Quantitative evaluation of left ventricular regional work from wall tension-regional area loop in canine heart

We evaluated left ventricular (LV) regional work from a wall tension-regional area (T-A) loop using sonomicrometers in the excised cross-circulated canine left ventricle connected to a volume servo pump. Regional work assessed from a T-A loop closely agreed with the predicted value calculated from LV stroke work and percent regional area under conditions of the control state, dobutamine infusion, and global ischemia. In addition, globally integrated regional work over the entire ischemic and non-ischemic zones agreed closely with LV stroke work either before or after coronary occlusion. These results indicate that LV regional work can be assessed reliably from the T-A loop in both normal and regionally ischemic hearts. Regional work correlated linearly with end-diastolic regional area, indicating a regional Frank-Starling relation, and the slope of this relationship increased with dobutamine infusion and decreased with global ischemia. The correlation between regional work and LV stroke work was also linear and the regression line was the same during the control state and global ischemia, indicating a constant relationship between the work of a specific wall region and LV stroke work regardless of global changes in contractile state. However, after regional ischemia, this regression line apparently shifted downward because T-A loops in the ischemic region were extremely deformed and regional work markedly decreased. From these results, we conclude that T-A loops are a reliable and useful means of assessing regional contractile performance of the LV.