Contractile state of hypertrophied left ventricle in long-standing volume overload.

The purpose of this investigation was to evaluate the contribution of hypertrophy, the length-tension phenomenon, and inotropism to adaptation of the left ventricle (LV) to volume overload of up to 3 yr duration. Overload was produced in dogs by heart block, and contractile state was evaluated with a Walton-Brodie arch. Recording of contractile force (CF) in grams vs. muscle length from the LV indicated that dogs with hypertrophy were functioning at a higher point on the ascending limb of the length-tension curve than normals (76 percent Lmax in hypertrophy vs. 61 percent Lmax in normal). Additionally, in hypertrophy, all points on the length-tension curve above 80 percent Lmax were significantly elevated. None of these changes were seen in dogs in which block was induced on the day of the experiment. When CF was normalized for hypertrophy and expressed as CF/cm2, the length-tension curves were practically superimposable. These data suggest that adaptation was accomplished by hypertrophy, a shift up the length-tension curve without a depression of inotropic state.