Hypertrophy of the Heart Invariably Leads to Failure

We have already explained how coronary artery disease can lead to failure by causing infarction (cell death) of part of the ventricular muscle when a coronary artery becomes occluded. Because cardiac muscle does not regenerate, such a lesion will be permanent. Another common source of heart failure is ventricular overload. Like any muscle, the heart tries to adapt to an increased workload by hypertrophy of its individual muscle fibers. Although such an adaptation is usually successful in skeletal muscle, it can lead to disaster in the heart.

Hypertrophy of the heart is undesirable for several reasons. First, the heart is dependent on the venous pressure to stretch the fibers during diastole, and the hypertrophied heart has a thickened wall, which decreases its diastolic compliance; such a condition is illustrated by a shift in the diastolic compliance curve, as shown in Fig. 2. The hypertrophied heart requires an elevated venous pressure to achieve a normal stroke volume. Indeed, diastolic dysfunction may become the primary defect in some heart failure patients.

A second problem is that the remodeling of the muscle cells to contain more myofibrils often results in inferior muscle. Although the exact cause of this lesion is poorly understood, it may involve expression of different iso-forms of contractile proteins that replace those normally present in the heart. A third problem is that the heart has a very high oxygen requirement and the coronary circulation does not seem to develop in proportion to the

Stroke Volume Compliance

FIGURE 2 Note how a loss of diastolic compliance reduces stroke volume in the concentrically hypertrophied heart. Hypertrophy is shown by the dotted line; the solid line shows normal data. Venous pressure would have to rise to 17 mm Hg to restore stroke volume in this example.

Ventricular volume (mL)

FIGURE 2 Note how a loss of diastolic compliance reduces stroke volume in the concentrically hypertrophied heart. Hypertrophy is shown by the dotted line; the solid line shows normal data. Venous pressure would have to rise to 17 mm Hg to restore stroke volume in this example.

increased muscle mass. As a result, such a heart may always be starved for oxygen and therefore be ischemi-cally depressed.

Your Heart and Nutrition

Your Heart and Nutrition

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