Lowering blood pressure too far 'may harm heart patients'
By Nigel Praities
Lowering blood pressure below recommended targets may increase the risk of death in patients with established heart disease, say researchers.
A reanalysis of data from the influential Treating to New Targets (TNT) trial – from 10,001 patients with coronary artery disease – has found a ‘J-shaped' curve for blood pressure when plotted against the risk of future major cardiovascular events or mortality.
The five-year data from the TNT study has sparked controversy on both sides of the Atlantic, with US researchers insisting their findings challenge the thinking that ‘lower is better' while critics insist their conclusions are misleading.
Statistical analysis found the lowest rates of major cardiovascular events were found at
systolic blood pressures of 139.9mmHg and diastolic blood pressures of 79.2mmHg.
As expected, the incidence of serious events – such as myocardial infarction, stroke or coronary death – was significantly higher above this point. But the same was true for pressures below.
British Hypertension Society guidelines advise a blood pressure target of 130/80mmHg or less for secondary prevention, and in patients with diabetes or renal disease.
The TNT study was designed to find out whether it was safe and effective to lower LDL-cholesterol below the US target of 2.4mmol/l but researchers presented the blood pressure data at the American Society of
Hypertension meeting in San Francisco.
Lead investigator Dr Sripal Bangalore, from Brigham and Women's Hospital in Boston, said: ‘Despite substantial lowering of LDL-cholesterol in both treatment groups, a J-curve relationship persists between blood pressure and cardiovascular events, suggesting that excessive lowering of blood pressure is harmful.'
Dr George Kassianos, a fellow of the European Society of Cardiology and a GP in Bracknell, Berkshire, said the research was a salient warning for GPs.
‘This is a very new finding. It means that you should not go lower than about 130/70mmHg in patients with cardiovascular disease,' he said.
But Professor Gordon McInn-es, president of the British Society of Hypertension, said the results were ‘completely mis- leading' as the study was not designed to look at this relationship. ‘If blood pressure is zero you are dead, so there must be some sort of U-shaped relationship, but the level at which it
does you more harm than good is not well-defined. These studies do more harm than good,' he said.
Dr Terry McCormack, former chair of the Primary Care Cardiovascular Society and a GP in Whitby, North Yorkshire, said the study was hypothesis generating, rather than evidence.
‘This is a chicken and egg situation. Is their blood pressure low because they have disease or it is low because they are on hypertensive medication?' he said.
US researchers says findings challenge thinking that 'lower is better' US researchers says findings challenge thinking that 'lower is better'