Fixed myocardial perfusion defects on SPECT are not associated with focal myocardial fibrosis on CMR in adult patients with systemic right ventricle

Type of funding sources: None. Myocardial fibrosis is a known prognostic factor in patients with systemic right ventricle (SRV). In these patients fixed myocardial perfusion defects are a common finding and are thought to represent areas of myocardial infarction and fibrosis. However, no study has yet correlated myocardial perfusion imaging findings with cardiac magnetic resonance (CMR) imaging, which is the imaging gold standard for detecting myocardial fibrosis. Our aim was to evaluate whether fixed myocardial perfusion defects in adult patients with SRV represent myocardial fibrosis. Patients with SRV followed at our outpatient clinic for congenital heart disease were prospectively included. Myocardial perfusion was evaluated with a two-day stress/rest single-photon emission computed tomography (SPECT) protocol, focal myocardial fibrosis with late gadolinium enhancement (LGE) and diffuse myocardial fibrosis with T1 mapping by CMR. The 12-segment model of the right ventricle was used to report segments with myocardial perfusion defects and fibrosis (Figure 1). Fifteen patients with SRV (12 patients with transposition of the great arteries following atrial switch procedure and 3 patients with congenitally corrected transposition of the great arteries; 4 (26.7%) females; mean age 34.6 ± 10.0 years) were included. Myocardial perfusion defects were present in 14 patients (93%), with predominate fixed perfusion defects (73%) and less common reversible perfusion defects (27%). Fixed myocardial perfusion defects were most frequent in anterior RV segments (figure 1), with multiple segments affected in 11 patients (median number of affected segments – 2 segments). CMR was possible in 11 (73%) patients, others had a permanent pacemaker. LGE indicating focal myocardial fibrosis was detected in only 1 (9%) patient, while increased T1 values indicating diffuse myocardial fibrosis were present in 7 (64%) patients. There was no matching between areas of fixed myocardial perfusion defects and focal myocardial fibrosis in individual patients. In our study, fixed myocardial perfusion defects detected on SPECT in patients with SRV did not represent areas of focal myocardial fibrosis on CMR. Other causes than scar may explain the frequently reported fixed perfusion defects, such as SRV anatomy with anterior position of the outflow tract and aorta, SRV morphology with variable degree of wall thickness and hypertrophy that influences tracer accumulation and image quality, or difficulties due to complex image acquisition and interpretation. To improve the diagnostic accuracy, the use of fused imaging modalities (SPECT-CT or PET-CT) is recommended in patients with SRV. Figure 1. Bull`s eye 12-segment plots of the right ventricle (RV) representing the number of segments with fixed myocardial perfusion defects detected by SPECT (1A) and LGE by CMR (1B) in patients with SRV. ANT – anterior, FW – free wall, INF – inferior, SEP – septal wall of RV. Abstract Figure.