Assessment of mitral valve geometry in nonvalvular atrial fibrillation patients with or without ventricular dysfunction: insights from high volume rate three-dimensional transesophageal echocardiography

The subjects were enrolled into the present study as illustrated in Fig. 1. FMR was defined as MR without structural MV abnormalities. LV dysfunction was defined as a LVEF ≤ 54% for females and ≤ 52% for males by transthoracic echocardiography (TTE) [8] or as a LV wall motion abnormality. Inclusion criteria were patients diagnosed with AF and without another type of arrhythmia. Patients with the following were excluded: without mitral regurgitation or mitral regurgitation volume < 10 mL, intrinsic abnormalities of the leaflet and/or subvalvular apparatus, severe mitral annular calcification, history of mitral valve surgery, and poor echocardiographic image quality. From April 2020 to April 2022, 68 of 265 nonvalvular AF patients referred for AF catheter ablation or transcatheter MV intervention who underwent TTE and TEE were included. AF patients were divided into two groups. The AFMR group comprised 36 patients with AF, FMR (regurgitation volume ≥ 10 mL), and preserved LV function. The VFMR group comprised 32 patients with AF, FMR (regurgitation volume ≥ 10 mL), and LV dysfunction. In addition, 36 patients with unexplained fever who underwent TEE to screen for infectious endocarditis and without positive findings on echocardiography and electrocardiography were included as the control group. The study protocol was approved by the West China Hospital Ethical Review Committee (approval number: 2020-85).

An EPIQ 7 C ultrasound platform (Philips Andover, MA, USA) with the S5-1 probe (frequency: 1–5 MHz) for TTE and the X7-2t probe (frequency: 2–7 MHz) for TEE was used. Routine TTE and TEE were performed by the same proficient physician throughout the study. The modified biplane Simpson method from the apical four- and two-chamber views was used to obtain the LA maximum volume, LA minimum volume, LA ejection fraction (LAEF), LV end-diastolic volume (LVEDV), LV end-systolic volume (LVESV), and LVEF. LVEDV, LVESV, and the LA maximum and minimum volumes were indexed to the body surface area. [8] All patients received local anesthesia before insertion of the TEE probe under the optimal depth and gain conditions. The HVR mode was used to obtain the 3D datasets of the MV, including the annulus, leaflets, and aortic valve. The 3D volumes were recorded at a frame rate of 25–53 volumes per second (Fig. 2). In patients who were in AF rhythm during examination, the volumes were acquired when the heart rate was less than 110 beats per minute.

On the 130–150° MV view, Color Doppler flow imaging was used to determine the presence or absence of MR. In patients with MR, MR was quantified using the PISA method. The effective regurgitant orifice area and regurgitant volume were measured. [9] A regurgitant volume < 10 mL was regarded as trivial MR. The measurements were averaged over five cycles.

All echocardiographic images were analyzed offline by a single investigator blinded to the clinical data. Offline analysis of the 3D datasets was performed using the latest QLAB software (version 15; Koninklijke Philips N.V. ADR, MA, USA). In contrast with the previous version, QLAB version 15 can tag the annulus and trace the leaflets automatically, delineating the anterior and posterior leaflets, as well as the coaptation line. This entire procedure requires barely no human intervention. The mitral annulus (MA) includes two regions. One region is located between the left and right fibrous trigones, and is connected anatomically to the aortic annulus at the aortomitral intervalvular fibrous or aortic mitral curtain, which is defined as the intertrigonal annulus. [10] The other region contains the remainder of the annulus, which is classified as the C-shaped annulus. The software automatically generated the following parameters describing the annular geometry (Fig. 3): (1) annulus indices including the anteroposterior diameter of the MA (APD), anterolateral-posteromedial diameter of the MA (ALPMD), sphericity index (SI, the ratio of APD to ALPMD), intertrigonal annulus perimeter (ITAP), C-shaped annulus perimeter (CAP), saddle-shaped annulus perimeter (SSAP), saddle-shaped annulus area (SSAA), annulus height (AH), and non-planar angle (NPA); and (2) leaflet indices: including the anterior leaflet length (ALL), posterior leaflet length (PLL), anterior leaflet area (ALA), posterior leaflet area (PLA), total leaflet area (TLA), distal anterior mitral leaflet (AML) angle, posterior mitral leaflet (PML) angle, coaptation depth (CD), and tenting volume (TV). Each parameter was measured frame by frame, and a parameter-time curve was generated during the whole systole. We observed that the values of most parameters peaked at the start and end of systole, as observed in previous studies; [11] therefore, these two time points were chosen for analyses. Early-systole was defined as immediately after the onset of mitral closure, while end-systole was defined as immediately before aortic closure.

Based on these parameters, dynamic indices were calculated including (1) the ratio of AH to ALPMD = AH/ALPMD, (2) annulus area fraction (AAF)=(SSAA_{end−systole}-SSAA_{early−systole})/SSAA_{early−systole}, (3) ALA systolic fraction=(ALA_{end−systole}-ALA_{early−systole})/ALA_{early−systole}, (4) adaptation ratio = TLA/AA, and (5) simplified adaptation ratio=(ALL + PLL)/APD.

All geometric parameters of the MV were measured by one practiced physician blind to the patients’ clinical data, and these measurements were compared with the blind measurements of another observer. Intra- and inter-observer variability was evaluated in 20 randomly selected subjects.