Background and objectives: Detection of myocardial ischemia in humans by strain Doppler and tissue velocity imaging was validated in a novel, experimentally designed study model during coronary bypass operation of the beating heart.
Methods: Assessment of ischemia was made with an opened chest and pericardium inherent in the operative procedure. Longitudinal strain and tissue velocity of interventricular septal regions were measured by transesophageal echocardiography during occlusion of the left anterior descending coronary artery (LAD).
Results: Unexpectedly, baseline velocities demonstrated that the apical and basal septum moved toward each other during systole. This occurred when the apex was dislodged from the pericardial sac to obtain access to the LAD, without any change in strain. The preceding motion of all septal regions toward the apex was reestablished after the heart was repositioned within the pericardium. In 16 patients with antegrade LAD flow, strain Doppler detected ischemia during LAD occlusion by disclosing systolic lengthening of the apical septum ( P <.01) and reduced shortening of the mid septum ( P <.05). The location and degree of ischemic changes coincided with the concomitant deterioration of wall motion. Tissue velocity changed in the basal and mid septum ( P <.05) but not in the apical region, explained by tethering effects and the distinctive motion pattern at baseline. There was no evidence of ischemia by invasive hemodynamic measures. In 7 patients with retrograde LAD flow, there were no significant changes in strain or tissue velocity measurements during LAD occlusion.
Conclusions: Strain by Doppler is a sensitive means for detecting myocardial ischemia, also capable of correctly localizing the ischemia, as opposed to tissue velocity assessment. However, velocity measurements provided new physiological information by disclosing the normal longitudinal motion of the heart to be dependent on the pericardial sac enveloping the apex, irrespective of the structural integrity of the pericardium.