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Hypertension and stroke

Introduction

Blood pressure is measured as the level of pressure when the heart is contracting ie. Systolic blood pressure) and when the heart is relaxed and filling with blood Diastolic blood pressure. These pressure levels change continually as part of everyday life. The British Hypertension Society Guidelines recommend that the diagnosis and treatment of hypertension should be based on an average of at least two readings after 5 minutes at rest in the seated position. There is no absolute level that defines BP.

Hypertension is a significant and treatable risk factor for both Ischaemic and Haemorrhagic stroke. It is estimated that 25% or more of strokes may be due to hypertension and this increases to 60-70% when discussing haemorrhagic stroke. It is by far the main risk factor for most causes of Intracranial haemorrhage. Those at most risk are those who are non compliant with therapy, those with hypertension at a young age < 55. Smoking also adds to risk. It is important to remember that hypertension is a chronic illness and prior to presentation has almost always been present for years, perhaps undiagnosed due to a lack of screening opportunities. In those in whom it has been diagnosed treatment may have been suboptimal and many patients, especially the young have difficulty taking antihypertensive therapies for a variety of reasons.

Chronic exposure of small arterioles to hypertension leads to lipohyalinolysis to the small penetrating arteries (i.e. Lenticulostriate from the middle cerebral artery, paramedian pontine perforators from the Basilar artery) in the brain predominantly supplying white matter. These vessels often come off abruptly from much larger vessels at right angles and it suggested that these vessels are exposed to higher than expected pressures than would be seen if there was a normal gradated step down in vessel calibre and so are more prone to ongoing damage. There is much overlap with the topic of Small vessel disease.

Vascular changes include obstruction to vessels which causes the typical lacunar stroke clinical syndrome with corresponding imaging or microaneurysms also called Charcot-Bouchard aneurysms may be apparant and they can rupture causing bleeding. The same areas of the brain affected by hypertensive lacunar strokes are also blighted by hypertensive bleeds. The typical areas are the basal ganglia, thalamus, cerebellum and the ventral pons. With time those with hypertensive changes have significant periventricular changes with hypodensity or bleeds.

Hypertension also plays a role in general atherosclerosis and is a cause of heart disease and left ventricular hypertrophy which can precipitate atrial fibrillation.

Blood Pressure Variability

Blood pressure is a dynamic physiological measurement that can fluctuate by minute, hour and day and that this variability in itself is a risk factor for stroke disticnt from the simple absolute measurement of DBP or SBP. Short and long term BP variability is associated with cardiac, vascular and renal disease. The suggestion is that treatment should focus on both lowering BP but alos reducing its variability. Notably β blockers have the poorest effect on blood-pressure variation.

Management

There is evidence that Lowering BP reduces the risk of stroke and the more the BP is lowered, the more effective it is. The PROGRESS trial showed that treatment to lower blood pressure in people who have had a stroke or TIA reduces the risk of further stroke.

Preventative Trials

  • HOPE study: Effects of an ACEI, Ramipril on Cardiovasacular Events in high risk patients. Ramipril significantly reduces the rates of death, myocardial infarction, and stroke in a broad range of high-risk patients who are not known to have a low ejection fraction or heart failure. (N Engl J Med 2000;342:145-53.)
  • PROGRESS study: Randomised trial of a perindopril-based blood-pressure-lowering regimen among 6105 individuals with previous stroke or transient ischaemic attack: This blood-pressure-lowering regimen reduced the risk of stroke among both hypertensive and non-hypertensive individuals with a history of stroke or transient ischaemic attack. Combination therapy with perindopril and indapamide produced larger blood pressure reductions and larger risk reductions than did single drug therapy with perindopril alone. Lancet. 2001 Sep 29;358(9287):1033-41.
  • PRoFESS Study: Yusuf S et al. Telmisartan to Prevent Recurrent Stroke and Cardiovascular Events : Therapy with telmisartan initiated soon after an ischemic stroke and continued for 2.5 years did not significantly lower the rate of recurrent stroke, major cardiovas- cular events, or diabetes. (N=20,332) N Engl J Med 2008;359:1225-37
  • ASCOT-BPLA: Blood Pressure-Lowering Arm of the Anglo-Scandinavian Cardiac Outcomes Trial. The amlodipine-based regimen prevented more major cardiovascular events and induced less diabetes than the atenolol-based regimen. On the basis of previous trial evidence, these effects might not be entirely explained by better control of blood pressure, and this issue is addressed in the accompanying article. Nevertheless, the results have implications with respect to optimum combinations of antihypertensive agents. Lancet September 2005, Vol. 366 Issue: Number 9489 p907-913

References

  • Carlberg B, Lindholm L. Stroke and blood-pressure variation: new permutations on an old theme. Lancet. Vol 375 March 13, 2010
  • Parati G, Ochoa JE et al. Assessment and management of blood-pressure variability. Nature Reviews Cardiology 10, 143-155 (March 2013)

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