The most likely diagnosis is ostium primum atrial septal defect (ASD). The patient has clinical features of an ASD, presenting with dyspnea, previous atrial fibrillation, and features of volume overload of the right heart with elevation of the central venous pressure and a right ventricular lift. A systolic murmur at the base results from increased flow across the right ventricular outflow tract from the left-to-right shunt. Fixed splitting of the S2 throughout the cardiac cycle is a characteristic clinical feature of ASD. The apical systolic murmur is from mitral regurgitation and is related to the mitral valve cleft. The electrocardiogram demonstrates left axis deviation, first-degree atrioventricular block, and interventricular conduction delay. This combination of findings, including fixed splitting of S2, mitral regurgitation murmur, and left axis deviation on the electrocardiogram, are most consistent with an ostium primum ASD.
Patients with coronary sinus ASD have features of right heart volume overload but do not have mitral valve disease and thus will not have a murmur of mitral regurgitation. The electrocardiogram may be normal or demonstrate first-degree atrioventricular block and incomplete right bundle branch block.
Patients with ostium secundum ASD have features of right heart volume overload but do not have mitral valve disease and thus will not have a murmur of mitral regurgitation. The electrocardiogram may be normal or demonstrate first-degree atrioventricular block and incomplete right bundle branch block. Left axis deviation on the electrocardiogram is not found in patients with an ostium secundum ASD.
Patients with patent foramen ovale have a normal echocardiogram and physical examination. These patients are also generally asymptomatic.
Patients with sinus venosus ASD have features of right heart volume overload but do not have mitral valve disease and thus will not have a murmur of mitral regurgitation. The electrocardiogram may be normal or demonstrate first-degree atrioventricular block and incomplete right bundle branch block.
