Combination proximal pulmonary artery coiling and distal embolization induces chronic elevations in pulmonary artery pressure in Swine

Abstract

Pulmonary hypertension (PH) is associated with aberrant vascular remodeling and right ventricular (RV) dysfunction that contribute to early mortality. Large animal models that recapitulate human PH are essential for mechanistic studies and evaluating novel therapies; however, these models are not readily accessible to the field owing to the need for advanced surgical techniques or hypoxia. In this study, we present a novel swine model that develops cardiopulmonary hemodynamics and structural changes characteristic of chronic PH. This percutaneous model was created in swine (n=6) by combining distal embolization of dextran beads with selective coiling of the lobar pulmonary arteries (2 procedures per lung over 4 weeks). As controls, findings from this model were compared with those from a standard weekly distal embolization model (n=6) and sham animals (n=4). Survival with the combined embolization model was 100%. At 8 weeks after the index procedure, combined embolization procedure animals had increased mean pulmonary artery pressure (mPA) and pulmonary vascular resistance (PVR) compared to the controls with no effect on left heart or systemic pressures. RV remodeling and RV dysfunction were also present with a decrease in the RV ejection fraction, increase in the myocardial performance index, impaired longitudinal function, as well as cardiomyocyte hypertrophy, and interstitial fibrosis, which were not present in the controls. Pulmonary vascular remodeling occurred in both embolization models, although only the combination embolization model had a decrease in pulmonary capacitance. Taken together, these cardiopulmonary hemodynamic and structural findings identify the novel combination embolization swine model as a valuable tool for future studies of chronic PH.

Fig 1. Study design and experimental protocol.

Fig 2. Infusion of dextran microspheres (100–300 μm) acutely obstructs pulmonary arteries.

Representative still images from pulmonary artery angiographies obtained at (A) baseline or (B) immediately after embolization of microspheres.

Fig 3. Acute changes in mPA pressure at the time of consecutive weekly embolization procedures.

Hemodynamic assessments were made by right heart catheterization immediately before and after each weekly infusion of dextran microspheres. Animals in the D-Embo group (n = 6) underwent 6 embolization procedures (top) while pigs in the P+D-Embo group (n = 6) underwent 4 procedures (bottom). Changes for individual animals are plotted with the mean for the group shown as a blue line. mPA, mean pulmonary artery, P+D-Embo, proximal and distal embolization group; D-Embo, distal embolization group.

Fig 4. Temporal changes in mPA pressure and PVR index.

The change over time in mPA pressure (top) and PVR index (bottom) measured at each embolization procedure and at the 8 week follow-up examination was evaluated in the P+D-Embo group (n = 6), D-Embo group (n = 6) and sham controls (n = 4). mPA, mean pulmonary artery; PVR, pulmonary vascular resistance; P+D-Embo, proximal and distal embolization group; D-Embo, distal embolization group. Data are reported as mean ± SD, *p<0.05 vs. sham, D-Embo by ANOVA.

Fig 5. Right ventricular fibrosis and hypertrophy.

Myocardial fibrosis was examined in RV sections from the P+D-Embo group (n = 6), D-Embo group (n = 6) and sham controls (n = 4) stained with Masson’s trichrome and quantified as % area fibrosis (top). Cardiomyocyte hypertrophy was evaluated by staining RV sections with wheat germ agglutinin and co-staining with phalloidin to assess cardiomyocyte cross-sectional area (bottom). Representative images are shown for each group. P+D-Embo, proximal and distal embolization group; D-Embo, distal embolization group; RV, right ventricular. *p<0.05 vs. sham, D-Embo by ANOVA.

Fig 6. The combination proximal coiling and distal embolization protocol results in occlusion of pulmonary arteries.

Explanted segments from the right inferior pulmonary artery showing silk coil and fibrin clusters obstructing the vessel lumen with dilation of the vessel. (left) Whole vessel segment explant; (right) cross-section through vessel showing silk suture and fibrin clusters occluding the lumen.

Fig 7. Pulmonary vascular remodeling.

At 8 weeks, lungs were harvested, processed, and stained with Masson’s trichrome to examine pulmonary vascular remodeling. Representative images from A) sham and B-D) embolization models with similar patterns of remodeling, including luminal encroachment and hypertrophic intimal and medial remodeling, were observed for the D-Embo (B, D) and P+D-Embo pigs (C). In selected images (D), microspheres are present in the vessel lumen. There is also extensive perivascular collagen deposition. The distal pulmonary arteries were examined in the periphery of the lung in vessels that were not occluded by beads in sections stained with hematoxylin and eosin. Representative vessels from E) sham, F) D-Embo, and G) P+D-Embo animals are shown. H) Vessel media thickness as an indicator of pulmonary artery remodeling was assessed. P+D-Embo, proximal and distal embolization group; D-Embo, distal embolization group. Scale bars for A, B, C, and D are 60 μm, 100 μm, 60 μm, and 60 μm, respectively. *p<0.05 vs. D-Embo, **p<0.01 vs. sham by ANOVA.