Hypertension ranks number one in the risk for future stroke . Surprisingly this is true for ischemic as well as hemorrhagic strokes.
What causes thrombosis or rupture of small cerebral arterioles ?
It is somewhat similar to coronary events . ( With one major exception, coronary vesels are not prone for rupture ) .It is believed sudden spikes of blood pressure and the resultant endothelial injury are responsible. Atherosclerotic plaque fissure and inflammation also contribute.
Is embolic stroke related to hypertension ?
The vast majority of embolic stroke are believed to arise from heart .This belief is getting gradually eroded , as we now know aortic arch and carotid arteries vie for this honour . .(This was indirectly proved in AFFIRM trial when rhythm control failed to reduce the incidence of stroke inpateints with AF , implying much of the strokes arise in the upstream rather than within the cardiac chambers )
Meanwhile , there is no controversy in SHT promoting both cardiac and non cardiac embolus to brain
Systolic , Diastolic or Mean pressure which is important in the genesis of stroke ?
All parameters are important , but the systolic blood pressure is vested with more vigour to damage the cerebral arterioles. The reason systolic pressure is more important lies in the fact , it can attain high pressure peaks instantly , unlike diastolic or pulse pressure which slowly builds up. Further , systolic BP carries leading edge of the pressure curve with high Dp/Dt and hits the target first !
At what pressure the cerebral artery becomes uncomfortable ?
We do not know the answer as yet , but any systolic pressure above 180 mmhg is a huge stress for the cerebral arterioles.The rapidity with which the BP raises (Dp/Dt) also becomes important . High blood pressure increases the shearing stress .It interferes with nitric oxide synthesis and promotes endothelin release which precipitates cerebro vascular event.
How do you identify people who are at risk for stroke ?
While cardiac physicians are obsessed with exercise stress test to predict CAD very few are worried about stroke . In fact the same exercise stress test can be used to stratify stroke risk. The exercise induced systolic blood pressure raise is a useful risk stratifying tool. This concept is there for more than a decade without reaching the clinical domain.
The following paper was published in stroke journal (2001) from the picturesque university of Kupio Finland.(See below ) It is a wonderfully done study and throws great insight into the new emerging science of Intra cerebral hypertension .
The following can be summed up as risk factors for stroke during EST (Derived from various sources and . . . with liberal dose of personal logic !)
- Raise of 20 mmhg SBP at 2 minutes .
- Increment of > 20mmhg in SBP any subsequent minute.
- Any SBP above 200mmhg during EST
- Failure to reach baseline SBP at 6 minutes recovery .
- SBP or DBP remaining high even after the heart rate reaches baseline.
Final message
For the kind attention of all cardiac physicians . . . whenever you do an EST for a cardiac indication , please spend the first few minutes carefully ,and look at the blood pressure response . It is encouraged , to specifically mention about the behavior of SBP and write a remark about the propensity for stroke in every EST/TMT report . Let us grow our brain sense as well . . . for the sake of our patients !
Thanks again to Dr S.Kurl et all from Finland for their nice article which stimulated me to write this post .
Reference
http://stroke.ahajournals.org/cgi/reprint/32/9/2036
http://heart.bmj.com/content/95/13/1072.abstract
Further queries
How common is stroke following a EST procedure ? Can high blood pressure dislodge a carotid plaque during a stress test ?
The answers will be posted soon once I get it . ( Of course you can do it if you know !)
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Dr.S.Venkatesan MD 