The audibility of the different sounds varies across the precordium. Normally auscultation takes place at the following sites [Figure 13]:
Figure 13: Auscultation points
A: left parasternal 3rd intercostal space (Erb’s point):
1st and 2nd sounds are of near equal clarity
B: right parasternal 2nd intercostal space:
Aortic valve components of the 2nd sound are most clear
C: left parasternal 2nd intercostal space:
Pulmonary valve component of the 2nd sound is most clear
D: left parasternal 4th/5th intercostal space:
Tricuspid valve component of 1st sound the most clear
E: 5th intercostal space on the left at the apex:
Mitral valve components of 1st sound the most clear
Opening click
A high-frequency click during systole occurs in the case of a mitral or tricuspid valve prolapse.
Opening snap
A high frequency opening sound in diastole occurs in the case of mitral valve or tricuspid valve stenosis.
Splitting of sounds
Splitting of the 1st sound
The 1st sound consists of two components: the closure of the mitral valve and the tricuspid valve. In healthy people there is normally a 0.02 to 0.03 second difference between the 2 components of the first sound.
Physiological conditions
In 85% of people, the splitting of the two components of the 1st sound can be observed under normal physiological conditions. Mostly this is only audible in the left 4th or 5th intercostal space.
Pathophysiological conditions
Under pathophysiological conditions the splitting of the two components of the 1st sound can increase (e.g. in the case of delayed activation of the right ventricle as a consequence of conduction disorders or in the case of right heart failure).
In the case of a left bundle branch block as a consequence of delayed mitral valve closure, reverse splitting occurs; the tricuspid valve then closes before the mitral valve.
Splitting of the 2nd sound
The components of the 2nd sound (closure of the aortic valve and pulmonary valve) can regularly be heard separately under physiological conditions. This is best heard parasternally in the left 2nd intercostal space.
Physiological conditions
During inspiration the right ventricle can fill further. The ejection period in systole then lasts longer as a result of which the pulmonary valve closes later. The splitting of the 2 components of the 2nd sound is then increased and therefore more audible. This is particularly the case in young people.
Pathophysiological conditions
Under pathophysiological conditions an increase in the splitting of the 2nd sound occurs in the case of delayed or extended right ventricular ejection (e.g. in the case of pulmonary hypertension or right bundle branch block).
Reverse splitting of the 2nd sound occurs in the case of delayed or extended left ventricular ejection (e.g. in the case of left congestive heart failure or left bundle branch block).
Loudness of the sounds
Normally at the height of Erb’s point the intensity of the first and second heart sound will be more or less comparable. The loudness depends on the distance between the valves and the stethoscope. In children and slender people the sounds are very loud and in patients with obesity, emphysema or pericardial fluid, for example, the sounds are soft.
Additionally, abnormalities in one of the valves or in the position of the valves can cause a change in the loudness of S1 or S2.
Rhythm
Under normal physiological conditions there is a regular heart rhythm generated by the sinus node with a frequency of between 60 and 100 beats per minute. A frequency of less than 60 beats per minute is referred to as bradycardia and a frequency above100 beats per minute is known as tachycardia.
A physiological change in the rhythm that may be observed in children and young adults is the so-called respiratory arrhythmia. During inspiration the pressure in the thorax decreases as a result of which more blood is sucked towards the heart. The sinus node becomes somewhat stretched as a result of this, which leads to an increase in frequency.
Under pathophysiological conditions cardiac arrhythmias can develop, for example, atrial fibrillation in which there is an irregular heart rhythm [Figure 14]. In that case the stroke volume is sometimes so reduced that the pulse wave is too small to be felt at the radial artery. There is then a difference between heart rate and pulse rate. This is called a pulse deficit.
Figure 14: Arrhythmias
1. Supraventricular extrasystoles
2. Ventricular extrasystoles
3. Sinus arrhythmia
4. Atrial fibrillation