Quantitative analysis of cardiac hypertrophy due to pressure load in reference to the relations of blood pressure, left ventricular weight and left ventricular capacity.
In almost all of the cases of cardiac hypertrophy due to sustained hypertension, left ventricular capacity is increased in proportion to increased left ventricular weight, even in the absence of manifest cardiac insufficiency. The condition is regarded as the general expression of cardiac response to pressure load, and the concept of "isomorphic hypertrophy" is proposed. Concentric hypertrophy of the current concept is observed only on rare special occasions, and its role in cardiac adaptation to pressure load is obscure. The increase in myocardial mass is sufficient to maintain the work done by a unit myocardial volume at a normal level. However, the calculation on pertinent models demonstrates that hypertrophied hearts of any type expel the normal stroke volume with smaller shortening of muscle fibers under larger stress, which is further elevated with the progress of cardiac contraction. Because the maximum force generated by muscle fibers declines with advancing cardiac contraction, hypertrophied hearts harbor a latent risk of mechanical insufficiency. Even under pressure load, ventricular dilation seems to precede the re-inforcement of ventricular wall in the development of cardiac hypertrophy. A common mechanism may be therefore assumed underlying the development and performance of all types of hypertrophied hearts, regardless of the difference in the character of physical loads.