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.

The availability of TAVI has extended the range of individuals that can benefit from intervention for AS, prolonging life. TAVR patients are generally older so more likely to have wtATTR. One recent abstract found a 16% (23% in men) prevalence of cardiac amyloid in in patients undergoing TAVR (n=75) using 99mTc-pyrophosphate scintigraphy (PYP, a bone tracer available in the USA, which is possibly inferior to DPD). WtATTR is also an increasingly recognized cause of heart failure with preserved ejection fraction (HFpEF). DPD scintigraphy in 120 hospitalized patients who also had LV wall thickness ≥12 mm and an EF ≥50%, showed that 16 patients (13.3%) showed moderate to severe myocardial uptake.

Why detect wtTTR amyloid in severe AS? There are two separate aspects of wtATTR in AS. First, wtATTR in patients with moderate AS may mimic severe AS, (particularly low-flow, low-gradient) causing misdiagnosis. Second, wtATTR may itself be a disease modifier, leading to a more severe phenotype with more heart failure, arrhythmia, and higher mortality. We think there is a large, now detectable, UK population of elderly patients undergoing sAVR or TAVR with a significant occult amyloid. This could influence therapeutic options (TAVR vs sAVR vs medical therapy), intervention timing and medications - specific amyloid therapies, drugs to avoid (e.g. digoxin and diltiazem).

How to detect wtATTR? There are multiple techniques that could detect cardiac wtATTR. Each has their pros and cons with different evidence bases. Our initial study used three imaging modalities and biopsy to detect the presence of cardiac amyloid in sAVR. DPD scintigraphy was the superior imaging modality, with the highest diagnostic sensitivity. There is now a rapidly growing body of evidence supporting DPD scintigraphy as the non-invasive investigation of choice for diagnosing cardiac ATTR. A recent multi-centre study of over 1,000 patients showed that bone scintigraphy had a >99% sensitivity for cardiac ATTR deposits and they proposed it should have a role in diagnosing the condition without the need for invasive cardiac biopsy, which has previously been considered the gold standard.

The investigators have recently created a new modality: equilibrium contrast computed tomography (EqCT), which requires a single extra image dataset of the heart to be taken 5 minutes after the routine TAVR work-up CT images are taken. Extracellular volume fraction (ECV) calculated by EqCT discriminated 100% between cardiac amyloid involvement and patients with AS in 53 patients.

TRIAL OBJECTIVES

Hypothesis:

In the elderly with severe AS being considered for intervention (TAVR, sAVR), wtATTR is:

• Common.
• Conveys a worse prognosis.
• Can be reliably detected non-invasively.

Aim:

To confirm the prevalence, clinical impact (procedural complications, symptom response to aortic valve replacement, 1-year mortality) and potential place of imaging (DPD scintigraphy, ECV by CT, CMR and echocardiography) in occult amyloid in severe AS.

STUDY PLAN

Design: prospective observational cohort with 1 year follow-up.

Population: patients aged 75 or older with severe AS referred to the Barts Heart Centre for consideration for intervention (sAVR or TAVR) or referred to the John Radcliffe Hospital in Oxford for consideration for TAVR.

Proposed sample size: two centre study (Barts Heart Centre and the John Radcliffe Hospital), 250 patients.

Recruitment: patients will be recruited from General Cardiology, TAVR and Cardiothoracic Surgery Outpatient Clinics. A large proportion of these patients are discussed in the Valve Multidisciplinary Team Meeting, which will provide another source of recruitment. This will take place over an 18-month period from August 2016 to February 2018.

Baseline assessment: will include clinical history, Quality of Life Questionnaire (EQ-5D/SF-12), a 6-minute-walk test, blood sampling for haematocrit, renal function, biomarkers (NT-pro-BNP and troponin), and biobanking (also for AL exclusions if scanning positive), a urine sample for biobanking (also for AL exclusion if scanning positive), as well as tests performed as the routine pre-operative work-up (clinical electrocardiogram, blood pressure to estimate global LV afterload, valvulo-arterial impedance).

Measures of exposure: the prevalence of cardiac amyloid assessed in three arms (sAVR, TAVI and medical therapy, with a likely patient ratio of 50:150:50), using five investigation modalities - all cohorts (echocardiography and DPD scintigraphy); sAVR cohort (biopsy and CMR); TAVR cohort (EqCT); medical therapy only cohort (as per work-up/trial prior to no intervention decision).

Follow-up: 1-year follow-up with clinical echocardiogram (for sAVR and TAVR patients) and/or telephone interview for all patients (if not carried out in person at the time of the echocardiogram). This will include a follow up Quality of Life Questionnaire as per baseline. If attending clinic or echocardiogram a 6-minute-walk test will also be performed. MACE and mortality endpoints will also be identified.