General Introduction, Classification, and Electrocardiographic Diagnosis of Cardiac Arrhythmias.

The conduction system includes a primary pacemaker, the internodal tracts, the atrioventricular node, and the His bundle with the right and left branches. In "emergency" conditions, accessory pacemakers may be triggered. The conduction system produces very low-intensity currents; a surface electrocardiogram (ECG) detects only the big myocardial masses. Electrogenetic mechanisms are reduced automaticity and/or impaired conduction at the base of bradycardias. An increased automaticity and/or reentry phenomenon are at the base of ectopic beats and tachycardias. A "wide QRS" is a ventricular activation time of 120 milliseconds or more. The "laddergram" helps in the fast and reliable ECG interpretation.