The diagnosis of aortic stenosis (AS) is made with auscultation. The systolic murmur of AS is usually best heard at the upper right sternal border and it typically radiates to the neck. It is an ejection type murmur with a crescendo-decrescendo pattern. The duration of the murmur is variable as is the peak intensity. A late peaking murmur is consistent with severe AS. An early peaking murmur is consistent with mild AS.
One auscultatory task is to distinguish the murmur of AS from that of mitral regurgitation (MR). The murmur of MR is usually best heard at the apex, but Gallavardin described a dissociation of the AS murmur into two components. The first component is the typical harsh systolic right sternal border murmur that radiates to the neck. It is due to the high velocity AS jet in the ascending thoracic aorta. The second component mimics MR. It is best heard at the apex. This apical component of the aortic stenosis murmur is musical. It therefore, cannot be easily distinguished from MR. It is presumably due to high frequency vibrations traveling to the apex from the calcific aortic valve. Maneuvers during auscultation are useful. Handgrip increases resistance to arterial forward flow and facilitates regurgitant reverse flow. It therefore, increases the murmur of MR and decreases the intensity of the AS murmur. An unusually long cardiac cycle will cause an AS murmur to increase in intensity, whereas the MR murmur will remain unchanged. This can be heard during a compensatory pause following a premature ventricular contraction, or during a long cardiac cycle in atrial fibrillation.
AS is quantitated and followed using transthoracic echocardiography. Thin, normally moving aortic leaflets exclude the presence of valvular AS. Thick aortic leaflets can be stenotic, or just sclerotic. A peak gradient greater than 25 mm Hg is used in our lab as the criterion for presence of stenosis rather than sclerosis. The peak and mean gradients across the valve can be determined non-invasively with Doppler. The area of the stenotic aortic valve orifice is calculated by multiplying the area of the left ventriclular outflow by the ratio of the left ventricular outflow gradient to the stenosis gradient. Both gradients are easily measured with Doppler and can be used for non-invasive follow-up of the progression of AS. Echocardiography also shows the degree and distribution of left ventricular hypertrophy.
However, when it comes to distinguishing whether the etiology of the murmur is AS or MR, it is color Doppler that clarifies the nature of the systolic murmur by showing the presence or absence of mitral insufficiency. Therefore, in the absence of color Doppler evidence of MR, the systolic murmur can be ascribed to the thick, or calcified aortic valve.
Unfortunately, in a large number of patients MR coexists with AS. There are many reasons for this. Progressive left ventricular hypertrophy in patients with progressive aortic stenosis is considered an adaptive response to prevent ventricular dilatation and progression of MR. When MR does progress along with the AS, it is a maladaptive consequence. Patients with aortic stenosis may have associated coronary artery disease. MR can occur following inferior myocardial infarction because of disrupted leaflet coaptation. Chordal rupture (rather than the catastrophic papillary muscle rupture) can cause different grades of MR. Left ventricular dilatation following an anterior myocardial infarction can involve the mitral annulus and cause MR. Patients with AS have variable degrees of left ventricular hypertrophy. Typically the hypertrophy is concentric with variable cavity to wall thickness ratios. Some patients may have an intracavitary gradient. Left ventricular ejection may result in intraventricular obstruction, which in turn, can cause MR. In the patient with calcific aortic stenosis, there is often calcification of the mitral annulus as well. This results in some disruption of mitral leaflet coaptation with consequent mitral insufficiency.
Although color Doppler can be very helpful in excluding the presence of MR, it can be misleading about the severity of MR when it coexists in patients with AS. Color Doppler is simply a spatial display of velocities. MR Doppler velocities are always high because there is always a large gradient between the left ventricle and left atrium in systole. Yet, when they are displayed two dimensionally with color Doppler, MR color flow velocities can both overrepresent and underrepresent the actual severity of the MR. In patients with severe AS there is an extremely high left ventricular systolic pressure which can make hemodynamically moderate MR appear severe on color Doppler.
Assessment of the mitral valve is important in the patient undergoing valve replacement for AS. The assessment of MR consists of two-dimensional and M-mode visualization of the mitral valve followed by evaluation of the color Doppler flow pattern. It then proceeds to Doppler evaluation of the pulmonary veins. Typically, the patient undergoing aortic valve replacement for AS will not require mitral valve replacement. The decision to repair or replace the mitral valve in an AS patient has to be made before starting the operation, since the surgeon prefers to operate on the mitral valve before operating on the aortic valve. Preoperative transesophageal echocardiography may be necessary to resolve this question because it can display pulmonary venous inflow with greater detail. It also provides better images of the mitral leaflets and chordae. After the stenotic aortic valve is replaced, the degree of MR on color Doppler is decreased because the left ventricular systolic pressure is decreased.
A systolic murmur is a valuable clinical finding that needs to be investigated with careful auscultation that includes hemodynamic maneuvers. Echocardiography complements auscultation by resolving some of the pitfalls.
Continuous wave Doppler measurement of aortic valve
gradient. The peak gradient is calculated as four
times the square of the peak velocity. Ealy peaking
flow in this patient has the same implication as an
early peaking murmur - mild aortic stenosis.
Transesophageal echo view of a calcified aortic
valve (arrows).
Color flow of the stenotic aortic valve.
Transesophageal echo view of the mitral valve.
Color Doppler of mitral regurgitation during the
isovolumic filling period (aortic valve is still
closed). MR denotes the regurgitant jet in the left
atrium. P is the proximal isovelocity flow convergence
used for quantitation of the degree of MR.
Left upper pulmonary vein pulsed wave Doppler flow
pattern obtained by transesophageal echocardiography.
There are three waves: systolic S wave, diastolic D
wave, atrial reversal A wave. This image shows an
abnormal diastolic dominant pattern. Normally the S
wave is larger than the D wave. In severe MR there
may be another wave of systolic flow reversal.
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