**4.2 Critical AS in neonates**

The term critical AS is used to describe very severe aortic valve stenosis who have high peak systolic pressure gradients across the aortic valve, signs and symptoms of congestive heart failure (CHF) are present, and/or a ductal-dependent systemic circulation exists. The pressure gradient across the aortic valve may not be high in some babies because of poor left ventricular function. They usually present during the first 24–48 hours after birth with symptoms of tachypnea, respiratory distress, cyanosis, pallor, lethargy, metabolic acidosis, and oliguria. Physical examination reveals signs of CHF and poor pulses in all four extremities. Ejection systolic click at the apex and ejection systolic murmur at the right upper sternal border may be heard, but not as prominent as non-critical AS patients.
