Analysis of Myocardial Flow Reserve in Patients with Transthyretin Cardiac Amyloidosis. Its Relationship with Cardiac Amyloid Distribution and Global Longitudinal Strain

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Abstract

Background: Transthyretin cardiac amyloidosis (ATTR-CA) is a disease characterized by the abnormal accumulation of amyloid protein in cardiac tissue, affecting ventricular function and global longitudinal strain (GLS).
Amyloid protein has a high affinity for Tc99m-labeled diphosphonate tracers. Cadmium zinc telluride (CZT) detector-equipped devices allow for evaluation of hydroxy methylene diphosphonate (HMDP) distribution due to their high resolution.
Myocardial perfusion imaging with Tc99m- MIBI using CZT technology devices allow simultaneous assessment of myocardial flow reserve (MFR).

Methods: Patients with ATTR-CA confirmed by cardiac scintigraphy with grade 3 uptake according to Perugini scale, and absence of monoclonal gammopathy were included. Doppler echocardiography with GLS assessment, myocardial perfusion with Tc99m-MIBI, and MFR estimation were performed. Amyloid distribution was analyzed by SPECT and segmented polar maps, calculating the percent uptake in each coronary territory.

Results: Twenty-two male patients with mean age of 78 ± 7 years were studied. Median total amyloid distribution in the
left ventricle was 88% (interquartile range, IQR, 81-97). In the left anterior descending artery territory, the median value was 94% (IQR 91-100), in the circumflex artery territory 94% (IQR 91–98), and in the right coronary artery territory 100%.
Median left ventricular ejection fraction was 56% (IQR 45–67.5) by echocardiography and 52.5% (IQR 39-57) by triggered SPECT, with no significant differences. Median GLS was –8.16 (IQR –9.67 to –6.27). No ischemia or necrosis was observed in the perfusion studies. Median MFR was 1.81 (IQR 1.33–2.02), with stress flow of 1.22 mL/min/g (IQR 0.95-1.74) and rest flow of 0.77 mL/min/g (IQR 0.64-0.91). No significant association was found between amyloid deposition, MFR, and GLS.
Conclusions: Myocardial flow reserve is reduced in patients with ATTR-CA, suggesting microvascular dysfunction. However, no association was found between the extent of amyloid deposit, MFR, and GLS, indicating the possible involvement of additional pathophysiological mechanisms.