Electrocardiographic changes in atrial septal defects: ostium secundum defect versus ostium primum (endocardial cushion) defect.

Abstract The electrocardiographic changes in 100 patients with ostium secundum type, and 33 patients with ostium primum type, of atrial septal defect have been described, and the difference between the electrocardiograms of these two groups has been emphasized. The most reliable single electrocardiographic change that has been found to be of greatest diagnostic value in all atrial septal defects is the presence of an rsR′ (with a QRS duration of less than 0.11 second) in Lead V 1 . This pattern was present in 65 per cent of the secundum defects and 44 per cent of the ostium primum defects. The R′ is a manifestation of the rightward and anteriorly directed terminal QRS vector. We call this rsR′ pattern "right ventricular outflow tract hypertrophy" and believe that it is actually due to right ventricular dilatation, especially dilatation and/or hypertrophy in the region of the right ventricular outflow tract, rather than to any interruption of conduction in the right bundle branch. An Rs or qR pattern in Lead V 1 was present in 23 per cent of the secundum and 28 per cent of the ostium primum defects. "Complete" right bundle branch block was present in 5 per cent of the patients with secundum, and 15 per cent of the patients with ostium primum, defects. The mean QRS axis and the rotation of the QRS vector loop are of cardinal importance in differentiating the secundum from the primum defect. True right axis deviation (mean QRS axis or vector more than +100° rightward) was present in 81 per cent of the secundum defects and in none of the primum defects. The mean QRS axis fell between +50° and 180° in all 100 cases of secundum defect. The QRS vector loop was clockwise and below the isoelectric line (0–180°) in all 100 cases of secundum defect. Left axis deviation (mean QRS axis or vector more leftward than −30°) was present in 82 per cent of the ostium primum defects and in none of the secundum defects. The mean QRS axis fell between 0° and −100° in 90 per cent of the primum defects. The QRS vector loop rotated counterclockwise and was above the isoelectric line (0–180°) in all 27 of the patients with ostium primum defect who had true left axis deviation. The terminal QRS vector fell between +120° and −150° in 91 per cent of the secundum defects, and between −60° and −140° in 91 per cent of the ostium primum defects. The height of the P waves suggested right atrial enlargement in 25 per cent of the secundum defects and in 18 per cent of the primum defects. The P-R interval was prolonged in 6 per cent of the secundum and 18 per cent of the primum defects. Attempted hemodynamic correlation with the electrocardiogram failed to add any useful information to this study or to studies already described by other authors. 6,7,11,12 Following surgical closure of the secundum defect the R′ begins to decrease within 2 months, and usually decreases significantly within 4 months. There is often a normal rSr′ or rS in Lead V 1 within 1 year after closure. If regression does not occur, then there is cause for doubt as to the complete closure of the defect, or the presence of irreversible pulmonary vascular changes may be suspected.