Abnormalities of the second heart sound (S2) and their mechanisms

Abnormalities of the second heart sound (S2) and their mechanisms

Wide splitting of S2 with maintained inspiratory delay of P2

Delayed activation and completion of right ventricular ejection

Complete right bundle branch block

Artificial left ventricular pacing

Pre-excitation of the left ventricle (Wolff-Parkinson-White syndrome)

Premature beats and idioventricular rhythm originating from the left ventricle

Prolonged right ventricular ejection time

Pulmonary hypertension with right heart failure

Right ventricular outflow obstruction (eg, pulmonic stenosis, acute massive pulmonary embolus)

Increased pulmonary hangout time

Idiopathic dilatation of the pulmonary artery

Mild pulmonic stenosis

Postoperative artial septal defect

Decreased left ventricular ejection time (early A2)

Mitral regurgitation

Ventricular septal defect with low pulmonary vascular resistance

Constrictive pericarditis

Fixed splitting of S2

Unchanged right ventricular stroke volume during respiration; severe right ventricular failure due to any cause

Interatrial communication; atrial septal defect; common atrium

Reversed splitting of S2

Delayed left ventricular activation and completion of ejection

Left bundle branch block

Artificial right ventricular pacing

Pre-excitation of the right ventricle (Wolff-Parkinson-White syndrome)

Premature beats of right ventricular origin

Prolonged left ventricular ejection time

Increased resistance to left ventricular ejection (aortic stenosis, obstructive hypertrophic cardiomyopathy, hypertension)

Isolated increase in left ventricular forward stroke volume (aortic regurgitation, patent ductus arteriosus)

Myocardial dysfunction (mild to moderate left ventricular failure, myocardial ischemia or infarction)

Increased aortic hangout time (not the sole cause)

Aortic regurgitation

Patent ductus arteriosus

Aortic stenosis

Single S2

Apparent: obesity, emphysema, pericardial effusion

Absent A2: severe aortic stenosis, sever aortic regurgitation

Absent P2: absent pulmonary valve, pulmonary atrasia, tetralogy of Fallot, truncus arteriosus

Fusion of A2 and P2: Eisenmenger's ventricular septal defect, common ventricle