Cardiovascular Magnetic Resonance Imaging in the Assessment of Myocardial Blood Flow, Viability, and Diffuse Fibrosis in Congenital and Acquired Heart Disease
Myocardial ischemia may occur after surgical correction of congenital heart defects involving the coronary arteries, in patients with congenital coronary artery anomalies, or in acquired heart disease. To assess myocardial ischemia disease in children, we used cardiac MRI as a non-invasive and radiation-free method to evaluate myocardial perfusion, viability, diffuse myocardial fibrosis, and heart function, to guide further therapy and for a better understanding of the pathophysiology of the microcirculation. In this study, a total of 77 patients and 68 healthy controls were enrolled. In 13 TGA patients (26.5%) with known or suspected coronary problems, such as occlusion, stenosis or hypoplasia. We found that 7/13 (53.8%) had regional ischemia, scar tissue in 4/13 (30.8%) and regional or global impairment of LV function in 4/13 (30.8%). In addition, absolute quantification of myocardial perfusion showed that coronary blood flow was impaired, and T1 mapping showed extracellular matrix expansion suggestive of diffuse myocardial fibrosis. As a consequence of our findings, one patient received MIDCAB surgery, and 4 patients (30.8%) were treated medically. In another TGA group (n=36) with patent epicardial coronaries, we also found that global coronary blood flow is impaired after the ASO. In addition, T1 mapping showed an increase of ECV. However, no focal regions of hypoperfusion or LGE were found in this group. In addition, in TGA patients with single-stage ASO, aortic root dilatation and impaired bioelastic properties of the thoracic aorta were present and were related to LV diastolic dysfunction but we did not find a significant association of aortic stiffness and myocardial perfusion reserve. In patients after Ross operation (n=12), coronary blood flow was not significantly reduced as compared to matched normal controls, and only 1 patient showed a perfusion defect. However, we found that mean ECV was increased, and mean LVEF was significantly reduced in this group. In BWG patients (n=7), we found regions of perfusion defects in 4/7 (57.1%) of patients. Scar tissue was detected in 5 cases (71.4%), and LVEF was significantly impaired in BWG patients. In patients with a history of Kawasaki Syndrome (n=4), a region of impaired myocardial perfusion was present in one patient. Global MBF at stress, and MPR were impaired in this group. LGE was not present. Additionally, in other patients with coronary problems, including an aberrant LCA (n=1), coronary fistula (n=1) and status post heart transplantation (n=2) our study showed that CMR imaging can be used to detect regional myocardial ischemia by visual qualitative, semi-quantitative, and quantitative myocardial perfusion analysis. In addition, LGE CMR also was used to uncover regions of focal myocardial fibrosis in this population. The present study shows that CMR imaging can provide a comprehensive assessment of myocardial perfusion, viability and function, and myocardial tissue characteristic in children with congenital and acquired heart disease. We used CMR as a non-invasive method for evaluation myocardial perfusion in children with a spectrum of cardiac diseases. Importantly, this is the first study that used quantification of myocardial perfusion to measure absolute MBF in such diseases. We found that it is a useful method for the early diagnosis of myocardial ischemia in children, even in the absence of ischemic symptoms. The combination of first-pass perfusion imaging and LGE can increase the diagnostic accuracy for the detection of ischemic heart diseases. Contrast enhanced CMR provides an accurate quantification of areas of scar and viable tissue in children. T1 mapping as used in our study can additionally detect diffuse myocardial fibrosis. It provides information about myocardial tissue pathology and seems to be a useful method for assessment of interstitial fibrosis in children with congenital and acquired heart disease. In conclusion, the present study provides new evidence with CMR techniques of increased diffuse myocardial fibrosis in TGA patients after ASO, and in patients after Ross. In addition, assessment of aortic function in TGA patients after ASO showed that the aortic wall is stiffer than in controls, which may be an important cardiovascular risk factor. Therefore, we suggest that these patients have regular follow-ups after ASO even in adulthood to detect early onset of degenerative cardiovascular disease.
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