![]() ![]() In addition, the QRS complex is wider in the precordial than in the limb leads. QRS duration may increase with increasing heart size. Global intervals, by definition, will be longer than measurements from single leads. Global intervals, from the earliest onset to the latest offset of the waveform in all leads (generally taken from a spatial vector magnitude or superimposed complexes), are the desirable standard. The QRS duration depends on the method of measurement, age, and gender. The purpose of the present report is to define the normal QRS duration, review the recommendations made in 1985, recommend alterations and additions to those recommendations, and provide recommendations for children and adolescents. Recommendations were made for the diagnosis of complete and incomplete left and right bundle-branch blocks (LBBB and RBBB), left anterior and left posterior fascicular blocks, nonspecific intraventricular blocks, and ventricular preexcitation ( 3). In 1985, the electrocardiography (ECG) criteria for intraventricular conduction disturbances and ventricular preexcitation were reviewed by an ad hoc working group established by the World Health Organization and the International Society and Federation of Cardiology. They may also be due to abnormal atrioventricular connections, which bypass the atrioventricular node, resulting in ventricular preexcitation. Alternatively, they may be functional and due to the arrival of a supraventricular impulse during the relative refractory period in a portion of the conducting system, in which case the term aberrant ventricular conductionis applied. They may be caused by structural abnormalities in the His-Purkinje conduction system or ventricular myocardium that result from necrosis, fibrosis, calcification, infiltrative lesions, or impaired vascular supply. These changes in intraventricular conduction may be fixed and present at all heart rates, or they may be intermittent and be tachycardia or bradycardia dependent. The term intraventricular conduction disturbancesrefers to abnormalities in the intraventricular propagation of supraventricular impulses that give rise to changes in the shape and/or duration of the QRS complex. The rationale for this initiative and the process by which it was achieved were described earlier ( 1). This statement was preceded by 2 articles, “The Electrocardiogram and Its Technology” and “Diagnostic Statements,” which were published previously ( 1,2), and it is followed by statements concerning abnormalities of repolarization, hypertrophy, and ischemia/infarction. The present article introduces the second part of “Recommendations for Standardization and Interpretation of the Electrocardiogram.” The project was initiated by the Council on Clinical Cardiology of the American Heart Association and has been endorsed by the American College of Cardiology Foundation, the Heart Rhythm Society, and the International Society for Computerized Electrocardiography. ![]()
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