Magnetic Resonance in Transthyretin Cardiac Amyloidosis
What are the findings on cardiac magnetic resonance imaging (CMR) of transthyretin (TTR) cardiac amyloidosis (ATTR), and what are the prognostic implications of those findings?
Patients with established (n = 227) or suspected cardiac ATTR (n = 17), TTR gene mutations without clinical involvement (n = 12), and light chain (AL) cardiac amyloidosis (n = 50) were prospectively recruited. Cardiac ATTR was defined as a symptom with suggestive echocardiogram and grade 2 or 3 uptake on 99mTc-DPD scintigraphy without monoclonal gammopathy or, if monoclonal gammopathy was present, cardiac biopsy positive for TTR. CMR was performed on a 1.5 Tesla scanner using intravenous gadolinium-containing contrast. ECG gated cine imaging, late gadolinium enhancement (LGE) imaging, and T1 mapping were performed. Extracellular volume (ECV) fraction was estimated based on the relative change in T1 in the myocardium and blood pool.
Asymmetric septal hypertrophy (ratio of septal to contralateral wall >1.5) was seen in 79% of patients with cardiac ATTR, most with sigmoid septum (55%). Symmetric, concentric left ventricular hypertrophy (LVH) was only present in 18% of patients with cardiac ATTR. Only 3% of patients with cardiac ATTR did not have LVH. Among AL cardiac amyloid patients, asymmetric septal hypertrophy was much less common than ATTR (14% vs. 79%, p < 0.001). In AL, most patients had symmetric concentric amyloid (68%), although 18% did not have LVH.
LGE was present in either a diffuse subendocardial pattern (29%) or diffuse transmural pattern (71%) in all patients with cardiac amyloid. Nearly all patients (96%) had right ventricular (RV) LGE. Transmural LGE was more common in ATTR compared with AL amyloid (71% vs. 50%, p < 0.01), as was RV involvement (96% vs. 77%, p < 0.01). ECV was elevated in cardiac ATTR, but varied based on underlying genetic mutation status. ECV was independently associated with mortality (hazard ratio, 1.164; p < 0.01) after adjustment for age, N-terminal pro–B-type natriuretic peptide, ejection fraction, E/E’, and LV mass index.
Patterns of LVH differ between cardiac ATTR and AL amyloidosis, with asymmetric septal hypertrophy being predominant in ATTR and symmetric concentric LVH being most common in AL. ECV is independently predictive of survival in cardiac ATTR.
This study adds to a rich body of literature supporting the use of CMR in patients with known or suspected amyloidosis. Much recent literature has focused on the excellent performance characteristics of bone scintigraphy in patients with cardiac ATTR. However, because this test is not able to evaluate for other forms of amyloidosis or for other etiologies of LVH and heart failure, its use is generally limited to patients where cardiac ATTR is highly suspected. Conversely, CMR is a versatile tool, which is often used early in the workup of unexpected LVH and heart failure. These data suggest that cardiac ATTR should be suspected in patients with LVH and a pattern of asymmetric septal hypertrophy. Furthermore, they underscore the value of ECV as a metric of disease burden and prognosis.
Keywords: Amyloid Neuropathies, Familial, Amyloidosis, Cardiac Imaging Techniques, Cardiac-Gated Imaging Techniques, Electrocardiography, Gadolinium, Heart Failure, Hypertrophy, Left Ventricular, Magnetic Resonance Imaging, Magnetic Resonance Spectroscopy, Mutation, Myocardium, Natriuretic Peptide, Brain, Peptide Fragments, Prealbumin
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