Imaging
Pitfalls and Challenges in the Echocardiographic Diagnosis of Aortic Stenosis
Adrian Chenzbraun
Department of Cardiology, Royal Liverpool University Hospital
Abstract
Aortic stenosis is the most prevalent valvulopathy in the developed world, and increasing numbers of elderly patients are considered for aortic valve replacement. Echocardiography displaced catheterisation from its long-standing use in the diagnosis of aortic stenosis and offers a simple, reliable, non-invasive method that is suitable for follow-up for the assessment of aortic stenosis patients. The truly complex nature of the haemodynamic patterns in these patients is responsible for possible inconsistencies and apparently unclear echocardiographic results. Patients with only mild aortic stenosis as supported by valve appearance and calculated area may nevertheless exhibit surprisingly high gradients. On the other hand, patients with truly severe aortic stenosis may have only modestly elevated gradients, whether due to decreased left ventricular function or to other mechanisms still under investigation. This article reviews the frequently encountered ‘puzzling’ echocardiographic scenarios together with their most likely haemodynamic background and significance in terms of final diagnosis and clinical management.
Keywords
Aortic stenosis, Doppler, echocardiography, continuity equation, pressure recovery
a.chenzbraun@talktalk.net
In the developed world, aortic stenosis (AS) represents the most prevalent valvular heart disease. The final stage of AS is transformation of the aortic valve in a severely restricted, thickened, calcific valve; however, the initiating process is less likely to be a degenerative one, but rather similar to atherosclerotic plaque formation. The process is age- dependent: more than 25% of individuals above 65 years of age have aortic sclerosis (i.e. valve thickening without significant leaflets motion reduction), but this prevalence reaches 48% in those over 85 years of age. A minority of these sclerotic valves progress to haemodynamic stenosis, which is noted in up to 7% of individuals over 65 years of age. While even severe AS may be well tolerated for long periods of time, once it becomes symptomatic the prognosis without surgery is dismal, with a yearly mortality rate of 25%, up to three-quarters of patients expected to die within three years and a median survival of about one year if cardiac failure is present.1,2
Peri-operative mortality for isolated aortic valve
replacement (AVR) is higher than for uncomplicated coronary artery bypass graft (CABG) – 3–5% below 70 years of age and 5–15% in the older population3
– but results are excellent and AS patients who undergo
successful AVR have a similar life expectancy to a matched population free of aortic valve disease. Current guidelines mandate AVR for patients with severe AS and any of the following symptoms: left ventricular (LV) systolic dysfunction (not related to other causes), need for CABG or aortic surgery or abnormal response to exercise.3
Of note, the presence of
symptoms, which is by definition subjective and, occasionally, difficult to interpret in the presence of other pathologies, has to be supplemented by objective evidence of AS severity and/or its effect on the LV.
Historically, cardiac catheterisation defined AS in terms of directly measured transvalvular gradient and aortic valve area (AVA) calculated by
10
Flow Velocities and Gradients
Both the peak flow velocity (Vmax) and the mean gradient are obtained by Doppler interrogation of the aortic flow. As such, good alignment of the Doppler line and the flow direction (<20º) is required for accurate
and reproducible results. As gradients are calculated as ∆P=4(V22–V12) (full Bernoulli equation), Vmax is used rather than peak gradient to minimise the effect of small variations of velocity readings on the final
result; this is less of a problem for the mean gradient that is obtained by integrating all the instantaneous gradients generated during ejection and is not a simple computation of mean velocity. For valvular jet velocities (V2) >3m/second and subvalvular velocities (V1)
© T O UCH BRIEFINGS 2010
the Gorlin formula. However, crossing the aortic valve and performing a full right and left study increases the duration and the risk of the procedure and provides only haemodynamic but little morphological and functional information, and is not suitable for serial follow-up. For all practical purposes, echocardiography has displaced heart catheterisation for the work-up of AS and today is the main diagnostic tool in assessing AS patients. Beyond gradient and area values, echocardiography provides a comprehensive assessment of the aortic valve and aortic root morphology, which is of interest when planning the surgery, and of co- existent cardiac pathologies (see Table 1). It is also instrumental in assessing special subgroups of patients with low gradients or decreased LV contractility, or those who may be considered for AVR even if asymptomatic. The central role of echocardiography in the management of AS patients is acknowledged by the use of echocardiographic indices to define AS severity and indications for surgery3,4
echocardiographic indices used to assess AS severity are summarised in Table 2 and discussed below.
(see Table 2). The main
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