Patients at high risk for myocardial infarction often receive varying advice from physicians on when to contact emergency services and this can lead to indecision when an acute event occurs, according to an article in the July 7 issue of BMJ.

Although at least 70 percent of people who die from coronary heart disease had previous, known heart problems, recent data from the British Heart Foundation showed that 40 percent of the general population would not immediately call an ambulance during a suspected myocardial infarction and the greatest delays in calling for help were among the high-risk group.

The authors speculated that high-risk patients do not receive clear effective guidance from their doctors or there is varying advice from the general care physicians and cardiologists that patients do not acknowledge or reconcile.

The British Heart Foundation advises patients with known ischemic heart disease to call an ambulance if chest pains last longer than 15 minutes and to use nitroglycerin three times during that period. The American College of Cardiology recommends one use of nitroglycerin and 5 minutes before calling an ambulance.

Manufacturer’s instructions are sometimes non-specific, for example, recommending no more than 3 doses and 15 minutes between treatments - leaving it to the prescribing doctor to guide the patient.

Waiting 15 minutes, wrote the authors, could be too long for some patients. One study has shown that the median time from onset of symptoms to cardiac arrest is 10 minutes.

The authors recommend patients and their relatives should be explicitly primed to recognize high-risk features of chest pain. They advise patients at high-risk or with known ischemic heart disease to carry nitroglycerin with them at all times, to take two metered doses immediately if they get chest pain and to wait 5 minutes before calling an ambulance. They should not waste time by calling a friend or relative first and should not drive themselves to hospital.