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Study Summary

The Low Risk TAVR (LRT) trial sought to evaluate the feasibility and safety of transfemoral transcatheter aortic valve replacement (TAVR) in 11 mostly low-volume centers in the U.S. Patients were considered low risk if their STS-PROM score was ≤3% without significant comorbid conditions. The primary endpoint was 30-day all-cause mortality. Two hundred low-risk patients underwent TAVR (88.2% with a balloon-expandable valve) and were compared with 719 historical controls who had undergone isolated surgical aortic valve replacement (SAVR) at the enrolling centers. Unadjusted 30-day all-cause mortality was 0.0% vs. 1.7% (P = 0.079) for TAVR vs. SAVR. In the TAVR group, mean length of stay (2.0 vs. 6.4 days; P <0.001) and new onset atrial fibrillation (3.0% vs. 40.8%; P <0.001) were reduced, no difference in new permanent pacemaker implantation was observed (5.0% vs. 4.5%; P = 0.742), and no disabling strokes occurred. At 30 days, 14% of patients who underwent TAVR had evidence of subclinical leaflet thrombosis on four-dimensional contrast-enhanced cardiac computed tomography imaging (in 192 patients) or transesophageal echocardiography (in 2 patients). Of the patients assessed by imaging, 79% were taking antiplatelet therapy only (aspirin, thienopyridine, or dual antiplatelet therapy) and 20% were taking oral anticoagulants (warfarin or direct oral anticoagulant). Overall, TAVR was found to be safe and efficacious (see accompanying Hurst’s Central Illustration) with zero mortality and zero disabling strokes for low-risk patients.

Commentary

Study Strengths: The LRT trial was the first trial in the US to evaluate the short-term outcomes of TAVR in patients with severe aortic stenosis considered low surgical risk. The study was multicenter, prospective, and performed at mostly low-volume TAVR centers. Therefore, these results most accurately represent the contemporary, real-world TAVR practice in the US. The study was investigator-initiated and fully funded and managed by the sponsoring center (Medstar).

Study Limitations: The study was unavoidably unblinded. While patients undergoing TAVR were prospectively enrolled, they were compared to historical controls in the STS registry. As discussed in the paper, using a non-adjudicated registry for the control group imposes limitations, such as inability to ensure low-risk status, inability to capture non-traditional baseline characteristics (i.e. frailty), limitations intrinsic to the registry (i.e. not recording vascular complications and major life-threatening bleeding), and relatively short follow-up. While baseline characteristics were controlled using inverse probability weighting, differences remained between the two groups, including body mass index, peripheral vascular disease, prior myocardial infarction, left-ventricular ejection fraction, and pre-existing permanent pacemaker.

Next Steps/Clinical Perspective: Future studies will evaluate the long-term outcomes for TAVR vs. SAVR in low-risk patients. For example, the PARTNER 3 trial and Medtronic Evolut Low Risk Trial will evaluate outcomes in low-risk patients with severe aortic stenosis for 5 to 10 years after TAVR implantation. In these and other studies, long-term valve durability, hemodynamics, and neurological events will need to be evaluated. Larger studies will need to specifically examine the finding of subclinical leaflet thrombosis and its impact on valve functioning and durability. The optimal method of valve thrombosis prevention, including antiplatelet therapy, anticoagulation, or a combination of the two will need to be ascertained. Finally, as this study predominantly evaluated balloon-expandable valves, determination of the benefits and shortcomings of balloon-expandable as compared with self-expanding TAVR devices will be important.

Trial Reference

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Waksman  R, Rogers  T, Torguson  R, et al. Transcatheter aortic valve replacement in low-risk patients with symptomatic severe aortic stenosis. J. Am. Coll. Cardiol. doi: 10.1016/j.jacc.2018.08.1033

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