Figure 1. Ultrasound monitoring showing shower of tinny clots (microemboli) flowing in the brain vessel.

Stroke is the second leading cause of death and the commonest cause of disability among the Chinese. More importantly, stroke is more common in the Chinese than in the Caucasians. Yet there were few data to confirm if there were any true ethnic differences in the cause of stroke between the East and the West. With the support of the RGC, we were the first in the world to confirm that narrowing of the blood vessels around the brain was the commonest cause of stroke in the Chinese, in contrast to previous studies that showed narrowing of the blood vessel in the neck region was the commonest cause in the Caucasians. The same observation was later confirmed in other Asian populations such as the Thai, Korean, Malaysian and Indian. Moreover, we discovered that the total burden of the narrowed vessel could predict the risk of further stroke among stroke survivors. We thought it would be a good idea if we could identify subjects with narrowed vessels before they developed stroke. We were first in the world to document that 7-8% of normal subjects aged >40 harboured brain narrowed brain vessel without knowing it. A study of > 3,000 subjects at the United Christian Hospital and the Prince of Wales Hospital medical clinics found that the risk of harbouring asymptomatic narrowed brain vessels were directly related to the number of risk factors present in an individual. These subjects with narrowed vessels were at double the risk for future stroke and deaths despite medical treatment. The next step of our projects aimed to elucidate the underlying mechanisms why narrowed vessels caused stroke. Using ultrasound monitoring of the blood flow in the brain vessels, we were able to detect tinny clots flowing in the blood vessels because the clots reflected more ultrasound energy than the normal red blood cells. Combining the results of the state-of-the-art magnetic resonance imaging and ultrasound, we found that narrowed vessels commonly produced stroke by releasing blood clots into the distal blood vessels and then occluding these vessels downstream. We were able to show that the amount of tinny blood clots released from the narrowed vessels predicted the amount of dead brain cells and also predicted the risk of further stroke, especially in the immediate few days after the first stroke. All these observations added on our understanding of the underlying mechanisms of stroke in the Chinese and provided the basis for more aggressive treatment of patients with recent stroke. Because the tinny blood clots in the circulation consisted mainly of platelet aggregation, we compared the effect of double anti-platelet drugs with just one anti-platelet drug in 100 patients with recent stroke and flowing blood clots. We found that double anti-platelet drug reduced the amount of flowing clots by about half after 24 hours. More importantly, use of double anti-platelet drugs was able to reduce the absolute risk of stroke by 6% during the first week after a stroke in patients with narrowed brain vessels.

　

Our series of studies established the value of using simple ultrasound in the community as well in hospital to detect narrowed vessels in the brain and to identify those with high risk of stroke. Using ultrasound and magnetic resonance imaging together, we were able to elucidate the mechanism of stroke in the Chinese and to establish the importance of detecting small flowing clots in the vessels. The use of double antiplatelet drug markedly reduced the number of flowing clots in the vessels and probably prevent further stroke. The results of our studies laid the foundation for better prevention by identifying high risk patients with abnormal vessels and for better treatment strategy such as using double anti-platelet drugs.

Prof Ka Sing Lawrence WONG
Department of Medicine and Therapeutics
The Chinese University of Hong Kong
ks-wong@cuhk.edu.hk