Echocardiography Clues to Suspect Transthyretin Cardiac Amyloidosis Diagnosed by Tc-Pyrophosphate SPECT Imaging

Abstract

Introduction Transthyretin (TTR) amyloidosis is a debilitating systemic disease often associated with symptomatic cardiac involvement. Cardiac amyloidosis remains underappreciated as its diagnosis has been challenging. Recently, Technetium99-m pyrophosphate (Tc-PYP) single-photon emission computed tomography (SPECT) imaging has emerged as a reliable modality to diagnose patients with TTR cardiac amyloidosis. However, there are no clear guidelines regarding which patients should be referred for Tc-PYP imaging. As electrocardiogram (ECG) and transthoracic echocardiography (TTE) are universally utilized in the diagnostic workup in patients with cardiac symptoms, we sought to evaluate the predictive value of longitudinal strain assessment and strain pattern by TTE in the diagnosis of TTR cardiac amyloidosis. Methods and Results In this single-center, retrospective study, patients who underwent Tc-PYP imaging between June 2016 and October 2018 were reviewed. ECG and TTE variables assessed are shown in Table 1. Relative apical longitudinal strain was calculated from left ventricular longitudinal strain (LV LS) values. Of 39 consecutive Tc-PYP scans, 24 positive scans and 12 negative scans were identified; 3 “equivocal” scans were excluded. No ECG parameters were predictive of “Tc-PYP positive” scans. LV mass index (p=0.003) demonstrated a significant difference between positive and negative Tc-PYP groups. Significantly, “Tc-PYP positive” patients had a higher relative apical sparing of LV LS (p=0.0004), and notably, no Tc-PYP negative patient had a ratio >1.0. Patients with “Tc-PYP positive” scans were significantly more likely to exhibit relative apical sparing of LV LS compared to other standard parameters assessed by electrocardiogram or echocardiography. Conclusions LV LS measurement should be routinely included as part of a standard echocardiographic protocol to better identify patients at risk. A patient with relative apical sparing of LV LS ratio >1.0 should be referred for Tc-PYP imaging to evaluate for TTR cardiac amyloidosis.