The Present Series

Summary An account is given of the collection of the present series, and of analysis of the primary data. The heterogeneous nature of these data is stressed; its influence on the results will be discussed when the relevant examinations are described. It is found that the ECG was recorded with simultaneous leads during the first attack of PT in 53.7 per cent of the cases. The ECGs recorded after this paroxysm have a similar distribution with respect to technical factors. A description is given of the bases used for measurement of the heart rate, duration of the QRS complex and amplitude of the P and T waves. Measurements of the amplitude are based only on those tracings with a distinct test. The criterion for the presence of pre‐excitation in the ventricular complex is stated. The direction of the mean QRS vector in the frontal plane is determined by the method of Grant (1957). It is pointed out that although this method has an accuracy of only ± 30°, it is suitable in the present series, in view of the lack of simultaneous ECG tracings in some cases, as well as the absence of a test in 6. The ECG was recorded by the author with the use of an esophageal lead during an attack of supraventricular PT in a 3‐day‐old infant. It is emphasized that this lead is of great value for establishing the site of origin of PT, since it enables the P wave to be visualized without superimposition of the T wave.