Abstract 11817: Calculating Aortic Root Z- Scores With Ideal Body Weight Reclassifies Risk in Overweight and Obese Patients

Abstract

Introduction: Indexing transthoracic echocardiography (TTE) aortic root diameter (AoR diam) measurements using body surface area (BSA) is important in children and small adults in whom non-indexed values may under detect dilation. However, the commonly used formula for expected AoR diam uses actual body weight, which may bias results in obese adults as AoR diam does not increase with body weight. Z-scores compare a patient’s AoR diam relative to an age, size, and sex specific population mean such that z- score = (observed AoR diam - expected AoR diam) /0.261. A normal AoR diam z-score is -2 ≤ z-score ≤2. Hypothesis: We hypothesize that using ideal body weight (IBW) in place of actual weight when calculating z-score reclassifies a significant proportion of overweight and obese patients with z-score < 2 to z-score ≥2. Methods: We performed a retrospective review of all patients with a TTE at Tufts Medical Center in 2022 and Ao root diam ≥ 4 cm. We excluded patients < 20 years old and those with inadequate TTE images or missing aortic measurements. Expected AoR diam and z-scores were calculated using both actual weight and IBW. A z-score difference, z diff = z actual weight - z ideal weight , was calculated. Results: 485 patients met our study criteria with a subset of 352 patients with BMI ≥ 25. The z diff was significantly different from zero across all BMI groups (p = 0.0003) and in the subset with BMI ≥ 25 (p<0.001). 17.9% of patients with BMI ≥ 25 with z actual weight < 2 were reclassified to z ideal weight ≥ 2 (p<0.001) compared with 2.2% of patients with BMI < 25 (p<0.001). Among AoR diam subgroups of 4 - 4.5 cm, > 4.5 - 5 cm, and > 5 cm, all reclassification occurred in the 4 - 4.5 cm group. Within the 4 - 4.5 cm group, 24.1% of patients with z actual weight < 2 reclassified to z ideal weight ≥ 2. Conclusions: Compared to current methods using actual weight, the use of IBW to calculate Ao root z-scores reclassifies nearly 2 in 10 patients with BMI ≥ 25 to Ao root dilation. Among patients with Ao root diam of 4 - 4.5 cm, nearly 1 in 4 are reclassified as dilated by z-scores calculated with IBW. Such reclassification would impact clinical decisions about increased surveillance and/or treatment. Further studies are needed to determine the optimal approach to indexing Ao root size and the implications for management.