Jianwen Wang

Delayed Onset of Subendocardial Diastolic Thinning at Rest Identifies Hypoperfused Myocardium

Background—Onset of myocardial relaxation is highly energy dependent. Perfusion and therefore energy substrate delivery are predominantly reduced in the subendocardial myocardium in the early stages of progressive ischemia. We hypothesized that delayed onset of subendocardial diastolic thinning will functionally identify regionally hypoperfused resting myocardium. Methods and Results—Progressive left anterior descending coronary artery stenosis was induced by an ameroid occluder and maintained for 1 or 2 weeks (end point) in 12 dogs. M-mode tissue Doppler images of the anterior apical and middle segments (testing region) and middle inferior segment (control region) were acquired selectively in the subendocardium and subepicardium. The time to the onset of thinning was measured with the use of tissue Doppler velocity (TOTv) and a thickness function (TOTt). At the end point in the testing region, myocardial flow was significantly lower in the subendocardial layer (P<0.05) in all animals, whereas viability staining showed preserved transmural viability in 10 dogs and thin subendocardial necrosis in 2 dogs. Both TOTv and TOTt were significantly (P<0.01) prolonged in the testing region. The mean difference between subendocardial and subepicardial TOTv values versus that in the control region identified the ischemic region, even when only dogs with hypoperfused but transmurally viable myocardium were considered (P<0.05). Systolic and diastolic myocardial velocities did not identify subendocardial hypoperfusion. Conclusions—In resting myocardium subtended to progressive coronary stenosis, a delayed onset of subendocardial thinning suggests an early stage of hypoperfusion, before the development of local wall motion abnormalities.

Doppler Strain Imaging Closely Reflects Myocardial Energetic Status in Acute Progressive Ischemia and Indicates Energetic Recovery After Reperfusion

BACKGROUND Capitalizing on mechanoenergetic coupling, we investigated whether strain echocardiography can noninvasively estimate the ratio of adenosine triphosphate (ATP) to adenosine diphosphate (ADP), a marker of energetic status during acute myocardial ischemia and reperfusion. METHODS Twenty-eight pigs were divided into 7 groups (1 baseline, 4 ischemic, and 2 reperfusion). Ischemia was induced by left anterior descending coronary artery occlusion. Longitudinal systolic lengthening (SL) and postsystolic shortening (PSS) strain were measured by echocardiography. The ATP/ADP ratio was obtained from myocardial biopsies in the ischemic and control regions. RESULTS SL and PSS strain and the ATP/ADP ratio progressively decreased (P < .05) with increased duration (12, 40, 120, and 200 minutes) of ischemia. A mathematical formula (ATP/ADP = -0.97 + 0.25 x PSS strain + 0.20 x SL strain) estimated best the ATP/ADP ratio (r = 0.94, P < .05). Reperfusion after 12 but not after 120 minutes of ischemia significantly improved the ATP/ADP ratio and decreased SL and PSS strain. CONCLUSIONS Strain echocardiography closely reflected changes and enabled the noninvasive estimation of the ATP/ADP ratio. A higher ATP/ADP ratio is associated with functional improvement after reperfusion.

Direct Identification of Subendocardial Postsystolic Thickening by Intracardiac M-Mode Doppler Echocardiography

Figure 1. Intracardiac images of apical anterior (i.e., testing) wall in an experimental dog. A and B, M-mode gray scale and Doppler tissue images, respectively; C and D, M-mode gray scale and Doppler tissue images, respectively, from the same region after 2 weeks of experimentally induced stenosis of the left anterior descending coronary artery. The presence of additional motion towards the intracardiac transducer after systole suggests the occurrence of postsystolic thickening (PST). Progressive coronary stenosis1 was induced by ameroid placement on the left anterior coronary artery in two female dogs. A permanent catheter was placed in the left atrium to allow

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.