CASE 4 ANSWER
The best two studies of the relation of exertion to myocardial infarction were done in the same way. People who’d just had an MI were interviewed about their usual activities and their activities right before their MI’s. Each patient served as his own control for a comparison of the observed frequency of heavy exertion (6 or more mets – roughly, the amount of exertion in jogging, sex, and snow-shoveling ) with the expected frequency of heavy exertion given their usual activity patterns. Both studies reached the same conclusions:
1) The vast majority of MIs occurred during periods of rest,
2) Nevertheless there was an increased frequency during heavy exertion. A German study (NEJM 12/2/93) yielded a relative risk of MI during exertion of 2.1. An American study (same issue) yielded a relative risk of 5.9.
3) The risk of heavy exertion for habitual heavy exercisers was much less (1.3 and 2.4) than for the habitually sedentary (6.9 and 107).
There are other less methodologically sound studies suggesting that arrhythmias occur more frequently during exercise.
Nevertheless, the evidence discussed in Case 3, which is substantial, shows that the net effect of exercising over the long term is to substantially reduce cardiovascular mortality. So, in the short run, the exercise program is deleterious and in the long run beneficial.
How to get from the short run to the long run? A couple of analogies may help in advising this patient. First, exercise stress testing on a treadmill with a technician or physician flogging the patient to walk faster is safe in the absence of aortic stenosis, unstable angina, severe hypertension, etc. If the patient gets symptomatic, she stops. The only real difference between the stress test and the home treadmill is the presence of the physician and the recording of asymptomatic ischemia. Second, the situation is analagous to a pre-operative assessment of coronary risk – the stressor is exercise not surgery.
Some groups – the US Preventive Services Task Force for one – recommend performing a stress test prior to beginning an exercise program in asymptomatic people with multiplecardiovascular risk factors. As a widespread recommendation for everyone that is underactive (about 60% of the adult population), it’s expensive, but for those with multiple risks probably prudent.
