title: The course of passive elasticity of myocardial tissue following experimental infarction in rabbits and its relation to mechanical dysfunction.
abstract: Given the substantial reserve of normal myocardium, its inability to sustain life in the presence of 30-50% necrosis of the left ventricle (LV) seems a paradox. It is known that dyskinesia of the infarcted area probably plays a dominant role in initiating failure after an infarction. To study this problem, a well defined experimental infarction was produced by cryogenic means in 58 rabbits, and the animals  were allowed to recover. Groups of rabbits were killed 4 hours and 1,2,5, or 10 days following infarction. As quickly as possible (within 4 minutes) a sample specimen from the infarcted area was removed from the LV and subjected to a force-elongation test while being bathed in Ringer solution at 37 degrees C equilibrated with 95% O2-5% CO2. The data were interpreted assuming an exponential stress-strain law with constants K and C. Mean values of K of 10.6 +/- 0.94 (SEM) were found for the noninfarcted control group, whereas, rather surprisingly, no significant trend in K over 10 days was found in the infarcted group. Mean values of K +/- SEM for the postinfarction groups were as follows: 4 hours, 9.51 +/- 0.63; 1 day 10.54 +/- 1.13; 2 days, 13.15 +/- 2.28; 5 days, 11.59 +/- 1.36; and over 10 days, 12.93 +/-1.02. The functional implications were estimated with a simple model of the shortening required of the viable muscle during the isovolumic phase. It was found that contractile reserve fell rapidly with increasing infarct size, reaching zero for a 60% infarct when K = 10. With K greater than 100, there was no appreciable reduction in reserve. With a constant infarct size, variation in reserve with the afterload-preload ration was found to be logarithmic.
mesh_terms: D000818:Animals; D004548:Elasticity; D006321:Heart / Q000503:physiopathology*; D066298:In Vitro Techniques; D009200:Myocardial Contraction; D009203:Myocardial Infarction / Q000503:physiopathology*; D009206:Myocardium; D011817:Rabbits; D013314:Stress, Mechanical