When I was a surgical technician, I mastered EKG interpretation. My father
was so proud of me that he took me to the intensive care unit of his hospital to spend a
week with the ICU nurses plying my knowledge. After bolstering my confidence for this
week, at lunch one day he grabbed my attention with a remark that sounded and was meant to
sound outrageously heretical. He said, "Well you understand, of course, that EKG
doesn't really mean much?" I was obviously bewildered, reflecting on how proud he had
been of my EKG knowledge and interpretive proficiency. He then quizzed me on the simplest
fundamentals of EKG. He asked, "What is the foundation of EKG?"
Like a beleagured medical student I stammered, trying to second guess to where he was
going with this line of questioning.
He asked the question again, dragging the answer from me, which I indeed produced,
"Einthoven's Triangle."
"And what is it about Einthoven's Triangle that makes EKG a virtual fantasy? What is
a major reason, among many others but particularly related to Einthoven's Triangle, that
you can not completely rely on EKG for cardiac assessment?"
I was totally baffled by this question. I replied that I was so.
"Don't you see anything wrong with Einthoven's Triangle?"
I was still lost.
"Look! Ken, it is two-dimensional! Do you really expect the cardiac firing potential
to conform to the flat piece of paper on which the sacred triangle is drawn? No! The heart
is three- dimensional and might do something like this:" He simultaneously twirled
his index finger and flipped his hand over and forward to represent something like the
orbit of the Space Shuttle.
Since this conversation my reverence for EKG and other medical testing has been replaced
with enlightened suspicion. Indeed, EKG and similar medical tests are valuable diagnostic
tools but note that physicians do not rely on a single test to confirm their conclusions.
EKG is an integral part of a stress test. This test is performed to assess heart function
and health as the heart is performing under the load of graded and increased activity
level such as that of walking or running on a treadmill. It is commonplace in cardiology
clinics and now a routine part of a cardiological assesment. According to Dr. Henry
Solomon, "Stress tests are not sensitive enough, specific enough, or reproducible
enough for anyone to be sure they're telling you anything at all."
In his 1984 book The Exercise Myth, Dr. Solomon reports that a stress electrocardiogram
may appear abnormal merely because of abnormal heart valves, certain medications, anemia,
high blood pressure, or a meal too recently eaten. The inability of a normal exercise test
to exclude the presence of coronary disease is about as common.
An abnormal test result is called a positive result, meaning something bad has been found.
A normal test result is called negative - meaning nothing bad has been found and that the
heart appears clear of disease.
An incorrectly positive result of a stress test is called a false positive test. An
incorrectly negative result is called a false negative.
The average sensitivity of the stress test is approximately 75 percent: the test corretly
identifies 75 percent of the people who have coronary disease. Therefore, the false
negative rate runs about 25 percent. Some studies show the false negative rate to be 60
percent. False positive rates vary from 5 percent to 35 percent. With certain subgroups
such as women, false positive tests have been recorded for as many as 64 percent.
"Women might as well toss a coin to see whether or not they have coronary disease as
rely on the results of a traditional stress test," says Solomon.