ECG (electrocardiogram) tests commonly given to people with suspected angina to predict the likelihood future of heart disease have limited accuracy, according to a study published on the British Medical Journal website.
Alternative tests which add predictive value to that obtained from the patient's clinical history are needed to improve the chances of detecting people at higher risk of future heart disease and heart attacks, say the authors.
Angina is the most common symptom of coronary artery disease and is experienced by about 2 in every 100 people in the UK. Patients are assessed at rapid access chest pain clinics, designed to ensure that people who develop new symptoms of suspected angina can be assessed by a specialist within two weeks of referral.
Prompt assessment using ECG while patients are resting and when they are exercising is the most commonly performed non-invasive test used in suspected angina patients, but its ability to predict future heart disease is unknown.
A team of researchers led by the London Chest Hospital studied 8 176 patients with suspected angina and no prior diagnosis of heart disease, who were referred by their doctor to one of six chest pain clinics.
All the patients were clinically assessed (studying data such as age, sex, ethnicity, duration of symptoms, description of chest pain, smoking status, history of hypertension, medications) as well as having an ECG done while they were resting.
4 873 (60%) of the patients had an exercise ECG performed and were split into two groups, one comprising 4 848 patients with a "summary" result recorded, and the other with 1 422 patients who additionally had "detailed" exercise ECG data recorded. All patients were followed up for the next few years.
The researchers found that almost half (47%) of all coronary 'events' that happened to people during the follow up period occurred in patients who had had a negative exercise ECG that did not indicate any heart problems.
This suggests that exercise ECGs are limited in how accurately they predict the risk of future heart disease, say the authors.
They found that a routine clinical assessment provided almost as much predictive information about future heart problems as having a ECG. The resting ECG showed no additional benefit to the information obtained from the history and examination.
The authors conclude that ECG tests are of limited value in identifying potential future coronary problems in patients with suspected angina and no prior diagnosis of heart disease, adding little to routine clinical assessment including the patient's history and an examination.
The researchers say: "The limited incremental value of these widely applied tests emphasises the need for more effective methods of risk stratification in this group of patients."
These findings are a reminder of "the importance of taking a detailed history and making a thorough physical examination, and that additional information from the ECG is helpful in some patients but does not predict risk in everyone", says Beth Abramson, Director of St Michael's Hospital in Toronto in an accompanying editorial.
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