How can the heart “fail” with normal strength?

Heart failure is a general term for a group of symptoms including fatigue, swelling and difficulty breathing. Each of these symptoms may have any number of causes. When evidence points to the heart as a root cause, the constellation is known as heart failure. The heart’s failure is its inability to circulate enough blood to support normal daily activities without relying upon help from various sources within the body. Its inability to perform is the source of fatigue and its calls for help produces many of the other symptoms.

Heart failure as a diagnosis is about as specific as headache. Without a genuine reason for the heart’s failure, no speculation can be offered as to its repair. The first step toward a more specific diagnosis classifies heart failure using the most readily available measurement of the heart’s function, the ejection fraction (EF). The fraction of blood leaving the main pumping chamber (left ventricle) during each heartbeat is called the ejection fraction. Heart muscle dysfunction causing heart failure is broken down into two large categories, heart failure with an ejection fraction below normal, suggesting weakened or disadvantaged muscle, and heart failure with the ejection fraction preserved.

Of course, the heart may be inefficient because the heartbeat is mistimed or because of a broken part, like a heart valve. In these instances, heart failure is mentioned secondarily because the diagnosis is apparent in the arrhythmia or the broken part. When the muscle is the source of dysfunction, the classification scheme using EF helps to orient physicians and caregivers to the tests that may find a cause and the treatments that may be most effective.

Historically, heart muscle was viewed in a very simple fashion, like all muscle, as a tissue that shortens on command. Any failure of the muscle must be apparent in a change in its ability to shorten. As a result, heart failure was under recognized. Blood tests and a number of other techniques have improved capacity to recognize when symptoms like shortness of breath are coming from the heart. Therefore, an increasing number of people are being told that their breathlessness is coming from the heart even though the “strength,” as judged by the ejection fraction, appears to be “normal”. A muscle may function poorly if it is weak, if it cannot relax, or if the support structure that houses muscle cells functions improperly. We now know that almost ½ of people with symptoms believed to be heart failure have a preserved ejection fraction.

This entity, often referred to with the awful abbreviation HFpEF, is very real, difficult for many of us to understand and equally difficult to treat. Fortunately, as understanding improves, the ability to recognize measurable abnormalities that correspond to symptoms is improving, for example using exercise testing with concurrent Doppler echocardiography to estimate blood pressures in different parts of the circulation.