Last week’s column dealt with the description of a relatively straight forward situation where a gentleman had a significant heart problem that needed attention.  Medical considerations are rarely that easy.  Diagnostic tests are only occasionally simple yes or no answers.  As an example, when a 23 year old recently married young lady is seen in the clinic because she has missed three of her menstrual cycles, a simple yes or no test is done to determine if she might be pregnant.  The conclusion is a yes or a no.  If a person comes to the clinic because they have a sore throat and suspect a streptococcal infection, there is a simple test done that gives a yes or no answer.

     But exercise stress tests are not that easy.  In a perfect world, anyone who had significant coronary artery disease would have a positive exercise stress test.  Unfortunately, due to the individual variability, 200 people out of a 1000 that have significant coronary artery disease will have a negative exercise stress test.  This means that 1 out of 5 people that are checked with this test will be told that the test does not indicate that they have heart disease when in fact they do.

     The clinical example of this situation is a gentleman who came in to be seen because he had chest pain when cutting the lawn.  It was the first time this spring that he had cut the lawn with his old push mower although with a power rotator.  He had some trouble getting it started but finally began cutting the yard after he had gotten it going.  He was somewhat peeved because it took it so long to get the lawn mower going and it was an unusually warm day.  He described making 3 or 4 passes through the yard and then developing a heavy sensation in his chest.  He broke out in a heavy sweat, became nauseated and felt as if he was going to pass out.  He turned off the lawnmower as he passed near the house and sat down on the porch.  His pain continued for several minutes and he vomited breakfast.  Following this, he felt somewhat better and attributed the problem to food poisoning.  He felt very weak the remainder of the day and felt very poorly the next morning when he got up.  He then came to the clinic for further evaluation.  His electrocardiogram was normal as were all of his blood tests.  An exercise stress test was ordered which he completed that morning.  It was negative.  It did not indicate that he had coronary artery disease.

     This is where clinical judgment of the healthcare provider comes into play.  This gentleman had a very compelling story consistent with heart disease and yet his stress test was negative.  In spite of the stress test being negative, he was referred to the cardiologist and an angiogram was done demonstrating extensive blocks in his coronary arteries that were then bypassed.  He has made an uneventful recovery.  This is an example of a false negative stress test.  Fortunately, clinical interpretation led to the appropriate care.

     While false negative stress tests are a very dangerous result, the opposite problem of the false positive is a nuisance leading to unnecessary evaluations.  In a perfect world, all people who have a positive stress test would have significant coronary artery disease.  Unfortunately, at least 50 out of a 1000 positive exercise stress tests will not be associated with significant coronary artery disease.  The clinical example here is of a 44 year old man who had a very rich family history of heart disease.  Two of his brothers, his father and one paternal uncle had all died in their 50’s of sudden heart attacks with very little warning. This 44 year old gentleman knew that his blood pressure was normal, his cholesterol was only 200 mg%, he was not a smoker and he was not diabetic.  Yet, here was this very threatening family history.  He wanted to have a stress test done to be sure that he did not have heart problems.  When the test was done, he did not develop chest pain, but he did have very significant electrocardiographic changes suggestive that his heart was not getting enough blood.  This is the problem of so called silent ischemia which is another word for saying even though the person doesn’t hurt, his heart may not be getting enough blood.  With the positive stress test and his strong family history, he was referred to the cardiologist and an angiogram was done to visualize this gentleman’s heart arteries.  They were squeaky clean.  There as no plaque or obstruction seen on any of the views taken.  While this is a time consuming anxiety producing and expensive endeavor, the gentleman said that he was very pleased to know that he did not have a heart problem.

     Thus, exercise stress tests are not 100% sensitive.  They will miss detecting 200 out of a 1000 individuals that have significant coronary artery problems. Thus, the test is said to be only 80% “sensitive”.

     By the same token in a perfect world, anybody who had a positive stress test would have significant coronary artery disease.  This is not the case.  Unfortunately, exercise stress tests are at best still positive in 50 people out of a 1000 who don’t have coronary artery disease.  In other words, they are only 95% “specific”.

     The healthcare providers’ job is to sift through the clinical story, the electrocardiographic changes, the various other possibilities that might cause the chest pain, and finally the exercise stress test itself.  And after considering all of the pertinent information, the healthcare provider uses their best judgment to give a simple yes or no answer that the person does or does not have coronary artery problems.  When all is said and done, I always tell patients that no matter what these various statistics are, for the one individual patient that I am dealing with there is either 100% chance or a 0% chance that they have coronary artery disease.  I, like the other healthcare providers in this area, do our best to get that answer right.  There is a great deal of thought and consideration that goes into those decisions but they are not perfect.