An Aortic Valve That Cannot Decide Whether It Is Severe
A 76-year-old retired teacher is referred after one episode of syncope while gardening and 6 months of exertional dyspnoea. She feels "fine" now and does not want surgery. Transthoracic echocardiography in your lab shows: LVEF 58%, LVEDD 42 mm, LVESD 26 mm, stroke volume index 31 mL/m², body surface area 1.55 m². The aortic valve is heavily calcified with restricted opening; peak velocity is 3.4 m/s, mean gradient 26 mmHg, dimensionless velocity index 0.19, and continuity-equation area 0.95 cm². The LVOT diameter was recorded as 18 mm. The LVOT pulsed-wave tracing in the report is noisy and the sample volume appears to have been placed partly in the aorta. The aortic jet is eccentric and the continuous-wave envelope is only faintly outlined on two of three beats. Blood pressure is 128/74 mmHg and heart rate is 62 in sinus rhythm with frequent premature atrial complexes. She lives with her daughter and walks 400 m daily without stopping, though more slowly than a year ago.
1. Is this severe aortic stenosis? Show which numbers you trust, which you do not, and why they disagree.
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The numbers disagree with each other, which is the central problem. An area of 0.95 cm² sits in the severe range, while a mean gradient of 26 mmHg and a peak velocity of 3.4 m/s sit in the moderate range. That discordance has to be resolved before anything is called severe.
The stroke volume index of 31 mL/m² confirms low flow, so the pattern is consistent with low-flow, low-gradient aortic stenosis with preserved ejection fraction, sometimes called paradoxical low-flow low-gradient stenosis. That diagnosis requires excluding measurement error first, because it is over-diagnosed.
The LVOT diameter is the weak link. Area scales with the square of the radius, so a 1-mm error in an 18-mm diameter changes the calculated area by roughly 12%. In a small woman with a body surface area of 1.55 m² an 18-mm annulus may be genuine, but it must be measured in mid-systole at the annulus, from a zoomed parasternal long-axis view, with the inner-edge to inner-edge convention used consistently.
The LVOT Doppler is more worrying. A sample volume placed partly in the aorta records higher velocities than the subaortic flow, which inflates the stroke volume and the area, and a noisy trace makes the VTI unreliable. The continuous-wave envelope is the other problem: an eccentric jet loses signal, so the peak velocity and mean gradient are underestimated. Two faintly outlined beats out of three is not adequate. Frequent premature atrial complexes also produce beat-to-beat variation, and post-extrasystolic beats should be excluded.
What I do trust: the heavy calcification, the dimensionless velocity index of 0.19, which supports severity and is less dependent on LVOT diameter than the continuity equation, and the low stroke volume index.
Conclusion: severe stenosis is plausible but not established by this study; the correct answer is to repeat the measurements properly rather than commit to either label.
2. How do you resolve the discordance? What tests would you order, and which ones would be unhelpful in this particular patient?
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The first step is a repeat study by an experienced sonographer, not a new test. Specifically: LVOT diameter measured at the annulus in mid-systole in the zoomed parasternal long axis, with an average of at least three measurements; LVOT VTI from the apical five-chamber or three-chamber view with the sample volume clearly subaortic and the trace confirmed on screen; continuous-wave Doppler from multiple windows, including the apical, right parasternal and suprasternal positions, to find the best-aligned envelope for the eccentric jet; and planimetry of the anatomical orifice in the short axis if the image quality allows. Recalculate the dimensionless velocity index and the stroke volume index from the corrected data.
Second, aortic valve calcium scoring by CT. In a patient with discordant measurements this is often the deciding test, using the sex-specific thresholds applied at your centre, because a heavily calcified valve above the threshold supports severe stenosis and a lightly calcified valve argues against it.
Third, symptom assessment. Her account of being fine is limited by her baseline. A careful functional history, ideally a walking or exercise test with supervision, and an NT-proBNP will help establish whether she is truly asymptomatic. Exercise stress echocardiography is reasonable in an apparently asymptomatic patient to provoke symptoms and assess contractile reserve.
What would be unhelpful: low-dose dobutamine stress echocardiography. That is the tool for low-flow low-gradient stenosis with reduced ejection fraction, to test contractile reserve and flow recruitment. Her ejection fraction is 58%, so dobutamine will not answer the question and carries some risk.
I would also assess for a competing cause of her dyspnoea, including diastolic function, mitral regurgitation and anaemia, since none of these is excluded by the aortic findings.
3. Assuming severe stenosis is confirmed, how do you counsel a woman who says she feels fine and does not want surgery?
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The counselling should be specific about what her own data show, and it should not begin with the word surgery.
First, establish her symptom status properly. She has had a syncope while gardening, which is not a benign feature in aortic stenosis, and her exercise tolerance has fallen over a year even if she still manages 400 m. Syncope in confirmed severe aortic stenosis is an indication for intervention, not a symptom to be watched. The fact that she feels fine now reflects how she has adapted her activity, not the absence of disease.
Second, explain the risk of waiting in concrete terms: once severe aortic stenosis produces symptoms, the untreated outlook is poor, with a substantial annual risk of death or heart failure, and the risk of sudden death is real but concentrated in those with symptoms. She should understand that the syncope may recur, and that the next episode may not happen where her daughter can help.
Third, explain that the choice is not 'surgery or nothing'. A heart team assessment would consider surgical replacement versus transcatheter replacement, and her age, frailty, anatomy and comorbidity will determine which is appropriate. She should be told that the assessment itself does not commit her to anything.
Fourth, be honest about uncertainty. If the repeat echocardiogram and calcium score show only moderate disease, the correct plan is watchful waiting with clinical review and echocardiography every 6-12 months, plus a clear instruction about which symptoms should bring her back immediately. That is a legitimate outcome, and telling her so makes the recommendation to intervene more credible if the repeat study confirms severe disease.