• arrhythmias
• Mitral valve prolapse
• degenerative Mitral regurgitation
• Mitral valve
• curling

Background: Systolic curling motion is an anomalous excessive end-systolic movement of the posterolateral mitral annulus (MA) downward, outward, and partially anteriorly. This results in an apparent inward excursion of the adjacent posterobasal wall of the left ventricle (LV), resulting in a curling. First described by Gilbert et al. in patients with mitral valve prolapse (MVP), through mechanical stretch, it might promote fibrosis, and hypertrophy of the LV inferobasal walls and papillary muscles (PMs), as well as the genesis of arrhythmias now described as Arrhythmic Mitral Valve Prolapse (AMPV). It remains a poorly understood phenomenon and, no reliable methods to assess and quantify it have been proposed in the last 40 years. As already described, to further evaluate it we previously developed and tested a transthoracic echocardiographic (TTE) quantification methodology defined as Mitral valve annulus to Inferobasal wall Rotation Angle (MIRA). MIRA was firstly validated in a group of patients who underwent MV repair for degenerative mitral regurgitation (DMR) showing that the angle changed after surgery, and then the normal MIRA value was defined in a group of healthy subjects. However, its incidence and role in patients with DMR is still unclear.
The aim of the present study is to evaluate curling magnitude in patients with DMR using MIRA. Our secondary aim is to find any possible variable that might influence curling severity.

Methods: We retrospectively analysed TTE datasets of patients with any grade of DMR, who had access to the Cardiac Surgery Unit - University of Pisa outpatient clinic between January 2022 and July 2023. Baseline demographic and echocardiographic data were collected. A dynamic full-cycle eyeball assessment was conducted to determine the presence or absence of systolic curling in a TTE parasternal long-axis (PLAX) view. After that, MIRA was measured at end-systole in the same PLAX, as the angle included between the line perpendicular to the LV posterobasal wall along long axis, from epicardium (A) to endocardium (B) – at the level of anterior mitral leaflet (AML) tip – and the line connecting B to the insertion of the posterior mitral leaflet (PML) to the MA. The mean value of three measurements was calculated; measurements were performed offline with dedicated software by the same operator (FT) and blindly validated by an experienced echocardiographer (GSF). Mean and median MIRA were calculated and categorized by percentiles for two groups of patients according to MR grade: mild-moderate and severe. Continuous and categorical variables were compared using one-way ANOVA and Chi-square tests respectively and a multiple linear regression model was finally performed. The P-value was set at 0.06.

Results: One-hundred-twenty-one patients were included. Seventy (57.8%) patients had mild-moderate (not-severe) MR while fifty-one (42.2%) had severe MR. In patients with not-severe MR mean MIRA was 71.7°±8.8° (95% CI 69.6°-73.8°), median value was 72.5°, I quartile was 68° and III quartile was 77°. In patients with severe MR mean MIRA was 59.8°±11.9° (95% CI 56.3°-63.2°), median value was 58°, I quartile was 50° and III quartile was 68°. In the not-severe group, curling was present at eyeball evaluation in 17 patients (24.3%) and in the severe group in 32 patients (65.3%). At linear regression, in the not-severe group, lower MIRA values (≤68°) were associated with curling (p<0.001), presence of ventricular arrhythmias (VA) (p=0.03), presence of prolapse (p=0.007), higher indexed LV end-systolic volume (iLVESV) (p=0.023) and indexed LV end-diastolic volume (iLVEDV) (p=0.01). At linear regression in the severe group lower MIRA values (<68°) were associated with curling (p<0.001), higher vena contracta (VC) (p=0.032), longer PML (p=0.025), wider flail gap (p=0.056), higher LVESV (p=0.055) and LVEDV (p=0.015). At multivariable analysis, only presence of curling was associated with lower MIRA value in both groups (not-severe r -0.623, p<0.001; severe r -0.789, p<0.001). In patients with severe MR also VC was associated with MIRA (r -0,349, p=0.057).

Conclusions: Based on our findings, MIRA angle ≤68° suggests the presence of curling, independently from MR severity. However, curling appears to be more prevalent in patients with severe MR, exhibiting lower mean MIRA values compared to those with not-severe MR. Moreover, in not-severe patients, lower MIRA angles were associated with presence of PML prolapse, presence of VA and larger LV. In patients with severe MR, larger MR jet, LV dilatation, PML length and flail gap were associated with lower MIRA. These observations suggest that curling might be determined and exacerbated by an abnormal distribution of mechanical stress among the posteromedial papillary muscle (PM), posterior MA and the LV inferobasal due to an abnormal “sail-effect” caused by the excess of force applied to prolapsing/flailing longer PML. This alteration might determine increased stress on PM and LV myocardium, leading to mechanical stretching, oedema and fibrosis – factors underlying AMVP. Further studies, including a larger population, are necessary to confirm these preliminary results.