Eccentric hypertrophy describes a specific pattern of growth in the heart muscle, where the walls of the ventricles thicken while the chambers themselves also enlarge. This dual change increases the heart’s internal volume. A useful analogy is a balloon being inflated; as more air is added, the rubber stretches and thins, but the balloon’s overall size and the volume it can hold increase. This structural change is a direct response to the heart having to manage a larger volume of blood.
Physiological and Pathological Causes
The reasons behind eccentric hypertrophy originate from either normal adaptive processes or from disease states. The development of this condition hinges on the stimulus of “volume overload,” where the heart is persistently required to pump a greater amount of blood than usual.
A common physiological cause is intense endurance training, often seen in athletes who run long distances or swim. This type of exercise increases the amount of blood returning to the heart, which must then be pumped out to the body. The heart adapts by enlarging its chambers to hold more blood and moderately thickening its walls to handle the increased workload, a state often called “athlete’s heart.” This adaptation enhances cardiac efficiency and is a normal, reversible response to physical conditioning.
Conversely, pathological eccentric hypertrophy arises from disease. A primary cause is chronic valve regurgitation, where a heart valve, such as the aortic or mitral valve, does not close properly. This leakiness forces the heart to re-pump blood that flows backward into the chamber, creating a constant state of volume overload. Over time, the chamber dilates and the wall thickens as a compensatory mechanism that eventually becomes harmful.
Comparison with Concentric Hypertrophy
While both eccentric and concentric hypertrophy involve a thickening of the heart’s muscular wall, the underlying cause and the resulting structural changes are different. The distinction lies in the type of stress placed on the heart: volume overload for eccentric hypertrophy versus pressure overload for concentric hypertrophy.
Eccentric hypertrophy results from the heart adapting to pump larger volumes of blood. This leads to both an increase in the chamber’s internal diameter and a proportional thickening of the heart wall. The addition of sarcomeres in series allows the muscle fibers to lengthen, which is the mechanism behind the chamber enlargement. This change allows the heart to handle more blood with each beat.
In contrast, concentric hypertrophy is triggered by pressure overload. This occurs when the heart must pump against high resistance, such as from chronic high blood pressure or a narrowed aortic valve (aortic stenosis). To overcome this pressure, the heart muscle thickens significantly, but the chamber size does not increase and may even shrink. This growth involves adding new sarcomeres in parallel, making the muscle fibers thicker and the heart wall denser and stiffer.
Impact on Heart Function and Health
The health consequences of eccentric hypertrophy depend on its origin. The impact can range from beneficial and enhancing performance to detrimental and leading to serious cardiac complications.
In the case of “athlete’s heart,” the eccentric hypertrophy is a positive adaptation. The enlarged chambers and stronger muscle improve the heart’s ability to pump blood, leading to enhanced cardiac output and superior physical performance. This type of growth is non-progressive and may even reverse if the individual ceases intensive training.
Pathological eccentric hypertrophy, however, has negative health implications. The continuous stretching of the heart muscle fibers can cause them to weaken, leading to a decline in the heart’s ability to contract effectively, a condition known as systolic dysfunction. The enlarged heart may also become stiff, impairing its ability to relax and fill with blood properly, which is called diastolic dysfunction. These functional impairments can lead to symptoms like fatigue, shortness of breath, and an increased risk of developing heart failure or abnormal heart rhythms.
Medical Diagnosis and Management
The primary tool for diagnosing eccentric hypertrophy is an echocardiogram, which is an ultrasound of the heart. This non-invasive test allows doctors to directly visualize the heart, measure the thickness of its walls, and assess the size of its chambers to classify its type. Additional tests, such as an electrocardiogram (ECG) or a cardiac MRI, can provide further details about the heart’s electrical activity and structure.
Management strategies for eccentric hypertrophy do not target the heart growth itself but focus on treating its underlying cause. For pathological cases stemming from conditions like a leaky heart valve or hypertension, treatment may involve medications to control blood pressure or surgery to repair or replace the faulty valve. The goal is to alleviate the chronic volume overload that drives the harmful remodeling process.
In instances of physiological eccentric hypertrophy, or “athlete’s heart,” medical intervention is unnecessary unless it is associated with symptoms, which is uncommon. Instead, the focus is on regular monitoring to ensure the heart’s structure and function remain stable. Differentiating between the physiological and pathological forms is a main objective of the diagnostic process.