Sept. 24, 2021
The diagnosis of severe aortic stenosis is straightforward in the context of high transvalvular gradients associated with a severely reduced valve area (high-gradient aortic stenosis, or HGAS). The presence of discordant measurements with severely reduced valve area but low gradients, however, makes diagnosis much more challenging. Low-gradient aortic stenosis (LGAS) has been reported in association with conditions including diastolic dysfunction, other concomitant valvular disease, right ventricular failure and atrial fibrillation.
Atrial fibrillation may further reduce stroke volume in its own right. Current practice is to average at least five consecutive cardiac cycles during atrial fibrillation when assessing transvalvular gradients, effectively concealing high-signal gradients that meet criteria for severe aortic stenosis that if taken alone would qualify as severe aortic stenosis.
Doppler signals during echocardiogram
Vuyisile T. Nkomo, M.D., M.P.H., a cardiologist at Mayo Clinic in Rochester, Minnesota, and research colleagues used the Mayo Clinic Echocardiography Laboratory database to determine the significance of high transvalvular gradients in atrial fibrillation LGAS. Results were published in Circulation: Cardiovascular Imaging in 2021.
Researchers identified 1,541 patients who received transthoracic echocardiography examination between Jan. 1, 2012, and Dec. 31, 2016, for assessment of native aortic stenosis with an aortic valve area ≤ 1 cm2 and left ventricular ejection fraction ≥ 50%. Patients were divided according to rhythm (sinus rhythm versus atrial fibrillation) at the time of echocardiography and further categorized with HGAS (average peak velocity ≥ 4 meters per second or mean gradient ≥ 40 mm Hg) or LGAS (average peak velocity < 4 meters per second and mean gradient <40 mm Hg). Researchers reported:
- Sinus rhythm HGAS in 1,036 patients (67%)
- Atrial fibrillation HGAS in 178 patients (12%)
- Sinus rhythm LGAS in 236 patients (15%)
- Atrial fibrillation LGAS in 91 patients (6%)
Baseline clinical characteristics and computerized tomography aortic valve calcium scores were collected from the medical record.
Dr. Nkomo notes: "Patients with atrial fibrillation LGAS had a high prevalence of high-signal gradients (33%) compared to patients with sinus rhythm LGAS (9%). While both patient groups (atrial fibrillation and sinus rhythm LGAS) were older with more comorbidities compared to patients with sinus rhythm HGAS, the prevalence of symptoms was higher in patients with atrial fibrillation LGAS and not different from patients with sinus rhythm HGAS.
"Aortic valve calcium scores also were higher in patients with atrial fibrillation LGAS compared to patients with sinus rhythm LGAS and were as high as aortic valve calcium scores in patients with sinus rhythm HGAS. Aortic valve calcium scores were even higher among the 33% of patients with atrial fibrillation LGAS with high-signal gradients.
"Over a median of 2.1 years of follow-up, there were 316 deaths in the HGAS group (sinus rhythm 238, atrial fibrillation 78) and 116 deaths in the LGAS group (sinus rhythm 75, atrial fibrillation 41). Adjusted for age, sex, Charlson comorbidity index and time-dependent aortic valve replacement, the mortality risk compared with the referent group sinus rhythm HGAS was higher in patients with atrial fibrillation HGAS, higher in patients with atrial fibrillation LGAS overall and in patients with atrial fibrillation LGAS with high-signal gradients, but was not different in patients with atrial fibrillation LGAS without high-signal gradients or in patients with sinus rhythm LGAS."
Implications for clinical practice
"Discordant aortic stenosis severity, especially during atrial fibrillation, should prompt an immediate comprehensive and integrative evaluation for severe aortic stenosis. The presence of high-signal gradients facilitates diagnosis of severe aortic stenosis," says Dr. Nkomo. "In the setting of LGAS, the presence of atrial fibrillation should prompt consideration of different management, given the marked differences in aortic valve calcium scores and outcomes according to the presence of this rhythm. Furthermore, using the single-highest signal to diagnose severe aortic stenosis would not only be accurate, but also simpler.
"Our study also shows that the excess mortality in patients with atrial fibrillation compared with patients with sinus rhythm is explained by more than older age and clinical comorbidities, and atrial fibrillation should probably be factored into decision-making about timing or urgency of aortic valve replacement."
For more information
Echocardiography Laboratory. Mayo Clinic.
Alsidawi S, et al. High prevalence of severe aortic stenosis in low-flow state associated with atrial fibrillation. Circulation: Cardiovascular Imaging. 2021;14:e012453.
Mayo Clinic Cardiovascular CME Podcast. Atrial fibrillation and underestimation of aortic stenosis severity. Mayo Clinic. 2021.