When a healthy heart beats, it makes a “lub-dub” sound.
The first heart sound “lub”, also known as S1, is caused by the closing of the AV
valves after the atria have pumped blood into the ventricles.
The second heart sound “dub”, or S2, originates from the closing of the aortic and pulmonary
valves, right after the ventricles have ejected the blood.
The time interval between S1 and S2 is when the ventricles contract, called SYSTOLE.
The interval between S2 and the NEXT S1 is when the ventricles relax and are filled with
blood, called DIASTOLE.
Diastole is longer than systole, hence the lub-dub, lub-dub, lub-dub…
Heart sounds are auscultated at 4 different sites on the chest wall which correspond to
the location of blood flow as it passes through the aortic, pulmonic, tricuspid, and mitral
valves, respectively.
This is how SIMILAR defects associated with DIFFERENT valves are differentiated.
Heart murmurs are whooshing sounds produced by turbulent flow of blood.
Murmurs are diagnosed based on the TIME they occur in the cardiac cycle, their changes
in INTENSITY over time, and the auscultation SITE where they are best heard.
Examples of conditions associated with common systolic murmurs include:
- MITRAL valve regurgitation, when the mitral valve does NOT CLOSE properly and blood surges
back to the left atrium during systole.
The murmur starts at S1, when the AV valves close, and maintains the same intensity for
the entire duration of systole.
This holosystolic murmur is best heard at the mitral region -the apex, with radiation
to the left axilla.
Because the valve closure in mitral regurgitation is INcomplete, S1 is often quieter.
On the other side of the heart, a TRICUSPID valve regurgitation has similar timing and
shape, but it is loudest in the tricuspid area and the sound radiates up, along the
left sternal border.
- AORTIC valve stenosis, when the aortic valve does NOT OPEN properly and blood is forced
through a narrow opening.
The blood flow starts small, rises to a maximum in mid-systole at the peak of ventricular
contraction, then attenuates toward the end of systole.
This results in a crescendo-decrescendo, or a diamond-shaped, murmur which starts a short
moment after S1.
It is often preceded by an ejection click caused by the opening of the STENOTIC valve.
Aortic stenosis murmur is loudest in the aortic area and the sound radiates to the carotid
arteries in the neck following the direction of blood flow.
Again, on the other side of the heart, a PULMONIC stenosis has the same characteristics but
is best heard in the pulmonic area and does NOT radiate to the neck.
Other conditions that cause audible systolic murmurs include ventricular septal defect
and mitral valve prolapse.
An example of diastolic murmurs is aortic valve regurgitation.
This is when the aortic valve does NOT CLOSE properly, resulting in blood flowing back
to the left ventricle during diastole- the filling phase.
As the blood flows in the REVERSE direction, the murmur is best heard NOT in the aortic
area, but rather along the left sternal border.
It peaks at the beginning of diastole when the pressure difference is highest, then rapidly
decreases as the equilibrium is reached.
Other common diastolic murmurs are associated with pulmonic regurgitation, mitral stenosis
and tricuspid stenosis.