Comment
Amyloidosis is a group of rare heterogenous diseases characterized by the abnormal extracellular deposition of toxic insoluble fibrillar protein that aggregates in different tissues. The incidence of CA is estimated at 18-55 per 100000 person-years and is commonly associated with immunoglobulin light chain (AL) or transthyretin amyloid (ATTR) (1). AL is a result of extracellular deposition of fibril-forming monoclonal immunoglobulin light-chains, usually secreted by a plasma cell clone. ATTR is most frequently wild-type (wtATTR) and acquired, associated with a male gender, and increasing age, but may be hereditary with mutated forms of transthyretin (2). The dominant pathophysiology of CA is biventricular restrictive cardiomyopathy and resultant diastolic followed by systolic heart failure. Common complications include conduction disorders, embolic events, and syncope. In the absence of epicardial coronary artery disease, angina is associated with obstructive intraluminal coronary microangiopathy. CA carries a poor prognosis, with a median survival of 24-66 months in AL, and 75 months in ATTR (2).
Treatment involves management of heart failure using loop diuretics and aldosterone antagonists; beta blockers and ACE inhibitors are often not tolerated. The underlying disease can be targeted with chemotherapy +/- autologous stem cell transplantation to eradicate the plasma cell clone responsible for AL amyloid, and in wtATTR Tafamidis given (a drug which stabilizes the transthyretin tetramer and therefore may reduce the formation of ATTR amyloid) (3).
Management of coronary artery disease with co-existing CA is challenging. What angiographically appears as surgical disease does not exclude underlying obstructive intraluminal microangiopathy, and results of revascularisation are therefore difficult to predict. Current preoperative risk models such as Euroscore II are invalid in patients with CA, as diastolic dysfunction is not considered. Usual indicators for pre-operative risk such as functional status and LVEF may offer false reassurance.
There is a growing body of evidence for the association between aortic stenosis and CA, with this subgroup of patients at increased risk following surgical valve replacement (4). Although more limited, current evidence of mitral valve surgery in patients with concomitant CA report excellent outcomes (5). Data on bypass surgery is far more limited but given reasonable reported outcomes in other cardiac surgical procedures, our initial view was that surgery, whilst high risk, was a reasonable approach. Subsequently, we are aware of only four published case reports (comprising five patients) of CABG in patients with CA. Four patients died shortly after surgery due to profound LCOS (6-8); and one survived the initial post-operative period only to succumb to electromechanical dissociation a few months later (9). Given our experience and the evidence available, we now conclude that percutaneous coronary intervention (PCI) must be preferred to CABG, even when coronary anatomy would normally suggest surgery the intervention of choice.