Cardiac and vascular anatomy of patients with congenital heart disease (CHD) is complex and accurate evaluation mandates MR image acquisition in several non-standard planes. The most important sequences for anatomical imaging in CHD are black-blood spin echo, 2D SSFP, and 3D SSFP techniques as well as contrast-enhanced MR angiography .
Greil et al. 2015 reported that the CMR is the current clinical gold standard for measurements of ventricular function and blood flow which are crucial components of a CMR examination in patients with CHD. Ventricular volumes and ejection fraction are assessed by acquisition of a stack of SSFP cine slices covering the entire heart .
In this study, the role of cardiac magnetic resonance imaging in the evaluation of conotruncal anomalies was assessed. The study enrolled 42 patients (25 males and 17 females) with an age range between 6 months and 18 years. All patients were at least subjected to one echocardiographic examination while seven of them underwent cardiac catheterization.
The most common conotruncal anomaly in our study was tetralogy of Fallot which represented 45% of the patients while the least common was double outlet right ventricle which represented only 7% of them. The primary goal of the cardiovascular MR imaging examination of the patients in our study is to assess the full anatomical details of the patients pre-operatively and to follow-up the patients post-operatively for early detection of complications.
Cardiac MRI detected 18 patients in this study with variable degrees of pulmonary artery stenosis ranging from atresia to mild stenosis. While echocardiography failed to detect eight of them due to left pulmonary artery agenesis, non-confluence of the pulmonary artery branches and due to technical problems. The agreement between CMR and echocardiography was 44%. Cardiac MRI also successfully detected eight of the aorto-pulmonary collaterals with 37% agreement with echocardiography as the latter did not visualize five of them.
In our study, no contrast-enhanced magnetic resonance angiography (CE-MRA) was used for the patients in our study because no bolus tracking software for delineation of pulmonary vasculature was available and manual injection of contrast with the rapid heart rate of the pediatric group of patients makes it difficult to assess pulmonary vessels without overlap of aortic and systemic vessels.
We acknowledge that the lack of utilization of contrast medium in our study as a limitation which probably reduced the sensitivity of the examination in anatomical measurements of the vascular structures. Büchel et al. 2005 stated that CE-MRA provides accurate quantitative anatomical information, which highly agrees with conventional angiographic data, and can therefore be used for planning catheter-guided procedures .
However, free-breathing whole-heart 3D SSFP or black-blood fast spin-echo sequence was efficient for visualization of the atretic/hypoplastic pulmonary arteries and visualization of the aorto-pulmonary collaterals. In our study, the size of the hypoplastic pulmonary arteries is well measured. The origin of the coronary arteries was seen as well.
This study enrolled 9 patients with D-TGA and 11 with L-TGA. Cardiac MRI played an important role in anatomical and functional assessment of those patients. This agreed with Fogel et al. 2010 which reported that CMR has been recognized as an accurate non-invasive imaging tool to diagnose and evaluate patients with TGA as it shows the discordant atrioventricular and ventricular connections which can be visualized by identifying the right atrial (triangular atrial appendage with wide ostium) and left atrial (tubular atrial appendage with narrow ostium) anatomy and situs, and biventricular as well as large vessel anatomy with the aorta anterior and to the left, and can also show the great arteries side-by-side. Also, details of AV valve anatomy may be visualized .
Assessment of right ventricular volumes and functions was an important issue in our study as the conotruncal anomalies affects them in different degrees. Thirty-seven of our patients were subjected to right ventricular volumes and functions measurements. They show 46% agreement with echocardiography as echocardiography significantly underestimated volumes in the 17 patients as a whole and the mean right ventricular end diastolic volumes (RVED) were significantly greater when measured by CMR. Furthermore, CMR was superior to echocardiography for the assessment of the stroke volume and ejection fraction of the right ventricle. Minor early changes in ventricular size and function are more readily detectable, given the reproducibility of CMR, and may lead to an early appropriate medical intervention
This was agreed with Andrew M et al. 2011 as they reported that 3D-Echo systematically underestimates right ventricular volumes compared to cardiovascular magnetic resonance in adult congenital heart disease patients with moderate or severe RV dilatation .
Geva et al. 2014 also concluded that CMR is presently the best diagnostic modality for assessment of RV size and function in patients with CHD. Furthermore, a growing literature informs clinicians on how to use CMR data to guide patient management. Echocardiography, which is more widely available, provides useful diagnostic information in many clinical circumstances that affect the right heart. However, when precise quantitative data are required to make important clinical decisions (e.g., when to recommend pulmonary valve replacement), CMR remains the diagnostic modality of choice. As new echocardiographic, CMR, and other imaging techniques continue to evolve, it would be interesting to revisit this controversy in the future .
Our results agreed with Laura et al. 2012; their study concluded that in correlation between CMR and echocardiography, the latter overestimated the pulmonary regurge when the RF < 20% resulting in a false-positive results of about 37% .
In this study, regarding the post-operative evaluation for the patients with transposition of great vessels, eight of the cases came for post-operative follow-up.
CMR quantified blood flow through valves and vessels and provided valuable information concerning outflow tract stenosis and regurgitation fractions that can be followed over time and aid in management decisions. MRI can also depict the abnormal position of the great arteries, with the aorta anterior to the pulmonary artery and arising from the right ventricle in cases of D-transposition of great arteries and double outlet right ventricle with D-malposed vessels.
CMR was a very important tool in evaluation of post-operative complications in those patients. The post-operative evaluation requires a thorough evaluation of the right ventricular function and possible tricuspid valve regurgitation, left ventricular outflow tract obstruction, arrhythmias, baffle leaks, and systemic and pulmonary venous pathway obstruction.
Adam et al. 2012 studied the evaluation with cardiovascular MR imaging of baffles and conduits used in palliation or repair of congenital heart disease and concluded that CMR imaging is the imaging modality of choice for evaluation of baffles and conduits used in repair or palliation of complex congenital heart disease as it provides a non-invasive assessment of anatomy, function, and flow without the use of ionizing radiation .
Sangeeta et al. 2015 studied managing heart failure in transposition of the great arteries and reported that although the right ventricle is difficult to evaluate because of its complex shape, cardiac MRI is the gold standard of right ventricular assessment because of its ability to completely visualize the right ventricle. It is not only used to quantify the size and function of the right ventricle but also to identify associated structural abnormalities and areas of concern after surgery, such as aortic root, branches of pulmonary arteries, and right ventricular outflow tract .
One of the patients in our study with D-TGA who underwent surgical intervention presented with symptoms of pulmonary arterial hypertension. CMR revealed marked dilatation of the pulmonary arteries. Pulmonary arterial hypertension which is a rare complication has been reported also by Janani et al. 2017 and reported that late-onset pulmonary arterial hypertension (PAH) is a rare but fatal complication in patients with childhood surgical repair of dextro-transposition of great arteries (D-TGA). The pathogenic mechanisms of pulmonary arterial hypertension in patients with repaired D-TGA are not well understood and treatment is not standardized .