In the present study, we sought to investigate the effects of differing inotropic conditions on regional myocardial function in ischaemic segments. In an experimental pig model (n=11), the regional deformation parameters peak systolic strain rate [SRSYS (peak velocity of thickening)], systolic strain [εSYS (systolic wall thickening)] and post-systolic strain [εPST (ongoing wall thickening after end of systole)] were measured during normal perfusion and regional ischaemia of the posterior wall. These parameters were compared with global contractility [EES (end-systolic elastance)] measured by a conductance catheter. Ischaemia was induced by an active coronary hypoperfusion in the circumflex coronary artery. Measurements were done at baseline, during dobutamine and during esmolol infusion. In normal perfused hearts, SRSYS (4.8±0.2 s-1 at baseline) increased during dobutamine infusion, decreased during esmolol infusion and correlated significantly with global EES. In addition, εSYS averaged 93±3% at baseline and there was almost no εPST (4±1%) in normal myocardium. In ischaemic myocardium, SRSYS and εSYS were significantly reduced compared with normal myocardium at baseline (SRSYS=2.8±0.3 s-1, and εSYS=43±6%; P<0.001 compared with normal perfused hearts), whereas global EES was unchanged. In contrast, εPST was significantly increased in regional ischaemic segments compared with the non-ischaemic myocardium (15±2%; P<0.001). During the dobutamine infusion, SRSYS remained unchanged. In contrast, εSYS decreased (25±5%; P<0.001) and εPST increased (25±4%; P<0.05) significantly during dobutamine infusion in ischaemic myocardium. In ischaemic segments, an inotropic stimulation with dobutamine resulted in a shift of strain from systole (εSYS) to post-systole (εPST). Thus dobutamine induced ineffective myocardial work in ischaemic segments.

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