Regionally heterogeneous tissue mechanics in cardiac amyloidosis

Analysis of Cardiac Amyloidosis Progression Using Model-Based Markers

Deposition of amyloid in the heart can lead to cardiac dilation and impair its pumping ability. This ultimately leads to heart failure with worsening symptoms of breathlessness and fatigue due to the progressive loss of elasticity of the myocardium. Biomarkers linked to the clinical deterioration can be crucial in developing effective treatments. However, to date the progression of cardiac amyloidosis is poorly characterized. There is an urgent need to identify key predictors for disease progression and cardiac tissue function. In this proof of concept study, we estimate a group of new markers based on mathematical models of the left ventricle derived from routine clinical magnetic resonance imaging and follow-up scans from the National Amyloidosis Center at the Royal Free in London. Using mechanical modeling and statistical classification, we show that it is possible to predict disease progression. Our predictions agree with clinical assessments in a double-blind test in six out of the seven sample cases studied. Importantly, we find that multiple factors need to be used in the classification, which includes mechanical, geometrical and shape features. No single marker can yield reliable prediction given the complexity of the growth and remodeling process of diseased hearts undergoing high-dimensional shape changes. Our approach is promising in terms of clinical translation but the results presented should be interpreted with caution due to the small sample size.

Cardiac MR elastography for quantitative assessment of elevated myocardial stiffness in cardiac amyloidosis

Purpose

To evaluate if cardiac magnetic resonance elastography (MRE) can measure increased stiffness in patients with cardiac amyloidosis. Myocardial tissue stiffness plays an important role in cardiac function. A noninvasive quantitative imaging technique capable of measuring myocardial stiffness could aid in disease diagnosis, therapy monitoring, and disease prognostic strategies. We recently developed a high‐frequency cardiac MRE technique capable of making noninvasive stiffness measurements.

Materials and Methods

In all, 16 volunteers and 22 patients with cardiac amyloidosis were enrolled in this study after Institutional Review Board approval and obtaining formal written consent. All subjects were imaged head‐first in the supine position in a 1.5T closed‐bore MR imager. 3D MRE was performed using 5 mm isotropic resolution oblique short‐axis slices and a vibration frequency of 140 Hz to obtain global quantitative in vivo left ventricular stiffness measurements. The median stiffness was compared between the two cohorts. An octahedral shear strain signal‐to‐noise ratio (OSS‐SNR) threshold of 1.17 was used to exclude exams with insufficient motion amplitude.

Results

Five volunteers and six patients had to be excluded from the study because they fell below the 1.17 OSS‐SNR threshold. The myocardial stiffness of cardiac amyloid patients (median: 11.4 kPa, min: 9.2, max: 15.7) was significantly higher (P = 0.0008) than normal controls (median: 8.2 kPa, min: 7.2, max: 11.8).

Conclusion

This study demonstrates the feasibility of 3D high‐frequency cardiac MRE as a contrast‐agent‐free diagnostic imaging technique for cardiac amyloidosis.

Level of Evidence: 2

Technical Efficacy: Stage 2

J. Magn. Reson. Imaging 2017;46:1361–1367.

Noninvasive Identification of ATTRwt Cardiac Amyloid: The Re-emergence of Nuclear Cardiology

More than half of all subjects with chronic heart failure are older adults with preserved ejection fraction (HFpEF). Effective therapy for this condition is yet to be delineated by clinical trials, suggesting that a greater understanding of underlying biologic mechanisms is needed, especially for the purpose of clinical intervention and future clinical trials. Amyloid infiltration of the myocardium is an underappreciated contributing factor to HFpEF that is often caused by misfolded monomers or oligomers of the protein transthyretin. While previously called senile cardiac amyloidosis and traditionally requiring endomyocardial biopsy for diagnosis, advances in our pathophysiologic understanding of this condition, coupled with nuclear imaging techniques using bone isotopes that can diagnose this condition noninvasively and the development of potential therapies, have resulted in a renewed interest in this previously considered "rare" condition. This reviewer focuses on the re-emergence of nuclear cardiology using pyrophosphate agents that hold promise for early, noninvasive identification of affected individuals.