Objective : To investigate the effects of dobutamine infusion on left ventriculo-arterial coupling and mechanical efficiency in acutely ischaemic pigs.
Methods : In 12 open-chest pigs, vascular properties were estimated with a windkessel model, while LV function was assessed by the slope (Ees) of end-systolic pressure-volume relationship (ESPVR) and stroke work (SW)–end-diastolic volume (EDV) relation. Ventriculo-arterial (VA) coupling was defined as Ees/effective arterial elastance (Ea), and mechanical efficiency as SW/pressure-volume area (PVA). In both groups, the left anterior descending (LAD) coronary artery was ligated [area at risk: 35 (4) %] after baseline. While group CTRL (n = 6) was followed for 180 minutes without further intervention, group DOBU (n = 6) was infused with dobutamine (5 mg kg-1 min-1) at T90 and onwards.
Results : In both groups, coronary occlusion induced a rightward shift of ESPVR, a decrease in Ees from 3.67 (0.33) to 1.92 (0.20) mmHg.ml-1 (p<0.001), and in the slope of the SW–EDV relation from 72.3 (3.4) to 40.4 (4.5) mmHg (p<0.001). In contrast, Ea increased from 3.33 (0.56) to 4.65 (0.29) mmHg.ml-1 (p<0.005), while peripheral resistance (R2) increased from 1.72 (0.30) to 2.38 (0.16) mmHg.sec.ml-1 (p<0.05) and compliance (C) decreased from 0.78 (0.16) to 0.46 (0.08) ml.mmHg-1 (p<0.05). VA coupling decreased from 1.22 (0.11) to 0.44 (0.07) (p<0.001) and SW/PVA from 0.76 (0.04) to 0.57 (0.03) (p<0.001). In group DOBU, Ees, position of ESPVR and slope of SW–EDV relation were restored to basal conditions. In the same interval, Ea decreased to 3.82 (0.34) mmHg.ml-1 (p<0.01), due to R2 decrease to 1.88 (0.24) mmHg.sec.ml-1 (p<0.05) while C was unaffected by dobutamine. VA coupling was also restored but SW/PVA remained impaired.
Conclusion : In acutely ischaemic pigs, dobutamine infusion restored left ventriculo-arterial coupling through an increase in left ventricular contractility and a decrease in arterial elastance, due to peripheral vasodilatation. However, myocardial oxygen consumption is increased and efficiency remained impaired. In a time of reduced oxygen supply, the implication is of greater ischemic damage in the long term.