Estimation of oxygen consumption in elderly patients with aortic stenosis.

BACKGROUND: Invasive evaluation of aortic stenosis requires measuring cardiac output. With the Fick equation, a measure of oxygen consumption (VO2) is required. Standard equations for estimating VO2 were derived in younger and healthier populations than the ones referred for possible transcatheter aortic valve replacement. The goal of this study was to determine the best method of estimating VO2 in elderly patients with aortic stenosis. METHODS: We directly measured VO2 in elderly patients undergoing invasive assessment of aortic stenosis. We compared standard equations estimating VO2 and two prespecified hypothesized equations for VO2 to determine which was most accurate. We also examined the subgroup of patients with low flow. RESULTS: Among 51 patients, aged 80-97 years, the mean VO2 was 198 mL/min. Using 125*body surface area (BSA) to estimate VO2 the average error was 35 mL/min, and 67% of values were within 25% of the true value. Using 3*Weight to estimate VO2, those numbers were 29 mL/min and 65%. The hypothesized equations did better: 100*BSA had error of -12 mL/min and 90% within 25% of measured VO2; for 2.5*Weight it was -9 mL/min and 84%. Among the 20 patients with low flow, hypothesized equations performed best. Using 2.5*Weight and 100*BSA there were 90% and 85% within 25% of measured VO2, respectively, compared to 55% and 75% when 3*Weight and 125*BSA were used. Weight and BSA were the only independent predictors of VO2. CONCLUSIONS: When estimating VO2 in an elderly population with aortic stenosis, the best equations are 2.5*Weight and 100*BSA.

Comparison of invasive and noninvasive assessment of aortic stenosis severity in the elderly.

BACKGROUND: Aortic valve area (AVA) in aortic stenosis (AS) can be assessed noninvasively or invasively, typically with similar results. These techniques have not been validated in elderly patients, where common assumptions make them most prone to error. Accurate assessment of AVA is crucial to determine which patients are appropriate candidates for aortic valve replacement. METHODS AND RESULTS: Fifty elderly patients (mean 86 years, 46% female) referred for cardiac catheterization to evaluate AS also underwent transthoracic echocardiography within 24 hours. To minimize assumptions all patients had 3-dimensional echocardiography (Echo-3D), and at catheterization using directly measured oxygen consumption (Cath-mVo(2)) and thermodilution cardiac output (Cath-TD). Correlation between Cath-mVo(2) and Echo-3D AVA was poor (r=0.41). Cath-TD AVA had a moderate correlation with Echo-3D AVA (r=0.59). Cath-mVo(2) (AVA=0.69 cm(2)) and Cath-TD (AVA=0.66 cm(2)) underestimated AVA compared with Echo-3D (AVA=0.76 cm(2;) P=0.08 for comparison with Cath-mVo(2); P=0.001 for Cath-TD). Compared with Echo-3D, the sensitivity and specificity for determining critical disease (AVA <0.8 cm(2)) were 81% and 42% for Cath-mVo(2), and 97% and 53% for Cath-TD. The only independent predictor of the difference between noninvasive and invasive AVA was stroke volume index (P<0.01). Resistance, a less flow-dependent measure, showed a stronger correlation between Echo-3D and Cath-mVo(2) (r=0.69), and Echo-3D and Cath-TD (r=0.77). CONCLUSIONS: Standard techniques of AVA assessment for AS show poor correlation in elderly patients, with frequent misclassification of critical AS. Less flow-dependent measures, such as resistance, should be considered to ensure that only appropriate patients are treated with aortic valve replacement.