The most seriously-ill A&E patients could be treated more quickly while others wait longer under changes to be tested out at a West Yorkshire NHS Trust.
Wakefield-based Mid Yorkshire Hospitals is among 14 NHS trusts selected for a trial which could lead to the official four-hour A&E waiting time target being scrapped.
The trust, which runs Pinderfields, Pontefract and Dewsbury hospitals, will take part in a pilot scheme which will streamline A&E treatment for the most urgent patients.
Critically-ill patients suffering from heart attacks, strokes, sepsis and severe asthma, and people with life-threatening mental health conditions, will have their treatment started within one hour under plans by NHS England.
The scheme also seeks to avoid overnight stays for some patients who would have diagnostic tests and treatment completed in a single day.
Mid Yorkshire is among trusts around the country which have struggled to meet the target for 95 per cent of A&E patients to be admitted, transferred or discharged within four hours.
Details are not yet available on exactly how the pilot scheme will work at the trust's hospitals.
Mid Yorkshire chief executive Martin Barkley said: “We welcome the fact that we have been invited to be one of the trusts to take part in the field testing of the proposed new urgent and emergency care standards.
"Our priority is always to deliver the safest and highest quality care possible to our patients.
"As one of the busiest emergency departments in the country relative to the size of population we serve, we are keen to embrace the opportunity to test whether these new standards may improve clinical care and enhance patient experience for our local communities, and for those findings to influence future national policy on the urgent and emergency care standards.”
NHS bosses have suggested that current A&E performance standards are not fit for purpose and are misunderstood by the public.
An NHS England report said: "The standard only reports performance during the first four hours and is therefore blind to the additional length of time patients spend in departments beyond this point.
"There is a misconception that four hours is the time for a patient first to be seen, rather than for their treatment to be completed or to be admitted, transferred or discharged."
The Royal College of Emergency Medicine previously warned against scrapping the four-hour A&E standard, saying that "moving the goalposts of measurement to make things seemingly look better is certainly not the way forward."
An NHS England spokesperson said: "The information we gather through field testing, and engagement will inform final recommendations from this Review, and ahead of full implementation beginning spring 2020.
The trusts taking part in the A&E pilot are:
Cambridge University Hospitals
Chelsea and Westminster Hospital
Imperial College Healthcare
Kettering General Hospital
Luton and Dunstable University Hospital
Mid Yorkshire Hospitals
North Tees and Hartlepool
Nottingham University Hospitals