In normal individuals, electrical activity in the heart is initiated in the sinoatrial (SA) node (located in the right atrium), propagates to the atrioventricular (AV) node, and then through the bundle of His to the ventricles of the heart. The AV node acts as a gatekeeper, limiting the electrical activity that reaches the ventricles of the heart. This function of the AV node is important, because if the signals generated in the atria of the heart were to increase in rate (as they do during atrial fibrillation or atrial flutter), the AV node will limit the electrical activity that conducts to the ventricles. For instance, if the atria are electrically activated at 300 beats per minute, half those electrical impulses are blocked by the AV node, so that the ventricles are activated at 150 beats per minute (giving a pulse of 150 beats per minute). Another important property of the AV node is that it slows down individual electrical impulses. This is manifest on the ECG as the PR interval, which is about less than 200 milliseconds, the time from activation of the atria (manifest as the P wave) and activation of the ventricles (manifest as the QRS complex). Individuals with<unk>  have a "short-circuit" in their heart, where the electricity bypasses the AV node, causing the heart to beat faster than normal. The cause of the arrhythmia, the<unk>  focus, is usually near the AV node in the triangle of Koch (a rough triangle with points at the coronary sinus, the tendon of Todaro, and the tricuspid valve). Patients of heart surgery may experience an accelerated narrow complex tachycardia, usually within the first 24–48 hours (but occasionally longer) after surgery. There may be atrio-ventricular disassociation with more ventricular signals than atrial signals. The cause of<unk>  is felt to be due to manipulation of the tissue surrounding the AV node during surgery, however debate exists regarding the exact cause, as it is seen after procedures even without significant manipulation of this area.<unk> -like symptoms can also manifest congenitally and in the first six months of life. This syndrome, which may also referred to as His bundle tachycardia, is resistant to therapy and can be difficult to treat.
Junctional ectopic tachycardia
AV nodal reentrant tachycardia
Wandering atrial pacemaker
Tachycardia
AV nodal reentrant tachycardia  AV-nodal reentrant tachycardia  1
Ventricular escape beat
Atrioventricular reentrant tachycardia
Accelerated idioventricular rhythm