• Curling
• MIRA
• Arrhythmogenic MVP
• Mitral Valve
• Mitral Annulus

Abstract
Background: Systolic curling is an abnormal downward and anteriorly directed motion of the posterior mitral annulus and adjacent left ventricular wall. Curling was initially observed in patients with mitral valve prolapse (MVP) and might be associated with arrhythmic MVP. Its presence is still determined on eyeball evaluation. We therefore developed a transthoracic echocardiographic (TTE) method to quantify curling based on the separation of the movement in its two vectors defining an angle. Aim of this study is to validate the method and determine the normal value of the angle in the healthy population.
Methods: We retrospectively analyzed healthy patients who underwent routine TTE at Cardiothoracic Surgery Unit-University of Pisa between March 2022 and July 2023. Retrospective off-line measurement of Mitral valve annulus to Inferobasal wall Rotation Angle (MIRA) was performed, along with visual assessment of the presence of curling. MIRA was measured on parasternal long-axis view at end-systole as the angle included between the line perpendicular to the LV posterobasal wall long axis from epicardium (A) to endocardium (B) (at the level of the anterior mitral leaflet tip) and the line connecting B to the insertion of the posterior mitral leaflet to the annulus.
Results: Thirty-one patients were included in the study. MIRA had a normal distribution. Mean MIRA was 71.9±8.2° (95% CI 68.9-74.9), median value was set at 74.9°, the I quartile was 68° while the III quartile was 76°. Visual presence of curling was observed only in patients included in the I quartile (MIRA<68°); linear regression analysis showed that lower MIRA values (<68°) were associated with presence of curling (p<0.05). Patients with lower MIRA values also tended to have larger left atrial volumes however at linear regression analysis the association was not significant (p=0.094).
Conclusions: Our findings suggest that curling can be assessed and quantified measuring MIRA. MIRA has a normal distribution in the healthy population and lower MIRA values are associated with presence of curling. MIRA <68° should be considered abnormal suggesting presence of curling. Further studies including larger population are necessary to confirm our preliminary results and to evaluate the importance of curling in the subset of arrhythmic MVP.