By Michael H. Crawford, MD, Editor
SYNOPSIS: Cardiac MRI could be used to make management decisions when treating patients living with chronic, asymptomatic aortic regurgitation with preserved left ventricular function, especially when trying to predict severity and possibility of adverse outcomes.
SOURCE: Malahfji M, Crudo V, Kaolawanich Y, et al. Association of cardiac remodeling with aortic regurgitation outcomes: The AR consortium of the SCMR Registry. J Am Coll Cardiol 2023; Mar 3: S0735-1097(23)04582-5. doi: 10.1016/j.jacc.2023.03.001. [Online ahead of print].
Cardiac MRI might be the clinical gold standard for measuring left ventricular (LV) volumes and ejection fraction (EF) in patients living with chronic aortic regurgitation (AR). However, the clinical utility of this information is uncertain because of a paucity of data regarding the relationship between cardiac MRI-determined LV volumes and outcomes in AR.
Malahfji et al combined four prospective U.S. registries from the 19-institution Society for Cardiovascular Magnetic Resonance Registry (SCMRR). These registries contained 1,286 patients with moderate or worse chronic AR (regurgitant volume greater than 30 mL or regurgitant fraction of more than 30% by cardiac MRI). The authors excluded patients with more than mild concomitant valve disease, prior valve interventions, symptomatic patients, an EF less than 50%, a primary cardiomyopathy, congenital heart disease (except for bicuspid aortic valve [AV]), AV replacement (AVR) less than 30 days after cardiac MRI, and an end-stage disease with a competing mortality risk. The researchers measured LV end-diastolic (ED) volumes, EF, and mass. They also calculated regurgitant volume (RV) and regurgitant fraction (RF).
The authors measured LVED and LV end-systolic (LVES) diameters in the three-chamber view at the mitral leaflet tips. All measures were indexed to body surface area (BSA). Investigators initiated clinical follow-up at the time of cardiac MRI. Researchers recorded appropriate outcome data. The primary outcome was whichever outcome occurred first: symptoms related to AR, EF less than 50%, referral for AVR based on current guideline criteria, or death. Patients who underwent surgery primarily for aortic aneurysm repair were censored at the time of surgery. The study population included 458 patients: median age = 60 years; 82% men; 26% non-Caucasian; and 37% with a bicuspid valve.
After a median follow-up of 2.4 years, the primary outcome occurred in 133 patients: 67 developed symptoms, four experienced a decline in EF, 34 met indications for surgery, and 28 died. A total of 121 patients underwent surgical AVR (SAVR) for AR. These patients exhibited larger RV vs. those who did not undergo SAVR (59 mL vs. 37 mL) and RF (44% vs. 35%). The optimal threshold above which adverse events were more frequent for the severity of AR were a RV of 47 mL and an RF of 43%. For LV remodeling, cutpoints were a LV end-systolic volume index (LVESVi) of 43 mL/m2, a LV end-diastolic volume index (LVEDVi) of 109 mL/m2, and a LV end-systolic diameter (LVESD) > 2 cm/m2.
After conducting a multivariable analysis, researchers noted LVESVi greater than 43 mL/m2 was highly associated with the primary outcome (HR, 2.53; 95% CI, 1.75-3.66; P < 0.001), as was LVEDVi greater than 109 mL/m2 (HR, 2.43; 95% CI, 1.65-3.59; P < 0.001) and an RF greater than 43% (HR, 2.53; 95% CI, 1.75-4.16; P < 0.001). However, this association was less so for LVESDi greater than 2 cm/m2 (HR, 1.51; 95% CI, 1.04-2.19; P = 0.03). The authors concluded cardiac MRI-based assessment of the severity of AR and degree of LV remodeling can be clinically useful for managing chronic, asymptomatic patients with AR and normal LVEF. Also, LVESVi performed better than LVESDi for this purpose.
COMMENTARY
When managing patients with chronic, moderate (or worse) AR, I have been frustrated by the variability of two-dimensional echocardiographic measurements of LV volumes and the quantitation of the severity of AR. In general, echo tends to underestimate LV volumes compared to cardiac MRI, especially in diastole. Therefore, cardiac MRI should be superior to two-dimensional echo for managing patients with chronic AR.
Malahfji et al showed cardiac MRI was better at determining the severity of AR and the extent of LV remodeling. Cardiac MRI also predicted adverse outcomes and showed LV volume measurements are superior to LV diameter. I predict that if cardiac MRI is available and affordable that echo will be used to screen for moderate to severe AR, but cardiac MRI will be used for the final stretch leading to the decision for valve replacement. As cardiac MRI becomes more widely available, it might be used earlier in the course of chronic AR, but this will be modulated to some extent by patient acceptance of cardiac MRI, which is not as convenient or comfortable as echo.
Interestingly, the SCMRR study revealed an LV diameter cutpoint of 4 cm (or 2 cm/m2). This is important because we might be intervening too late too often in chronic AR patients. Whether this paper or the accumulating evidence will affect future guidelines is unknown. Part of the reason for the more conservative approach to recommending AVR in chronic AR is that currently, this means ordering a SAVR procedure. If a percutaneous technique for AVR is perfected, then the guidelines might become more aggressive.
Consider some limitations to the SCMRR study. Since it is a registry, there likely was a selection bias regarding who underwent cardiac MRI. Also, the clinicians caring for the patients were not blinded to the cardiac MRI results. However, to account for this possibility, patients who underwent SAVR within 30 days of the cardiac MRI were excluded. In addition, echo and cardiac MRI studies were not coordinated, so researchers did not compare the two techniques. Finally, there were no stress tests or other objective confirmation indicating the patients were asymptomatic. For now, I plan to use cardiac MRI more liberally, when possible, especially in difficult-decision patients for whom the echo data are inconsistent or technically challenging.
Cardiac MRI could be used to make management decisions when treating patients living with chronic, asymptomatic aortic regurgitation with preserved left ventricular function, especially when trying to predict severity and possibility of adverse outcomes.
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