According to Dutch researchers almost fifty percent of heart attacks are not recognised as such.

The authors, from the Department of Epidemiology & Biostatistics at Erasmus Medical Centre in Rotterdam, assessed over 4,000 men and women over 55 to see how many heart attacks went undiagnosed at the time they occurred, and found the figure was more than 4 in 10.

They say their findings suggest that the role of ECGs in existing cardiovascular prevention programmes needs to be evaluated.

The analysis involved men and women enrolled in the Rotterdam Study, a prospective population study investigating chronic disabling diseases.

A total of 5,148 participants with no evidence of prevalent myocardial infarction (MI) were enrolled from 1990-93.

They underwent a baseline ECG and examination and over the years that followed data from clinically recognised MIs were analysed.

The 4,187 of the total who had at least one repeat ECG during two rounds of follow up assessment between 1993-96 and 1997-99, were analysed for clinically unrecognised MI.

Senior author Dr Jacqueline Witteman, Associate Professor of Epidemiology, says they found that over a 6 year follow period an incidence rate of nine heart attacks per 1,000 person years.

There were around 12 heart attacks per 1,000 person years in men and around seven per 1,000 person years in women.

In men as well as in women, there was one sudden death per 1,000 person years.

Witteman says that 43% of the total heart attacks had been clinically unrecognised - a third of the male heart attacks and more than a half of the female heart attacks.

Dr Witteman says that in each of the age bands between 55 and 80, men had a higher incidence of recognised MIs than women and a similar incidence of unrecognised MIs, evidence that heart attacks are less often recognised in women, irrespective of characteristics that have previously been associated with MI.

According to co-author Dr Eric Boersma, Associate Professor of Clinical Cardiovascular Epidemiology, heart attacks may go unrecognised because of atypical symptoms, and the explanation for the worse figures for unrecognised heart attacks in women was not straightforward and multiple factors may be involved.

Men and women apparently experience chest pain in different ways. MIs can occur without typical symptoms in women (also in people with diabetes and the elderly). They may sense shoulder pain instead of chest pain, they may think they have severe flu that is taken a long time to recover from, and those with an inferior-wall infarction may complain of stomach pain.

So women may hold back from reporting symptoms and doctors may also be in doubt whether or not to consider heart disease as a source of the complaints.

Dr Boersma says another problem is that women and their doctors have traditionally worried more about death from breast and gynaecological cancer, than from heart disease.

Dr Boersma said that although the study was conducted in the Netherlands the results were likely to be equally applicable to any other developed country.

He says says that patients with a history of MI are at increased risk of repeat cardiovascular complications, irrespective of their awareness and people with unrecognised infarctions may also benefit from effective preventive treatment such as drugs, including aspirin, beta-blockers and statins, and specific lifestyle advice.

In most developed countries cardiovascular prevention programmes are installed, which aim to identify high-risk individuals on the basis of classical risk factors, including smoking and obesity, and co- conditions, such as diabetes mellitus.

The researchers believe their findings indicate that these programmes might be enhanced with an ECG systems which are readily available and ECG measurements are easily obtained; their interpretation might be facilitated by computer software. Even so, the researchers emphasise that formal cost-benefit studies are needed before definite conclusions on the role of ECGs in prevention programmes can be drawn.

Their report is published in the current edition of the European Heart Journal, which is the journal of the European Society of Cardiology.