Cardiac muscle (myocardium) in patients with transthyretin amyloid cardiomyopathy (ATTR-CM) appears to have reduced contractile force compared to healthy cardiac muscle, according to a recently published study in JACC: Basic to Translational Science.
Though ATTR-CM has been extensively studied from clinical, genetic and pharmacologic perspectives, research on cardiac amyloidosis at the molecular level remains limited.
To address this gap, the authors analyzed cardiac muscle samples from five patients with ATTR-CM and compared them to samples from five healthy organ donors.
Heart muscle contracts with less force in ATTR-CM
Researchers observed that myocardium from ATTR-CM patients contracted with significantly less force than healthy tissue. In cardiac muscle, contraction force is crucial for pumping blood out of the ventricles and into the rest of the body. Reduced contractile force means less blood reaches tissues, and the heart must beat faster to compensate, thereby increasing oxygen demand.
Cardiac stiffness in ATTR-CM is driven by fibrosis
The study also showed that, although the myocardium in ATTR-CM was not intrinsically stiffer than healthy tissue, it contained significantly more scar tissue (fibrosis). This fibrosis contributes to overall cardiac stiffness and impairs the heart’s ability to fill properly during the relaxation phase (diastole), reducing the amount of blood the ventricles can pump.
Furthermore, fibrosis levels were consistent across different regions of the heart, suggesting that fibrosis develops homogeneously.
Calcium deposits are common in ATTR-CM
Another key finding was the presence of a high density of calcium deposits in the myocardium of those with ATTR-CM. This may help explain why bone scans are a useful diagnostic tool in ATTR-CM.
The authors concluded that the clinical manifestations of ATTR-CM result from a combination of cellular factors (impaired contractility) and extracellular changes (fibrosis and calcification).
These insights on fibrosis levels and calcium deposits may help improve the diagnosis of ATTR-CM. “Improved diagnostic techniques will be vital as awareness and screening of cardiac amyloidosis increases,” the study’s authors said.
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