THE ATRIAL SEPTAL SIGN

A NEGLECTED AID IN THE INTERPRETATION OF ANGIOCARDIOGRAMS

1. The interatrial septum is responsive to relative changes in atrial pressures.

2. Normally the septum bulges toward the right atrium which normally has a lower pressure than the left atrium.

3. Most types of acquired cardiac disease relatively increase left atrial pressure, resulting in more prominent bulging of the septum toward the right atrium.

4. The atrial septum may oscillate in position when interatrial pressure differential intermittently reverses direction— usually when atrial pressures are of similar magnitude, the "floppy atrial septum."

5. In constrictive pericarditis the dorsal wall of the right atrium including the septum may be unusually straight.

6. When the right atrial pressure is higher than that in the left atrium, the left atrium may be remarkably deformed and display a characteristic filling defect produced mainly by the bulging interatrial septum, the "crushed left atrium." The filling defect can be mistaken for a tumor mass (i.e., myxoma).

7. The above alterations may be observed by angiocardiography, although artifacts (pressure changes) due to this examination must also be considered. Since the steady state is disturbed by the angiocardiography, conclusions must be made with caution and confirmatory evidence sought.

8. Knowledge of the various configurations of the interatrial septum is essential for accurate interpretation of angiocardiograms.

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