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Risk of MI after sex

Patients with cardiac disease, and especially those who have already had an infarct, often believe that sexual activity can bring on a heart attack. Portrayal of such events on TV and in films serves to reinforce this commonly held belief.

So it is good to see some high quality evidence which allows us to put figures on the risks, and to be able to use these in advising patients. A study from Harvard [1] gives us the numbers.

Study

Between 1989 and 1993 1774 patients were interviewed soon after an MI (median 4 days, range 0 - 30 days). For inclusion the patients had to have elevated cardiac enzymes, pain or other symptoms of MI and ability to complete a structured interview.

The interviews were conducted by trained personnel, and about a third of the interviews were audiotaped and checked for quality control. The interview identified issues surrounding the MI, including sexual intercourse immediately before, and during the year before the MI. Patients who reported sexual intercourse within 26 hours of the MI were asked about all sexual activity in the previous 26 hours. Undertaking regular physical exercise, the amount of heavy exertion and its frequency also formed part of the interview.

Design

A new design was used for this study, in which control information for each patient was based on his or her past exposure.

The two-hour period immediately before MI onset was compared with two types of control: their usual frequency of sexual activity during the past year and their sexual activity in the comparable two-hour period at the same time the day before the MI.

Results

1774 patients were interviewed. 141 chose not to answer questions about sexual activity. Of the remaining 1633 (643 of whom had angina or a previous MI), 858 (48%) reported sexually activity in the year before their MI.

The frequency of sexual activity in the 858 active patients (mean age 55 years, 82% men) is shown in the figure. Of these, 9% reported sexual activity in the 24 hours before their MI and 3% in the two hours before their MI.
The relationship between the relative risk of onset of MI and sexual activity in the four hours immediately preceding it is shown in the second figure. The relative risk was increased only during the first two hours after sexual activity. In the first two hours after sexual activity the risk that an MI would occur was 2.5 (95%CI 1.7 - 3.7).
A number of potential modifiers of the risks were examined, including age, sex, clinical history, smoking, drugs and exertion. Only frequent moderate exercise was shown to modify the risk. The risk of an MI in the two hours after sexual activity decreased from 3.0 to 1.9 to 1.2 for patients who engaged in heavy physical exercise once or not at all, twice, and three or more times a week respectively.

Effect of exercise on risk of MI in two hours after sexual activity

Frequency of heavy physical exertion Relative Risk
(95% CI)
None or once a week 3.0 (1.3 - 4.3)
Twice a week 1.9 (0.2 - 17)
Three times or more a week 1.2 (0.4 - 3.7)

One in a million

Only 27 of the 1774 patients reported sexual activity in the two hours before their MI. After correcting chance occurrence, sexual activity was a likely contributor in only about 0.9% of the cases in this study.

Data from the Framingham Heart Study indicates that the baseline risk that a 50-year old, nonsmoking, nondiabetic man will experience an MI is about 1% per year, or 1 chance in a million in any hour. Since the relative risk of MI is about 2, engaging in sexual activity increases his risk to 2 in a million, and only for a two-hour period.

A baseline yearly risk of reinfarction or death for an individual with a prior MI is about 10%, but less than 3% if the individual can exercise without symptoms on an exercise test. For individuals in the higher risk category, sexual activity would double the risk of MI from 10 in a million per hour to only 20 in a million per hour, and then only for about two hours.

Perspective and risk

The effect of sexual activity on annual risk is negligible because the absolute risk difference is small, the risk is transient, and the activity is relatively infrequent. Not exercising, smoking and getting angry are all more likely to pose bigger risks, at the trivial level because we get angry more frequently than we have sex (at least in the Bandolier office).

It is also interesting to compare the risk from sexual activity with risks of travel, sport, or even walking highlighted elsewhere in this issue. It is good to know there are things we can do without particular risk, like drinking moderately (Bandolier 27) and eating vegetables (Bandolier 20) .

Reference:

1 JE Muller, MA Mittleman, M Maclure et al. Triggering myocardial infarction by sexual activity. Low absolute risk and prevention by regular physical exercise. Journal of the American Medical Association 1996 275: 1405-9.



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