By Michael H. Crawford, MD, Editor

SYNOPSIS: An analysis of transcatheter vs. surgical aortic valve implantation showed modified BMI, a measure of frailty, predicted one-year all-cause mortality and postoperative complications.

SOURCE: Driggin E, Gupta A, Madhavan MV, et al. Relation between modified body mass index and adverse outcomes after aortic valve implantation. Am J Cardiol 2021;153:94-100.

Although clinical frailty is known to be associated with worse survival rates after transcatheter or surgical aortic valve implantation (TAVI and SAVI), it is not measured routinely, in large part because of the lack of a standardized metric that is easy to use. So-called modified BMI (mBMI), which is BMI × serum albumin × 10, has been advanced as a simple-yet-accurate estimate of frailty.

To determine its prognostic value in patients undergoing AVI, researchers assessed the tool in patients recruited for the PARTNER trials I, II, and S3, which were comparisons of TAVI to SAVI.1-3 These trials included patients with severe aortic stenosis (AS) randomized to the two implantation methods. There were 6,593 patients in the pooled analysis, after the exclusion of valve-in-valve implantations. All patients were deemed acceptable for surgery, albeit at high risk for some. The mBMI calculation was the product of BMI in kg/m2 and serum albumin in g/L. The lower the resulting number, the more frail the patient. Also, the Clinical Frailty Index (CFI) score was calculated based on gait speed, grip strength, serum albumin, and disability in activities of daily living (ADL). The primary outcome was all-cause mortality at one year following AVI. The authors also assessed a variety of secondary clinical endpoints.

Patients were divided into quartiles of mBMI to compare clinical characteristics. Eighty-four percent of patients underwent TAVI, the mean age was 83 years, and 57% were men. As mBMI decreased, the patients were older, there were more women, there were more symptoms, and the surgical risk scores were higher. Laboratory data with decreasing mBMI exhibited higher brain natriuretic peptide and lower hemoglobin. Echocardiography with a lower score showed smaller valve areas and lower left ventricular ejection fractions. In addition, lower mBMI patients stayed in the hospital longer or spent more time on the ICU. Overall mortality at one year was 16.5% and was highest in the lowest mBMI quartile at 26% (out of four total quartiles). As the mBMI values increased across the remaining three quartiles, the mortality rates progressed from 17% to 13% to 11% at the highest mBMI. Compared to the claims-based CFI, the C-statistic for mBMI was 0.68. The authors concluded since mBMI performs similarly to the more complicated CFI, mBMI is a simple, easily assessed measure of frailty in patients under consideration for TAVI.

COMMENTARY

The mBMI was independently associated with one-year all-cause mortality and a higher incidence of adverse clinical outcomes following the intervention. The importance of frailty as a contraindication to AVI is widely recognized because outcomes can be anticipated to be worse than in non-frail individuals. However, how best to measure it is unclear. Current techniques run the gamut from the complex CFI to the simple 0, 1, 2 scale, where 0 is the patient cannot perform any ADL; 1 is can perform some ADL; and 2 is can perform all ADL. The CFI includes gait speed and grip strength, which require special equipment. The Essential Frailty Toolset requires a Mini-Mental State Examination, which involves taking time to answer 30 questions.

None of these are entirely satisfactory for routine clinical use. Thus, the mBMI is attractive because it is simple yet quantitative. Also, it predicts higher one-year mortality and more postoperative complications, such as longer ICU stays and the need for mechanical circulatory support. In addition, it predicts higher rates of major adverse events, such as stroke and need for reintervention. Surprisingly, mBMI did not predict rehospitalization, perhaps because of longer initial hospital lengths of stay and the high mortality in the lowest quartiles. Considering the PARTNER participants all were at least intermediate surgical risk patients, they were older, with more comorbidities. A frailty measurement would be more discriminating in such a group. Consequently, the mBMI may not be as useful in younger, healthier patients undergoing AVI, but then no index of frailty would be useful for these patients.

REFERENCES

  1. Smith CR, Leon MB, Mack MJ, et al. Transcatheter versus surgical aortic-valve replacement in high-risk patients. N Engl J Med 2011;364:2187-2198.
  2. Leon MB, Smith CR, Mack MJ, et al. Transcatheter or surgical aortic-valve replacement in intermediate-risk patients. N Engl J Med 2016;374:1609-1620.
  3. Kodali S, Thourani VH, White J, et al. Early clinical and echocardiographic outcomes after SAPIEN 3 transcatheter aortic valve replacement in inoperable, high-risk and intermediate-risk patients with aortic stenosis. Eur Heart J 2016;37:2252-2262.