Anesthesia & Analgesia: December 2015
Whitener, George MD et al
BACKGROUND: Current guidelines define severe aortic valve stenosis (AS) as an aortic valve area (AVA) <=1.0 cm2 by the continuity equation and mean gradient ([DELTA]Pm) >= 40 mm Hg. However, these measurements can be discordant when classifying AS severity. Approximately one-third of patients with normal ejection fraction and severe AS by AVA have nonsevere AS by [DELTA]Pm when measured by preoperative transthoracic echocardiography (TTE). Given the use of positive pressure ventilation and general anesthesia in the pre-cardiopulmonary bypass (pre-CPB) period, we hypothesized that discordance between [DELTA]Pm and AVA during pre-CPB transesophageal echocardiography (TEE) would be higher than previously reported by TTE.
METHODS: We retrospectively examined pre-CPB TEE data for patients who had aortic valve replacement, with or without coronary artery bypass grafting, from 2000 to 2012. Patients were excluded if they had ejection fraction <55%, emergency surgery, repeat sternotomy, moderate or severe mitral regurgitation, or severe aortic regurgitation. Only patients with both pre-CPB AVA and [DELTA]Pm measurements were included. Patients were grouped according to severity (mild, moderate, and severe) by AVA or [DELTA]Pm. Discordance was defined as disagreement between severities based on either parameter.
RESULTS: A total of 277 patients met inclusion criteria. There were 227 patients with AVA <= 1.0 cm2. The proportion of these patients with a [DELTA]Pm < 40 mm Hg was 54% (95% confidence interval, 47%-61%). The rate of discordance was significantly higher than the rate (37%; P < 0.001) found in previously reported analyses using TTE. Of the patients with a [DELTA]Pm >= 40 mm Hg, only 8% (n = 9/113) had a discordant AVA. In contrast, of the patients with [DELTA]Pm < 40 mm Hg, 80% (n = 131/164) had a discordant AVA.
CONCLUSIONS: We confirmed our hypothesis that grading AS by [DELTA]Pm and AVA during pre-CPB TEE exhibits higher discordance than reported for TTE by others. It remains unclear whether these discrepancies reflect the effect of general anesthesia, imaging modality (TTE versus TEE) differences, inaccuracies in AS grading cutoffs when applied to pre-CPB TEE, or selection bias of the surgical population.