Quantitative technetium pyrophosphate and cardiovascular magnetic resonance in patients with suspected cardiac amyloidosis

Background: Quantitation of myocardial ^99m Tc-pyrophosphate activity may have high diagnostic accuracy, but its correlation with disease burden is unknown. We examined the relationship between ^99m Tc-pyrophosphate quantitation and cardiac magnetic resonance (CMR) measures in patients with suspected transthyretin cardiac amyloidosis (ATTR-CM) or light chain cardiac amyloidosis (AL-CM).

Methods: Consecutive patients who underwent ^99mTc-pyrophosphate imaging and CMR were included. ATTR-CM and AL-CM were diagnosed using standard criteria. ^99mTc-pyrophosphate images were assessed with standard parameters and quantified with cardiac pyrophosphate activity (CPA) and volume of involvement (VOI). We assessed the association between ^99mTc-pyrophosphate image interpretation and CMR tissue characteristics.

Results: Seventy patients were identified, mean age 70.4 ± 11.4 years, with ATTR-CM and AL-CM diagnosed in 22 (31%) and 11 (16%) patients, respectively. In patients with ATTR-CM, there were significant correlations between CPA (r² = 0.509, P < 0.001) and VOI (r² = 0.586, P < 0.001) with native myocardial T1 mapping values. Additionally, CPA (adjusted hazard ratio (aHR) 1.04, P = 0.016), VOI (aHR 1.12, P = 0.034), and average myocardial T1 (aHR 1.12, P = 0.025) were associated with incidence of heart failure hospitalization or death.

Conclusion: CPA and VOI were correlated with CMR measures of myocardial fibrosis in patients with ATTR-CM. ^99mTc-pyrophosphate quantitation may have a role in ATTR-CM disease staging, guiding treatment, or following response to therapy.