Rethinking high blood pressure
A recent study (Lancet 2010;375:895–905), suggests that visit-to-visit variation in systolic blood pressure (SBP) and maximum SBP are strong predictors of stroke, independent of mean SBP.Here one of the authors, Professor Peter Rothwell of the Stroke Prevention Research Unit at Oxford's John Radcliffe Hospital discusses some clinical implications of the work.
Hypertension is the most prevalent treatable risk factor for stroke. One in two adults is affected by it, and the risk of being hypertensive during a lifetime is about 90 per cent. Despite this, the underlying mechanisms by which raised blood pressure (BP) can cause cardiovascular disease are poorly understood. Clinical guidelines for the diagnosis and treatment of hypertension focus heavily on average blood pressure.
The dominant hypothesis is that we each have an underlying average 'true' blood pressure, which is difficult to measure precisely, but which accounts for the vast majority of the complications of hypertension, and explains the benefits of BP-lowering drugs. Variability in BP is dismissed as uninformative and 'random', only noteworthy as an obstacle in the measurement of true underlying BP. Under-diagnosis and under-treatment of hypertension is a major, seemingly intractable problem in all healthcare systems. The new research shows that part of the problem is likely to have been under-recognition of the impact of variability in BP on diagnosis in routine clinical practice in primary care. It shows that doctors have to make diagnoses on the basis of BP measurements that often vary substantially from visit to visit.
All current clinical guidelines encourage doctors to ignore variability and occasional high readings and to rely exclusively on the average BP from multiple visits or 24-hour monitoring. The new research shows that increased variability in BP, a high maximum BP and episodic hypertension are associated with high risks of stroke and other vascular events, and emphasise that any reassurance taken from the fact BP is sometimes normal is false.Importantly, the new research shows that excess variability in blood pressure is treatable, and also that it can be made worse by some drugs used to treat hypertension. Some BP-lowering drugs increase variability, some have no effect and some decrease it. The choice of drug or combination should now therefore take into account their likely effect on variability as well as on the average level. Future drug trials should routinely report effects on variability.There should also be a greater emphasis on consistency of control of BP in patients who are already on treatment. The research showed that even patients with well-controlled BP had a five-fold excess risk of vascular events if their BP was highly variable, even when fully compliant with their medication. Recent calls to abandon measurement of BP after treatment are premature. The fact that many people now monitor their own BP at home will be helpful in identifying variability.New antihypertensive drugs should be developed to be BP-stabilising as well as BP-lowering. Drugs that reduced variability without reducing average BP should still prevent stroke, and would be likely to be helpful in patients who cannot tolerate reductions in their average BP.
Safety testing of all new drugs, irrespective of the indication, should include assessment of effects on instability and variability in BP, as well as on average BP.
*NICE recommends that calcium channel blockers or diuretics should be used first-line for most people (patients aged 55 or older or black patients of any age) with uncomplicated hypertension. NICE also currently recommends angiotensin-converting enzyme inhibitors (or angiotensin-II receptor antagonist where not tolerated) for first-line treatment of patients under the age of 55. Beta-blockers, unless otherwise indicated, are an inappropriate first- or second-line antihypertensive choice.For more information seeNHS Evidence - cardiovascular
A recent study (Lancet 2010;375:895–905), suggests that visit-to-visit variation in systolic blood pressure (SBP) and maximum SBP are strong predictors of stroke, independent of mean SBP.Here one of the authors, Professor Peter Rothwell of the Stroke Prevention Research Unit at Oxford's John Radcliffe Hospital discusses some clinical implications of the work.
Hypertension is the most prevalent treatable risk factor for stroke. One in two adults is affected by it, and the risk of being hypertensive during a lifetime is about 90 per cent. Despite this, the underlying mechanisms by which raised blood pressure (BP) can cause cardiovascular disease are poorly understood. Clinical guidelines for the diagnosis and treatment of hypertension focus heavily on average blood pressure.
The dominant hypothesis is that we each have an underlying average 'true' blood pressure, which is difficult to measure precisely, but which accounts for the vast majority of the complications of hypertension, and explains the benefits of BP-lowering drugs. Variability in BP is dismissed as uninformative and 'random', only noteworthy as an obstacle in the measurement of true underlying BP. Under-diagnosis and under-treatment of hypertension is a major, seemingly intractable problem in all healthcare systems. The new research shows that part of the problem is likely to have been under-recognition of the impact of variability in BP on diagnosis in routine clinical practice in primary care. It shows that doctors have to make diagnoses on the basis of BP measurements that often vary substantially from visit to visit.
All current clinical guidelines encourage doctors to ignore variability and occasional high readings and to rely exclusively on the average BP from multiple visits or 24-hour monitoring. The new research shows that increased variability in BP, a high maximum BP and episodic hypertension are associated with high risks of stroke and other vascular events, and emphasise that any reassurance taken from the fact BP is sometimes normal is false.Importantly, the new research shows that excess variability in blood pressure is treatable, and also that it can be made worse by some drugs used to treat hypertension. Some BP-lowering drugs increase variability, some have no effect and some decrease it. The choice of drug or combination should now therefore take into account their likely effect on variability as well as on the average level. Future drug trials should routinely report effects on variability.There should also be a greater emphasis on consistency of control of BP in patients who are already on treatment. The research showed that even patients with well-controlled BP had a five-fold excess risk of vascular events if their BP was highly variable, even when fully compliant with their medication. Recent calls to abandon measurement of BP after treatment are premature. The fact that many people now monitor their own BP at home will be helpful in identifying variability.New antihypertensive drugs should be developed to be BP-stabilising as well as BP-lowering. Drugs that reduced variability without reducing average BP should still prevent stroke, and would be likely to be helpful in patients who cannot tolerate reductions in their average BP.
Safety testing of all new drugs, irrespective of the indication, should include assessment of effects on instability and variability in BP, as well as on average BP.
*NICE recommends that calcium channel blockers or diuretics should be used first-line for most people (patients aged 55 or older or black patients of any age) with uncomplicated hypertension. NICE also currently recommends angiotensin-converting enzyme inhibitors (or angiotensin-II receptor antagonist where not tolerated) for first-line treatment of patients under the age of 55. Beta-blockers, unless otherwise indicated, are an inappropriate first- or second-line antihypertensive choice.For more information seeNHS Evidence - cardiovascular
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