Dobutamine induces ineffective work in regional ischaemic myocardium: an experimental strain rate imaging study

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 [SR_SYS (peak velocity of thickening)], systolic strain [ε_SYS (systolic wall thickening)] and post-systolic strain [ε_PST (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 [E_ES (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, SR_SYS (4.8±0.2 s^-1 at baseline) increased during dobutamine infusion, decreased during esmolol infusion and correlated significantly with global E_ES. In addition, ε_SYS averaged 93±3% at baseline and there was almost no ε_PST (4±1%) in normal myocardium. In ischaemic myocardium, SR_SYS and ε_SYS were significantly reduced compared with normal myocardium at baseline (SR_SYS=2.8±0.3 s^-1, and ε_SYS=43±6%; P<0.001 compared with normal perfused hearts), whereas global E_ES was unchanged. In contrast, ε_PST was significantly increased in regional ischaemic segments compared with the non-ischaemic myocardium (15±2%; P<0.001). During the dobutamine infusion, SR_SYS remained unchanged. In contrast, ε_SYS decreased (25±5%; P<0.001) and ε_PST 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 (ε_SYS) to post-systole (ε_PST). Thus dobutamine induced ineffective myocardial work in ischaemic segments.