Dutch researchers who assessed over 4,000 men and women over 55 to see how many myocardial infarction went undiagnosed at the time they occurred, found that the figure was more than four in 10.
The authors, from the Department of Epidemiology & Biostatistics at Erasmus Medical Centre in Rotterdam, say their findings suggest that the role of ECGs in existing cardiovascular prevention programmes should be evaluated.
The results come from an analysis of a large proportion of the men and women involved 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 were enrolled from 1990-93.
They underwent a baseline ECG and examination.
Data from clinically recognised myocardial infarctions over the years that followed 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 myocardial infartcions.
Jacqueline Witteman said: " Over our median follow up time of more than 6 years, we found an incidence rate of nine myocardial infarctions per 1,000 person years. There were around 12 myocardial infarctions per 1,000 person years in men ( 8.4 recognised and 4.2 unrecognised ) and around seven per 1,000 person years in women ( 3.1 recognised and 3.6 unrecognised ).
Additionally, in men as well as in women, there was one sudden death per 1,000 person years.
" Overall, 43% of the total myocardial infarctions had been clinically unrecognised a third of the male myocardial infarctions and more than a half of the female myocardial infarctions. This is a significant proportion of all the myocardial infarctions."
Witteman said that in each of the age bands between 55 and 80, men had a higher incidence of recognised myocardial infarctions than women and a similar incidence of unrecognised myocardial infarctions.
This provided the evidence that myocardial infarctions are less often recognised in women, irrespective of characteristics that have previously been associated with myocardial infarctions.
According to co-author Eric Boersma, myocardial infarctions may go unrecognised because of atypical symptoms, and the explanation for the worse figures for unrecognised myocardial infarctions in women was not straightforward.
" There are likely to have been multiple factors. Men and women experience chest pain in different ways. Myocardial infarctions 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. It is also a problem that women and their doctors have traditionally worried more about death from breast and gynaecological cancer, than from heart disease."
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 said the findings of the Rotterdam Study suggest that the role of ECGs in existing cardiovascular prevention programmes should be evaluated.
" Patients with a history of myocardial infarction are at increased risk of repeat cardiovascular complications, irrespective of their awareness. Therefore, people with unrecognised infarctions may also benefit from effective preventive treatment. By that I mean preventive 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. Our findings indicate that these programmes might be enriched with an ECG."
ECG-systems 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.
Source: European Society of Cardiology, 2006