Acute and Chronic Swine Rete Arteriovenous Malformation Models: Hemodynamics and Vascular Remodeling

Abstract

BACKGROUND AND PURPOSE: An acute and a chronic arteriovenous malformation (AVM) model were developed by using the swine rete to study hemodynamics and vascular remodeling. The models were also used to study in vivo polymerization kinetics and the distribution of various n-butyl 2-cyanoacrylate (NBCA) and Lipiodol mixtures.

METHODS: In the acute swine AVM model, retrograde flow through the left side of the rete was created by the placement of an endovascular shunt through the ipsilateral ascending pharyngeal artery. In the chronic model, flow was redirected retrograde through the left side of rete and ascending pharyngeal artery by creating an arteriovenous fistula between the ipsilateral jugular vein and the common carotid artery. After a period of at least 6 months, the entire head with the rete was connected to a perfusion loop driven by a peristaltic pump. A total of 30 swine were used for both the acute (n = 23) and chronic groups (n = 7). Hemodynamic parameters, including the flow and pressure drop across the rete, were recorded before NBCA embolization. Image processing was used on high-resolution radiographs of the explanted retia to measure the total rete length. Measurements of rete vessel calibers were based on histology.

RESULTS: The pressure gradients across retia were higher in the chronic model than in the acute model, but they did not reach the level of statistical significance (23.7 ± 12.0 mm Hg vs 15.4 ± 1.4 mm Hg). The rete blood outflow was significantly higher in the chronic model compared with the acute one (139.9 ± 100.3 mL/min vs 32.5 ± 17.6; P = .03). The rete length in the chronic model was significantly higher than in the acute model (593.1 ± 39.9 vs 401.3 ± 65.2 pixel; P < .001). The average vessel diameter of the rete in the chronic group was 520 μm and 320 μm in the control animals.

CONCLUSION: Increased pressure gradients and flow in the chronic swine rete AVM model may be related to increased size and decreased impedance. The resulting hemodynamic changes reflect a true flow-induced vascular remodeling rather than a simple change related to aging and size of the animal.