Right ventricular (RV) dysfunction is an important cause of perioperative morbidity and mortality, particularly in cardiac surgery. However, assessment of RV contractility remains difficult in clinical practice. Our goal in this study was to examine the value of preload-adjusted maximal power (PWR(max)/end-diastolic volume [EDV](2); PAMP) as an alternative to the load-independent pressure-volume-derived indices of contractility in the RV. In anesthetized dogs, RV end-systolic elastance and preload-recruitable stroke work were studied as "gold standards" by using the conductance technique. PAMP was calculated with pulmonary artery flow and RV pressure measurements. Changes in these indices were compared after modulation of the inotropic state (dobutamine infusion; n = 12) and loading conditions (pulmonary artery and inferior caval vein occlusion; n = 14). All indices increased dose-dependently with dobutamine. PAMP was slightly influenced by preload reduction (the slope of the relation between PAMP and EDV was 0.00397 +/- 0.01026 W. mL(-3). 0.10(-4); mean +/- SD). PAMP decreased significantly during pulmonary artery banding (from 1.1 +/- 0.7 to 0.7 +/- 0.5 W. mL(-2). 0.10(-4); mean +/- SD), whereas end-systolic elastance and preload-recruitable stroke work did not change. We conclude that the value of PAMP as an index of RV contractility is limited in the open-chest/open-pericardium setting, primarily by its sensitivity to alterations in afterload.
Implications: Preload-adjusted maximal power (PAMP), a load-independent contractile index in the left ventricle, could offer a solution to the problem of measuring right ventricular (RV) contractility in clinical practice. However, this study in open-chest dogs suggests that PAMP is unreliable for assessment of RV contractility because of its sensitivity to afterload changes.