Heart sound splitting

Splitting.
Splitting of the first heart sound is usually not detectable clinically; however, when it occurs it is
most often due to the cardiac conduction abnormality known as complete right bundle branch block.

Increased normal splitting (wider on inspiration) of the second heart sound occurs when there is
any delay in right ventricular emptying, as in right bundle branch block (delayed right ventricular
depolarisation), pulmonary stenosis (delayed right ventricular ejection), ventricular septal defect
(increased right ventricular volume load), and mitral regurgitation (because of earlier aortic valve
closure, due to more rapid left ventricular emptying).
In the case of fixed splitting of the second heart sound, there is no respiratory variation (as is
normal) and splitting tends to be wide. This is caused by an atrial septal defect where equalisation
of volume loads between the two atria occurs through the defect. This results in the atria acting as a
common chamber.
In the case of reversed splitting P2 occurs first and splitting occurs in expiration. This can be due to
delayed left ventricular depolarisation (left bundle branch block), delayed left ventricular emptying
(severe aortic stenosis, coarctation of the aorta) or increased left ventricular volume load (large
patent ductus arteriosus). However, in the last-mentioned, the loud machinery murmur means that
the second heart sound is usually not heard.