Imaging cardiac ATTR amyloid

Abstract

The heart is the principal site of involvement in non-hereditary ATTR amyloidosis and a major driver of treat-ment options and prognosis in hereditary forms of the disease. The goals of cardiac imaging in amyloidosis are to aid diagnosis, provide prognostic information, track disease progression and evaluate response to therapy. Echocardiography has long been the mainstay of cardiac evaluation in amyloidosis, particularly that of diastolic dys-function, but its precision is limited and both inter and intra-observer variability constrain its capacity to detect changes. The recent refinement of myocardial strain ima-ging provides more reproducible and more sensitive eva-luation of systolic impairment, which may be overlooked in amyloidosis, and the longitudinal strain pattern of relative apical sparing strongly supports diagnosis of amyloidosis. Two investigations that are transforming our under-standing of cardiac amyloidosis are bone scintigraphy and cardiovascular magnetic resonance (CMR). CMR with gadolinium contrast has proved to be invalu-able for identification of cardiac amyloid, showing charac-teristic patterns of global subendocardial and transmural late gadolinium enhancement associated with abnormal myocardial and blood pool kinetics. The recent refinement of phase-sensitive inversion recovery sequence is highly sensitive and specific, producing findings that are virtually pathognomonic for amyloid. CMR is inferior to echocar-diography for evaluating diastolic function but can assess the heart's structure and systolic function with greater accuracy and precision. A key advantage of CMR is its unique ability to give insight about tissue composition through myocardial tissue characterization. T1 mapping studies can quantify the massive expansion of the extracel-lular space caused by amyloid deposition as well as evaluating the myocyte response to it, i.e. associated hypertrophy or cell loss. The ability to independently track changes in amyloid load and myocardial cell mass will be invaluable in assessing new therapies. One significant lim-itation of CMR is its incompatibility with most implanted pacemakers and ICDs, an issue that may be addressed by the development of dynamic equilibrium CT, in which gated five minute contrast-enhanced scans have shown excellent potential for diagnosis and quantification of cardiac amyloid.