Regional asynchrony in acute ischemia and stunning : an experimental myocardial velocity and strain rate imaging study

• Objective: To quantify motion and deformation asynchrony using Doppler myocardial imaging (DMI) during acute total ischemia, and stunning of the posterior left ventricular wall (PW) in comparison with the interventricular septum (IVS).Methods: Ischemia of the PW was induced in closed-chest pigs using an angioplasty balloon positioned in the circumflex coronary artery. Animals were divided into three groups: normal controls (Group I - n = 6), total ischemia (Group II - n = 8), and stunning (Group III - n = 6) induced by coronary occlusion with distal coronary perfusion maintained via a perfusion catheter coupled to a roller pump (Group III). In addition, a 2-step dobutamine challenge (5 and 10 µg.kg-1 .min-1) was performed in groups I and III. Doppler myocardial velocity and strain rate cineloops were acquired from a parasternal short axis view.Results: The pre-ejection time (T1) and the duration of regional mechanical systole (SYS) became shorter with inotropic stimulation. During total ischemia T1 was prolonged and SYS shortened significantly compared to baseline values [62 ± 14 vs. 55 ± 13 ms (P < 0.05)], [164 ± 13 vs. 240 ± 27 ms (P < 0.001)], respectively. The fraction T1/SYS was accordingly higher. No changes were observed for the contra lateral non-ischemic wall. In group III, the post-ischemic myocardium had a similar response as non-ischemic myocardium to the dobutamine challenge.Conclusion: Consistent changes in local pre-ejection time and regional mechanical systole are induced by intropic stimulation and by total ischemia. However, the response to intropic stimulation did not differ between normal and stunned myocardium.

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