Questions about the proper way the FAA wants airmen to perform an exercise stress test come up just about each day. I am going to attempt to demystify what the FAA would like when they or your aviation medical examiner recommends you have one.
A person performs stress testing for several reasons. The most common reason is to determine if there is a lack of blood supply (medical term, ischemia) getting to your heart. So, the person walks on a treadmill and every 3 minutes the incline and speed are increased. Electrodes are placed on the chest so electrocardiogram tracings can be performed and the blood pressure is monitored generally every 3 minutes as well. The FAA wants the airman to exercise as close to 100 percent of their maximal heart rate as possible, but at a minimum, to at least 85 percent. If you reach only 84 percent of maximum predicted, the FAA will kick back the test and you will have to repeat it. The maximal heart rate is calculated by subtracting one’s age from 220. They would like you to remain on the treadmill for at least 9 minutes.
Another common indication for stress testing is to evaluate cardiac arrhythmias (irregular heart rhythms). They want to see if the irregular rhythm goes away with exercise or gets worse!
The FAA will allow airmen who are requesting third class medical certification to undergo what is called plain stress testing as described above. One needs to understand that the plain stress test can have both “false positive” test results (when the test suggests lack of blood supply, but more definitive testing is performed and it is discovered not to be so) and “false negative” (when the test is performed and appears negative, but with more definitive testing later discovers lack of blood supply).
In the case of airmen applying for first and second class medical certificates, the FAA wants them to perform more sensitive testing. This type of test is called a nuclear exercise perfusion scan, or a nuclear stress test. In this case, the airman is given an intravenous injection of radioactive isotope material. This isotope enters the bloodstream and migrates into the coronary circulation in the heart. Since the isotope is “commingled” with blood, it will avoid areas in the heart where there was scarring of the heart muscle from a prior infarct or where narrowing of vessels is such that there is significant lack of blood supply. At that time the airman is scanned with a large camera and pictures of the heart are taken and saved. The airman is then hooked up and walks on the treadmill as I noted above. When the airman nears the completion of the test, another injection of the radioactive substance is given, the treadmill is continued for another minute, and he or she is re-scanned. A comparison is made between the resting portion and the post-exercise portion. If a comparison of imaging indicates a difference in the area of isotope distribution in the heart muscle, the inconsistency may indicate a lack of blood flow to the heart, called reversible ischemia. This is a disqualifying condition for all classes of medical certification.
Performing the nuclear portion in addition to the regular stress electrocardiogram (EKG) monitoring part increases the sensitivity of the test. So, if an individual has a negative or normal EKG response but the nuclear portion demonstrates lack of blood supply, that would be a positive (abnormal) test. However, if a person has an EKG portion that appears positive but the nuclear scan films do not demonstrate ischemia, more than likely the airman does not have coronary disease.
The FAA in general requires airmen applying for first and second class medical certificates to have the maximal nuclear stress testing. Should a third class medical applicant have a positive plain EKG stress test for ischemia, he or she will then have to undergo a nuclear stress test to determine if ischemia is really present.
Next time, we will talk about another acceptable alternative form of nuclear stress test that is acceptable to the FAA under some circumstances.