The results of the trial, stopped early due to the significance of the findings, were presented in a late-breaking session at the World Stroke Congress and simultaneously published in The Lancet.
Professor Craig Anderson, Director of Global Brain Health at The George Institute for Global Health, said the rapid emergence of this effect suggested the more aggressive approach was compromising the return of blood flow to the affected area.
"Our study provides a strong indication that this increasingly common treatment strategy should now be avoided in clinical practice," he said.
Around 85 percent of strokes are ischaemic strokes, caused by the loss of blood flow to an area of the brain due to a blockage in a blood vessel, leading to a loss of neurological function.
Endovascular thrombectomy is an increasingly used non-surgical treatment for ischaemic stroke, in which microcatheters or thin tubes visible under X-rays are inserted into the blood clot to dissolve it.
"A potential downside of this now widely used and effective treatment is that the rapid return of blood supply to an area that has been deprived of oxygen for a while can cause tissue damage known as reperfusion injury," said Professor Anderson.
"This has resulted in a shift in medical practice towards more intensive lowering of blood pressure after clot removal to try and minimise this damage, but without evidence to support the benefits versus potential harms."
To try and address the evidence gap, researchers recruited 816 adults with acute ischaemic stroke who had elevated blood pressure after clot removal from 44 centres in China between July 2020 and March 2022. They had an average age of 67 and just over a third were female.
407 were assigned to more-intensive (target
Researchers looked at how well the patients in both groups recovered according to a standard measure of disability, ranging from 0-1 for a good outcome without or with symptoms but no disability, scores of 2-5 indicating increasing levels of disability (and dependency), and a score of 6 being death.
Patients in the more-intensively treated group had significantly worse scores on the scale compared to those allocated to those treated less intensively.
Compared to the less-intensive group, they had more early brain tissue deterioration and major disability at 90 days but there were no significant differences in brain bleeds, mortality, or serious adverse events.
Patients who had their blood pressure more intensively controlled also rated their quality of life as significantly worse due to limitations on their physical abilities resulting from their stroke.
Prof Anderson said that after scouring the medical literature the research team had been unable to find strong enough evidence to recommend the ideal target for blood pressure control after blood clot removal in patients with acute ischaemic stroke.
"While our study has now shown intensive blood pressure control to a systolic target of less than 120 mm Hg to be harmful, the optimal level of control is yet to be defined," he said.
