Update your Knowledge with MKSAP 18 Q&A: Answer and Critique


A: Atrial septal defect

Educational Objective

Diagnose ostium secundum atrial septal defect.


An ostium secundum atrial septal defect (ASD) is the most likely diagnosis in this patient. Adults with an ASD most often present with dyspnea or atrial arrhythmias; elevated central venous pressure, fixed splitting of the S2, and a right ventricular heave are characteristic findings. The fixed splitting of the S2 in patients with an ostium secundum ASD results from prolongation of right ventricular systole and lack of respiratory change in the right ventricular stroke volume. With expiration, the decrease in venous return is counteracted by an increase in left-to-right shunting, resulting in a fixed right ventricular preload. A large left-to-right shunt causes a pulmonary midsystolic flow murmur and a tricuspid diastolic flow rumble owing to increased flow. In ostium secundum ASD, the electrocardiogram (ECG) demonstrates right-axis deviation and incomplete right bundle branch block.

Aortic stenosis due to a bicuspid aortic valve causes a systolic murmur at the second right intercostal space. The central venous pressure is normal in aortic stenosis, and a right ventricular impulse would not be expected. A systolic ejection click is often heard in patients with bicuspid aortic valve, but fixed splitting of the S2 is not heard. The ECG typically demonstrates a normal axis and features of left ventricular hypertrophy.

Pulmonary stenosis is usually congenital, and severe obstruction can cause exertional dyspnea. Physical examination features depend on the severity of obstruction and associated elevation of right heart pressure; these include central venous pressure elevation with a prominent a wave and a parasternal impulse. The systolic murmur of pulmonary stenosis is generally heard at the second left intercostal space, and the timing of the murmur is related to stenosis severity. An ejection click is often heard; the proximity of the click to the S2 varies depending on the severity of stenosis. S2 becomes fixed in severe pulmonary stenosis. The ECG demonstrates right axis deviation and features of right ventricular hypertrophy.

Patients with mitral stenosis might present with symptoms of dyspnea. A right ventricular impulse can occur, and the central venous pressure might be elevated with associated pulmonary hypertension or tricuspid regurgitation. The murmur of mitral stenosis is generally best heard at the apex. An opening snap might be heard, followed by a diastolic murmur. Fixed splitting of the S2 is not heard. The ECG typically demonstrates left atrial enlargement.

Key Point

Elevated central venous pressure, fixed splitting of the S2, a right ventricular heave, and right-axis deviation and incomplete right bundle branch block on electrocardiogram are characteristic findings in patients with ostium secundum atrial septal defect.


Baumgartner H, Bonhoeffer P, De Groot NM, de Haan F, Deanfield JE, Galie N, et al; Task Force on the Management of Grown-up Congenital Heart Disease of the European Society of Cardiology (ESC). ESC guidelines for the management of grown-up congenital heart disease (new version 2010). Eur Heart J. 2010;31:2915-57. [PMID: 20801927] doi:10.1093/eurheartj/ehq249

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