A model of ischemic mitral regurgitation in pigs with three-dimensional echocardiographic assessment

Ischemic mitral regurgitation (IMR), the incidence of which is increasing, results from annular and subvalvular remodeling after myocardial infarction (MI). Although a sheep model of IMR has been used extensively over the past two decades, the ventricular, coronary and leaflet anatomy in sheep is significantly different from that in humans. In contrast, pigs are more similar to humans with regard to these parameters, and therefore may serve as a better animal to test emerging new technologies designed to treat IMR.

Twenty-nine pigs (body weight 30-35 kg) underwent left thoracotomy and ligation of the mid main circumflex and distal right posterior descending coronary arteries to create a posterolateral MI. Of these pigs, 18 were used for acute data acquisition, while 11 surviving animals in the chronic group were assessed at eight weeks after MI. Real-time three-dimensional echocardiography was performed at baseline, and at 30 min and eight weeks after MI, to assess geometric changes in the mitral annulus, mitral leaflets and left ventricle.

Compared to baseline, the MR grade was increased significantly at eight weeks (0.7 + 0.5 versus 2.0 +/- 1.2), together with a significant decrease in left ventricular ejection fraction (40.3 +/- 6.6% versus 25.8 +/- 7.7%). Significant increases were also noted at eight weeks in the commissural width (30.1 +/- 3.2 mm versus 35.1 +/- 2.9 mm) and septolateral diameter (25.0 +/- 2.0 mm versus 33.8 +/- 5.9 mm), with a resultant increase in mitral annular area (596 +/- 85 versus 931 +/- 181 mm3) and a decrease in the annular height to commissural width ratio (15.7 +/- 2.6% versus 13.7 +/- 1.9%). The mitral valve tenting volume was also increased significantly (1577 +/- 645 versus 2440 +/- 755 mm3). The distance between the papillary muscle tips at baseline and at eight weeks was increased significantly (23.9 +/- 2.5 versus 30.9 +/- 5.2 mm), as was the distance between the posterior papillary muscle tip and the posterior commissure (20.9 +/- 2.7 versus 24.1 +/- 2.8 mm).

The surgical model described here reliably replicates the changes seen in humans with IMR. Hence, this model can be used for further studies of the pathophysiology of IMR, and of any novel interventions in this challenging clinical area.