Tricuspid has anterior, posterior and septal cusps; mitral has anterior and posterior
Mnemonic
Count the cusps: “tri before you bi” on the right side, and the reverse on the left:
- Tricuspid - 3 cusps: anterior, posterior, septal
- Pulmonary - 3 cusps: anterior, left, right
- Aortic - 3 cusps: right coronary, left coronary, non-coronary
- Mitral - 2 cusps: anterior and posterior. The only bicuspid valve
“The mitral is the only one with two, and it is named after a bishop’s mitre.”
The aortic cusps name the coronary origins: the right coronary artery arises from the right coronary sinus, the left from the left, and the non-coronary sinus gives nothing.
A bicuspid aortic valve occurs in 1 to 2 per cent of people, is the commonest congenital cardiac abnormality, causes stenosis decades earlier than a normal valve, and is associated with aortic coarctation and aortic root dilatation.
The atrioventricular valves have chordae and papillary muscles; the semilunar valves have neither, which is why papillary muscle rupture affects only mitral and tricuspid.
Expansion
Atrioventricular valves
- Tricuspid - anterior, posterior and septal cusps
- Mitral (bicuspid) - anterior and posterior cusps
Semilunar valves
- Aortic - right, left and posterior (non-coronary) cusps
- Pulmonary - right, left and anterior cusps
The atrioventricular cusps are held by chordae tendineae attached to papillary muscles, which prevent prolapse during systole. The semilunar cusps have no chordae and close passively under the pressure of the column of blood above them.
Rupture of a papillary muscle after myocardial infarction therefore causes sudden severe mitral regurgitation, whereas semilunar valve failure is usually a disease of the cusps themselves.