The Department of Health has issued a ''hazard'' warning to all health authorities, and cardiac specialists are having urgent talks about what to do.
The deaths were in Japan but about 1,100 British men and women with pacemakers could be at risk, Dr Anthony Nathan, cardiologist at St Bartholemew's Hosptial, London, said last night.
''We have not had a pacemaking problem like this before. Less than 1 per cent of pacemakers in the UK are affected. The risk is small but it does exist. We are concerned and very urgent work is going on to decide on the best course of action,'' said Dr Nathan, secretary of the British Pacing and Electro-physiology Group.
A J-shaped loop hooked into the heart tissue delivers an electric impulse from the pacemaker to make a patient's heart beat regularly. A tiny wire that supports the J-loop has fractured in 13 cases out of 42,000 of the pacemakers world-wide. All the potentially affected pacemakers were fitted in the past seven years.
Dr Nathan said that to the best of his knowledge no UK patients had been affected. In the four cases the support wire ''popped'' and made a hole in either the front or back of the heart, causing bleeding. All four patients suffered cardiac tamponade, the condition in which the heart becomes squashed because of a build-up of blood or fluid.
The pacemaker leads involved are Accufix Atrial J Pacing Leads, models 330-801, 033-812 and 329-701, made by Telectronics. ''Most patients have a pacemaker identity card with information about the leads printed on it, which they can check.
''At present we are contacting all patients and advising them to be calm while we decide on the next step,'' Dr Nathan said.
The problem facing cardiologists is that to remove the lead surgically may put patients at greater risk than leaving it in.
Dr Nathan said: ''The difficulty is that it is screwed into the heart tissue and is very hard indeed to remove. There is a risk of tearing the heart, which could kill a patient.''
He said they were now gathering all the information available on the best way to X-ray those patients who are fitted with the leads, to see if they can then establish which patients may be at risk.
''The problem then is: how often should we X-ray? - every three days, every three weeks of every three months? If the lead is going to fracture, when will it happen?''
Heart pacemakers were first fitted in 1957. They are implanted in the chest and run on batteries, which are replaced in a minor operation. Between 13,000 and 14,000 pacemakers are fitted in the UK each year with a total of about 20,000 leads.