S2 splitting S2 splitting Recall that the second heart sound (S2) is generated by two heart valves: the aortic valve and pulmonic valve. Nearly simultaneous closing of these valves normally generates a single S2 sound. S2 splitting is heard when aortic and pulmonic valves close at slightly different times. Normal S2 splitting can be heard in persons with no heart disease. Note widening of S2 splitting with inspiration and narrowing with expiration in the following sound: Normal S2 splitting is associated with inspiration. During inspiration the diaphragm contracts and moves inferiorly toward the abdomen by up to 10 cm. The associated increase in abdominal pressure and corresponding decrease of intrathoracic pressure leads to increased venous return from the systemic circulation to the right heart. It takes a little longer for the right ventricle to pump the increased amount of blood. Consequently, pulmonic valve closure is delayed compared to aortic valve closure. The delay between the aortic and pulmonic sounds (A2-P2) is observed as S2 splitting. Prolonged or fixed S2 splitting can be a sign of heart desease such as atrial septal defect or right bundle branch block. Note the fixed S2 split in the following example: Learning to appreciate S2 splitting can be difficult. The following exercise can help you appreciate degrees of S2 splitting. The sound was recorded by striking knuckles on a surface of a table. Note the gradual increase and following decrease of the split. In infants listen for S2 splitting at the left sternal border. Splitting in infants may not be heard until the pulmonary resistance decrease to normal. In older children splitting maybe heard better at the left upper sternal border. In normal children S2 splitting can persist during expiration in the supine position. Sitting upright decreases venous return to the right heart and usually results in S2 becoming single during expiration. Paradoxical Splitting of the second heart sound: In its milder form, paradoxical splitting of the S2 is associated with narrowing of S2 split with inspiration. In the advanced form, the aortic valve closes later than pulmonic valve causing A2 of the second heart sound to appear after P2 (normally aortic valve closes before pulmonic valve). Contrary to the “normal” splitting, the delay between P2 and A2 declines with inspiration in paradoxical splitting. Paradoxical splitting can occur when left ventricular ejection time is prolonged. Paradoxical splitting can be seen in patients with severe aortic stenosis, left ventricular outflow obstruction, and large left ventricular overload such as large patent ductus arteriosus. It can also be observed in patients with conduction abnormalities that cause prolongation of left ventricle ejection, such as left bundle branch block, some types of premature ventricular contraction and Wolf Parkinson White Syndrome.