Fixed Splitting of the Second Sound
When you hear the terms, wide, fixed splitting of the second heart sound, your brain should immediately convert this to "atrial septal defect." This finding on physical examination is very specific but not sensitive for atrial septal defect.
The principle is that with ventilation, right ventricular filling is accentuated, thus increasing the time for right ventricular ejection. During expiration, systemic venous filling is diminished while pulmonary venous filling of the left atrium is accentuated. With free access to the right atrium, the relatively under-filled chamber fills with shunted blood so that with inspiration or expiration, the right and left ventricles see the same amount of blood with each systole, the right ventricle seeing more. As a result, no matter whether in inspiration or expiration, the difference in time between the aortic and pulmonary valve closure sound remains very closely the same. Additionally, during physical exam of the patient, note also the visible evidence of a pulmonary valve impulse and listen for a short, midsystolic murmur. All these combine in a triumvirate of the physical diagnosis findings of atrial septal defect.
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Updated December 2010