Low BP is a good BP

Ideal blood pressure is lower than you think

Blood Pressure Lowering Treatment Trialists' Collaboration (BPLTTC) presented at the ESC Congress on 31st August 2020.

Lowering blood pressure with antihypertensive medication reduces future cardiovascular events even in individuals with normal or only mildly elevated blood pressure, according to the BPLTTC meta-analysis of 48 studies of antihypertensive treatment with almost 350,000 patients. The benefit from lowering blood pressure was seen even in patients with a baseline systolic blood pressure of 120 mmHg, regardless of presence of heart disease.

The researchers divided patients into seven groups depending on their baseline blood pressure, from <120 mmHg, 120-129 mmHg, 130-139 mmHg etc. up to the group with systolic blood pressure 170 mmHg and more. Over the 4-year follow-up, each 5 mmHg reduction in systolic blood pressure lowered the relative risk of stroke by 13%, ischemic heart disease by 7%, heart failure by 14% and death from cardiovascular disease by 5%. The benefit was observed regardless of presence or absence of heart disease or baseline blood pressure.

The previous research documented cardiovascular benefit of antihypertensive treatment up to systolic 130 mmHg; the BPLTTC meta-analysis extends these findings to systolic as low as 120 mmHg. SPRINT trial showed benefit of lowering blood pressure below 120 mmHg, but only in high-risk patients; this new meta-analysis extends this to patients without previous cardiovascular disease.

The current UK practice is to prescribe medication only if blood pressure is at least 140/90 mmHg in high-risk patients or 160/100 mmHg in low-risk patients. The NICE guidelines for diagnosis and treatment of hypertension, published in August 2019, recommend drug treatment if the clinic blood pressure is at least 140/90 mmHg (135/85 mmHg on subsequent 24-hour BP monitor) - so called stage 1 hypertension - in patients with target organ damage, established cardiovascular disease, renal disease, diabetes or with an estimated 10-year risk of cardiovascular disease of 10% or more. In patients with no pre-existent cardiovascular disease, clinic blood pressure must be at least 160/100 mmHg (150/95 mmHg on 24-hour BP monitor) - i.e. stage 2 hypertension - to qualify for antihypertensive medication.

The new meta-analysis challenges this thinking. Instead of using a single threshold, the decision to treat with antihypertensive medication should instead be made by assessing the overall cardiovascular risk of each patient. There are patients with normal blood pressure (i.e. under current UK guidelines <140/90 mmHg) who have high cardiovascular risk and will therefore benefit from antihypertensive treatment. The opposite may also be true: A patient with blood pressure above the current treatment threshold will not derive any benefit from anti-hypertensives if their overall cardiovascular risk is very low. The BPLTTC meta-analysis should therefore not necessarily result in more patients receiving treatment, but in better targeting of patients who would benefit most.

It will be interesting to see if NICE will change their guidelines in response to this meta-analysis. What are potential objections? Well, it was a meta-analysis rather than a double-blinded randomized clinical trial. It is not clear how many more patients would qualify for anti-hypertensive treatment under BPLTTC criteria, what would be the side effects of aggressive blood pressure lowering - especially in the elderly - and what economic impact would the expansion of prescription have. Would labelling asymptomatic people with a disease help them to mobilize and improve their prognosis or lead to therapeutic nihilism and poor compliance?

The take-home message is perhaps that the decision to treat blood pressure with medication should be based on individual cardiovascular risk rather than a simple label of hypertension.

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