Figure 40.5.1 Diagnostic algorithm for narrow QRS tachycardia. For the purposes of this algorithm, P waves are used to describe all atrial activity (including flutter and atrial fibrillation). * Rare or extremely rare diagnoses. AF, atrial fibrillation; AFL, atrial flutter; APB, atrial premature beat; AT, atrial tachycardia; AVNRT, atrioventricular nodal reentrant tachycardia; AVRT, atrioventricular reentrant tachycardia; JPB, junctional premature beat; JT, junctional tachycardia (automatic); MAT, multifocal atrial tachycardia; ms, milliseconds.