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.