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Instructions about using GTN and when to call an ambulance need to be clearer
How long people with chest pain should wait before calling an ambulance is a question familiar to general practitioners and emergency doctors. The answer is complicated by the use of sublingual nitrate sprays, which promptly relieve the pain of stable angina.1 Ideally, patients would be able to distinguish stable angina from a potentially life threatening acute coronary syndrome, but in reality they do not. Therefore the decision about when to call an ambulance needs to balance between an overly cautious strategy that could overburden emergency medical services and one where delayed action leads to higher morbidity and mortality. The balance is difficult to find because international guidance indicates that consensus has not been reached, even among cardiologists.2 3 4
The British Heart Foundation advises patients with known ischaemic heart disease that chest pain that lasts more than 15 minutes is probably a heart attack.2 Within this time patients are advised to use their glyceryl trinitrate (GTN) spray three times at five minute intervals before calling an ambulance. Yet a recent British Heart Foundation campaign advises members of the general public with potential “de novo” chest pain (a lower risk population) that “A chest pain is your body saying call 999. Doubt kills—call 999 immediately.”
Campaigns aimed at the general population have been unsuccessful in reducing mortality from acute coronary syndromes.5 6 However, no studies have examined the effect solely in people at high risk—those with an established diagnosis of ischaemic heart disease and those with established cardiovascular disease or risk factors for cardiovascular complications 7—and the potential of sublingual nitrates to prompt a rapid, appropriate response (in turn reducing mortality and morbidity associated with late presentation).
The European Society of Cardiology does not offer precise guidance; it simply advises “carefully instructing patients on the use of short acting nitroglycerin.”5 The recommendations of the American College of Cardiology and American Heart Association were previously in line with the British Heart Foundation. However, updated guidelines in 2004 encouraged patients with symptoms suggesting ST elevation myocardial infarction (STEMI) to contact emergency medical services earlier. They now recommend “one GTN spray and 5 minutes” before calling an ambulance.6
Manufacturers of nitrate sprays also give varying and sometimes non-specific instructions regarding the dose, such as “No more than three metered doses at any one time and a minimum of 15 minutes between consecutive treatments.” Therefore, the onus is on the prescribing doctor to guide the patient.
The evidence for early presentation and treatment of STEMI has long been established. Necrosis of viable myocardium predominantly occurs between 30 to 90 minutes after coronary artery occlusion. This has formed the basis of “the golden hour” during which prompt reperfusion strategies (thrombolysis or primary angioplasty) prevent extensive myocardial necrosis that leads to left ventricular dysfunction and worse prognosis. Even before angioplasty became widely used, thrombolysis within the first hour cut deaths by half.8 This led to the advent of prehospital thrombolysis and “call to needle” targets, which are generally being met.
If the patient has a cardiac arrest out of hospital, early attention from a paramedical team with defibrillator is life saving, but the chance of successful defibrillation declines 7-10% each minute after cardiac arrest.9 One early study of out of hospital cardiac arrest showed that the median time from onset of symptoms to cardiac arrest was 10 minutes.10 Clearly, waiting 15 minutes, as the British Heart Foundation suggests,2 will be too long for some patients.
Recent data on sudden cardiac death do not confirm the early series; the symptoms were present for a median of 30 minutes before ventricular fibrillation started.11 However, the data do confirm that most sudden cardiac deaths occur in patients with known cardiac disease, at home, and in the presence of relatives. This reaffirms the importance of clear and precise education for patients and relatives.
Most acute coronary syndromes occur in people already known to have ischaemic heart disease or to be at high risk. In this group the risk of subsequent myocardial infarction or death is 5-7 times higher than in the general population, and at least 70% of deaths from coronary heart disease occur in people who have had previous manifestations of cardiovascular disease.12 However, recent data have shown that 40% of the general population would not immediately call an ambulance during a suspected myocardial infarction, and the greatest delays in calling 999 are in people at high risk.13 The obvious implication is that people at high risk are not receiving clear, effective guidance despite receiving care from a doctor at some stage.
The advent of rapid access chest pain clinics, patient information leaflets, and cardiac rehabilitation clinics may have made the medical community complacent about face to face doctor-patient counselling. However, any clinician faced with a patient with existing ischaemic heart disease should be able to give clear and precise instructions about when to call an ambulance.
On the basis of the pharmacodynamics of sublingual nitrates and the benefit of early presentation, we advise patients with known ischaemic heart disease or at high risk of myocardial infarction to carry a GTN spray at all times and, should they develop acute chest pain, to take two metered doses (800 µg) immediately. If the pain persists at five minutes they should call an ambulance. They should not waste time by first calling a friend or relative and should not drive themselves to the emergency department.14 15 Patients and their relatives should also be taught how to recognise high risk features of chest pain, such as increasing frequency and severity of attacks (unstable angina), and autonomic features (common in STEMI).
Competing interests: None declared.
Provenance and peer review: Non-commissioned, externally peer reviewed.