The researchers suggest that regular ECG screening of patients over 55 should be introduced to identify those who have had a previous MI that was missed.
The study, which was carried out between 1990 and 2000, included 5,148 patients aged 55 or more who had not previously suffered an MI, according to medical history or baseline ECG.
The researchers recorded the number of cardiac events in these patients reported by their GPs over an average of 6.4 years of follow-up. In addition, they used an expert analysis of ECG readings taken at least three years after the start of the study, to identify unrecognised MI.
Over 40 per cent of total MIs and nearly half of MIs in women had not been recognised.
At the end of the study, 86 men and 55 women had a recorded diagnosis of MI. Another 37 men and 52 women had experienced an unrecognised MI, according to the ECG readings.
In addition, eight men and 10 women suffered sudden cardiac death over the course of the study.
Researcher Dr Eric Boersma, associate professor of clinical cardiovascular epidemiology at Erasmus MC in Rotterdam, said many heart attacks went undiagnosed because patients did not present with 'classic' symptoms.
'MIs can occur without typical symptoms in women and also in people with diabetes and the elderly,' he said. 'Women particularly may hold back from reporting symptoms.'
Hertfordshire GP and member of the Primary Care Cardiovascular Society, Dr Mike Kirby agreed. 'We need to be alert to atypical presentation, particularly in women,' he said.
He suggested using ECG to carry out case-finding in selected patients with strong risk factors.
- Shoulder, back or jaw pain.
- Stomach pains or abdominal discomfort.
- Shortness of breath, nausea and dizziness.
- Anxiety or other altered mental state.