Table 1.

Noninvasive imaging techniques and features in cardiac amyloidosis

Echocardiogram	• Classical findings: biatrial enlargement, valvular and interatrial thickening, pleural and pericardial effusion, biventricular hypertrophy with a bright and sparkling appearance with preserved left ventricular ejection fraction, and a restrictive pattern with diastolic dysfunction. • A regional pattern of strain with severe impairment of strains at the middle and basal segments and relative apical sparing of longitudinal strain [20]. • Myocardial deformation analysis, identifying changes in its measurement on 2-dimensional speckle tracking imaging with a high prevalent rate (93 to 100%) [21]. It has been observed that this strain pattern, known as apical sparing or “cherry on top,” is not specific to CA, since it is also present in other conditions such as aortic stenosis, cardiotoxicity, and dilated cardiomyopathy. • The ejection fraction strain ratio (a ratio of LV ejection fraction/global longitudinal strain > 4.1) improves its accuracy [22].
Cardiac Magnetic Resonance (CMR)	• Provides tissue characterization using multiple sequences. • In patients with atrial fibrillation and in patients with some metallic devices, its application may be limited or restricted. • Typical findings are a nonischemic heterogeneous LGE pattern, ranging from transmural or subendocardial to patchy focal LGE, commonly in association with suboptimal myocardial nulling [12]. • An abnormality in the gadolinium kinetics, also occurring because of systemic amyloid infiltration, drops the blood pool signal to null before the myocardial signal [23]. • A global subendocardial, transmural, and patchy LGE pattern is very suggestive of CA [13]. • More recently, different groups worldwide have investigated the utility of novel CMR metrics based on T1 mapping techniques, with very promising results [23–27].
Nuclear Medicine	• Among the available bone tracers, the most studied has been 99mTc-DPD, which seems to be much more specific to TTR CA compared with AL CA [28, 29]. • 99mTc-DPD is unable to differentiate between inherent and wild-type TTR CA [30]. • Typically, patients with TTR CA have a visual grade ≥ 2, and LA CA patients commonly have no uptake. • It was demonstrated that more than 1 in 5 patients with AL CA have significant uptake of Tc-99m PYP/DPD/HMDP (grades 2 and 3). • The semiquantitative approach using Tc-99m PYP relies on the heart-to-contralateral-lung uptake (H/CL) ratio of > 1.5 at 1 h after tracer administration. This approach was able to precisely differentiate TTR CA from AL CA with high sensitivity (97%) and specificity (100%) [31]. • The semiquantitative approach is also gaining attention because unlike the visual score, it may also provide prognostic information [31].

99mPYP/DPD/HMDP, 99m pyrophosphate/dicarboxypropane diphosphonate/hydroxymethylene-diphosphonate

TTR CA, transthyretin cardiac amyloidosis

AL CA, light chain cardiac amyloidosis

LGE, late gadolinium enhancement

ECV, extracellular volume