Background: Tissue Doppler imaging (TDI) is a potentially powerful method for diagnosing myocardial ischemia. This study was designed to investigate how velocity patterns in ischemic myocardium relates to regional function, and to determine whether timing of velocity measurements relative to ejection and isovolumic phases may increase the diagnostic power of TDI.
Methods and results: In 17 open-chest anesthetized dogs we measured pressures by micromanometers, myocardial longitudinal segment lengths by sonomicrometry, and velocities by TDI. Myocardial longitudinal strain rate was calculated as velocity divided by distance to the left ventricle apex. Moderate ischemia (left anterior descending coronary artery stenosis) caused parallel reductions in regional systolic shortening by sonomicrometry (P<0.05) and in peak systolic velocities by TDI (P<0.05). Severe ischemia (left anterior descending coronary artery occlusion), however, induced systolic lengthening by sonomicrometry (P<0.001), whereas peak TDI velocity during ejection remained positive (P<0.05). When velocities during isovolumic contraction (IVC) and isovolumic relaxation (IVR) were included, TDI correlated well with sonomicrometry; ie, systolic lengthening occurred predominantly during IVC and was evident as negative velocities (r=0.70, P<0.001), and postsystolic shortening during IVR (r=0.72, P<0.001) as positive velocities. In nonischemic myocardium peak systolic strain rates were more uniform than velocities.
Conclusion: The present results indicate that peak ejection velocity is an inappropriate measure of function in severely ischemic myocardium. Dyskinetic myocardium deforms predominantly during the isovolumic phases, and therefore IVC and IVR velocities are better markers of function. When isovolumic as well as ejection velocities are measured, TDI has excellent ability to quantify regional myocardial dysfunction. Longitudinal strain rates are more uniform than velocities and may further improve the diagnostic power of TDI.