Use of Ventilatory Efficiency Slope as a Marker for Increased Mortality in Wild-Type Transthyretin Cardiac Amyloidosis

Abstract

Wild-type transthyretin amyloidosis (ATTRwt) results in an infiltrative cardiomyopathy often culminating in symptomatic heart failure. The use of cardiopulmonary exercise testing (CPET) in determining outcomes in ATTRwt cardiac amyloidosis is unknown. Given the emergence of novel therapies to treat transthyretin amyloidosis, we sought to investigate the utility of CPET on outcomes in patients with ATTRwt cardiomyopathy. Fifty-six patients, with biopsy and immunohistochemically proved ATTRwt, were enrolled between 2005 and 2015, as part of an NIH ATTRwt substudy at the Boston University Amyloidosis Center. Patients were prospectively studied, which included laboratory tests, electrocardiogram, echocardiography, in addition to CPET. In this cohort of ATTRwt patients who performed CPET were elderly, all were male, and predominantly white (69.9%). The overall median survival was 59.01 months (95% confidence interval [CI] 49.29 to 88.69). By multivariate analysis, C-reactive protein (CRP; hazard ratio [HR] 1.10 [1.03 to 1.18]), decreased sodium (HR 0.75 [0.58 to 0.97]), creatinine (HR 7.48 [2.44 to 22.98]) and VE/VCO₂ (HR 1.10 [1.05 to 1.16]) were significant risk factors for mortality (p <0.05). Peak VO₂ was insignificant by both univariate and multivariate analyses. ATTRwt patients with VE/VCO₂ >40 had a worse median survival of 38.54 months (95% CI 32.63 to 51.47) versus 88.69 months (95% CI 56.26 to 89.49) than patients with VE/VCO₂ slope ≤40. Receiver-operating characteristic curve showed that the combination of VE/VCO_2, CRP, sodium, and creatinine (Area under the ROC Curve [AUC], 0.89) predicted 1-year mortality in ATTRwt cardiac amyloidosis. In conclusion, increased VE/VCO₂, in combination with CRP, sodium, and creatinine, may identify patients at increased risk of death in ATTRwt cardiomyopathy. VE/VCO₂ might have a role in objectively assessing therapeutic response in ATTRwt cardiac amyloidosis.

Figure 1:

Receiver-operating characteristic (ROC) curves demonstrated that VE/VCO2 slope, creatinine, sodium and CRP are predictors of 1-year mortality in patients with ATTRwt cardiac amyloidosis.

Figure 2:

Kaplan Meier Survival curve for all-cause mortality in VE/VCO2 > 40 and ≤ 40 in ATTRwt cardiac amyloidosis. Survival was significantly worse in patients with VE/VCO2 > 40 than those with VE/VCO2 ≤ 40 (P<0.01)