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Left Atrial Circumferential Strain for Evaluation of Mitral Regurgitation: A Feasibility and Reproducibility Study

Siva Sreedhar¹, Aakash Gupta², Teodora Chitiboi³, Maurice Pradella⁴, and Mohammed S.M. Elbaz¹
¹Northwestern University Feinberg School of Medicine, Chicago, IL, United States, ²Radiology, Stanford University, Stanford, CA, United States, ³Digital Technology and Innovation, Siemens Healthineers, Erlangen, Germany, ⁴Cardiothoracic Radiology, University Hospital of Basel, Basel, Switzerland

Synopsis

Keywords: Myocardium, Valves, strain

Short-axis CMR left atrial (LA) circumferential strain has not yet been investigated as a cardiac biomarker. This study assessed feasibility and reproducibility of LA circumferential strain in a healthy cohort, examined changes in strain within mitral regurgitation (MR) patients, and assessed correlations between reproducible strain measures and MR severity and cardiac function. Reservoir strain globally and at superior and mid LA regions was found to be reproducible, was significantly different between healthy volunteers and MR patients, and was correlated with cardiac function. CMR LA circumferential strain is reproducible with potential utility in evaluating impaired LA mechanics in MR patients.

Background

Mitral regurgitation (MR) is the most prevalent valvular disease. Monitoring MR severity is critical for guiding management¹. Left atrial (LA) strain is a measure of LA deformation and has been shown to be a useful biomarker of impaired cardiac mechanics². Strain can be quantified retrospectively from cine steady-state free-precession (SSFP) cardiac MRI (CMR) through feature-tracking (FT). To assess complex cardiac deformations, strain is quantified over three principal directions: radial, longitudinal, and circumferential. Clinical CMR exams typically include long-axis cine SSFP (LAX) images, which cover both left ventricle (LV) and LA, enabling FT LA longitudinal and radial strain calculation. However, circumferential strain requires short-axis views (SAX) to measure circumferential deformation. Since routine short-axis cine SSFP exams are for LV evaluation, they do not typically cover the LA. Thus, feasibility and clinical utility of CMR circumferential LA strain remains unknown. The aims of this study were to assess 1) feasibility and test-retest reproducibility of global and regional LA FT circumferential strain from cine SAX SSFP; 2) test utility of identified reproducible circumferential LA strain parameters in quantifying differences between MR patients and healthy volunteers; 3) correlation of reproducible LA circumferential strain parameters with MR severity and cardiac function in MR patients.

Methods

Fifty-one MR patients (27 male, age: 62.2 [52.4, 70.3]) who were prospectively recruited based on echocardiographic evidence of MR within 3 months from CMR and 12 healthy volunteers (6 male, age: 45.8±16.1 years) were retrospectively analyzed [Fig. 1]. Each participant underwent a cine SAX SSFP scan with 3 cross-sectional LA slices: superior, mid, and inferior [Fig. 2]. One MR patient was excluded due to insufficient number of slices. For test-retest reproducibility, the LA cine SAX SSFP scan was repeated 2 weeks later for the 12 healthy volunteers. Circumferential strain was computed from CMR as the strain component tangential to the LA contour using a FT prototype (TrufiStrain, Siemens) [Fig. 2]. Regional strain was computed for each LA slice separately (superior, mid, and inferior) by averaging strain over each slice. This was repeated for each time point to create a strain-time curve to calculate reservoir, conduit, and booster strain per slice³ [Fig. 2]. Global circumferential strain parameters were computed by averaging over all 3 slices. Test-retest reproducibility was assessed using the intraclass correlation coefficient (ICC). A parameter was defined reproducible if ICC> 0.75⁴. The identified reproducible circumferential strain measures were 1) compared between MR patients and healthy volunteers; 2) tested their association in MR patients with regurgitant fraction, LA volume, and LV cardiac function: stroke volume (SV) and ejection fraction (EF).

Results

Test-retest reproducibility showed that most ‘global’ circumferential strain parameters were reproducible with circumferential reservoir strain ICC = 0.88 and circumferential booster strain ICC = 0.82 [Fig. 3A]. All three superior LA circumferential strain parameters were reproducible: ICC = 0.82 to 0.93 [Fig. 3BI-III]. Within the mid LA region, only circumferential reservoir strain was reproducible with ICC = 0.77 [Fig. 3BI]. In the inferior LA region, only circumferential conduit strain was reproducible with ICC = 0.85 [Fig. 3BII]. MR patients showed significantly lower values of circumferential strain than healthy volunteers at the reservoir phase when calculated globally (p=0.01), at the superior LA region (p=0.02), and at the mid LA region (p=.03) [Fig. 4A]. Similar results were found for volume-indexed circumferential strain parameters [Fig. 4B]. Global circumferential reservoir strain was inversely correlated with regurgitant fraction (ρ= -0.39) and directly correlated with SV (ρ = 0.57) and EF (ρ = 0.67) [Fig. 5A-B]. Superior LA circumferential reservoir strain was inversely correlated with LA volume (ρ = -0.39) and directly correlated with SV (ρ = 0.37) and EF (ρ = 0.51) [Fig. 5B]. Mid LA reservoir strain was inversely correlated with regurgitant fraction (ρ = -0.46) and LA volume (ρ = -0.31), and directly correlated with SV (ρ = 0.33) and EF (ρ = 0.52) [Fig. 5A-B].

Discussion

To our knowledge, this is the first study to assess feasibility, reproducibility, and utility of LA circumferential strain by FT from CMR cine SAX SSFP. Realizing the importance of reproducibility, we first identified reproducible LA circumferential strain measures, by a conservative ICC>0.75, then only tested the reproducible measures. Global LA circumferential reservoir and booster strain are reproducible. Regionally, the superior LA region had the highest reproducibility potentially due to lesser bulk movement versus the inferior region that is prone to out-of-plane motion given proximity to mitral valve. The results show that adding only two SAX slices –using the same LV cine SSFP SAX protocol– at the superior and mid LA region allow reproducible measures of circumferential strain changes in MR patients. Global and regional circumferential reservoir strain are associated with MR severity as well as cardiac function parameters (EF, SV). Therefore, highlighting potential clinical utility.

Conclusion

This study demonstrates the feasibility and reproducibility of quantifying global and regional circumferential LA strain by FT from cine CMR SAX SSFP and its potential utility in evaluating impaired LA mechanics in MR patients. Hence, it may facilitate clinical adoption given that it builds on the existing LV SAX pipeline. Future studies are needed to assess potential added value of CMR LA circumferential strain in prognosis of MR patients.

Acknowledgements

AHA Student Scholarship in Cardiovascular Disease

References

1. Enriquez-Sarano, Maurice, et al. “Mitral Regurgitation.” The Lancet., vol. 373, no. 9672, 2009, pp. 1382–94, https://doi.org/10.1016/S0140-6736(09)60692-9.

2. Cau, Riccardo et al. “The emerging role of atrial strain assessed by cardiac MRI in different cardiovascular settings: an up-to-date review.” European radiology vol. 32,7 (2022): 4384-4394. doi:10.1007/s00330-022-08598-6

3. Gan, Gary C. H., Aaisha Ferkh, Anita Boyd, and Liza Thomas. “Left Atrial Function: Evaluation by Strain Analysis.” Cardiovascular Diagnosis and Therapy 8, no. 1 (2018): 29–46. https://doi.org/10.21037/cdt.2017.06.08.

4. Koo, Terry K., and Mae Y. Li. “A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research.” Journal of Chiropractic Medicine, vol. 15, no. 2, 2016, pp. 155–63, https://doi.org/10.1016/j.jcm.2016.02.012.

Figures

Figure 1: Demographic data of healthy and MR cohort. Categorical data shown as n (%). Continuous data reported as mean ± standard deviation if normal or as median [25% quartile, 75% quartile] if not normal. Significant differences (p<0.05) between demographic variables indicated with an asterisk (*). MR volume (difference from SV and forward aortic flow) determined MR severity: none-trivial (<10 mL, mild (10-30 mL), moderate (30-60 mL), and severe (≥ 60 mL).

Figure 2: Workflow Steps. 1) Superior, mid, and inferior LA slices defined based on SAX slice position on corresponding 2C and 4C slices. 2) Contouring done by manually segmenting first frame with automatic propagation to remaining frames. 3) TrufiStrain calculated strain magnitude. 4) Strain curve determined by strain at each time point, with peaks used to calculate reservoir, conduit, and booster strain. Steps 2-4 repeated for each slice, with global strain as the average strain across 3 slices.

Figure 3: LA Circumferential Strain Reproducibility. A) Reproducibility of strain values by slice and globally. Bolded values indicate ICC>0.75. B) Bland-Altman plots of reproducible strain parameters bolded in 3A, separated by phasic strain parameter.

Figure 4: Comparison of reproducible strain values (traditional and indexed to LA volume) between healthy and MR cohorts. Sample size (n=) listed after each cohort name.

Figure 5: Association between Global and Regional Strain Parameters with Regurgitant Fraction and Cardiac Function. 5A depicts global and mid LA strain correlation with regurgitant fraction, while 5B depicts global and regional strain correlation with cardiac function parameters (stroke volume, ejection fraction).

Proc. Intl. Soc. Mag. Reson. Med. 31 (2023)

4851

DOI: https://doi.org/10.58530/2023/4851