Recurrence of myocardial infarction. Observations on patients participating in the Ontario Multicentre Exercise-Heart Trial.

The circumstances attending a fatal or non-fatal recurrence of myocardial infarction have been analysed for participants in the Ontario Multicentre Exercise-Heart Trial. After an average of some 20 mth observations, 51 of the 751 participants had sustained a recurrence (rate 4.07 per 100 participant years). Some 24% of episodes were closely associated with various types of physical activity, and a further 22% noted vigorous exercise (sometimes of an unusual nature) a few hours previously. Exercise-related episodes were associated with poor programme compliance and ST segmental depression during test exercise, but were unrelated to the prescribed regimen (high or low intensity physical activity). Continuing smoking and a history of recent angina were associated with a risk of recurrence; both were seen less commonly with recurrence in high intensity exercisers than in their low intensity exercise counterparts. Exercise-induced ST segmental depression was associated with a higher frequency of fatal recurrences in high than in low intensity exercisers (P less than 0.05); there may thus be a 'high-risk' subgroup for whom vigorous exercise is contraindicated, and the existence of such a group could confound therapeutic trials of exercise-centred rehabilitation.