Cardiac disuse atrophy during LVAD pumping.

The authors investigated morphologic changes of myocardial tissue of goats supported with a long-duration left ventricular assist device (LVAD). The bypass flow rates of the LVAD were kept at maximum levels (about 80% of total cardiac output) in four goats for 30 days, and at a limited flow rate (around 60%) in one goat each for 30 and 90 days. Morphometric studies using light and electron microscopy were performed on the left ventricles, comparing them to those in the four control studies. The results disclosed: 1) relative volume densities of the myocytes and interstitial tissue in the myocardium were unchanged; 2) cross-sectional areas of the myocytes in the maximum bypass cases were significantly reduced in comparison with pre-experimental data; 3) relative myocyte volumes, calculated by myocytes and nuclear volume densities, were reduced in three goats in the maximum bypass group; and 4) relative volume density of myofibrils was reduced in the maximum and 90 day bypass groups, whereas that of mitochondria was reduced only in the 90 day bypass case. These results indicate that LVADs cause cardiac atrophy which correlates with bypass flow rate and duration of assistance.