How can we prevent functional mitral stenosis after surgery?

To the Editor:

The recent report by Kubota and colleagues1 gave new insight on the mechanism of “functional mitral stenosis (MS)” after mitral annuloplasty (MAP) for ischemic mitral regurgitation (IMR). Persistent subvalvular leaflet tethering in the presence of down-sized MAP causes functional MS, which is related to heart failure symptom after surgery. Down-sized MAP has been a standard procedure for IMR and believed to be safe and effective for 10 years. In 2008, Magne and colleagues2 first reported functional MS after MAP. However, its mechanism was not clarified in this study. On the other hand, Kubota and colleagues examined subvalvular apparatus during exertion and indicated that not only MAP but also further mitral tethering causes functional MS. This study has a considerable impact on the surgical strategy for IMR in the future.

In 2003, we developed mitral complex reconstruction, which consists of MAP, papillary muscle (PM) approximation,3 and (since 2005) suspension (PMS),4 and have aggressively adopted this procedure for patients with heart failure and functional mitral regurgitation. In PMS, we place a subvalvular expanded polytetrafluoroethylene (ePTFE) suture between the site of the chordal attachment of the approximated PM and the mitral annulus. We considered that posterior PMS, in which ePTFE suture is sewn to the middle of the posterior annuloplasty ring, causes further anterior mitral valve tethering in diastole. Therefore, we recently changed from posterior to anterior PMS, in which ePTFE suture is sewn to the middle of the anterior annuloplasty ring. Table 1 shows the postoperative transmitral gradients and mitral complex parameters (n = 8, for each group). The left ventricular (LV) inflow line was measured using Doppler color flow mapping at the time of maximal early diastolic rapid filling by an apical long-axis view. The angle between this line and the annulus was measured as the LV inflow angle. PM angles were also measured with the line between the tip of the PM and the septal side (anterior) or posterior side (posterior) of mitral annulus in end diastole. LV inflow angle was significantly larger and posterior PM angle was significantly smaller in the anterior PMS group. Mitral peak pressure gradient was significantly smaller in the anterior PMS group (5.8 ± 1.9 mm Hg) than in the posterior PMS group (10.0 ± 2.6 mm Hg), which is comparative to that of Kubota and colleagues' report1 (10.6 ± 6.2 mm Hg).

Table 1. Postoperative transmitral gradient and mitral complex parameters

		Posterior PMS	Anterior PMS	P value
	E (m/s)	1.6 ± 0.2	1.2 ± 0.2	.004
	Peak pressure gradient (mm Hg)	10.0 ± 2.6	5.8 ± 1.9	.004
	Papillary muscle angle (anterior)	47 ± 10	55 ± 8	.131
	Papillary muscle angle (posterior)	106 ± 10	93 ± 12	.042
	Left ventricular inflow angle	60 ± 6	78 ± 9	<.001
	Stroke volume index (mL/m2)	28 ± 5	37 ± 11	.054

PMS, Papillary muscle suspension to annuloplasty ring. Values ± standard deviation.

Although our parameters are different from those of Kubota and colleagues' report,1 LV inflow and PM angles would correspond well to the parameters determining mitral valve tethering in their report. We consider that mitral valve tethering during diastole could be ameliorated by anterior PMS, which can relocate the PM toward the septal side of the ventricle but not the posterior side. Langer and colleagues5 recently reported a better mitral regurgitation recurrence rate with a subvalvular procedure termed “RING + STRING.” We should further examine the relationship between these subvalvular procedures and functional MS after operation.