**2. Imaging for aortic regurgitation**

The incompetence of aortic valve leaflets during diastole results in the backflow of blood into the left ventricle. The regurgitation leads to increased blood volume at the end of diastole and elevated stress on the ventricular walls, eventually causing compensatory eccentric hypertrophy due to excessive volume.

Transthoracic echocardiography (TTE) is the primary tool to assess the mechanism, severity, secondary impact on LV remodeling, and hemodynamic consequences of AR. Moreover, TTE and computerized tomography (CT) are valuable in assessing aortic root size. Wenzel et al. demonstrated a proportional relationship between the degree of aortic root dilation and AR severity [10]. Even with nondilated aortic roots, pure AR is associated with degeneration of aortic walls as evidenced by histological and immunohistochemical analyses by Balint et al [11]. According to the 2020 ACC/ AHA valvular heart disease guidelines [3], severe AR is defined by specific criteria: Doppler jet width of ≥65% of the left ventricular outflow tract (LVOT), vena contracta width >0.6 cm, regurgitant volume of ≥60 mL/beat, regurgitant fraction of ≥50%, and effective orifice area of ≥0.3 cm. However, identifying subtle LV dysfunction in the early stages of the disease is desirable, as severe dilation and reduced LVEF indicate a late stage of the disease.

#### **2.1 Speckle tracking echocardiography in aortic regurgitation**

With chronic AR, speckle tracking echocardiography reveals that the eccentric changes in the LV predominantly affect the circumferentially arranged fibers, leading to more severe impairment in global circumferential strain (GCS) compared to global longitudinal strain (GLS). Therefore, circumferential strain is a more sensitive marker for AR and volume overload compared to longitudinal strain for AS and pressure overload [12]. A retrospective study of 314 patients with chronic moderate to severe AR demonstrated that reduced GLS independently predicted mortality, with a threshold of −12.5% [13]. Patients with progressive AR and symptoms had significantly lower longitudinal strain compared to those with stable disease, despite similar LVEF.

In a longitudinal study of 64 patients, reduced GLS, strain rate, and early diastolic strain were associated with progressive disease and worse outcomes following surgery [14]. Impaired LV radial systolic strain rate was predictive of LVEF post-surgery, and decreased baseline GLS or GCS predicted the need for surgery in asymptomatic patients [15].
