Quick Fire Session
SCMR 22nd Annual Scientific Sessions
Congenital heart defect (CHD) is the most common birth defect, affecting nearly 1% of live births. With the advancement in surgical palliation, many CHD patients survive into adulthood. Despite of successful palliation and advanced cardiovascular care, many CHD patients still suffer from chronic cardiac dysfunction, even heart failure. The highest morbidity and mortality are observed in patients with randomization of left-right patterning, so called heterotaxy; which raises the possibility that the disturbance of laterality may drive the poor outcome in CHD patients with heterotaxy. We hypothesize that the disturbance of the left-right patterning may change the ventricular myofiber architecture that results in compromised ventricular function. The goal of this study is to evaluate ventricular mechanics and myofiber architecture in patients with dextrocardia and heterotaxy.
Cardiac MRI (CMR) for cardiac mechanics: Deidentified CMR from 9 pediatric CHD patients with dextrocardia or heterotaxy as well as patients with normal situs are included for functional evaluation, including cine, tagging, and MRA (GE Signa, 1.5T). Strain, rotation and torsion are derived from tagging MRI with HARP software.
Diffusion Tensor Imaging (DTI) for myofiber structure: Autopsy pediatric heart samples with dextrocardia, heterotaxy and normal situs underwent DTI with isotropic 156 micron resolution, diffusion encoding duration 4ms, diffusion gradient separation 8ms, 30 gradient directions, and b=1200 s/mm2 (Bruker BioSpec,7T). The diffusion data were reconstructed using GQI with a diffusion sampling length ratio of 0.4, angular threshold 600, the step size 0.021 mm, the anisotropy threshold 0.0263 and total 100000 tracts calculated.
Pediatric CHD patients with heterotaxy or dextrocardia exhibited compromised strain and reduced ventricular twisting and untwisting. Fig.1 shows CMR of a 10-year-old male with dextrocardia, double-outlet right ventricle (DORV), pulmonary atresia, totally anomalous pulmonary venous return into a common confluence open to superior vena cava, and abdominal situs inverses. Although the ejection fraction (EF) is normal (61%), there is a 23% decrease in circumferential strain and markedly reduced ventricular twisting, from 120 to only -40. On the other hand, a 11-year-old patient (Fig.2) with normal situs and comparable EF (62%) displayed normal circumferential strain and ventricular torsion.
Fig.3 shows tractography of a heart with normal situs (Fig.3AC) and a heart with transposed great arteries (TGA) and double outlet right ventricle (DORV) (Fig.3BD), which displayed more aberrant myofiber organization (Fig.3BD). Its fractional anisotropy (FA) is significantly lower (Fig. 3E) than that of a normal situs heart, indicating the myofibers are less coherent in this heterotaxy heart.
Our data suggest that the abnormal myofiber architecture leading to compromised ventricular mechanics may drive the poorer outcome in heterotaxy patients.