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ABSTRACT & COMMENTARY
By Michael H. Crawford, MD, Editor
SOURCE: Clavel MA, et al. Paradoxical low-flow, low-gradient aortic stenosis despite preserved left ventricular ejection fraction: New insights from weights of operatively excised aortic valves. Eur Heart J 2014;35:2655-2662.
Low-flow, low-gradient aortic stenosis (AS) is usually associated with reduced left ventricular (LV) performance. When LV systolic function is normal, it has been labelled “paradoxical.” Such patients have considerable concentric LV hypertrophy and a restrictive physiology with a normal LV ejection fraction (EF) but low stroke volume. The prognosis of these patients compared to those with similar severity of AS but normal stroke volume is unclear from the literature, raising the questions of whether AS severity can be determined accurately. Thus, these investigators from Quebec, Canada, hypothesized that aortic valve weight after excision at surgery would be a surrogate for AS severity, and sought to compare it in the paradoxical low-flow, low-gradient (PLF-LG) patients vs AS patients with normal flow and high gradients (NF-HG). They studied two groups: 250 patients with severe AS (valve area ≤ 1.0 cm2 and index ≤ 0.6, n = 33) and either paradoxical AS or high-flow, high-gradient AS (n = 105) undergoing surgical aortic valve (AV) replacement, and 150 patients with moderate-to-severe AS with NF-HG undergoing AV replacement during coronary bypass surgery. The latter group was used to define a valve weight cutoff for severe AS using echo Doppler as the standard.
Baseline data showed that PLF-LG patients had more dyslipidemia and coronary artery disease. PLF-LG patients had smaller LVs with lower mass than NF-HG patients. Interestingly, BNP levels and AV area were not different between these two AS groups. There were more patients with bicuspid valves in the NF-HG group (42% vs 15%, P = 0.003). AV weight was higher in the NF-HG group compared to the PLF-LG group (P = 0.02), but when dichotomized by sex, the difference was not significant in women. Using the established AV weigh cutoff from the 150 patients with moderate-to-severe AS undergoing coronary artery bypass grafting (CABG) plus AV replacement, severe AS was present in 70% of the PLF-LG group and 86% of the NF-HG patients. This finding was also only significant in men. The authors concluded that a majority of patients with PLF-LG AS have severe stenosis as defined by valve weight after surgery, and the valve gradient may underestimate stenosis severity in such patients.
This is a novel approach to studying patients with low-flow, low-gradient AS. A major issue in studying these patients is determining the gold standard for measuring AS severity. Many studies in the area suffer from measurement errors, failure to take body size into consideration, and lack of a more in-depth analysis of orifice area. They chose the weight of the aortic valve excised at surgery as compared to a comprehensive Doppler-echo evaluation to establish a weight cutoff for severe AS in patients with moderate-to-severe AS undergoing CABG and AV replacement. They then applied this cutoff to selected patients presumed to have severe AS who had an isolated AV replacement by surgery. The patients selected were divided into two groups: NF-HG and PLF-LG, the latter being paradoxical because their left ventricular ejection fraction (LVEF) was normal. More than 80% of the NF-HG patients of either sex had severe AS by valve weight and 65-80% of PLF-LG patients, depending on sex, had severe AS. These finding validate their selection criteria for surgery,
but, more importantly, highlight the fact that patients with normal LVEFs with low-flow, low-gradient AS on echo often have severe AS and benefit from valve replacement.
How do we identify the PLF-LG patients who have severe AS? The authors suggest a multimodality approach. Clinically, these patients often have considerable hypertrophy with small cavity sizes, normal LVEF, but reduced longitudinal function and high valve-arterial impedance. The first step is a comprehensive echo-Doppler approach to quantifying AV area, which could include dobutamine stress testing to identify pseudo AS and transesophageal echo to measure orifice area. If there is still uncertainty, a CT scan to quantify AV calcium content could be helpful. In this study, brain natriuretic peptide was not particularly useful. Also, in this study, only echo-Doppler AV area at rest was used to clinically characterize the patients and make surgical decisions. So this multimodality approach has not been prospectively tested.