Late Effects: Heart-damage, Diagnostic Tests

Echocardiogram. An echocardiogram is an ultrasound of the heart. Ultrasound is sound with a frequency greater than 20,000 cycles/sec. When ultrasound waves travel through the body, they bounce - or echo - off areas of the body depending on the density of the different components. A detector responds to the patterns of sound, the data is processed by a computer, and an ultrasound picture is displayed on a screen.

Many different analyses can be made of the echocardiogram results. For left ventricle cardiomyopathy, the following measurements are applicable:

Left ventricle wall dimensions. This determines the thickness of the left ventricle muscle. The problem in anthracycline-induced myopathy is thinning of this wall.

Two methods of assessing pumping ability of the heart:

Ejection fraction. The left ventricle is a chamber which relaxes to fill with blood and then contracts to pump the blood out. Even in a healthy heart, the left ventricle does not pump all of the blood out with each beat. The ejection fraction is defined by the following formula:

The ejection fraction is a useful measure of left ventricular performance. The normal range is 63-77% for males and 55-75% for females (reference: Measurements in Cardiology). If the left ventricle wall is thinned, a decrease in the ejection fraction is seen.
Shortening fraction. The shortening fraction is a slightly different way of measuring left ventricle performance. Instead of measuring and ratio-ing blood volumes, the shortening fraction measures and ratios the change in the diameter of the left ventricle between the contracted and relaxed states:

The normal range is 0.18-0.42, or 18-42% (reference: Measurements in Cardiology). According to the Oeffinger/Keene article, " . . . above 30% is considered normal, with 26 to 30% representing a mild decrease in function. . . . A decrease in the shortening fraction usually precedes a detectable decrease in the ejection fraction."

The echocardiogram is the "work horse" test for anthracycline-induced cardiomyopathy. For instance, the COG Enalapril Study requires echocardiogram results to determine entrance criteria:

"Echocardiographic evidence of reduced fractional shortening (> 2 s.d. below the normal mean), reduced contractility (stress-velocity index >2 s.d. below the normal mean), or increased afterload (end-systolic wall stress >2 s.d. above the normal mean) or any combination at the time of enrollment." [Ed. note: reduced contractility and increased afterload are terms used to describe problems with the left ventricle. They can both be measured by echocardiography. Reference: Cardiology. Fractional shortening is described in the paragraphs above.)

I found a bit of controversy about echos: it seems the carrying out and interpretation of echos is technician/doctor dependent.

Echocardiogram explanations on the web:

Multiple uptake gated acquisition, or MUGA. MUGA is another way of estimating the ejection fraction. A radioactive tracer is injected into the blood stream and then the heart is viewed using a gamma camera, resulting in a "movie" of the heart beating from which various measurements can be made. In general, it is more precise than an echo, but it is also more expensive, and somewhat limited.

Cardiopulmonary Stress Test. Many of us are familiar with the "treadmill test." I had one myself in spring of 2001 as part of an optional wellness evaluation. This test tells you how well your heart is working by determining how well it can oxygenate your blood during physical exercise, which is measured as "VO₂ max". First, they prep you with sticky electrodes on your chest which monitor your heart. Then you get on a treadmill and they pinch your nose and place a tube in your mouth so that they can monitor expelled breath. They attach a blood pressure cuff to your arm. Then you start walking; they increase the speed of the treadmill in 2 minute stages. You keep going until, I guess, you or they decide you have had enough. In my case, they kept cheering me on - this is probably what they do for everyone, but it made me feel like someone in a race and was sort of fun. From my stress test, I was given a safe range within which to exercise.

Jon's Place

The stress tests, cardiopulmonary stress test (above) and the stress echocardiogram (below) are important because they allow symptoms that not obvious at rest to become apparent.

Stress Echocardiography. A echocardiogram test done while the patient is under stress, either from exertion (treadmill) or a drug.

Holter Monitor. This is a monitor that detects the electrical activity of the heart. To detect abnormal heart rhythms, it is worn for 24 hours, providing a tape for the doctor. Non-typical heart rhythms can be a symptom of left ventricle problems.

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