5478. Cardiac MRI Right-to-Left Ventricular Blood Pool T2 Ratio is Associated with Adverse Events and Impaired Cardiopulmonary Exercise Function
Authors * Denotes Presenting Author
  1. Moran Drucker Iarovich ; University of Toronto
  2. Fadi Ibrahim; University of Toronto
  3. Joao Francisco Ribeiro Gavine De Matos; University of Toronto
  4. William Holden Lowes; University of Toronto
  5. Nilushi De Silva; University of Toronto
  6. Yas Moayedi; Toronto General Hospital
  7. Kate Hanneman *; University of Toronto
Cardiac MRI T2 mapping is sensitive to blood oxygenation levels. Right ventricular (RV) to left ventricular (LV) blood pool (BP) T2 relaxation time is reduced in patients with heart failure. However, there is limited data on the association of T2 BP ratio with adverse clinical events or physiologic parameters. The purpose of this study was to evaluate the prognostic value of RV/LV BP T2 ratio and the association with cardiopulmonary exercise parameters in patients undergoing cardiac MRI for evaluation of cardiomyopathy.

Materials and Methods:
In this single-center retrospective cohort study, adult patients undergoing clinically indicated cardiac MRI for assessment of cardiomyopathy between 2018-2020 were included. Cardiac MRI included cine acquisitions, T2 mapping and late gadolinium enhanced (LGE) imaging. RV and LV blood pool T2 values were evaluated on a mid-ventricular short axis slice avoiding trabeculations, papillary muscles and inflow artifact with calculation of RV/LV BP T2 ratio. A random subset of 100 MRIs were blindly evaluated by a second observer to assess inter-observer agreement. Clinically indicated cardiopulmonary exercise testing (CPET) was available in a subset of patients within one year of cardiac MRI and was evaluated according to standard guidelines. Major adverse cardiac events (MACE) were evaluated as a composite of cardiovascular death, appropriate ICD shock, or hospital admission for decompensated HF.

Overall, 718 patients were included (58% men, mean age 50 ± 16 years, mean LVEF 55 ± 10%, LGE present in 54%). After median clinical follow-up of 3.2 years (IQR 2.3, 3.8), 53 (7%) patients experienced MACE. RV/LV BP T2 ratio was lower in men compared to women (0.66 ± 0.16 vs 0.71 ± 0.16, p < 0.001) and among those with LGE compared to those without (0.64 ± 0.16 vs 0.72 ± 0.15, p < 0.001) with high inter-observer agreement (ICC 0.95, 95% CI 0.9 - 0.97). RV/LV BP T2 ratio was a significant predictor of MACE in univariable analysis (HR 0.97, 95%CI 0.95 - 0.98, p < 0.001). After adjusting for patient age, sex, and LGE presence, each 1% increase in RV/LV BP T2 ratio was associated with a 2% reduction in the hazard of MACE (adjusted HR 0.98, 95% CI 0.96 - 0.99, p = 0.02). A RV/LV BP T2 ratio cut-point of <0.50 had 89% specificity and 26% sensitivity (AUC 0.58) for one-year MACE. In the subset of patients with CPET (n = 194), RV/LV BP T2 ratio correlated with multiple parameters including percent predicted oxygen uptake (VO2, r = 0.34, p < 0.001), ventilatory efficiency (VE/VCO2) at anaerobic threshold (r = -0.20, p = 0.02), and heart rate recovery (heart rate drop at 1 minute of rest, r = 0.23, p = 0.005).

Decreased RV/LV T2 ratio is independently associated with higher risk of MACE and is associated with impaired CPET parameters as a physiologic correlate. This ratio can be evaluated using data that is routinely acquired in cardiac MRI and could be used to identify at-risk patients who might benefit from further investigation or closer monitoring.