Non-Elastic Deformation of Myocardium in Low-Flow Ischemia and Reperfusion: Ultrastructure–Function Relations

This study tested the hypothesis that regional low-flow ischemia and reperfusion alter myocardial material properties by causing non-elastic deformation. Twenty-two anesthetized, open-chest pigs were studied. Pigs underwent 90 min of regional low-flow ischemia (anterior LV subendocardial blood flow 29±7% of baseline) followed by 90 min reperfusion. LV pressure and regional subendocardial segment length were recorded to derive end-diastolic pressurevssegment length (EDPvsEDL) and preload-recruitable stroke work (PRSW) relations.In vivo, non-elastic myocardial deformation was inferred from increases in minimally loaded myocardial dimensions: the EDL at zero EDP (L0) and the EDL at which no regional external work was performed (Lw, the PRSW intercept). In 15 pigs, ultrastructural confirmation of non-elastic deformation was obtained from sarcomere dimensions measured by transmission electron microscopy afterin situperfusion fixation under non-ischemic conditions, after 90 min ischemia, or after 90 min ischemia plus 90 min reperfusion. Ischemia increased L0and Lwto 1.17±0.05 and 1.13±0.04 times baseline, respectively. After reperfusion, L0and Lwremained increased to 1.09±0.03 and 1.15±0.02 times baseline (allP<0.05). After reperfusion, PRSW slope was not different from baseline, but regional external work remained depressed (0.38±0.03 times baseline) due to the persistent increase in Lw. Neither L0nor Lwchanged in the posterior (non-ischemic) region. In hearts fixed after ischemia or after ischemia plus reperfusion, sarcomere length was significantly greater and transverse distance between thick myofilaments was significantly smaller in the anterior (ischemic) subendocardium than in the posterior (non-ischemic) subendocardium (P<0.01). We conclude that regional low-flow ischemia and reperfusion cause non-elastic deformation of myocardium, manifestin vivoby increased minimally loaded myocardial dimensions (L0and Lw) and ultrastructurally by increased sarcomere length and decreased transverse interfilament distance. Non-elastic deformation of myocardium may contribute to contractile dysfunction in low-flow ischemia and reperfusion.