In conjunction with his PhD thesis defense today, fellow ISB researcher Harald Edvard Mølmen Hansen held an interesting introductory lecture on physiological versus pathological left ventricle hypertrophy, and how to tell the two apart. He concluded that there is no single test that can give a unilateral answer, however by combining multiple diagnostic tools it should be possible to differentiate between them in a clinical setting.
The heart consists of four chambers; two atria (upper chambers for blood collection), and two ventricles (larger chambers that push the blood into circulation). The right side of the heart pumps blood into the lungs to pick up oxygen, while the left side of the heart pumps freshly oxygenated blood to the rest of the body. Harald Edvard’s lecture focused on enlargement of the left ventricle – a condition called left ventricle hypertrophy.
An enlarged heart is not always a sign of disease. A so-called physiological (or healthy) adaptation occurs both during pregnancy and with exercise. A pathological (or diseased) hypertrophy can be the result of high blood pressure, or cardiovascular disease such as heart failure. In all of these, there is an increased burden on the heart, and it expands in order to match the body’s requirements. The walls thicken and the chamber itself can also become bigger as a means of compensating.
If expansion happens uniformly, and the chamber thickness and chamber size keep the same relative proportions, it’s probably a healthy adaption. However, if the walls thicken unevenly and the chamber becomes smaller relative to the expanding walls, it is more likely a sign of disease. Another clue might be in change over time; if you stop training (or the pregnancy ends) then a healthy enlarged heart should return to normal by itself. By contrast a pathological hypertrophy will not likely improve without an intervention. These are just some of many measures that can give an indication of healthy or sick.
But why is it so important to distinguish between the two? A left ventricle hypertrophy is a risk factor for cardiovascular disease and death. It gets particularly tricky in athletes, where hypertrophic cardiomyopathy (HCM) – a genetic disease where the heart muscle is thickened – is the most common cause of sudden cardiac death. If an athlete’s heart is larger than normal, it’s very important to determine whether it’s the result of this genetic disease, or the healthy adaptation from intensive training over a longer period of time.
In 2005, Maron introduced the “grey zone” of overlap between HCM and the athlete’s heart with ten criteria to help distinguish which one it is. In addition, there are many fancy technical tools to assist in the process. These range from MR, 3D echocardiography, and tissue Doppler, to oxygen uptake and even CT scan. Improved imaging techniques, especially with the use of the appropriate contrast can light up unhealthy tissue and predict your prognosis. Nevertheless, many of these tests are expensive, and are not generally clinically inclined if simpler tests come back fine.
Harald Edvard argued that for a borderline patient, the three most important tools are taking an accurate medical history, and performing an ECG and an Echocardiography. If all these are normal, he does not recommend further screening. Although the exact numbers vary by population, the risk of sudden cardiac death is quite low, and a false positive diagnosis may be just as harmful by the needless worry that it causes.
Written by Hanna Sofie Ellingsen at CERG.