His frowning face was pallid and quivered.
An electrocardiogram (ECG, EKG) that records the electrical activity in the heart may be used to check for heart rhythm abnormalities, such as long QT syndrome, in children who have had a pallid breath holding spell.
The child cries or gasps, forcibly exhales, stops breathing, and turns either blue (cyanotic form) or pale (pallid form).
About 25 percent of affected children-particularly those who experience pallid BHS-have a family history of BHS or fainting.
Pan's own science fiction list is also rather pallid, I'm afraid.