Seeing the risks and benefits with our own eyes
Patrick Ryan, MD
The sense of vision is an extraordinary gift and the prospect of its loss can be
terrifying. The chance to see the sunrise, a child’s first steps, or a beautiful sunset
are all unique experiences; one may even describe these as priceless.
Mr. R was an 81-year-old gentleman with a history of CAD, PVD, and diabetes who
had been experiencing declining vision due to diabetic retinopathy and glaucoma.
Subsequent development of bilateral eye pain with an associated “rusty haze” to his
vision raised concern for the potential of an ocular ischemic syndrome, such as
retinal ischemia. Carotid artery ultrasound was obtained and revealed stenosis
bilaterally: greater than 95% on the left and 70-90% on the right. Despite these
findings, it was not clear that his vision loss was due to an ischemic process at all.
Ultimately it was deemed that carotid stenosis was an unlikely cause of his
symptoms.
After several months, Mr. R stopped having eye pain, though his vision remained
poor. The newly diagnosed carotid stenosis placed him at a higher risk of further
vision loss, debilitating stroke, and even death. Faced with these prospects, he was
referred for consideration of left carotid endarterectomy (CEA).
During pre-operative evaluation his risk of major cardiac complications was
estimated at 11% based on his RCRI score. Mr. R was informed of the benefits of
undergoing a CEA and the potential risks of surgery including stroke, myocardial
infarction and death. He elected to proceed with the surgery. Unfortunately, his
post-operative course was complicated by myocardial infarction, cardiogenic shock,
surgical site hematoma, vocal cord paralysis, pneumonia, urosepsis with bacteremia,
and intestinal ischemia. After spending over a month in the hospital and an
additional few weeks at a long-term care facility, the patient passed away.
While the patient was informed and accepted the risks of this procedure, it is useful
to take a closer look at the balance of risks and benefits as applied to Mr. R. Often
times the potential benefit of an intervention is presented in relative terms, though
this can be difficult for patients to interpret. For this reason it is preferable to
describe benefit and risk in absolute terms, optimizing the chance that patients
make a decision most in accordance with their wishes.
On review of the data in patients with asymptomatic carotid artery stenosis, CEA
can reduce risk of stroke by 30% at three years compared to usual care.1-7 When
viewed in terms of absolute risk, however, the estimated potential benefit is about
3%, yielding a number needed to treat of 33 over 3 years. 4-7 This is the benefit for
the average patient in the studied populations. In contrast, Mr. R’s risk of a major
perioperative cardiac event (defined as: myocardial infarction, pulmonary edema,
ventricular fibrillation, primary cardiac arrest, or complete heart block) was
estimated to be 11%. Additionally, even though studies have shown a longer-term
reduction in the risk of stroke, there is a short-term increase in morbidity due to
surgery. The peri-operative risk of stroke or death at 30 days averages about 3% in
the randomized studies of CEA for asymptomatic stenosis.5-6, 8 Though not a direct
comparison of exact outcomes, it does suggest that on balance, CEA may not be as
beneficial as it seemed on the surface for this particular patient.
There were reasonable indications for obtaining the carotid ultrasound and
pursuing CEA based on the degree of asymptomatic stenosis. However, when the
risk-benefit data is applied at the individual level, not all cases are created equally,
and thus probably should not be approached in the same manner. Perhaps during
Mr. R’s perioperative evaluation, had we discussed the benefits and harms in
absolute terms and the trade-off between a short-term risk increase and a long-term
benefit, his decision to pursue surgery may have been different; at the least, we may
have ensured that Mr. R was able to see the odds he was faced with as clearly as
possible.
References:
1. Abbott AA, Chambers BR, Stork JL, Levi CR, Bladin CF, Donnan GA. Embolic
signals and prediction of ipsilateral stroke or transient ischemic attack in asymptomatic
carotid stenosis: a multicenter prospective cohort study. Stroke 2005;36:1128–33.
2. Barnett HJM, Eliasziw M, Meldrum HE, Taylor DW. Do the facts and figures warrant
a 10-fold increase in the performance of carotid endarterectomy on asymptomatic
patients?. Neurology 1996;46:603–8.
3. Chambers BR, Norris JW. Outcome in patients with asymptomatic neck bruits. New
England Journal of Medicine 1986;315:860–5.
4. Chambers BR, Donnan G. Carotid endarterectomy for asymptomatic carotid stenosis.
Cochrane Database of Systematic Reviews 2005, Issue 4. Art. No.: CD001923. DOI:
10.1002/14651858.CD001923.pub2.
5. Endarterectomy for asymptomatic carotid artery stenosis. Executive Committee for the
Asymptomatic Carotid Atherosclerosis Study. JAMA 1995; 273:1421.
6. Halliday A, Mansfield A, Marro J, et al. Prevention of disabling and fatal strokes by
successful carotid endarterectomy in patients without recent neurological symptoms:
randomised controlled trial. Lancet 2004; 363:1491.
7. Hobson RW 2nd, Weiss DG, Fields WS, et al. Efficacy of carotid endarterectomy for
asymptomatic carotid stenosis. The Veterans Affairs Cooperative Study Group. N Engl J
Med 1993; 328:221.
8. Wolff T, Guirguis-Blake J, Miller T, Gillespie M, Harris R. Screening for
Asymptomatic Carotid Artery Stenosis. Evidence Synthesis No. 50. AHRQ Publication
No. 08-05102-EF-1. Rockville, MD: Agency for Healthcare Research and Quality,
December 2007.