Effects of partial ischaemia and volume loading on myocardial efficiency and cardiac performance in dogs

To determine whether volume loading may be beneficial for the performance of ischaemic heart, myocardial ischaemia was created by partial occlusion of the left anterior descending coronary artery (LAD) to reduce the blood flow to 30 approximately 40% of basal level in 11 open chest anaesthetised dogs. Global left ventricular function as well as regional performance were studied under four different levels of volume loading, euvolemia (EUVO), hypervolemia (HYPER), normovolemia and hypovolemia.

Left ventricular dP/dt(max) and cardiac output were decreased significantly during partial occlusion (3511.2+/-425.2 mmHg/s and 0.9+/-0.1 l/min) compared with pre-occlusion (4486.5+/-419.2 mmHg/s and 1.3+/-0.1 l/min) (P<0.05). Cardiac work was also lowered during partial occlusion (75.4+/-5.2 vs. 106.5+/-2.4 mmHgxl/min) (P<0.05). During volume loading, cardiac output and work were elevated (1.2+/-0.2 l/min and 94.0+/-5.4 mmHgxl/min) compared with EUVO (P<0.05). Local contractile dysfunction occurred in the LAD region after partial occlusion. There were no significant differences of dysfunction between any conditions of volume loading. Percentage shortening of the LAD region was decreased during partial occlusion (8.3+/-1.1 vs. 25.0+/-2.7%) and also was higher in HYPER (13.5+/-2.6%) than that in EUVO (P<0.05). Partial occlusion and different conditions of volume loading did not significantly change the force and local work in the LAD region. Myocardial O(2) consumption (MVO(2)) in LAD region was decreased during partial occlusion with different levels of volume loading (P<0.05). Local myocardial efficiency (work/MVO(2)) was increased during partial occlusion compared with pre-occlusion (941.3+/-56.2 vs. 551.0+/-65.5 gxmm/ml O(2)/min/100 g, P<0.05) and was also higher in HYPER (1208.6+/-48.4 gxmm/ml O(2)/min/100 g) than that in EUVO (P<0.05). Local systolic work was decreased during partial occlusion compared with pre-occlusion (9.5+/-1.5 vs. 14.2+/-1.3 gxmm/beat), whereas local myocardial systolic mechanical efficiency was increased (496.3+/-45.7 vs. 667.2+/-39.8 gxmm/ml O(2)/min/100 g). There were no significant changes of local systolic work and local systolic myocardial efficiency between different volume loading, although they tend to be elevated with increasing volume loading.

Increase of blood volume by 15% improved the impaired global performance caused by partial occlusion of the LAD in open-chest dogs. This improvement was not accompanied by further dysfunction or increased MVO(2) of ischaemic myocardium, and therefore might be beneficial without causing further damage to the insulted myocytes.