Invasive and non-invasive evaluation of the right ventricle mechanical performance in an acute open chest porcine model of progressive right-ventricular pressure-overload

The assessment of the right ventricle (RV) mechanical performance during open chest surgery is still based on invasive cardiac catheterization, transesophageal echocardiography, and the subjective evaluations of surgeons and anesthesiologists. Very few studies have tried to exploit the visibility of the RV by extrapolating kinematic parameters from videos. In this study, we established a porcine model of acute RV dysfunction with the aim to investigate the underlying hemodynamic alterations in open chest surgery. Then, we conducted a proof-of-concept experiment in one pig to test the validity of the 3D-video kinematic assessment of the Videocardiograph (VCG) against hemodynamics. 

Seven healthy Landrace pigs were acutely instrumented closed-chest under fluoroscopic guidance with a Swan-Ganz and a RV conductance catheter. Following a median sternotomy, the heart was suspended in a pericardial cradle. After baseline measurements, we performed two steps of surgical pulmonary artery banding (PB) to achieve both minimum and maximum degree of acute RV pressure overload (PB_min and PB_max, respectively), defined as an increase of the end-systolic pressure (Pes) compared to baseline value < or ≥ 25%. A proof-of-concept experiment was conducted in one pig to achieve and characterize intermediate steps of PB as well. For that, videos of the RV were recorded with the VCG to calculate epicardial kinematic parameters. Additionally, videos acquired for this experiment were eye-balled by five senior consultant surgeons to test whether direct visual assessment of the RV function and filling status holds any clinical value.

Results: 

A progressive pressure-overload was achieved in the study group upon surgical PB, as showed by a significant Pes increase at PB_max compared to baseline (from 21.17±3.31 mmHg to 39.85±7.82 mmHg, p=0.001). This was accompanied by a geometrical remodeling of the RV with dilation, i.e. increased end-systolic volume and depressed RV Ejection Fraction compared to baseline (52.80 ± 10.36% vs 33.99 ± 9.88, p= 0.012). In line with that, a progressive increase of ventricular potential and kinetic energy (pressure-volume area) upon PB were detected, leading to a compromised myocardial efficiency. In the proof-of-concept experiment, we found that the absolute agreement between the hemodynamics and the subjective evaluation of both RV function and filling status was poor (ICC=0.343; ICC=0.265, respectively). The relationship of VCG-derived parameters of epicardial RV kinematics with the RV PV-loops showed excellent non-linear and linear relationships for both z-axis systolic and diastolic displacements and for the systolic time. 

We successfully established a model of progressive RV pressure-overload combined with accurate pressure-volume loops assessment in Landrace swine. While the clinical subjective evaluation of the RV was not reliable in assessing acute afterload changes induced by PB, the epicardial kinematic evaluation of the VCG was able to provide quantitative data on the RV mechanical activity, showing promising relationships with the gold-standard, pressure-volume assessment. Epicardial kinematic assessment in is a non-invasive and cost-effective promising tool for early detection of acute RV dysfunction in the operating room and merits further clinical investigation.