Z- score classification of coronary aneurysms in Kawasaki disease
Z-score is the standard deviation from coronary artery internal lumen diameter normalized for body surface area. AHA classification of coronary artery aneurysms based on Z-score is as follows : 1. No involvement with Z score less than 2 always. 2. Dilatation only with Z scores from 2 to less than 2.5 or a decrease in Z score of 1 or more during follow up if it was less than 2 initially. 3. Small aneurysm with Z score of more than 2.5, but less than 5. 4. Medium aneurysm with Z score 5 or more, but less than 5 and absolute dimension less than 8 mm. 5. Large or giant aneurysm with Z score 10 or more or absolute dimension 8 mm or more. The decrease in dimension in Class 2 over time means that though the diameter was in normal range initially, it was actually dilated for that person and decreases in size over time.
A previous Japanese guideline classified coronary aneurysms in acute phase of Kawasaki disease based on absolute or relative internal lumen diameter . In that classification, small aneurysm or dilatation was a localized dilatation with internal diameter 4 mm or less. In children of 5 years or more, internal diameter of a segment measures less than 1.5 times the adjacent segment. Medium aneurysm was with internal diameter above 4 mm, up to 8 mm. In children of 5 years or more, internal diameter of a segment measures 1.5 to 4 times that of an adjacent segment. Giant aneurysm was with internal diameter above 8 mm. In children 5 years or more, internal diameter of a segment measures more than 4 times that of an adjacent segment. This classification is easier to follow as you need not check the nomogram for Z scores each time you do an echocardiographic measurement of the coronary arteries. Disadvantage of course is that the variation in coronary size with age is not fully accounted for.