Wolff-Parkinson-White syndrome.

minor discrepancies existing. It is generally accepted that in the presence of anomalous bypass conduction or preexcitation the QRS complexes are the result of a first component due to anomalous bypass conduction and a second component due to the normal atrioventricular conducted impulse. Vera et al.' have shown that the participation of each of these two components in building up or fusing together the final QRS complex can vary from 0 to 100%. The concertina effect is one example of these variable fusion beats. Therefore we believe that the direction and sense of the delta-wave vector and of the main QRS vector in the more or less prolonged QRS complex of the WolffParkinson-White syndrome are two independent factors which may or may not be similar in the electrocardiographic leads. Most electrocardiographers quote the criteria of Rosenbaum et al.2 in classifying the Wolff-ParkinsonWhite syndrome in type A: "R is the sole or by far the largest deflection in all of these leads (V1V2)" and in type B: "S or QS is the chief QRS deflection in at least