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Nicole K Bart, Is the left atrium the key in the amyloid imaging lock?, European Heart Journal - Cardiovascular Imaging, Volume 24, Issue 2, February 2023, Page e36, https://doi.org/10.1093/ehjci/jeac223
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Amyloidosis is a devastating multisystem disease, in which misfolded amyloid fibrils deposit in different body structures. Cardiac amyloid (CA) amyloidosis portends a particularly poor prognosis with an untreated life expectancy of ∼4 years.1 There are two main types of CA, transthyretin (ATTR) and light chain (AL) which account for 95% of cases of CA.1 There has been an explosion of recent original research and guidelines with regards to imaging in amyloidosis due to non-invasive diagnosis, and disease modifying treatment.2 Importantly, targeted treatment depends on accurate subtyping.
The left atrium plays a significant role in the pathophysiology of CA, with amyloid fibrils depositing throughout the atria leading to impaired atrial function and disproportionate rates of atrial fibrillation. Atrial function contributes to and modulates left ventricular filling and can be used as a surrogate marker for left ventricular filling pressure. Changes in left atrial function can serve as an early warning system, with these parameters becoming abnormal before changes in left ventricular function.3 A recent study published in this journal showed that in 423 consecutive patients, peak left atrial longitudinal stain (LA PALS) was an independent predictor of CA, specifically TTR.3 This was especially true for an LA PALS of <6.65% which was associated with a 3.68-fold higher risk of ATTR.3
Late gadolinium enhancement (LGE) can be used to quantify the degree of atrial fibril deposition, which has been linked with all cause hospitalization and mortality. Cardiac magnetic resonance (CMR) imaging is an excellent imaging modality for differentiating CA from other phenocopies. The recent guidelines suggest CMR should be performed in all new cases of AL amyloidosis,3 and in fact extracellular volume may be a way of quantifying disease burden and guiding treatment.4 Strain techniques allow for understanding of left atrial deformation throughout the cardiac cycle. This is an independent prognostic marker in both ischaemic and non-ischaemic cardiomyopathy in patients with heart failure.5
To date, CMR imaging has been unable to differentiate between ATTR and AL amyloidosis. A recent study has shown that atrial geometry and function may help distinguish between amyloid subtypes.6 A total of 54 patients with confirmed CA (24 ATTR, 30 AL) underwent detailed CMR imaging examinations and were compared with 15 health age and gender matched controls. Interestingly, there was no meaningful difference in left or right atrial size between ATTR and AL amyloidosis patients. Comparatively, the atria in patients with CA were significantly larger than the healthy controls. Patients with ATTR had worse reservoir and booster strain patterns than those with AL. Left atrial reservoir strain emerged as the most robust differentiator between ATTR and AL amyloid.
LGE burden in the atria may also serve as a guide of disease burden and may correlated with impairment in LA strain.7 It would be interesting to link studies of LA function to CA prognosis including hospitalization, heart failure, and death. Overall, left atrial function is a marker to watch.Conflict of interest: none declared.
Funding
The author receives research funding and speakers fees from Pfizer, unrelated to this work.
