“In the past the risk of stroke among patients with asymptomatic carotid stenosis was higher, because medical therapy was less intense,” lead researcher Dr. J. David Spence, who is with the University of Western Ontario in London, Canada, told Reuters Health.
He noted that in two pivotal studies, the ACAS trial and the ACST trial, endarterectomy for asymptomatic carotid stenosis was associated with a significant 50% reduction in the risk of stroke. This, however, was based on two risk-benefit assumptions that no longer hold.
First, the stroke/death risk with surgery in the trials was only 3%; however, in the “real world” it is about 5%. Second, the risk with medical therapy in those days was higher than it is now with more intensive therapy.
Dr. Spence said that his team published evidence in 2005 showing that embolus detection on transcranial Doppler (TCD) could be used to discriminate low-risk from high-risk patients with asymptomatic carotid stenosis. In the study, the presence of microemboli conferred a 1-year stroke risk of 15.6%, while without emboli — the finding in 90% of patients — the risk was just 1%.
In the current investigation, the researchers examined how implementation of more intensive medical therapy at their clinics in 2003 affected TCD microemboli rates and cardiovascular events. According to Dr. Spence, the treatment approach changed from “treating risk factors according to guidelines, to treating arteries — intensifying therapy in those patients with plaque progression, regardless of the levels of risk factors such as LDL.”
In the study, 199 patients with asymptomatic carotid stenosis of 60% or more were treated prior to 2003 and 272 were treated during or after 2003. Overall, 12.6% of patients treated during the earlier period had microemboli compared with just 3.7% of patient treated in the later period (p < 0.0001).
In the pre-2003 cohort, the 1-year risks of stroke and MI were 4% and 6.5%, respectively. In the later cohort, the corresponding figures were just 0.8% and 0%.
The message for clinicians, Dr. Spence said, is that asymptomatic carotid stenosis patients “are at high risk and should all receive intensive medical therapy, but only those with microemboli on TCD should be considered for revascularization.”
As he pointed out, “This has huge implications, particularly in the United States, where between half and two thirds of patients with carotid stenosis being subjected to revascularization are asymptomatic.”