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INTRODUCTION

KEY POINTS

  • Cardiac transthyretin (ATTR) amyloidosis is increasingly recognized as a common underlying cause of heart failure with preserved ejection fraction in the elderly.

  • Echocardiography is often the first test that raises the suspicion of amyloidosis; but echocardiographic features cannot definitively distinguish amyloidosis from nonamyloid hypertrophic heart disease or light chain (AL) from ATTR cardiac amyloidosis.

  • Cardiac magnetic resonance imaging with tissue characterization using gadolinium can distinguish amyloidosis from nonamyloid hypertrophic heart disease but cannot distinguish AL from ATTR cardiac amyloidosis.

  • Cardiac scintigraphy with bone avid radiotracers can definitively identify ATTR cardiac amyloidosis noninvasively, in select patients, avoiding the need for endomyocardial biopsy.

  • Targeted amyloid-binding positron emission tomography tracers are emerging as quantitative tools to image AL and ATTR cardiac amyloidosis.

  • Tafamidis is a therapy that stabilizes transthyretin protein and has been FDA approved for the treatment of ATTR cardiac amyloidosis, and additional agents for treatment are undergoing clinical trials.

Cardiac amyloidosis is a subset of systemic amyloidosis, which is caused by deposition of insoluble, nonbranching, protein aggregates of amyloid fibrils into the extracellular space of the myocardium. This results in increases in left ventricular wall thickness, left ventricular diastolic and systolic dysfunction, and a restrictive (infiltrative) cardiomyopathy. As a result, heart failure is a frequent cause of death in these patients. Two major forms of systemic amyloidosis have cardiac involvement1: (1) Light chain amyloidosis (AL) where amyloid fibrils are formed from immunoglobulin light chains produced by a clonal population of plasma cells and (2) transthyretin amyloidosis (ATTR) where the liver synthesized transthyretin protein is misfolded and subsequently deposits as fibrils in the myocardium. The variant type (ATTRv) is an autosomal dominant disorder, while, the more common, the wild-type disorder (ATTRwt) is associated with aging (previously known as senile systemic amyloidosis). Cardiac involvement in ATTRv phenotypes is highly variable, with some ATTRv diseases having predominantly cardiomyopathic manifestations, while others have coexistent or predominantly neuropathic symptoms, including carpal tunnel syndrome and autonomic neuropathy/dysfunction. Cardiac involvement is estimated in greater than 50% of primary AL amyloidosis patients2 and in almost all ATTRwt patients, and is almost always the cause of death in these patients.3

Distinction between the two types of cardiac amyloidosis (AL and ATTR) is critical as the treatment and prognosis are vastly different. In AL amyloidosis, chemotherapy is used to inhibit the plasma cell dyscrasia, which results in the abnormal light-chain production. Mortality for AL patients is markedly increased in individuals with cardiac involvement. Demonstrating cardiac involvement is not only useful in determining patient prognosis, but also for guiding treatment in these patients. AL cardiac amyloidosis can be rapidly progressive (median survival, if untreated, is less than 12 months after heart failure onset).1 On the other hand, median survival after heart failure onset is better for ATTR patients (median survival 75 months)4 and within this subset, individuals with ATTRwt do better than those with ATTRv. Nonetheless, ATTR cardiac amyloidosis ...

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