Assessment Of Right Ventricular Function By Pressure-Volume Loops In Off-Pump Coronary Artery Bypass Surgery

Objective Right ventricular function plays an important role in the hemodynamic derangement during off-pump coronary artery bypass (OPCAB) surgery. Pressure-volume loops have been shown to provide load-independent information of cardiac function. Therefore, the aim of this study is to investigate the feasibility of construction of right ventricular pressure-volume loops with pressure and volume data measured by a volumetric pulmonary artery catheter (PAC) and to evaluate right ventricular systolic and diastolic function by end-systolic elastance (Ees) and end-diastolic stiffness (EED) in OPCAB surgery.Methods Twenty-eight patients who underwent OPCAB surgery were included. After anesthesia induction, a volumetric PAC was placed via the right internal jugular vein. Data were recorded at: anesthesia steady-state before skin incision (T1); 5min after stabilizer device placed for anastomosis of the heart's anterior wall (T2), lateral wall (T3), posterior wall (T4), respectively; after sternal closure (T5). Three sets of data were collected at each time point: firstly, hemodynamic variables were measured; secondly, right ventricular end-systolic elastance (Ees) was estimated by end-systolic pressure divided by end-systolic volume, and end-diastolic stiffness (EED) was estimated by end-diastolic pressure divided by end-diastolic volume; thirdly, right ventricular pressure-volume loops were constructed with pressure and volume data measured from end-diastole point, end-isovolumic systole point, peak-ejection point, end-systole point and end-isovolumic diastole point.Results Right ventricular pressure-volume loops were constructed successfully with pressure/volume data measured from several specific time-points by a volumic PAC, and they generally shifted to the left during OPCAB surgery. Especially, shift upward and to the left in end-diastole point indicated that right ventricular passive relaxation properties were impaired compared with that at T1. The change of Ees was not statistically significant during operation (P>0.05), whereas EED increased throughout the OPCAB surgery (P<0.05). Decrease in right ventricular ejection fraction, stroke volume index and end-diastolic volume index occurred (P<0.05) at T4 compared with values at T1. Pulmonary vascular resistance index at T4 increased relatively compared with that at T2 and T3. Right atrial pressure increased only during coronary anastomoses (P<0.05)Conclusion Right ventricular pressure-volume loops can be constructed and Ees and EED can be estimated using a volumetric PAC. Right ventricular systolic dysfunction occurred during anastomoses on the heart's posterior wall not due to impaired contractility but as a result of reduced stroke volume and preload and a relative increase in afterload. Right ventricular diastolic function was impaired throughout OPCAB surgery.