Làn sóng đồng bằng của hội chứng Wolff-Parkinson-White, một đầu QRS bất thường, thường được coi là một bất thường dẫn. Tuy nhiên, nó thực sự là do kích hoạt đầu tiên của một phần vẫn còn tương đối vật liệu chịu lửa của tâm thất bình thường. | 141 The delta wave of the Wolff-Parkinson-White syndrome an early QRS abnormality is usually considered to be a conduction abnormality. However it is actually due to early activation of a still relatively refractory part of the normal ventricle. While one can consider many abnormalities of the QRS complex as being due to altered conduction within the ventricular muscle this discussion is limited to alterations of the conduction system itself and to alteration of the conduction system plus myocyte damage. For example the sequence of depolarization responsible for the abnormal Q waves of myocardial infarction could be considered a conduction defect but it occurs because myocytes have been removed see Chapter 10 to be posted at a later date . QRS complexes of greater than second duration are often associated with damage to the ventricular myocytes in conjunction with conduction system abnormalities the combination however is viewed as a conduction defect. At times therefore abnormalities of the conduction system itself overlap with and are superimposed on abnormalities produced by damage to the myocytes. Left or right ventricular hypertrophy alone rarely produces a QRS duration of greater than second. Therefore when the duration is greater than second it is proper to consider a conduction system abnormality in addition to ventricular hypertrophy. When however the QRS duration is second it is necessary to distinguish between a primary conduction defect and left or right ventricular hypertrophy based on the direction of the initial and terminal QRS forces. Although the QRS duration is usually second or longer when there is a conduction defect certain types of defects may be present even when the QRS duration is less than second. These are recognized by identifying an abnormal direction of the terminal QRS electrical forces. Right Ventricular Conduction Delay The electrocardiographic characteristics of right ventricular conduction delay are
