A study of patients with hypertension has found that those who had variable blood pressure readings between clinic visits appeared to be at greater risk of heart attack and stroke than those with high blood pressure readings and low variability.
Published in the European Heart Journal, the ASCOT Legacy Study, led by a team from Imperial College London, analysed data from a 20-year study of more than 8,000 UK patients with hypertension.
They found that variation in systolic pressure over time was a strong predictor of stroke, heart attack and atrial fibrillation even in those who appeared to have well-controlled blood pressure. Highly variable blood pressure was also a strong predictor of risk at all levels of average blood pressure from low to high.
The researchers noted that based on current guidelines, clinical practice dictates that treatment decisions in patients with hypertension are determined by levels of systolic and diastolic blood pressure.
‘Our studies, however, provide robust evidence that visit-to-visit blood pressure variability is a far more powerful determinant of cardiovascular outcomes and that at least half of all cardiovascular events in our cohort occurred in those with controlled blood pressure but high blood pressure variability,’ they said.
As a result, the researchers are calling for medical guidelines to be changed to take into account interventions where a patient’s blood pressure varies between readings.
Professor Peter Sever is professor of clinical pharmacology and therapeutics at Imperial College London, honorary consultant physician at the Imperial Healthcare NHS Trust and co-director of the International Centre for Circulatory Health, as well as senior author of the study.
He said: ‘We’ve long known that high blood pressure increases the risk of heart attacks and stroke, but our latest findings highlight the importance of tracking variability in blood pressure over time as well.
‘While a degree of this was known to doctors, without clinical trials it has been difficult to quantify the risk of blood pressure variability over the long term, or the impact of interventions such as calcium blockers to reduce patients’ risk.‘
Analysing blood pressure variability
The ASCOT Legacy Study followed up 8,580 participants from the original ASCOT study, 50% of whom were taking amlodipine to manage their hypertension.
The researchers split the group into thirds, based on their average systolic blood pressure and their blood pressure variability.
They found that among patients with an average systolic blood pressure of less than 140 mmHg, the group with the highest variability was at a 16% greater risk for heart attacks, strokes and other cardiovascular events compared with the group with the lowest variability.
Some 53% of all cardiovascular events occurred in patients whose blood pressure was well-controlled with medication and who would not have been considered for additional treatment under the guidelines in place at the time of the trial.
The findings indicated that a systolic blood pressure variability of 13 mmHg or more over the course of five years may be associated with a significantly increased risk of cardiovascular events.
The Imperial team also confirmed that the drug amlodipine proved effective in lowering blood pressure variability during trials and could help to reduce risk.
At-home monitoring and clinical decision-making
Commenting on the next steps for the trial, Professor Sever said: ‘We urgently need to explore new practical ways to assess blood pressure variability and are currently studying the possibilities of incorporating data from home blood pressure monitoring into clinical decision-making.
‘The low cost and wide availability of digital blood pressure monitors and health apps means people can readily track their blood pressure over time and this could provide invaluable data for doctors to make the best treatment decisions – though we’d urge patients not to be overly concerned, as we would expect a degree of variation in their readings over time.
‘Crucially, we need international guidelines for clinicians to be updated to reflect these latest findings and to include blood pressure variability as a major risk factor for heart attack and stroke.‘