Morphofunctional Abnormalities of Mitral Annulus and Arrhythmic Mitral Valve Prolapse

Abstract

Background: Arrhythmic mitral valve prolapse (MVP) is characterized by myxomatous leaflets and left ventricular (LV) fibrosis of papillary muscles and inferobasal wall. We searched for morphofunctional abnormalities of the mitral valve that could explain a regional mechanical myocardial stretch.

Methods and results: Thirty-six (27 female patients; median age: 44 years) arrhythmic MVP patients with LV late gadolinium enhancement on cardiac magnetic resonance and no or trivial mitral regurgitation, and 16 (6 female patients; median age: 40 years) MVP patients without LV late gadolinium enhancement were investigated by morphofunctional cardiac magnetic resonance. Mitral annulus disjunction (median: 4.8 versus 1.8 mm; P<0.001), end-systolic mitral annular diameters (median: 41.2 versus 31.5; P=0.004) and end-diastolic mitral annular diameters (median: 35.5 versus 31.5; P=0.042), prevalence of posterior systolic curling (34 [94%] versus 3 [19%]; P<0.001), and basal to mid LV wall thickness ratio >1.5 (22 [61%] versus 4 [25%]; P=0.016) were higher in MVP patients with late gadolinium enhancement than in those without. A linear correlation was found between mitral annulus disjunction and curling (R=0.85). A higher prevalence of auscultatory midsystolic click (26 [72%] versus 6 [38%]; P=0.018) was also noted. Histology of the mitral annulus showed a longer mitral annulus disjunction in 50 sudden death patients with MVP and LV fibrosis than in 20 patients without MVP (median: 3 versus 1.5 mm; P<0.001).

Conclusions: Mitral annulus disjunction is a constant feature of arrhythmic MVP with LV fibrosis. The excessive mobility of the leaflets caused by posterior systolic curling accounts for a mechanical stretch of the inferobasal wall and papillary muscles, eventually leading to myocardial hypertrophy and scarring. These mitral annulus abnormalities, together with auscultatory midsystolic click, may identify MVP patients who would need arrhythmic risk stratification.

Keywords: gadolinium; mitral valve; mitral valve annulus; mitral valve prolapse; papillary muscles.

Figure 1.

Cardiac magnetic resonance measures in patients with mitral valve prolapse. A, On 3-chamber, long-axis view, the length of mitral annulus disjunction (MAD; continuous white line) is measured from the left atrial (LA) wall–posterior MV leaflet junction to the top of the left ventricular (LV) inferobasal wall during end systole. B, On the same systolic frame, the prolapsed distance is measured as the maximum distance of the leaflet beyond the mitral annulus (white arrows). C, The LV thickness of basal and mid segments of the inferolateral wall is measured in the same long-axis view on diastole. D, The quantitative assessment of curling (white arrow) is provided by tracing a line between the top of LV inferobasal wall and the LA wall–posterior MV leaflet junction, and from this line, a perpendicular line to the lower limit of the mitral annulus during end systole.

Figure 2.

Representative case of arrhythmic mitral valve prolapse with mitral annular disjunction, curling, and late gadolinium enhancement (LGE). A 36-y-old woman with mitral valve prolapse and complex ventricular arrhythmias. On cine cardiac magnetic resonance (CMR) 3-chamber, long-axis view (diastolic frame A, systolic frame B), a mitral annulus disjunction is detectable; on contrast-enhanced CMR, a midmural LGE in the LV inferobasal region under posterior valve leaflet is visible (C). The 12-lead ECG (D) shows a negative T wave in III-aVF. Nonsustained ventricular tachycardia with right bundle branch block morphology originating from the LV inferobasal wall near the mitral annulus is also recorded in the 24-h Holter ECG (E).

Figure 3.

Relationship between length of mitral annular disjunction and curling in vivo. A significant correlation (R=0.85) between the depth of curling and length of mitral annulus disjunction (MAD; both expressed as mm) on cardiac magnetic resonance is observed. LGE indicates late gadolinium enhancement.

Figure 4.

Relationship between length of mitral annular disjunction and amount of late gadolinium enhancement in vivo. A significant correlation (R=0.61) between the length of mitral annulus disjunction (MAD; expressed as mm) and the amount of late gadolinium enhancement (LGE; expressed as percentage of left ventricular [LV] mass) on cardiac magnetic resonance is observed.

Figure 5.

Length of mitral annular disjunction (MAD) in sudden cardiac death (SCD) patients: controls vs mitral valve prolapse (MVP) patients. The length of MAD (measured as micrometers) in SCD patients with MVP is significantly higher than in controls (A). Representative histology of the mitral annulus showing the absence of MAD in a SCD control (B) as compared with an elongated MAD in a SCD patients with MVP (C).