Narrow QRS complex A. Sinus tachycardia B. Paroxysmal supraventricular tachycardias (PSVTs) 1. Atrial tachycardias, including single-focus or multifocal (MAT) variants 2. AV nodal reentrant tachycardia (AVNRT) 3. AV reentrant tachycardia (AVRT) involving a bypass tract C. Atrial flutter D. Atrial fibrillation Wide QRS complex A. Ventricular tachycardia B. SVT/AF or flutter, with aberrant ventricular conduction usually caused by either of the following: 1. Bundle branch block patterns 2. Atrioventricular bypass tract (Wolff-Parkinson-White preexcitation patterns)