Brain natriuretic peptide (BNP) or NT-proBNP is a biomarker for diagnosis and prognostication in conditions associated with myocardial wall stress, including aortic stenosis. In such conditions, activation of the BNP gene in cardiomyocytes results in the production of an intracellular precursor called proBNP-108. This is cleaved to generate the biologically inactive NT-proBNP and the biologically active BNP. BNP stimulates natriuresis and vasorelaxation via inhibition of renin, aldosterone and sympathetic nervous activity, in an attempt to correct increased myocardial wall stress.

NT-proBNP levels are known to correlate with ventricular wall stress and severity of HF (Abraham WT et al. N Engl J Med 2002;347:161–167). Likewise, NT-proBNP is elevated in aortic stenosis and has been associated with increased all-cause 3-year mortality in patients with severe aortic stenosis (Auensen et al. PLOS One 2017; https://doi.org/10.1371/journal.pone.0179304)

Adapted from: http://circ.ahajournals.org/content/123/18/2015

Although left ventricular hypertrophy is a physiological, compensatory response to preserve cardiac output, it results in reduced diastolic compliance. Eventually, LV end-diastolic pressure (LVEDP) rises, which causes a corresponding increase in pulmonary arterial pressure. While patients with severe aortic stenosis typically have preserved LV systolic function and cardiac output for many years, cardiac output often fails to rise during exercise, resulting in exertional symptoms of the type described by Mr Smith. Furthermore, diastolic dysfunction and raised pulmonary arterial pressure results in pulmonary oedema, like in this CXR.

Eventually, severe aortic stenosis results in LV systolic dysfunction. Consequent activation of the renin-angiotensin-aldosterone system compounds the fluid overload and results in an overt heart failure syndrome.

Echocardiography measures the anatomical structures of the heart and how they move in the cardiac cycle. It can be used to measure the fraction of blood ejected during systole, the effective cross-sectional area of the aortic valve and the pressure gradient across the valve (the higher this number, the bigger the drop in pressure between the left ventricle and aorta, and the more severe the aortic stenosis).

All of these parameters have normal ranges, which are easily accessible online if you’re interested, and these help grade the severity of aortic stenosis. In this case, the parameters point to severe disease.

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Revision of aortic valve anatomy

The aortic valve has 3 equally sized cusps, separated by commisures and supported by a fibrous annulus. The cusp-free edges form a slight thickening at the mid-point; this is known as the Arantius nodule. There is a Valsalva sinus behind each cusp, which shares a name with the cusp (right, left and non-coronary cusps). At the superior margin of the sinuses is the sinotubular junction.

In ‘short axis’ (an echocardiography description of a cross-section), all three cusps are visible. This makes the ‘Mercedes Benz’ sign, seen in the above pathological image (Fig 5 and associated videos with normal and abnormal examples).

From top, going clockwise, these are the right-, left- and non-coronary cusps (the latter so called because there is no associated coronary artery).

The view seen in the video is a ‘parasternal long axis view’. This is demonstrated in Fig 6, where the aortic valve is labelled.

In a patient with breathlessness and chest tightness, it is important to exclude ischaemic heart disease as a cause. While the examination and investigations to date point to a diagnosis of aortic stenosis, it is nonetheless important to exclude coronary artery disease.

Furthermore, aortic valve surgery may be a treatment option in this patient and it is therefore necessary to exclude concomitant coronary artery disease (that could be fixed simultaneously with coronary artery bypass grafting). While non-invasive assessment (CT coronary angiogram, for example) is an option, his age and risk factors make invasive angiography a more appropriate test.