AV nodal re-entry tachycardia

This is caused by the presence of an extra pathway of connection between the atria and the ventricles. This means that impulses generated in the SAN have the potential to travel back up through the extra pathway and depolarise the SAN. This is known as retrograde conduction. This can create a loop, sustaining the tachycardia. 

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Class Ic Ventricular tachycardia Tachycardia associated with the Wolff-Parkinson-White (WPW) syndrome AV-nodal re-entry tachycardia... 

These slow and fast pathways can exist in different places, such as the SAN, this leads to what is termed SAN re-entry tachycardia (Fig. 6.30). When the pathway is in the AV node, this is termed AV nodal re-entry tachycardia (AVNRT). This form of re-entry tachycardia is the most common (Fig. 6.31) and presents on the ECG with a regular rhythm, fast rate usually above 130 BPM. There may also be retrograde P waves present as the SAN is triggered from below. 

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