Myocardial Architecture, Mechanics, and Fibrosis in Congenital Heart Disease

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

Three-dimensional late gadolinium enhancement cardiovascular magnetic resonance predicts inducibility of ventricular tachycardia in adults with repaired tetralogy of Fallot

Background - Adults with repaired tetralogy of Fallot (rTOF) die prematurely from ventricular tachycardia (VT) and sudden cardiac death. Inducible VT predicts mortality. Ventricular scar, the key substrate for VT, can be non-invasively defined with late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) but whether this relates to inducible VT is unknown. Methods - Sixty-nine consecutive rTOF patients (43 male, mean 40{plus minus}15 years) clinically scheduled for invasive programmed VT-stimulation were prospectively recruited for prior 3D LGE CMR. Ventricular LGE was segmented and merged with reconstructed cardiac chambers and LGE volume measured. Results - VT was induced in 22(31%) patients. Univariable predictors of inducible VT included increased RV LGE (OR 1.15;p=0.001 per cm3), increased non-apical vent LV LGE (OR 1.09;p=0.008 per cm3), older age (OR 1.6;p=0.01 per decile), QRS duration ≥180ms (OR 3.5;p=0.02), history of non-sustained VT (OR 3.5; p=0.02) and previous clinical sustained VT (OR 12.8;p=0.003); only prior sustained VT (OR 8.02;p=0.02) remained independent in bivariable analyses after controlling for RV LGE volume (OR 1.14;p=0.003). An RV LGE volume of 25cm3 had 72% sensitivity and 81% specificity for predicting inducible VT (AUC 0.81;p10cm3 was 100% sensitive and >36cm3 was 100% specific for predicting inducible VT. Conclusions - 3D LGE CMR-defined scar burden is independently associated with inducible VT and may help refine patient selection for programmed VT-stimulation when applied to an at least intermediate clinical risk cohort

9 ECV and T1 mapping in repaired tetralogy of fallot – CMR diffuse fibrosis measurement needs the right method for the right ventricle?

Introduction It is increasingly appreciated applying parametric mapping to the RV has inherent challenges. Methods We studied native LV and RV T1 mapping and ECV measures at 1.5 T in repaired tetralogy of Fallot (rTOF) patients (n=44, 24 male, 32±14 years, 35 (80%), NYHA class I). Single slices targeted perpendicular to to the LV septum or RV inferior wall using 11HB-MOLLI (6 mm slice thickness/TR 279 ms/TE 1.1 ms/Flip-angle 35°). Like image planes were repeated using ‘high sensitivity native T1’ 14HB-MOLLI (6 mm slice thickness/TR 300 ms/TE 1.1 ms/Flip-angle 5°) in attempt to improve sensitivity to tissue collagen. Haematocrit for ECV calculation was obtained within a few hours of CMR. Results RVECV correlated with LVECV (r=0.7; p35%) and 3 (8%) increased LVECV (>30%). Associations with all standard risk factors in rTOF were tested. RVECV correlated with right atrial area, (r=0.4; p<0.05). ‘High-sensitivity native T1’ correlated with akinetic RVOT length (r=0.6; p<0.05), and left atrial area (r=0.3; p=0.07) and QRS duration (r=0.3; p=0.4). RVECV did not correlate with high-sensitivity’ native T1. No diffuse RV fibrosis measure correlated with ejection fraction. Conclusion Diffuse fibrosis was only associated with increased right atrial and RVOT akinetic area size which if true may relate to RV diastolic dysfunction. Given the lack of consistency of findings between techniques more data are needed, including determination of how the measures obtained relate to myocardial composition. Despite best efforts to obtain optimum RV T1 maps these findings suggest current approaches have limited use and dedicated RV sequence development is required