Ventricular hypertrophy

Ventricular hypertrophy is the enlargement of ventricles in the heart.^[1][2] Although left ventricular hypertrophy is more commonly encountered, enlargement can occur in either the right or left ventricle (or sometimes both). This condition is often brought up by the media when athletes have allegedly used anabolic steroids, although these are not required for ventricular hypertrophy to occur in athletes.^[3]

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Physiology

  The ventricles are the chambers in the heart responsible for pumping blood either to the lungs (right ventricle)^[4] or the rest of the body (left ventricle)^[5]. There are many reasons for an increased ventricular mass, usually due to an adaptation by the ventricle(s) of the heart because of the following factors:

• Obesity
• Age
• Diabetes
• Arterial hypertrophy

It is a physiological response that enables the heart to adapt to increased stress; however, the response can become pathological and ultimately lead to a deterioration in function. For example, hypertrophy is a normal physiological adaptation to exercise that enables the ventricle to enhance its pumping capacity (the same adaptation also occurs during pregnancy)^[6]. Aerobic training results in the heart being able to pump a larger volume of blood through an increase in the size of the ventricles. Anaerobic training results in the thickening of the myocardial wall to push blood through arteries compressed by muscular contraction.^[7] This type of physiologic hypertrophy is reversible and non-pathological, increasing the heart's ability to circulate blood. Chronic hypertension causes pathological ventricular hypertrophy. This response enables the heart to maintain a normal stroke volume despite the increase in afterload. However, over time, pathological changes occur in the heart that lead to a functional degradation and heart failure.^[8]

If the precipitating stress is volume overload (as through aerobic exercise, which increases blood return to the heart through the action of the skeletal-muscle pump), the ventricle responds by adding new sarcomeres in-series with existing sarcomeres (i.e. the sarcomeres lengthen rather than thicken). This results in ventricular dilation while maintaining normal sarcomere lengths - the heart can expand to receive a greater volume of blood. The wall thickness normally increases in proportion to the increase in chamber radius. This type of hypertrophy is termed eccentric hypertrophy.^[9]

In the case of chronic pressure overload (as through anaerobic exercise, which increases resistance to blood flow by compressing arteries), the chamber radius may not change; however, the wall thickness greatly increases as new sarcomeres are added in-parallel to existing sarcomeres. This is termed concentric hypertrophy.^[10] This type of ventricle is capable of generating greater forces and higher pressures, while the increased wall thickness maintains normal wall stress. This type of ventricle becomes "stiff" (i.e., compliance is reduced) which can impair filling and lead to diastolic dysfunction.

References

See also

• Cardiac fibrosis
• Cardiology
• Cardiomegaly
• Cardiovascular disease
• Right ventricular hypertrophy