Quantitation of regional myocardial function during short-lived events with ultrasound imaging

Short-lived (tens through hundreds of milliseconds) cardiac motion events, such as post-systolic thickening, have diagnostic importance and are detectable by echocardiography. Selection and quantitative analysis of these events cannot be adequately done using conventional clinical measurements of heart function. We have developed an interactive tool using MATLAB (The MathWorks, Inc., Natick, MA) that allows the user to select events in time from graphs of available data including ECG, strain, left ventricular (LV) pressure, and the time derivative of the LV pressure trace. After selection of an event in time, the program calculates the area for that section of a pressure-strain loop, which is known to correlate to myocardial contraction work. Using the new tool, we present data from a canine model of prolonged (1-2 week) local myocardial ischemia. We found that following ischemia, a proportion of the loop area in the affected cardiac muscle takes place during a postejection phase. That is, the muscle contracts but during the postejection (post-systolic) phase and hence no longer contributes to ejecting blood to circulation.