“Out of all this struggle a good thing is going to grow. That makes it worthwhile.”
John Steinbeck, In Dubious Battle
After a fatal aircraft crash, the formal investigative report usually identifies a “chain of catastrophic events” that doomed the “mishap aircraft”. In modern aviation, it usually takes multiple errors or failure to lead to a disaster. In the constant effort of medicine to improve, increasingly, it adopts safety procedures from aviation, such as checklists. You don’t want to forget to lower the landing gear or find that you’ve forgotten to apply a safety device to a patient.
For many years, I was a research volunteer at a world-class cardiac research group, typically coming in annually for a week of testing. After various stays, I came to expect that while the visit would have much scientific precision performed by superb staff, something would not go as planned. More often than not, it reminded me of a Frederico Fellini movie, mixing medical drama with erotica. This visit was no exception.
Before I get into the specifics of the test, my reader should know that the hospital did not require nurses to wear formal uniforms, although that was an option. It was one of the few facilities that had a long waiting list of applications from nurses, so you knew that every nurse was at the top of the profession.
One such nurse, appropriately named Joy, was the principal research assistant in the echocardiography laboratory. Picture a tiny Sophia Loren, probably 5’1” or so, with a dramatic Italian look. Long, thick black hair that had to be pinned up or covered during procedures. A beautiful face. A large and apparently perfectly shaped bosom. Womanly hips, and graceful legs. She rarely wore scrubs, instead some quite attractive street clothing. Among the patients, there was a rumor that Joy walking into the room was a special stress test. If the heart did not accelerate, it was very sick.
Seriously, stress testing is an important part of cardiology. It reveals things that do not happen unless the heart is working hard, for exercise, or because illness puts demand on it. The basic way to do stress testing is exercise, usually by running in place on a treadmill, or sometimes using a stationary bicycle. If the patient’s disease, or the nature of the test being performed, prevents physical exercise, the alternative is injecting a drug, such as dobutamine or adenosine, which forces the heart to beat quickly.
Let us return to Joy’s area of specialization, research involving echocardiography. This involves the use of extremely high frequency, inaudible, sound waves -- ultrasound -- to form images of the heart or circulatory system. There are various techniques, but all involve placing a transducer, which generates the sound wave, against some part of the body. The generated energy hits the heart or other target, and then bounces back to the receiving element in the transducer -- hence the “echo” part. Like radar, the time from generating the energy, the angle it was aimed, and the energy and direction of the returned signals, is used to make measurements and form images.
Routine echocardiography is a tremendously useful, inexpensive, and widely used test. In the basic form, a highly trained technician puts gel on the patient’s chest, to improve transmission of sound. Yes, it’s essentially KY jelly, the same used for erotic lubrication. If you’re lucky, the technician warms it. The transducer moves over specific anatomic regions, forming a picture or measurement on the computer-controlled screen. This gives a moving picture of the heart, with false colors corresponding to the speed of blood flow. Higher-resolution still images also are recorded, which allow precise measurements. By measuring the distance between the walls of parts of the heart, at various stages of heartbeat, the pumping efficiency can be calculated; the main such measurement is the left ventricular ejection fraction. This is especially useful for diagnosing heart failure, or a condition where the pumping efficiency is decreased. That may be treated with things including drugs, pacemakers, devices inserted through catheters, and surgery. Over the years, I’ve developing worsening congestive heart failure, effectively treated with echocardiography giving Superman-style X-ray vision, or the equivalent, to the cardiologist.
About a year ago, my heart failure worsened, and was treated in a community intensive care unit. Part of the problem was that my aortic valve, through which pumped blood enters the circulation through the aorta, the largest artery in the body, was failing. I was too sick to tolerate open-heart surgery, the usual way to replace valves. In the intensive care unit (ICU), with guidance from both X-rays and ultrasound, a balloon pump was inserted, by catheter, into my heart. It supplemented the heart as a pump for several days, until I could tolerate a less invasive procedure to replace my aortic valve. The transaortic valve replacement (TAVR) also uses a catheter threaded into a blood vessel in the heart. A replacement valve, partially of plastic and partially of muscle from a cow’s heart, slides up the tube, and snaps open, rather like an umbrella opening. It crushes the damaged natural valve, pushing it aside at taking over. Respecting my donor, I do make a point, whenever I see the cardiologist, of giving a loud, clear, MOOOOOO.
For the basic imaging of a moving heart, conventional echocardiography is an excellent technique. It does not, however, tell the cardiologist about things that go wrong only when the heart is stressed, beating fast as in exercise.
On another of my research hospital visits, I was a test subject for a new diagnostic procedure, cardiac stress testing using transesophageal echocardiography. What does involve?
Conventional stress testing
A very common type of stress testing is done to find scar tissue in the heart, destroyed by heart attacks, or areas that don’t contract under stress, because not enough oxygen-carrying blood gets to them from the coronary arteries of the heart itself. In the most common sort of cardiac scan, one gets an injection of a radioactive substance that mimics the metabolism of potassium, and then the heart is stressed either by exercising on a treadmill or getting an injection of a drug that stimulates the heart (usually dobutamine or adenosine). Next, one is rolled into a machine called a gamma camera. It looks much like what you think of as a CT or MRI scanner: a doughnut-shaped gantry surrounding the table on which the patient reclines. The camera rotates around the patient, constructing a rather blurry picture whose colors correspond to the level of radiation taken up by heart muscle. Named for its inventor, the Anger camera has to focus gamma rays, for which glass lenses and mirrors are useless. It does so using lead plates with precision-drilled holes, which do focus the rays, but not with the resolution of conventional photography or echocardiography.
If some muscle doesn’t absorb the radioactive tracer, one of two things is wrong. It is dead and just scar tissue, the result of a myocardial infarction (heart attack). Alternatively, it may be that the coronary arteries of the heart aren’t providing it with enough blood and oxygen to absorb the tissue, a correctable condition of blocked or narrowed arteries are opened. This latter case is myocardial ischemia, associated with angina and transient pain.