• „ ORIGINAL ARTICLE

Aortic regurgitation and left ventricle remodeling on cardiac magnetic resonance and transthoracic echocardiography

Maciej Haberka¹, Mariusz Bałys¹, Zbigniew Gąsior¹, Bartłomiej Stasiów²

¹Department of Cardiology, School of Health Sciences, Medical University of Silesia, Katowice, Poland

²Department of Electroradiology, School of Health Sciences, Medical University of Silesia, Katowice, Poland

Editorial

by Markl et al.

see p. 945

INTRODUCTION

Transthoracic echocardiography (TTE) is the main imaging modality used to assess patients with chronic aortic regurgitation (AR). It is used for screening, grading, and monitoring patients with AR and mild symptoms. Current guidelines recommend aortic valve (AV) replacement or repair in patients with overt symptoms and/or severe left ventricle enlargement or systolic dysfunction [1]. The AR is usually well tolerated by most patients over several years and it is crucial to detect the optimal time to surgery and when the clinical prognosis is reduced. However, due to the limitations of ultrasound and the complex nature of AV disease, it is not possible to provide precise quantification of AR and dimensions of the left ventricle (LV) in all patients. Therefore, our aim was to compare TTE and cardiovascular magnetic resonance (CMR) measurements in grading AR and LV remodeling in patients with chronic AR.

METHODS

Study population

All the consecutive patients scheduled for routine TTE in the echocardiography laboratory were screened (2018–2019) and 51 patients were included in the study group after consideration of exclusion criteria. The chronic regurgitation of the native aortic valve (with or without concomitant stenosis) was the inclusion criterion.

The main exclusion criteria were as follows: acute aortic regurgitation and/or endocarditis of any native valve, aortic valve prosthesis, any stenosis or more than mild mitral regurgitation, acute coronary syndrome or decompensated congestive heart failure in prior 1 month, infectious diseases in prior 1 month, significant anemia, and contraindications to CMR.

This was a prospective single-center study performed in accordance with the principles of the Declaration of Helsinki and the Bioethics Committee of the Medical University of Silesia. All patients signed the informed consent. This work was supported by the research non-commercial grant from the Medical University of Silesia (KNW-1-027/K/9/K).

Echocardiography

Echocardiography (TTE) was performed with a commercially available 2-dimensional imaging system (General Electric company Vivid e9, Milwaukee, WI, USA). All the patients were scanned in the left lateral decubitus position and each of the examinations followed the EACVI/ASE 2015 recommendations for cardiac chamber quantification by echocardiography in adults [2]. Left ventricular ejection fraction (LVEF) was calculated with the biplane Simpson method (without an ultrasound contrast) and LV mass was estimated using the linear method and Cube formula [2]. Given the main aim of the paper, the grading of the AR was based on the extensive multiparametric approach following the 2017 ASE recommendations for noninvasive evaluation of native valvular regurgitation [3]. The integrative AR measurements were obtained in all patients using qualitative, semi-quantitative (SQ) and quantitative (Q) parameters depending on the quality of the acoustic window and the type of AR itself. Each of the TTE followed the steps of the SQ and Q described in the guidelines [3]. The AR volume (AR vol) and AR regurgitant fraction (AR RF) were estimated using the Doppler method based on proximal isovelocity surface area (PISA). The final severity of AR was a multiparametric assessment with the focus on Q parameters or SQ, if PISA method was not measurable (acoustic window, asymmetric jet, multiple jets). The following quantitative criteria for the AR severity were used: severe (AR vol ≥60 ml; RF ≥50%; ERO ≥0.3 cm²), moderate (AR vol = 30–59 ml; RF = 30%–49%; ERO = 0.1–0.29 cm²) and mild (AR vol <30 ml; RF <30%; ERO <0.1 cm²) [3]. The degree of AV calcifications was based on the subjective assessment, where „0” was for elastic leaflets with no calcifications and „3” was for hyperechogenic severe calcifications. The angle of AR was assessed manually by the single observer as the angle between the axis of the aortic root and the axis of the jet in the parasternal long-axis view. The AR jet angle 0 was central and the more asymmetric jet (in either of the sides) the larger the AR angle.

All the TTE images were obtained, stored anonymously, and then analyzed offline by a single observer (MB) blinded to patient clinical characteristics and CMR results.

Cardiovascular magnetic resonance imaging

The CMR images were acquired on 1.5T system (GE Optima MR450w, GE Healthcare, Wisconsin, WI, USA) with a dedicated phased-array cardiac coil. The study CMR protocol included a non-contrast examination with a multi-planar cine steady-state free precession (SSFP) acquisitions and flow visualization using phase-contrast (PC) flow imaging. Cardiac chambers volumes and functions were analyzed by SSFP in several planes, including 2-chamber, 4-chamber, orthogonal LV outflow track, and parallel short-axis planes covering both atria and ventricles. The typical scan parameters used were TE/TR (time to echo/time of repetition) 1.9/4.3 ms, slice thickness 4–8 mm (no interslice gap), and temporal resolution 30–40 ms. The SSFP planes for the aortic valve complex and ascending aorta were placed perpendicular to the aortic root. The through-plane PC flow imaging was obtained at the slices perpendicular to the axis of flow with the positions just above the valve and velocity encoding maximum values set at 200 cm/s. The PC imaging was repeated, and the position of the slice and maximum velocity values were modified to avoid aliasing or artifacts [4]. The severity of AR was based on AR vol and AR RF obtained in PC imaging and volumetric data calculated from cine images and manual endocardial tracings. The CMR grades of AR were defined according to the 2017 ASE guidelines and the criteria for AR vol and RF were similar as described above for echocardiography [3].

Statistical analysis

The results presented in the manuscript are expressed as means (standard deviation [SD]) for normally distributed variables or medians (interquartile range [IQR]) for abnormal distribution. In the case of descriptive data, a number (percentage) was used. The distribution was tested for normality with the Kolmogorov-Smirnov test. Baseline clinical parameters and the measures were compared between the subgroups using the t-tests for the normally distributed continuous variable (Student’s t-test); in case of abnormal distribution, the Mann-Whitney U test was used. Associations between parameters were assessed using Pearson correlation analysis (parametric variables). The Bland-Altman analysis was performed to measure the agreement between the main parameters of CMR and TTE (AR vol and AR RF). Intermodality agreement for AR severity classification was performed using κ statistics. The calculated kappa coefficients were graded as follows: 0–0.2 low, 0.2–0.4 fair, 0.4–0.6 moderate, 0.6–0.8 good, and >0.8 excellent [5]. A value P <0.05 was considered statistically significant. Statistical analysis was undertaken using Medcalc software (version 19.1, Osten, Belgium).

RESULTS

Clinical characteristics

A total of 51 consecutive patients with AR in TTE were enrolled into the study and finally 49 individuals (age: 57.1 [14]; 61% males) completed a non-contrast CMR (2 excluded for CMR contraindications).

The clinical characteristics, symptoms, and baseline parameters of AV disease are presented in Table 1.

In brief, the study patients revealed cardiovascular risk factors, including dyslipidemia (91%), hypertension (83%), obesity (16%), or diabetes (12%). Ischemic heart disease was found in almost half of the patients (45%), and most subjects showed moderate symptoms (New York Heart Association I or II).

Most individuals had some degree of AV calcification (72%), which resulted in a mild (19 patients; 38%) or a moderate (1 patient; 2%) AV stenosis. Half of the subjects showed AR with eccentric jets, and multiple jets were found in 14% of cases.

Left ventricle remodeling

Left ventricle dimensions and systolic function were assessed in both modalities. The LV end-diastolic diameters (EDD) and end-diastolic volumes (EDV) measured in CMR were larger compared to TTE: 57.4 (7) mm vs 54 (6) mm (P = 0.02) and 185.5 (61) ml vs 158.5 (61) ml (P = 0.03). However, there were no differences in the LV end-systolic diameters (35.6 [8] mm vs 35.1 [6] mm; P = 0.7), end-systolic volumes (ESV) (78.5 [36] ml vs 71 [33.2] ml; P = 0.3) and there was a trend towards higher LV ejection fractions in CMR compared to TTE (59 [8] % vs 56.2 [8] %; P = 0.08). Despite some differences, there were significant associations between both modalities in LV EDV and ESV (Figures 1, 2), but not in LV EF. Moreover, LV mass calculated in TTE was overestimated compared to CMR (245 [84] g vs 152 [52] g; P <0.0001), but there was also an association between modalities (r = 0.8; P <0.0001).

Aortic regurgitation

The main SQ measures found in TTE were as follows: jet/LVOT ranged from 15% to 65% (31% [22–36]) and PHT was between 35 ms and 752 ms (404 ms [320–510]). The comprehensive quantitative assessment by the Doppler PISA method with AR vol and AR RF were measurable in TTE in 24 cases: AR vol 38 ml (26–57 ml) and AR RF 43% (33%–57%).

The CMR AR vol ranged from 5 ml to 92 ml (18 ml [6–39]) and AR RF ranged from 5% to 75% (21% [7–36]). In the subgroup of 24 cases, the TTE AR vol was larger compared to CMR AR: 38.5 ml (26–57) vs 18 ml (6–39) (P <0.01) and TTE AR RF was higher compared to CMR RF: 43% (33–57) vs 21% (7–36) (P <0.0001).

Both modalities showed significant associations in AR vol and AR RF (Figures 3, 4).

Both TTE and CMR provided the conclusions for AR grading, which were compared in all patients. The intermodality agreement (TTE-CMR) in AR grading across a mild, moderate and severe AR was low (κ = 0.15, SE = 0.08; 95% CI, –0.006–0.309) (Table 2).

Both modalities provided similar conclusions mostly in mild AR (91%). TTE overestimated the grade of AR in 51% and underestimated the AR severity in 15% of patients (Figure 5).

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