CMR Could Refine Early Management Decisions in Aortic Regurgitation

In patients with chronic aortic regurgitation and minimal or no symptoms, cardiovascular magnetic resonance (CMR) imaging added to clinical and echocardiographic findings may enhance risk assessment, a small multicenter study suggests.

The timing of intervention in patients with aortic regurgitation (AR) relies on accurate assessment of valvular insufficiency and LV remodeling. However, the disease often progresses silently, with patients tolerating volume overload for years while they are in a “watchful-waiting” mode and potentially suffering irreversible damage, said senior study author João L. Cavalcante, MD (Minneapolis Heart Institute Foundation, MN).

“It's not uncommon that we might not have the full picture and the capability to quantify how much aortic regurgitation these patients have,” he told TCTMD. “What this paper highlights is that we should have a low threshold to consider cardiac MRI up front in the decision-making for these patients.”

In the study, published online July 20, 2022, ahead of print in JAMA Cardiology, Cavalcante and colleagues found that LV remodeling measurements on CMR were more likely to identify symptomatic patients than those obtained by transthoracic echocardiography (TTE). But even in patients with no or minimal symptoms, CMR added prognostic value in identifying those at risk of death, hospitalization, or progression of NYHA class.

In an accompanying editorial, Robert O. Bonow, MD (Northwestern University Feinberg School of Medicine, Chicago, IL), and Patrick T. O’Gara, MD (Brigham and Women’s Hospital, Boston, MA), say it is “time to evolve to measurement of true LV volumes as the clinical standard rather than relying on the surrogate of LV diameters.”

Additionally, Vidhu Anand, MBBS (Mayo Clinic, Rochester, MN), who wrote a viewpoint that accompanies the study, noted in a related JAMA Cardiology podcast that the new data, along with work her group has previously published, suggest that the long-held concept of LV remodeling being symmetrical in shape may be wrong, and it instead “may be more oblong or in the shape of an American football rather than a soccer ball.” If that hypothesis is true, then assessment of serial changes in LV volume rather than dimension would provide the most accurate estimation of remodeling and disease severity.

Bonow and O’Gara say that while echocardiography is likely to remain the “clinical workhorse” for routine assessment of AR—due in part to issues of cost, availability, and logistics—the improved accuracy of MRI over echocardiography in detecting LV volumes as well as regurgitant volume and regurgitant fraction deserves serious consideration.

To TCTMD, Cavalcante agreed that TTE will always be the “front door” in assessment, but added that the growing body of evidence, including this study, suggests that CMR could be an important complementary tool for many patients.

Inadequate Thresholds

For the study, Cavalcante and colleagues, led by Go Hashimoto, MD (Minneapolis Heart Institute Foundation), compared LV remodeling measurements from TTE and CMR in 178 patients (median age 58; 67% male), most of whom had NYHA class I or II heart failure. The TTE and CMR tests for each patient were performed within 90 days of each other.

Those with symptoms (NYHA class III to IV) were more likely than patients with minimal or no symptoms to have greater LV end-systolic volume index (LVESVi) on CMR (66 mL/m² vs 42 mL/m²; P < 0.001), whereas on TTE, no significant difference was seen between the groups. Both forward stroke volume index and cardiac index were underestimated by TTE in comparison with CMR.

Over 3 years of follow-up, 50 patients (32%) had a clinical event, which included eight deaths and 29  hospitalizations for worsening HF. Patients with no or minimal symptoms who had a clinical event had larger LVESVi (57 mL/m² vs 45 mL/m²; P = 0.03) and greater aortic regurgitation fraction (ARF; 37% vs 28%; P = 0.006) than those who did not have an event. Additionally, CMR assessment of AR severity incorporating ARF was independently associated with outcome prediction.

Current American College of Cardiology/American Heart Association guidelines define the threshold for surgical intervention to be 45 mL/m² or greater for LVESVi and 25 mm/m² or greater for linear LV end-systolic diameter index (LVESDi). In the study, the observed threshold for excess risk of composite events was 45 mL/m² with CMR, which provided excellent discrimination. The same degree of discrimination was not seen, however, for TTE at the guideline-recommended threshold of 25 mm/m². Instead, a lower TTE LVESDi threshold of 20 mm/m² was better at discriminating risk. In multivariable analyses, higher LVESVi either as a continuous or dichotomous variable on CMR was associated with increased risk of composite events. For TTE, however, higher LVESDi as a continuous variable was marginally associated with a greater risk of events but not at either of the guideline-recommended cutoffs.

Among 143 patients with LVESDi < 25 mm/m², 115 patients had no or minimal symptoms at baseline. Those patients would not have met criteria for AVR based on TTE and symptoms alone, yet more than one third of them had LVESVi measurements of 45 mL/m² or greater on CMR and thus were at increased risk for adverse events.

“I think this proves the limitation of what we're currently using as threshold recommendations in the guidelines,” Cavalcante told TCTMD. The next step, he added, is performance of RCTs to understand which patients should receive CMR and further test the limitations of LVESVi thresholds.

Bonow and O’Gara note that MRI as a modality for management of AR has other potential uses beyond improved assessment of regurgitant volume and fraction. It also can, they add, offer “unique insights into interstitial myocardial content and fibrosis that accompany the development of LV hypertrophy and remodeling.”