An extensive body of evidence supports the concept that cardiac hypertrophy and normal cardiac growth develop in response to increased hemodynamic loading and abnormal systolic and diastolic stresses at the myocardial fiber level. The pattern of hypertrophy reflects the nature of the inciting stress. Experimental studies indicate that if the stress is moderate, gradually applied, and the animal young and healthy, physiologic hypertrophy of muscle with normal contractility develops. In this circumstance, cardiac hypertrophy may be regarded as a useful adaptation to increased hemodynamic loading. When the inciting stress is severe, abruptly applied, or the animal old or debilitated, pathologic hypertrophy develops: in this circumstance, the cardiac muscle produced is abnormal and exhibits depressed contractility. Of particular clinical relevance is the intermediate situation which seems to develop in many patients with chronic left ventricular pressure-overload and perhaps also in left ventricular volume-overload. In this situation, chronic left ventricular pressure or volume overload is initially matched by adequate hypertrophy in the appropriate pattern. Eventually, in some patients, hypertrophy fails to keep pace with the hemodynamic overload so that a systolic stress imbalance occurs at the myocardial fiber level and left ventricular pump failure ensues. If this situation persists uncorrected, it is possible that the increasingly high wall stresses will convert physiologic to pathologic hypertrophy. The task of the clinician is to identify this intermediate stage and to correct the abnormal hemodynamic loading before the transition to pathologic hypertrophy becomes complete.
