Question 7.1

List the classic cardiac auscultatory signs of atrial septal defect, ventricular septal defect and patent ductus arteriosus. What typical findings on a right heart catheterization will also support your diagnosis? (You may tabulate your answer)

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College Answer

ASD	VSD	PDA
Fixed split of second heart sound	Harsh pansystolic murmur confined to the left sternal edge	A continuous murmur heard over the pulmonary area
Mid diastolic flow murmur over tricuspid area if significant shunt	Mid diastolic flow murmur over mitral area if significant shunt	Mid diastolic flow murmur over mitral area if significant shunt
Step up in oxygen saturation at atrial level	Step up in oxygen saturation at ventricular level	Step up in oxygen saturation at pulmonary artery level

Discussion

There really is no way to answer this question without having either memorised or having become freakishly familiar with the details of cardiological examination.

A summary for these physical examination findings exists elsewhere.

The "step up" findings in right heart catheterisation are self-explanatory once you think about it. They are all the features of "acyanotic" heart defects.

The atrial septal defect contributes oxygenated blood to the right atrium, and the "step-up" occurs there. The VSD contributes oxygenated blood to the ventricle with similar consequences. The PDA carries oxygenated blood from the aorta to the pulmonary artery, and again this change occurs.

Dexter et al first explored this in healthy patients in 1947; a good review article addresses his workand outlines what precisely an abnormal "step up" looks like (turns out it is about 5-7% difference in oxygen content - less than 1 % of such people would be free from septal defects).

References

Freed, MICHAEL D., OLLI S. Miettinen, and ALEXANDER S. Nadas. "Oximetric detection of intracardiac left-to-right shunts." British heart journal 42.6 (1979): 690.

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