Left Ventricular Unloading in Chronic Ovine Biventricular Failure with Functional Tricuspid Regurgitation

M. Lucyna. Piekarska¹, M. Gaddam², M. Malinowski³, T. Jazwiec⁴, M. Rausch⁵, B. Gaweda⁶, T. Timek^7
1Division of Cardiothoracic Surgery, Department of Cardiovascular Research, Corewell Health, Grand Rapids, Michigan, USA, Grand Rapids, Michigan ²Research Department, Meijer Heart and Vascular Institute at Spectrum Health; Department of Urology, Stanford University School of Medicine, Stanford, California ³Department of Cardiac Surgery, Medical University of Silesia, School of Medicine in Katowice, Katowice, Poland, Katowice, Slaskie ⁴Department of Cardiac, Vascular and Endovascular Surgery and Transplantology, Silesian Centre for Heart Disease, Medical University of Silesia in Katowice, Zabrze, Poland, Zabrze, Slaskie ⁵Aerospace Engineering & Engineering Mechanics, The University of Texas at Austin, USA, austin, Texas ⁶Division of Cardiothoracic Surgery, Corewell Health, Grand Rapids Michigan, USA, Department of Cardiac Surgery, Clinical District Hospital No. 2, Faculty of Medicine University of Rzeszow, Rzeszow, Poland, Grand Rapids, Michigan ⁷Division of Cardiothoracic Surgery, Corewell Health, Michigan State University College of Human Medicine, Grand Rapids, MI, USA, Grand Rapids, Michigan

Purpose: Right ventricular (RV) failure and functional tricuspid regurgitation are frequently associated with left ventricular (LV) assist device implantation. Whether this is due to altered myocardial performance or RV geometry remains unclear. We set out to investigate effect of acute LV unloading on RV subvalvular geometry in ovine biventricular heart failure.

Methods: Seven healthy Dorset adult male sheep (58 ± 4kg) underwent left thoracotomy and pacemaker implantation with an epicardial lead. Animals were paced at 220-240 beats/min (22 ± 7days) until development biventricular dysfunction and functional tricuspid regurgitation. Subsequently with pacemaker paused, animals underwent sternotomy and cardiopulmonary bypass (CPB) for implantation of sonomicrometry crystals around the tricuspid annulus (6), on each papillary muscle tip (3), and on RV epicardium (14). After weaning from CPB, continuous flow left ventricular assist device was implanted by inserting a drainage cannula in the left atrial appendage and using CPB carotid cannula as return. Simultaneous hemodynamic, sonomicrometry, and echocardiographic data were acquired before (Baseline) and after full LV unloading (LVAD; 3.9±0.2l/min) for 10 minutes. RV volume, tricuspid annular area and perimeter, papillary muscle area, and distance between papillary muscle tips and the annular plane were calculated from 3D crystal coordinates (Figure 1).

Results: Pacing resulted in significant increase in LV end-diastolic dimension (3.8±0.4 vs 4.7±0.5 cm, p=0.01), tricuspid annular size (2.5±0.3 vs 3.4±0.6 cm, p=0.013), and tricuspid (+0±0 vs +2.9±0.9, p=0.001) and mitral (+0±0 vs +2.0±0.8, p=0.006) regurgitation. There was a significant reduction in LV ejection fraction (60±6 vs 34±11% , p=0.002) and RV fractional area contraction (56±8 vs 38±12%, p=0.001). These changes are reflective of clinical findings in patients presenting for mechanical support. Heart rate (116±15 vs 111±22b/min, p=0.15), central venous pressure (14±8 vs 17±9, p=0.18) and RV end-diastolic volume (181±42 vs 178±40ml, p=0.41) did not change from Baseline to LVAD but systolic right ventricular pressure increases significantly (30±11 vs 38±9mmHg, p=0.01). Sonomicrometry based measurements of annular and subvalvular geometry are summarized in Table 1. Inter-papillary muscle distances and papillary muscle area increased significantly without changes in the distance of each papillary muscle tip to the tricuspid annular plane. The septal region of the tricuspid annulus tended to increase at end-diastole during unloading (43.1 ± 5.0 mm to 44.3 ± 4.6mm, p=0.088) while the anterior and posterior regions remained unaltered. Tricuspid regurgitation did not change during LVAD unloading (3.0±1.0 and 3.6±0.8 for CTL and LVAD, respectively; p=0.17).

Conclusion: Left ventricular unloading in an ovine model of biventricular failure with tricuspid regurgitation was associated with increased inter-papillary distances and papillary muscle area most likely due to septal shift. These geometric alterations in subvalvular geometry may contribute to valvular insufficiency and right ventricular failure over time.

Identify the source of the funding for this research project: This work was supported by internal grant from Meijer Heart and Vascular Institute at Spectrum Health.