Can Non-Invasive Global Myocardial Work Index Calculation Improve Exercise Stress Echocardiography?

Abstract

Background: Myocardial work index (MWI) is derived from echocardiographic strain assessment in combination with estimated non-invasive pressure-volume loops. It has been characterised to describe global and regional myocardial work. Aim of the presented study is to evaluate the effect of exercise and ischaemia on global MWI. Method: Patients were retrospectively enrolled from an existing database of exercise stress echocardiography. Inclusion criteria were a clinical indication of possible ischaemia and technical suitability to calculate MWI. Exclusion criteria were abnormal baseline LV function (relevant cardiomyopathy, LVEF <50%, baseline wall motion abnormalities) or poor image quality. Percentage change in global MWI from rest to peak exercise was calculated. Echocardiograms positive for ischaemia were defined by independent visual assessment with matching angiographic findings. Results: 152 patients met inclusion criteria, 17 were excluded for poor image quality and 85 for LV function. 40 normal and 9 positive tests remained for analysis. Mean change in MWI was +54% in normal patients, −4% in ischaemic patients respectively (p = 0.001). ROC curve comparing normal and ischaemic echocardiograms had an AUC of 0.95. The optimal cut off point for a normal test (by index of union method) was a greater than 22% increase in myocardial work (sensitivity 89%, specificity 90%). Conclusion: This pilot study examining global MWI response to exercise shows promising discrimination between ischaemic and normal myocardial responses. This is limited by image quality. Further prospective research with a larger sample is needed.