ON VENTRICLE PUMPING EFFICIENCY IN MIXED AORTIC VALVE DISEASE AND A NEED FOR NEW PARAMETERS

Abstract

Aortic stenosis (AS) and aortic regurgitation (AR) are frequently encountered in both pediatric and adult populations. Data on combined AS and AR are however scarce and little is known regarding how to better evaluate patients with mixed aortic valve disease (MAVD). The specific objective of this work is to evaluate in silico the combined volume and pressure overloads on the left ventricle (LV) using a newly developed non-invasive parameter inspired by classical thermodynamic concepts: LV efficiency. A mathematical model has been developed to simulate several combinations of MAVD. We have developed a new non-invasive parameter, LV efficiency, combining the effects of AS and AR on LV function: ELV=(1-Rf)*(Psys/(Psys+TPGmean)), where Rf is the regurgitant fraction, Psys is the systolic arterial pressure and TPGmean is the mean transvalvular pressure gradient. The LV efficiency was evaluated for AS valve effective orifice areas ranging from 0.6 to 3.5 cmˆ2 combined with AR valve effective orifice areas ranging 0 to 0.7 cmˆ2. The simulations have been performed for four different stroke volumes: 50, 60, 70 and 80 ml with a fixed heart rate of 70 bpm and systolic pressure of 120 mmHg. The effect of heart rate (60, 70, 80 and 90 bpm) and systolic pressure (120 and 140 mmHg) on LV efficiency was also evaluated at a fixed stroke volume of 70 ml. Our results show that LV efficiency has a strong nonlinear power law relationship with LV stroke work (Rˆ2=0.81). In healthy simulated cases, LV efficiency was higher than 90%. Very severe cases (severe AS + severe AR) led to LV efficiencies below 20%. Cases with moderate MAVD display a wide variation in LV efficiencies ranging from 61.71% down to 34.36%. Those values were found to be equivalent to LV efficiencies corresponding to severe pure AS simulated cases. We have introduced a new patient-specific non-invasive parameter capable of capturing the combined pressure and volume overloads supported by the LV. This parameter has the potential to unify the decision-making process in patients with aortic valve disease.