The bell of the stethoscope is better for detecting lower-frequency sounds whilst the diaphragm is better for higher frequencies. The bell is usually used to listen to the mitral valve and the diaphragm at all other sites. Auscultation is usually performed with the patient sitting up or reclined at about 45°. Where variations are required, they will be described.
Mitral area: At the apex beat, as the left ventricle is closest to the thoracic cage.
Tricuspid area: Inferior right sternal margin is the point closest to the valve in which auscultation is possible.
Pulmonary area: Left second intercostal space close to the sternum is where the infundibulum is closest to the thoracic cage.
Aortic area: Right second intercostal space close to the sternum is where the ascending aorta is nearest to the thoracic cage. The best place to hear the heart valves is not necessarily directly over the anatomical site.
Heart sounds The intensity of heart sounds and murmurs is graded as follows on Levine’s scale:
I – lowest intensity, difficult to hear even by experts.
II – low intensity, but usually audible to all listeners.
III – medium intensity, easy to hear even by inexperienced listeners, but without a palpable thrill.
IV – medium intensity with a palpable thrill.
V – loud intensity with a palpable thrill. Audible even with the stethoscope placed on the chest, with the edge of the diaphragm.
VI – loudest intensity with a palpable thrill. Audible even with the stethoscope raised above the chest. Listen first for the heart sounds. They are called S1 and S2 and are traditionally described as ‘lub’ and ‘dub’ respectively.
The first sound (S1) is caused by closure of the mitral and tricuspid valves and the two sounds tend to merge as one. When considered separately, the closure of the mitral and tricuspid valves is called M1 and T1 respectively.
The second sound (S2) is caused by closure of the aortic and pulmonary valves. They are slightly apart with the aortic component, also called A2, slightly after the pulmonary closure called P2.
Additional sounds The differentiation of 3rd sounds, 4th sounds, opening snaps and widely split S1 or S2 can be daunting.
A 3rd sound occurs in heart failure and produces a cadence like a galloping horse. Hence the term ‘gallop rhythm’. An innocent 3rd sound can occur in children and young adults but never over 30 years old.
A 4th sound occurs just before the 1st and is an abnormal sound of the A-V valves opening as the atria contract. Therefore it cannot occur in atrial fibrillation. It occurs with ventricular hypertrophy, ischaemic heart disease, dilated cardiomyopathy, hyperdynamic circulation, arrhythmia and heart block. The timing of an opening snap in mitral stenosis is similar. It is usually of rheumatic origin. Again atrial systole is essential and so it cannot occur in atrial fibrillation. An atrial myxoma can ‘plop’ during atrial systole and cause a late diastolic sound.
Note the timing of murmurs. Is it systolic or diastolic? First listen to the lub dub and then get the timing. Some murmurs may obscure the heard sounds. Systolic murmurs can be innocent but are rarely so unless the patient is a child or pregnant. Diastolic murmurs are always pathological.
- Mitral murmurs are best heard at the apex and radiate to the axilla.
- Mitral sounds can be accentuated with the patient in the left lateral position.
- Hence, to listen to a mitral murmur, first listen to the apex, then listen round to the mid-axillary line at the same level. Return the bell to the apex and, keeping it there, ask the patient to lie on the left side.
- Note the timing of any murmur. Mitral regurgitation produces a pansystolic murmur of roughly even intensity throughout systole.
- Mitral stenosis produces a diastolic murmur described as presystolic. As soon as the murmur finishes, the first sound is heard.
- Mitral valve prolapse produces a mid-systolic click.
Austin Flint’s murmur may occur in aortic regurgitation. This is a soft, rumbling, low-pitched, late diastolic murmur which is heard best at the apex. It is thought to be due to a functional mitral valve stenosis, as the backflow of blood from the aorta presses on the anterior leaflet of the mitral valve, slightly occluding the flow from the atria.
The atrial kick just before systole accentuates this flow, to produce Austin Flint’s murmur.
- Tricuspid murmurs are uncommon. The timing is as for mitral murmurs but they are best heard at the lower right sternal edge.
- Tricuspid stenosis is very rare. Regurgitation may occur in right ventricular hypertrophy and dilated cardiomyopathy. It will produce a marked wave on the JVP.
- Tricuspid regurgitation will not radiate to the axilla.
Pulmonary and aortic murmurs
The pulmonary and aortic valves are both best heard in the 2nd intercostal space, to the left and right respectively. This can make differentiation quite difficult. Sound from the aortic valve is often transmitted to the carotid and can be heard by placing a stethoscope over the carotid bifurcation.
- Pulmonary stenosis will produce a flow murmur that gets louder then softer (crescendo-decrescendo) during systole. Pulmonary ejection sounds, unlike aortic ones, tend to diminish or disappear in inspiration.
- A similar sound occurs with aortic stenosis but it is transmitted to the carotids.
- Aortic sclerosis occurs in the elderly and produces a murmur similar to aortic stenosis but it is poorly transmitted or not transmitted to the carotids. It is transmitted to the apex and the mid-axillary line.
- In aortic stenosis, A2 is soft. In aortic sclerosis, A2 is normal or loud. Systolic murmurs in the elderly are quite common.
- They indicate cardiac disease and are associated with increased cardiac mortality.
- Pulmonary or aortic regurgitation produces an early diastolic murmur, as this is when the arterial pressure is at its height. An aortic murmur of regurgitation is best heard using the diaphragm of the stethoscope with the patient sitting forward in full expiration. Ask the patient to sit forward, and put the stethoscope in place. Say, ‘Take a big breath in – breathe right out – and hold it’. This will give a few seconds to listen for the murmur. Few people can hold their breath in full expiration for more than a few seconds, especially if unfit.
- Note all murmurs arise from valves. Some are flow murmurs where rapid flow during ejection causes turbulence, especially at the pulmonary or aortic outlet. This occurs in a hyperdynamic state as in anaemia, severe thyrotoxicosis or possibly with fever. It may also occur in pregnancy but it is essential to exclude cardiac disease. The flow murmur of atrial septal defect is described below.
- Atrial septal defect (ASD) with a significant left to right shunt will produce a pulmonary flow murmur. The murmur does not originate from the atria and, unless there is a significant shunt, there may be no murmur.
- Ventricular septal defect (VSD) produces a harsh systolic murmur, heard best along the left sternal edge. It may be necessary to auscultate all along the line to find it if it is small. There is little correlation between the size of VSD and the intensity of the murmur. Maladie de Roger can be very loud and a massive defect quiet. It may be part of a more complex syndrome such as Fallot’s tetralogy.