Trying to Find a Better Way to Test for Angina
A close friend of mine, like me of an age when angina is likely to strike, recently had symptoms that could have been angina. He underwent a series of tests such as exercise electocardiography and echocardiography, after which he was declared free of the disease. Unfortunately, it is difficult to prove a negative and no number of tests can altogether exclude the possibility of one dropping down dead tomorrow. Reassurance in this field is therefore only relative.
Diagnostic and prognostic tests are improving all the time. That is what we doctors like to think, at any rate. The tests mentioned above are only functional, that is to say they show the physiological changes indicative of angina when the patient is subjected to exercise of a degree that might be expected to provoke an attack. If those changes don’t occur, the patient is assumed to be free of the disease.
It has been suggested that a test showing the anatomical state of the coronary arteries would be more accurate, both prognostically and diagnostically, than mere functional testing: for, after all, it is obstruction in those arteries that gives rise to the symptoms in the first place.
A recent paper in the New England Journal of Medicine attempted to prove that anatomical testing, using a technique called coronary computed tomographic angiography, was better than the kind of testing my friend underwent. It failed to do so.
Ten-thousand patients complaining of symptoms suggestive of angina, and who were thought to be in need of investigation for angina, were randomly allocated to either of the two methods. Ten-thousand, the number thought necessary to show a 20 percent superiority of one method over the other, is a lot of patients, and so it is not surprising that many centers took part in the trial.
I found a couple of characteristics of the 10,000 patients surprising, though the authors of the article made no comment on them. The first is that there were more women than men in the sample, though coronary disease is more common in men than in women; and the second was the sheer size of the people involved. Their average Body Mass Index (BMI) was just over 30, which puts them in the category of the obese. There must have been some real whales among them, for surely not all of them could have been obese. That an average BMI of over 30 should have gone unremarked shows how fat we now expect people to be.
The patients were followed up for a minimum of 12 months after the tests, though the median follow-up was 25 months. There was no difference between the groups in death rates or non-fatal heart attack. This was curious, in a way, because twice as many of the anatomical test group as the functional test group went on to have more definitive invasive angiography, and only half as many turned out to have no discernible blockage in their arteries as detected by that method as those sent for such angiography after functional testing. Twice as many of them went on to have coronary artery bypass grafting (CABG), but that appeared not to cause an increase in the survival rate of the patients undergoing the original anatomical testing. Perhaps if the sample had been 50,000 instead of 10,000, such a difference might have manifested itself: but if you have to test 50,000 people to show a difference, it cannot be very great. Suffice it to say that penicillin didn’t have to be tested on 50,000 people to show its efficacy.
Perhaps most surprisingly, only about 10 or 11 percent of the 10,000 were thought really to have had angina. Is it possible that people have those symptoms because they know what the symptoms of angina are?