Importance of Discordant Grading of Moderate Aortic Stenosis
By Michael H. Crawford, MD, Editor
SYNOPSIS: A study of patients with moderate aortic stenosis by Doppler echocardiographic calculated valve area revealed 40% exhibit discordant measures, where pressure gradient is lower than expected. These patients died more often than those with concordant measurements, especially those where the discrepancy was caused by low flow.
SOURCE: Stassen J, Ewe SH, Singh GK, et al. Prevalence and prognostic implications of discordant grading and flow-gradient patterns in moderate aortic stenosis. J Am Coll Cardiol 2022;80:666-676.
Severe aortic stenosis (AS) by Doppler echocardiography calculated aortic valve area (AVA) is known to present with four categories of flow-gradient measurements: concordant (both gradient and AVA are severe) and three categories of discordant gradient and AVA — classic low-flow, low-gradient severe AS with a low left ventricular ejection fraction (LVEF); paradoxical low-flow, low-gradient severe AS with preserved EF; and normal flow, low-gradient severe AS. The prognosis can be worse for classic and paradoxical low-flow, low-gradient severe AS patients if treated conservatively than the other two categories. Similar discrepancies in measurements are seen in moderate AS, but their prognostic importance is not well defined.
Stassen et al interrogated registries for patients between 2001 and 2019 whose first echocardiogram demonstrated moderate AS, defined as a valve area between 1.0 and 1.5 cm2, a mean gradient (MG) less than 40 mmHg, and a peak aortic jet velocity of < 4 m/s. Patients with prior valve surgery, bicuspid valves, endocarditis, or other additional forms of LV outflow obstruction were excluded. Patients were divided into concordant moderate AS (MG 20 mmHg to 40 mmHg) or discordant moderate AS (MG less than 20 mmHg). The latter group was further divided into normal flow, low gradient (stroke volume index [SVi] > 35 mL/m2; LVEF greater than 50%); paradoxical low-flow, low-gradient (SVi less than 35 mL/m2; LVEF > 50%); and classical low-flow, low-gradient (LVEF < 50%). Clinical data were analyzed retrospectively from the cardiology information systems. The primary endpoint was all-cause mortality. Of the 1,974 patients included in the study (mean age = 73 years; 51% men), 60% were classified with concordant moderate AS. Those with discordant moderate AS were older, more symptomatic, and living with more comorbidities than the concordant group. Also, they recorded larger LV end-systolic volumes, lower EF and SVi, more impaired right ventricular function, and more mitral and tricuspid regurgitation.
After a median follow-up of 50 months, 44% of patients died. Those with discordant moderate AS recorded higher mortality rates (47% vs. 36% at five years; P < 0.001). Also, the discordant group were less likely to undergo AV replacement (17% vs. 40%; P < 0.001). After adjustments for other relevant prognostic variables, the discordant group still was associated with a higher mortality rate (hazard ratio, 1.19; 95% confidence interval, 1.01-1.40; P = 0.043). When examining the discordant subgroups, those with paradoxical and classical low-flow, low-gradient moderate AS recorded higher mortality rates (51%; P = 0.002 and 64%; P < 0.001 at five years, respectively) — but not the normal flow, low-gradient subgroup (36%; P = 0.77) compared to the concordant group. Adjustment for other clinical prognosticators confirmed the independent association with all-cause mortality of the classical and paradoxical groups. The authors concluded that for patients with moderate AS by calculated AVA, discordant grading by Doppler echocardiography is frequent, and the low-flow, low-gradient varieties are associated with higher mortality rates.
A discordant Doppler echocardiographic profile of a patient with a calculated AVA in the moderate range (1.0 cm2 to 1.5 cm2) is manifest when the mean pressure gradient is less than what is expected (less than 20 mmHg instead of 20 mmHg to 40 mmHg). This occurred in 40% of moderate AS patients. In 55% of these patients, the flow was normal; namely, LVEF was > 50%, SVi was > 35 mL/m2, and they received a similar prognosis to those who had concordant measurements. Likely explanations for their low gradient include measurement errors (especially of the LV outflow tract area), reduced body size, or decreased arterial compliance.
Classic low-flow, low-gradient moderate AS occurred in 31% of the discordant patients and is caused by a low EF. In these patients, the low EF usually is caused by comorbidities, such as ischemic heart disease. Paradoxical low-flow, low-gradient moderate AS was present in 14% of the discordant group. The paradox is that these patients recorded a normal EF. However, their SVi is < 35 mL/m2, usually because of a markedly thickened LV with a small end-diastolic volume. They often present with systemic hypertension or other stimuli to LV hypertrophy.
The classical and paradoxical low-flow, low-gradient AS patients receive a worse prognosis than concordant or normal-flow, low-gradient patients. Thus, perhaps the former patients should be followed more closely and for longer. Also, efforts should be made to correct the underlying reason for low flow, if possible. The only criterion in the guidelines for AV replacement in moderate AS is if cardiac surgery will be performed for other reasons. However, reducing afterload by AV replacement may improve EF or regress LV hypertrophy. Perhaps AV replacement, especially by the transcatheter method, may be reasonable in selected cases. Studies are underway to answer this question.
A study of patients with moderate aortic stenosis by Doppler echocardiographic calculated valve area revealed 40% exhibit discordant measures, where pressure gradient is lower than expected. These patients died more often than those with concordant measurements, especially those where the discrepancy was caused by low flow.
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