A Guide to Noninvasive Diagnosis Techniques for Cardiac Amyloidosis

Cardiac biopsy is the gold standard for diagnosing cardiac amyloidosis (CA), but the procedure has risks of serious complications. A review in the Canadian Journal of Cardiology presented a guide to noninvasive tools that can be used as alternatives to cardiac biopsy.1

The investigators stressed that clinical suspicion is crucial to enable early diagnosis and treatment initiation. Red flags related to the heart include heart failure with preserved ejection fraction and biventricular wall thickening, poor tolerance of standard heart failure medications, persistently elevated cardiac biomarkers, tachyarrhythmias, African-American ethnicity, and a family history of cardiomyopathy. Red flags outside the heart include bilateral carpal tunnel syndrome and signs of involvement of other systems, such as renal, neurologic, and musculoskeletal symptoms.

Noninvasive imaging methods are unable to reliably differentiate between CA caused by light chain (AL) amyloid and those caused by transthyretin amyloid (ATTR). Therefore, when CA is suspected, clinicians should initially test for plasma-cell dyscrasia by serum AL assay and serum and urine protein electrophoresis with immunofixation. The 2 common types of amyloid require different disease-modifying therapies, so early identification is important to begin treatment.

Echocardiography, cardiac magnetic resonance (CMR) imaging, and scintigraphy are the main tools used for noninvasive diagnosis of CA after laboratory tests.

Echocardiography

Echocardiography is a safe starting point for noninvasive testing for CA. Typical echocardiography findings for CA are left ventricular wall thickening and diastolic dysfunction. Right ventricular free wall, atrioventricular valves, and interatrial septum are also frequently thickened. Severe aortic stenosis is another sign of CA. Strain analysis is also useful as CA commonly features reduced longitudinal strain with apical sparing.

The investigators stated, however, that positive findings on echocardiography should prompt further testing, since they are not specific to CA or to either type of amyloid.

CMR Imaging

Amyloid deposition and expanded extracellular volume produce changes by CMR such as increased T1 values and diffuse gadolinium uptake with delayed global washout. Extracellular volume, which is increased in CA, can also be measured by CMR.

CMR cannot distinguish between AL and ATTR. However, the investigators stated that it is useful in screening for CA, determining the presence of CA in patients already diagnosed with amyloidosis, and following disease progression.

99mTechnetium Pyrophosphate Scintigraphy

CA can be diagnosed with 99mtechnetium pyrophosphate scintigraphy, a highly sensitive and specific test for ATTR-CA. When there is no evidence of plasma-cell dyscrasia and AL amyloidosis by laboratory tests, the predictive value for a diagnosis of ATTR-CA is 100%. However, false positives with scintigraphy are possible, so single photon-emission computed tomography images should be obtained during scintigraphy and analyzed to confirm that signals are coming from the myocardium.

Finally, although noninvasive tools are useful, the investigators recommended a cardiac biopsy when the diagnosis remains uncertain.

Reference

  1. Music S, Szilagyi A, Chetrit M. A guide to the noninvasive imaging assessment of cardiac amyloidosis. Can J Cardiol. 2022;38:384-388.

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