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Is Your Heart Attack More Likely to Kill You at Night or During the Day?


It is a hard lesson in life that many of the most important things that happen to us are beyond our control. Indeed, a large part of wisdom consists of the willingness and ability to distinguish what is and what is not happenstance. The distinction, however, may be very difficult: and while too little fatalism leads to fruitless struggle, too much leads to acceptance of the avoidable.

A recent study from the Mayo Clinic published in the British Medical Journal examines patients with myocardial infarction (heart attack) presenting to hospital out of hours and those who present during normal working hours. They pool the data from all the studies that have been done around the world, and come to the conclusion that patients presenting at nights and weekends have a 5 percent increased risk of death. It therefore seems best, if you must have a heart attack, to have it during regular hours, though this is difficult to arrange for yourself.

Interestingly, subsidiary findings are first that the difference between the death rates has been increasing of late; and second that the difference is less in the United States than in Europe, where it is less than in other parts of the world. Could this mean that, at least in one respect, the American health care system is better than others around the world?


The figures cannot be taken at face value for a number of reasons. First, the patients presenting out of hours may not be the same as patients presenting during regular hours. They may, for example, have waited to call for the ambulance: such misguided, or at least unfortunate, stoicism is by no means uncommon. Second, there may be publication bias: studies that showed no difference in death rates were less likely to be published than those that did, and thus skew the overall findings. (Publication bias, however, may be decreasing: two trials in the New England Journal of Medicine in the same week found that two proposed innovations, screening for tuberculosis among South African miners and immunotherapy for Alzheimer’s disease, did not work; and in the same issue of the BMJ, another paper showed that the guidelines to doctors for distinguishing between ordinary low back pain and back pain that derived from fracture or metastasis were useless.)

However, the paper from the Mayo Clinic gives a reason to think that the differences in death rates from heart attack presenting at different times to hospitals may indeed be attributable to differences in treatment. There is a delay, on average, of 15 minutes in administering life-saving treatment to patients who arrive at night or on weekends by comparison with those who arrive at regular hours. Since it is known that a delay of 30 minutes, irrespective of time of arrival at hospital, results in an increased death rate of 30 percent, the findings of the paper are likely to be real and not just a statistical artefact caused by the factors cited above.

One of the frustrating things about papers that report relative risk is that they fail to report the absolute risks. Risk may be so miniscule that a doubling or a trebling may still mean that it is trivial and not worth worrying about. In this case, the authors estimate that if in the United States the death rate of those who presented out of hours (two thirds of all patients) could be brought down to that of patients presenting during regular hours, about 3800 deaths a year could be avoided. They issue a call to managers to bring this equalization about: though it ought always be borne in mind (though it seldom is) that overconcentration on one target may result in missing others.


images courtey shutterstock / jurasy / Sebastian Kaulitzki