RV free wall longitudinal strain as an independent predictor of survival in wtATTR-CA patients
Authors: Tan T.S , Grogan M , Borgeson D , Pislaru S.V , Dispenzieri A , Garvan K , Oguz D , Lin G 
Published: October 2021

Abstract

Background
Wild type transthyretin cardiac amyloidosis (wtATTR-CA) is increasingly recognized as a cause of heart failure with preserved ejection fraction (HFpEF) but prognosis is often limited due to late or misdiagnosis.Longitudinal left ventricular strain and biomarkers are established as markers of disease severity, but the role of RV free wall strain, reflecting RV contractility, is less well understood.

Purpose
We sought to determine whether RV free wall strain might add incremental prognostic value in wtATTR-CA.

Methods
Consecutive patients diagnosed with wtATTR-CA with tissue confirmation at Mayo clinic between 2013 and 2015 were included. Patients with TTR gene mutations were excluded. Baseline characteristics and transthoracic echocardiography measurements were obtained from the medical records. Speckle tracking RV free wall longitudinal 2D strain and peak LA longitudinal 2D strain were measured using Tom Tec Imaging System. Survival was determined using Kaplan Meier estimates and using the cox proportional hazard ratio, univariate and multivariable analysis were performed to identify predictors of mortality in patients with wtATTR.

Results
The study group comprised 139 patients (mean age 74.9±8.6, 92.8% male), of which 102 had adequate image quality for RV strain, and 99 for LA strain. Amongst these, 102 (73.3%) had AF and 118 patients (84.8%) had HF. During 3.23±2.0 years of follow up, 66 patients died. Both mean RV and LA strain were impaired at baseline: RV free wall strain was −14.7±4.9, and peak atrial longitudinal strain (PALS) was 13.2±8.8%. Using ROC analysis, RV strain of −16.8% was an independent predictor of all-cause mortality. In univariate modeling, higher levels of NT-proBNP (HR: 1.1 per 1000 pg.ml; 95%, CI 1.05–1.15, p&lt;0.001) and Troponin T (HR: 2.0 per 0.1ng/ml; 95% CI 1.49–2.61, p&lt;0.001) were associated with increased all-cause mortality. In addition, LV GLS (HR: 1.13 per 1%; 95% CI1.04–1.24, p=0.003), RV free wall LS (HR: 2.16 per 5%; 95%, CI 1.57–3.03, p&lt;0.0001), and PALS (HR: 0.91 per1%; 95% CI 0.85–0.96, p&lt;0.0001) were univariate predictors of all-cause mortality. In multivariate analysis using a stepwise regression model, RV free wall longitudinal strain (HR: 1.81; 95% CI 1.29–2.62, p&lt;0.001) and Troponin T (HR: 1.7; 95% CI 1.25–2.26, p=0.001) remained independent predictors. Kaplan-Meier survival analysis demonstrated a higher mortality rate above −16.8 RV strain cut-off (Wilcoxon &lt;0.0001). All stages were divided into two groups by −16.8% RV strain, and survival in individual stages analyzed. Stage 1 and 2 with &lt;−16.8 RV free wall strain value had higher mortality than ≤-16.8% RV strain (Stage 1: Wilcoxon = 0.0041 and Stage 2: Wilcoxon = 0.023). However, there was not a survival difference between two RV strain groups in stage3 (Wilcoxon = 0.34)

Conclusion
RV free wall strain is an independent predictor of survival in wtATTR patients and may add incremental prognostic value to NT-proBNP and Troponin.

Funding Acknowledgement
Type of funding sources: None. Kaplan-Meier curve of all patientsKaplan-Meier curve of stages