sudden cardiac death (SCD) are the predominant causes of mortality in TGA patients (4). Patients who undergo atrial switch operation and congenitally corrected TGA (ccTGA) patients are at risk of developing SRV failure in the future (3). The RV is a thin-walled triangular structure acting as a low pressure pump in the normal heart. Because of having only 2 layers, the RV cannot cause the torsion caused by the LV. Due to this geometry and anatomy, the right ventricular function is highly dependent on the loading conditions. The increased afterload that the RV faces in the systemic position causes compensatory RV dilation to maintain the stroke volume. Subsequently, there is increased myocardial wall stress and oxygen demand. The development of heart failure in the SRV is multifactorial. Other potential factors contributing to the SRV failure are impaired coronary reserve or ischemia, myocardial fibrosis, chronotropic incompetence, volume overload from tricuspid regurgitation and arrhythmias (4). Another contributing factor is the reduced baffle compliance in patients with atrial switch. This impairs the preload and stroke volume, especially when there is increased demand. The non-contractile atrial baffles cause impaired atrioventricular transport during tachycardia, therefore causing an inadequate RV filling (4).
Unfortunately, at the moment, the hypothesis that angiotensin-converting enzyme inhibitors (ACE inhibitors), angiotensin II receptor blockers (ARBs), aldosterone antagonists, and beta-blockers can improve the outcome of such patients alone or in combination is not supported by data and evidence. There is no solid recommendation in the 2020 guidelines for the management of ACHD (3).
Previous studies evaluating the fate and outcome of patients with an SRV are either mostly single-centered with a small number of patients or have a short follow-up period (5,6). In a study done by Richard Dobson and colleagues on a national cohort in Scotland, the investigators concluded that patients with an SRV who survive to adulthood have low mortality and good functional status up to the age of 40 (7).
It is of paramount importance to understand the course and fate of these patients during a long-term follow-up to identify the determinants of adverse outcomes. This will enable the investigators to investigate mechanistic pathways of such outcomes. By understanding the risk factors and pathophysiological basis, the investigators can also investigate new diagnostic methods and therapeutic options to improve the quality of life and reduce the mortality of patients with an SRV.
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