* Atrioventricular nodal reentrant tachycardia (AVNRT), a reentrant form of narrow QRS complex tachycardia, is based on a dual (slow and fast) pathway of the compact AV node (FIGURE 4).
* Orthodromic atrioventricular reciprocating tachycardia (AVRT), or Wolff-Parkinson-White syndrome, is a narrow QRS complex tachycardia in which antegrade conduction is via the AV node and retrograde conduction is via an accessory pathway (bundle of Kent).
There are a number of characteristics to consider in the differential diagnosis of a patient with narrow QRS complex tachycardia (ALGORITHM).
AV dissociation is rarely seen in narrow QRS complex tachycardia. Its presence raises the possibility of junctional ectopic tachycardie, ventricular tachycardia, or complete AV node block.
* Analyze P wave axis, morphology, and timing for help in diagnosing narrow QRS complex tachycardia. (c)
Usefulness of ST-segment elevation in lead aVR during tachycardia for determining the mechanism of narrow QRS complex tachycardia. Am J Cardiol.
While most narrow QRS complex tachycardias are easily diagnosed, some pose a diagnostic challenge.
We start with a summary of the various types of narrow QRS complex tachycardias, accompanied in some cases with 12-lead electrocardiogram (EKG) strips.
Narrow QRS complex tachycardias fall into 2 broad categories: those that are sinus node-generated, and those that are not.
* P wave axis and morphology can help with both the differentiation and the origin of narrow QRS complex tachycardias. A superior-to-inferior axis of P waves (positivity in leads II, III, and aVF) is seen in sinus node-generated tachycardias and sometimes in focal atrial tachycardia.