Ventricular Hypertrophy

Ventricular hypertrophy (i.e., increased ventricular mass) occurs as the ventricle adapts to increased stress, such as chronically increased volume load (preload) or increased pressure load (afterload). Although hypertrophy is a physiological response to increased stress, the response can become pathological and ultimately lead to a deterioration in function. For example, hypertrophy is a normal physiological adaptation to exercise training that enables the ventricle to enhance its pumping capacity. This type of physiologic hypertrophy is reversible and non-pathological. In contrast, chronic hypertension causes pathologic ventricular hypertrophy. This response enables the heart to develop greater pressure and to maintain a normal stroke volume despite the increase in afterload. However, over time, pathologic changes occur in the heart that can lead to heart failure.

In the case of chronic pressure overload, the inside radius of the chamber may not change; however, the wall thickness greatly increases as new sarcomeres are added in parallel to existing sarcomeres. This is termed concentric hypertrophy (Figure 1). This type of ventricle is capable of generating greater forces and higher pressures, while the increased wall thickness maintains normal wall stress. A hypertrophied ventricle, however, becomes "stiff' (i.e., compliance is reduced -see CD9 - compliance), which impairs filling, reduces stroke volume and leads to a large increase in end-diastolic pressure (Figure 2). Changes in end-systolic volume depend upon changes in afterload and inotropy. Concentric hypertrophy, which is one cause of diastolic dysfunction (see Chapter 9), can lead to pulmonary congestion and edema.

If the precipitating stress is volume overload, the ventricle responds by adding new sar-comeres in series with existing sarcomeres. This results in ventricular dilation while maintaining normal sarcomere lengths. The wall thickness normally increases in proportion to the increase in chamber radius. This type of hypertrophy is termed eccentric hypertrophy, and often accompanies systolic dysfunction.

Eccentric Concentric Hypertrophy

FIGURE 1 Concentric versus eccentric ventricular hypertrophy. With concentric hypertrophy, the ventricular wall thickens and the internal radius remains the same or is reduced. Eccentric hypertrophy occurs when the ventricle becomes chronically dilated; the wall thickness usually increases in proportion to the increase in radius.

FIGURE 1 Concentric versus eccentric ventricular hypertrophy. With concentric hypertrophy, the ventricular wall thickens and the internal radius remains the same or is reduced. Eccentric hypertrophy occurs when the ventricle becomes chronically dilated; the wall thickness usually increases in proportion to the increase in radius.

Cardiac Pressure Volume Curves

FIGURE 2 Effects of concentric hypertrophy on left ventricular pressure-volume loops. Hypertrophy (red loop) reduces compliance (increases the slope of the relationship between filling pressure and volume) leading to impaired filling (reduced end-diastolic volume), increased end-diastolic pressure, and reduced stroke volume (reduced width of pressure-volume loop). Left ventricular (LV) end-systolic volume may or may not change depending upon how afterload and inotropy change.

FIGURE 2 Effects of concentric hypertrophy on left ventricular pressure-volume loops. Hypertrophy (red loop) reduces compliance (increases the slope of the relationship between filling pressure and volume) leading to impaired filling (reduced end-diastolic volume), increased end-diastolic pressure, and reduced stroke volume (reduced width of pressure-volume loop). Left ventricular (LV) end-systolic volume may or may not change depending upon how afterload and inotropy change.

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