Normal splitting widens on inspiration; wide, fixed and reversed splitting are abnormal
Mnemonic
“A2 before P2, and inspiration widens the gap”, because inspiration increases venous return and delays pulmonary valve closure.
- Normal (physiological) splitting - widens on inspiration, closes on expiration
- Wide splitting - anything delaying P2: right bundle branch block, pulmonary stenosis, right ventricular failure
- Fixed splitting, unchanged with respiration - atrial septal defect
- Reversed (paradoxical) splitting, widening on expiration - anything delaying A2: left bundle branch block, severe aortic stenosis, right ventricular pacing
“Fixed is an ASD; reversed is left sided.”
Fixed splitting occurs in atrial septal defect because the shunt equalises filling between the atria throughout the respiratory cycle, so respiration no longer alters right sided volume.
A loud P2 suggests pulmonary hypertension; a soft or absent A2 suggests severe aortic stenosis.
Expansion
- Physiological (normal) - inspiration increases venous return to the right heart, delaying pulmonary valve closure, so the split widens on inspiration
- Wide splitting - anything delaying right ventricular emptying: right bundle branch block, pulmonary stenosis
- Fixed splitting - splitting that does not vary with respiration: atrial septal defect, because the shunt equalises the effect of respiration between the atria
- Reversed (paradoxical) splitting - the aortic valve closes after the pulmonary, so the split is heard in expiration and disappears on inspiration: left bundle branch block, severe aortic stenosis
The organising idea is timing. Normally the pulmonary valve closes second; delay it further and the split widens, but delay the aortic valve past the pulmonary and the order reverses, which flips the respiratory pattern.