Improving ventricular-arterial coupling during resuscitation from shock: Effects on cardiovascular function and systemic perfusion

Background: Efficacy of circulation depends on interactions between the heart and the vascular system. Ventricular-arterial coupling (VAC) has been described as an important determinant of cardiovascular function during resuscitation from shock. However, no prospective studies examining VAC and systemic perfusion have been performed. VAC is measured by the ratio of afterload (aortic input impedance [E_a]) to contractility (end-systolic elastance [E_es]). Lowering E_a/E_es is associated with better VAC and improved myocardial work efficiency. Our hypothesis was that optimizing VAC during resuscitation results in improved myocardial work efficiency while simultaneously improving systemic perfusion. Methods: This was a prospective study in a consecutive series of critically injured patients. Hemodynamic variables, including E_a, E_es, and myocardial work efficiency were evaluated by constructing ventricular pressure-volume loops at the bedside during resuscitation. After pulmonary artery catheterization and adequate fluid resuscitation, left ventricular power output and E_a/E_es were optimized with inotropic agents and/or afterload reduction. Efficiency was calculated as stroke work/total left ventricular energy expenditure. Tissue perfusion was estimated by calculating base deficit clearance per hour. Results: Twenty-three patients were studied over a 9-month period. Fifteen patients required inotropic support or afterload reduction. Improvements were seen in E_a/E_es (from 1.0 ± 0.4 to 0.6 ± 0.2 mm Hg/mL/m², p = 0.0004), and left ventricular power output (from 280 ± 77 to 350 ± 81 L/min/m²·mm Hg, p = 0.003) with resuscitation. A concomitant improvement in myocardial efficiency (from 70% ± 8.0% to 77% ± 5.0%, p = 0.0001) and base deficit clearance (from 0.1 ± 0.4 to -0.2 ± 0.1 mEq/L/h,p = 0.006) was seen. Conclusion: Improved ventricular-arterial coupling during resuscitation is associated with improved myocardial efficiency and systemic tissue perfusion. Perfusion can be improved at lower energy cost to the heart by focusing on thermodynamic principles during resuscitation.