Dr. Anne L. Abbott: What is the Role of Noninvasive Medical Intervention in Stroke Prevention?
- Volume 9 - Issue 5 - May 2012
- Posted on: 5/1/12
- 0 Comments
- 6756 reads
Interview by Amanda Wright
A: I am advocating medical (non-invasive) intervention alone to reduce the risk of stroke associated with asymptomatic carotid stenosis (of any severity). Medical intervention, here, refers to combined non-invasive strategies to reduce risk of stroke (and other vascular disease complications). It comprises optimal diagnosis of heart and vascular disease risk factors and risk reduction using support of healthy lifestyles and appropriate drugs.
Q: Tell me about your asymptomatic carotid artery disease research. How did it begin?
A: It began officially when I started my PhD in 1998. My main PhD responsibility was an observational cohort study of 202 patients with 60%-99% asymptomatic carotid stenosis being managed with medical intervention alone. The average follow-up was 34 months. These people had carotid stenosis but no previous symptoms of stroke or TIA on the same side of the brain as the carotid artery lesion. We assessed them clinically (risk factors, stroke and TIA symptoms, other diagnoses and medication) at baseline and every 6 months. We were also using a new technique called transcranial Doppler (ultrasound) to detect tiny emboli traveling downstream from the carotid lesion into the brain to see if this may be a method to better risk stratify patients. That is to identify those with higher than average stroke risk who may benefit more than average from invasive carotid procedures (such as surgery).
Q: Why do you believe medical intervention looks superior to surgical intervention?
A: The most surprising result from our study of patients with asymptomatic carotid stenosis was that the average annual rate of first, same-sided stroke (‘ipsilateral’ to the carotid lesion) in our patients was only 1.0%. This was about 2-3 times lower than expected based on results in the literature when our study was planned and commenced. Our rates of embolus detection with transcranial Doppler were also very low (about 0.16/hour on average). This meant we needed a much larger sample size than we originally thought to test our main hypothesis that the detection of embolic signals would identify a subgroup of patients with a significantly higher risk of same-sided stroke or TIA. Our study was never funded in the first place and we simply had no resources to continue. However, more important was this lower than expected stroke rate. It made me wonder that perhaps medical intervention had improved enough since the randomized trials of surgery versus medical intervention alone (Veterans’ Affairs Cooperative Study [VACS], Asymptomatic Carotid Atherosclerosis Study [ACAS] and the Asymptomatic Carotid Surgery Trial [ACST]) and that routine carotid surgery for asymptomatic carotid stenosis was now inappropriate.
This suspicion was confirmed during my post-doctoral studies by the results of my meta-analysis of stroke risk with medical intervention alone over time (Abbott, Stroke 2009). With the help of world-renown medical statistician, Dr. John Ludbrook, I demonstrated that the risk of same-sided or any stroke (and/or TIA) has fallen significantly since the 1980s (when the first reliable measurements were made) to at least match rates for randomized trial operated patients. These findings have been independently, internationally validated. Using most recent studies, we are now seeing an average annual rate of first ipsilateral stroke of only about 0.5%. This is about 5 times lower than non-operated randomized surgical trial asymptomatic patients, 3 times lower than randomized surgical trial operated asymptomatic patients, twice as low as operated asymptomatic patients in the recent Carotid Revascularization Endarterectomy versus Stenting Trial (CREST) and 3 times lower than CREST stented asymptomatic patients. In addition, what makes the choice for medical intervention alone in routine practice obvious is that medical intervention alone is much cheaper for stroke prevention; it prevents other complications (like heart attack, caused by invasive carotid procedures); and in routine practice procedural complications are not usually measured, or if measured, they are often higher than in randomized trials. The bottom line is that all patients with carotid stenosis should receive optimal current medical intervention to reduce their risk of stroke and other heart/vascular disease complications. Additional routine practice carotid surgery or stenting is now more likely to cause harm or, at best, be an expensive, ineffectual procedure that the community pays for.
Q: Tell us more about the studies you included in your meta-analysis. How many patients total? What time period was covered?
A: The studies used in my meta-analysis were selected because they satisfied basic criteria for sound methodology (reliability). These included prospective design with at least 100 patients with directly imaged 50%-99% asymptomatic carotid stenosis. Asymptomatic meant no previous symptoms of same-sided stroke or TIA. Only 11 studies were identified satisfying these criteria (including VACS and ACAS but not ACST). They were published between 1985 and 2007). The total number of patients involved in the 11 studies was 3724. With the latest studies (published since 2009), it is now 4285.
Q: What other surprising results were found during your research?