A sTudy invesTigating the Role of Occult cArdiaC Amyloid in The Elderly With Aortic Stenosis

INTRODUCTION

Calcific aortic stenosis (AS) is the most common valve disease in the West with a prevalence of 2.8% in patients over 75 years. Once symptomatic with severe AS, outcome is poor, unless the valve is replaced surgically (sAVR) or via transcatheter aortic valve replacement (TAVR), which is predominantly used in elderly patients for whom surgery is deemed too high risk.

Systemic amyloidosis is a multisystem disease characterised by extracellular deposition of abnormally folded protein, which over time results in progressive organ dysfunction. These protein deposits bind Congo red stain, producing the pathognomonic apple-green birefringence under polarised light. Cardiac involvement is the leading cause of morbidity and mortality in these patients. Amyloidosis due to transthyretin deposition (ATTR) can be due to wild-type transthyretin amyloid deposits, also known as senile systemic amyloidosis, which predominantly accumulates in the heart. Primary light chain (AL) amyloidosis and hereditary transthyretin amyloidosis can also affect the heart.

Wild-type ATTR (wtATTR) amyloid deposition is present in up to a 25% of individuals aged over 85 at autopsy. To date, this has been no more than an academic observation, but technology is changing this: cardiac imaging, particularly cardiovascular magnetic resonance (CMR) and 99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid (DPD) scintigraphy, can now detect the disease antemortem, which is generating a major increase in national awareness. There are also significant advances being made in the treatment of amyloidosis. There are several drugs in clinical trial including novel antisense and interfering RNA therapeutics that can reduce production of TTR by up to 80-90%. Also on the horizon are treatments to promote clearance of established amyloid, notably including monoclonal anti-SAP (serum amyloid P component) antibodies. Despite the prevalence of wtATTR amyloid deposits at autopsy, their clinical significance and prognostic impact of in severe AS has not been explored.

Co-existent cardiac amyloid and AS. Given the prevalence of wtATTR in octogenarians at autopsy, AS and wtATTR are likely to co-exist - the literature has early evidence for this. In a cohort of 20 patients with AS, who had undergone TAVI and subsequently valve explantation at autopsy (n=17) or surgery (n=3), cardiac amyloid was found in a third of these patients and was thought to contribute to death in the majority. Our research also supports this - the "RELIEF-AS" study. In 146 patients with severe AS undergoing sAVR, we found cardiac amyloid deposits in 6 patients. All were wtATTR, all calcific AS, with the youngest patient being aged 69. Comprehensive imaging was performed, which showed a diagnostic imaging hierarchy: echocardiography was non-contributory, CMR detected a third of cases, whereas DPD scintigraphy was positive in all four patients scanned (2 died before the test). Biopsy ATTR deposits were prognostic and the strongest predictor of adverse outcome - regardless of infiltration degree or its imaging detection: post sAVR 50% with wtATTR died by 1 year vs 9% without (p<0.001). Occult amyloid has also been implicated in the need for pacemakers in TAVR patients.