Discussion
There are several issues in patients with ankylosing spondylitis
undergoing CABG. Intubation in these patients has been historically
difficult and fiber optic intubation is often required. In addition, in
the current COVID pandemic risk of aerosol generation is excessive
during fibre optic bronchoscopy and a prolonged intubation process. This
is especially relevant in patients who present urgently without
pre-admission quarantine or the option of a double screening RT-PCR. As
a result adequate protective measures have to be in place to safeguard
health care personnel during the intubation process. In order to
minimize the risk of aerosol generation we decided to perform the
intubation under endoscopic guidance at the very outset. The most
experienced anaesthetic consultant available conversant with fibre-optic
bronchoscopy performed the procedure. Several pitfalls are identified
with airway management and awake fibreoptic intubation is thought to be
the safest option that allows continuous neurological monitoring while
achieving a definitive airway.(6)
Also, legs should be routinely inspected to identify the suitability of
vein harvesting. Skin changes in AS are rare and often limited to
Psoriasis but leukocytoclastic vasculitis in AS has also been
reported(1)
Lipodystrophy as seen in our case renders the vein a poor conduit
choice. In this patient, BITA were used partly because of skin changes
in both lower limbs, with poor veins that felt narrow and hard from the
outside. The patient also had significant peripheral vascular disease.
Also, because of the fixed flexion deformity of the cervical spine the
access to the proximal aorta is quite limited and hence using BITA
precludes the need to access the aorta for construction of proximal
anastomosis.
Nephrolithiasis as seen in our patient is a lesser recognized but
extremely important association of ankylosing spondylitis and has been
considered to be a novel extra-articular manifestation. As seen in our
case male patients with AS are at increased risk of nephrolithiasis as
seen in our case.(3) It has been reported that compared to the general
population patients with AS have almost three-fold increased risk of
surgical intervention for kidney stones.(7)
Manubrio-sternal joints are involved in 80% of patients with AS with
features of erosions or fusion and it has been shown that in the eroded
joints in ankylosing spondylitis cartilage is replaced by collagenous
and fibrous tissue spreading into the bone. (8) The bones can thus be
hard to saw through but brittle and may pose significant problems with
sternal union. AS also commonly involves the hip joint and usually
bilateral hip replacements are required. (5) This poses significant
issues with post-operative mobilisation after CABG especially if veins
have been harvested from the legs. In addition peripheral vascular
disease and associated lipodystrophy of the vein as observed in our case
might preclude their usage. (2)
There is also an increased association between AS and coronary artery
disease. Based on a meta-analysis conducted it has been seen that a
statistically significant increased risk of CAD exists in patients with
AS. The risk is quantified as 41% greater than the general
population.(1) Spondyloarthritis also predisposes these patients to
develop CAD almost 6 years earlier than in the general population. It
has been reported to be a stronger predictor of early CABG than most of
the traditional cardiovascular risk factors.(9)
The pathophysiology behind the association between AS and CAD is not
well-described though an increasing number of evidence are pointing
toward the detrimental effect of chronic inflammation to the endothelial
cell integrity. It has been demonstrated that endothelial dysfunction
and direct endovascular injury from inflammatory cytokine, activated
inflammatory cells and oxidative stress can accelerate the progression
of atherosclerosis.(1)
As far as the prognosis of CABG is concerned while AS increases the risk
of adverse outcomes it is not significantly associated with overall
mortality and adverse cardiac outcomes.(10) As a result the patients
should not be denied surgical revascularization. Awareness of issues
around intubation, choice of conduits, access to the aorta, sternal
closure, and mobilisation are important for a satisfactory outcome.
Utilization of BITA grafting where possible can ameliorate some of these
issues and improve outcomes and minimize the need for reoperation in a
challenging subset of patients. .