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Cardiac MR for aortic regurgitation may outshine echo for post-TAVR risk stratification

QUEBEC, QC — Moderate or severe aortic regurgitation (AR) on cardiac magnetic resonance (CMR) within 40 days of transcatheter aortic-valve replacement (TAVR) strongly predicts poorer long-term outcomes, a multicenter study finds[1].

"There were already data showing that in native aortic regurgitation CMR is useful for risk stratification, but now for the first time this can also be the case in patients post-TAVR," senior author Dr Josep Rodés-Cabau (Quebec Heart & Lung Institute, Laval University) told heartwire from Medscape.

The findings, published in the August 9, 2016 issue of the Journal of the American College of Cardiology, also suggest that post-TAVR CMR risk stratification may be superior to that with echocardiography, the most common method used to quantify AR post-TAVR.

"But we have to be cautious, because the two exams were performed in different time points," and confirmatory data will be needed in a much larger cohort, he added.

Among the 135 patients with severe symptomatic aortic stenosis, phase-contrast velocity mapping CMR was performed within a median of 40 days post-TAVR and Doppler transthoracic echocardiography (TTE) within a median of 6 days post-TAVR.

Moderate to severe residual AR (regurgitant fraction [RF] >30%) was identified in 17.1% by echocardiography and 12.8% by CMR.

The lack of agreement is not entirely surprising, as echocardiography has been shown to misclassify AR grade compared with CMR, with discordance between the two techniques observed in nearly half of TAVR patients.

Accurate quantification of AR is challenging with echocardiography because multiple, eccentric AR jets are often present, note the investigators, led by Dr Henrique Ribeiro (Quebec Heart & Lung Institute). In addition, acoustic shadowing from the annulus and left ventricular outflow tract calcifications as well as Doppler attenuation from the prosthetic valve may also interfere with accurate quantification of regurgitant jets.

Not to put too fine a point on it, Drs Róisin Morgan and Raymond Y Kwong (Brigham and Women's Hospital, Boston, MA) write in an accompanying editorial[2], "echo-based assessment uses four measurements, any one of which may include significant inaccuracies, thus making echocardiographic evaluation of [paravalvular leak] PVL a well-validated but flawed technique."

When the investigators examined outcomes at 2-year follow-up, RF >30% on CMR was associated with higher all-cause mortality (hazard ratio [HR] 1.18 for each 5% increase in RF; 95% CI 1.08–1.30; P<0.001) and the combined end point of mortality and rehospitalization for heart failure (HR 1.19 for each 5% increase in RF; 95% CI 1.15–1.23; P<0.001).

Kaplan-Meier survival curves also showed that moderate/severe vs mild or no AR on CMR at 2 years was significantly associated with higher mortality (35.1% vs 13%; log rank P=0.032) and mortality and HF rehospitalization (47.3% vs 15.2%; log rank P=0.002).

Patients with moderate/severe AR on TTE also had numerically higher rates of these outcomes, but the differences did not reach statistical significance for either mortality (19.6% vs 15.2%; log rank P=0.70) or the combined end point (32% vs 17.6%; log rank P=0.175).

In all models, CMR-quantified AR also provided significant additive prediction value to that of post-TAVR TTE AR grade and the other clinical variables (P<0.005 for all models).

Not all patients, however, will need to be followed with CMR, Rodés-Cabau said. CMR can be avoided in patients with no regurgitation 30 days post-TAVR but can be very useful in patients who at 30 days have mild regurgitation on echo and are not doing well or have signs of heart failure and in those with moderate to severe AR.

"Honestly, I don't think this can replace echocardiography; that's not the objective," he added. "The idea is to be a complementary exam to echocardiography that can be applied in some cases."

Morgan and Kwong also cite as possible candidates for post-TAVR CMR patients with poor echo windows, inconclusive TTE and/or transesophageal echocardiography, and where there is difficulty acquiring accurate quantitative data.

Both the investigators and editorialists note that the study was limited by the use of 2D rather than 3D echocardiography, which is well-known to improve the evaluation of AR.

Rodés-Cabau observed that the number of centers that have performed with 3D echocardiography varies widely and that at this point much more data have accumulated with CMR than 3D echocardiography.

"Maybe in 5 years this will change completely, and that would be great because echo is much more available; it's the standard way we evaluate these patients and for sure echo is far less costly," he added.

Although the study adds new knowledge regarding the use of CMR post-TAVR, Morgan and Kwong write that relevant clinical questions remain, most notably whether all-cause mortality is an appropriate clinical outcome of interest, as most TAVR patients have substantial comorbidities apart from high-risk aortic stenosis.

"Whether CMR-measured PVL quantitation can guide repeat TAVR in the appropriate clinical settings and improve patients' quality of life is an important question," they write.

The study was funded in part by research grants from the Canadian Institutes of Health Research. Ribeiro is supported by a research PhD grant from CNPq, Conselho Nacional de Desenvolvimento Científico e Tecnológico–Brasil. Rodés-Cabau reports research grants from Edwards Lifesciences, Medtronic, and St Jude Medical. Disclosures for the coauthors are listed in the paper. Drs Morgan and Kwong report no relevant financial relationships.

Follow Patrice Wendling on Twitter: @pwendl.
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Source: Heartwire from Medscape