Abstract
Congenital heart disease (CHD) is the most common category of birth defect, affecting 1% of the population and requiring cardiovascular surgery in the first months of life in many patients. Due to advances in congenital cardiovascular surgery and patient management, most children with CHD now survive into adulthood. However, residual and postoperative defects are common resulting in abnormal hemodynamics, which may interact further with scar formation related to surgical procedures. Cardiovascular magnetic resonance (CMR) has become an important diagnostic imaging modality in the long-term management of CHD patients. It is the gold standard technique to assess ventricular volumes and systolic function. Besides this, advanced CMR techniques allow the acquisition of more detailed information about myocardial architecture, ventricular mechanics, and fibrosis. The left ventricle (LV) and right ventricle have unique myocardial architecture that underpins their mechanics; however, this becomes disorganized under conditions of volume and pressure overload. CMR diffusion tensor imaging is able to interrogate non-invasively the principal alignments of microstructures in the left ventricular wall. Myocardial tissue tagging (displacement encoding using stimulated echoes) and feature tracking are CMR techniques that can be used to examine the deformation and strain of the myocardium in CHD, whereas 3D feature tracking can assess the twisting motion of the LV chamber. Late gadolinium enhancement imaging and more recently T1 mapping can help in detecting fibrotic myocardial changes and evolve our understanding of the pathophysiology of CHD patients. This review not only gives an overview about available or emerging CMR techniques for assessing myocardial mechanics and fibrosis but it also describes their clinical value and how they can be used to detect abnormalities in myocardial architecture and mechanics in CHD patients.
Highlights
Specialty section: This article was submitted to Pediatric Cardiology, a section of the journal Frontiers in Cardiovascular Medicine
Investigators have studied hypertrophic cardiomyopathy and have identified abnormal orientation of myocardial fibers in diastole that remains in a relatively systolic conformation [10]. This was thought to be responsible for the abnormal wall thickness seen in hypertrophic cardiomyopathy rather than replacement fibrosis seen by late gadolinium enhancement (LGE). Cardiac Diffusion Tensor Imaging (cDTI) has been used to study ventricular remodeling postinfarction [25, 26]
A study by Jensen et al found that Cardiovascular magnetic resonance (CMR) derived RV ejection fraction (RVEF) less than 40% and LVEF less than 50% was associated with increased risk of death in Eisenmenger’s patients with post-tricuspid shunts [60]
Summary
The normal myo-architecture of the heart differs between the LV and the right ventricle (RV). The ventricular myocardial fibers are connected and are generally aligned with their neighbors, with only gradual change in the direction of the fibers from layer to layer [3, 4] Because of their opposing helical orientation, myocytes of the subepicardial and subendocardial layers of a given wall region contract almost orthogonally to one another during systole. It may be the case that diastolic relaxation of the laminar structures facilitates perfusion, in diastole, of blood through microvessels passing between the sheetlets; the papillary muscles and the trabeculars that are prevalent in the RV lack laminar microstructures [11] Their less complex but dense local myocardial structure, combined with their relative remoteness from epicardial coronary arteries, may predispose them to ischemia if abnormally loaded, for example, by ventricular volume and/or pressure loading. A change in orientation of the subendocardial fibers was noted [13, 14]
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