Tachyarrythmia originating from within the atria but outside the SA node, usually a single ectopic focus mechanishms can include: -reentry -triggered activity -increased automaticity distingushed by abnormal P-waves which have different morphology (inverse MAT multifocal atrial tachycardia same as above but requires 3 or more unique origins of waves.

AVNRT requires re-entry (duh) but this is through a congential accessory pathway that permits re-entry of the signal. This affects BOTH the fast and slow pathways. the atrium, AV node and ventricles ALL need to be part of this pathway Slow-Fast AVNRT (Common AVNRT) Accounts for 80-90% of AVNRT Associated with Slow AV nodal pathway for anterograde conduction and Fast AV nodal pathway for retrograde conduction. The retrograde P wave is obscured in the corresponding QRS or occurs at the end of the QRS complex as pseudo r’ or S waves ECG: P waves are often hidden – being embedded in the QRS complexes. Pseudo r’ wave may be seen in V1 Pseudo S waves may be seen in leads II, III or aVF. In most cases this results in a ‘typical’ SVT appearance with absent P waves and tachycardia

AVRT has two arms to the re-entry circuit. One is the AV node, the other is the accessory pathway AVRT only requires the AV node to be part of the circuit. There are two types: Orthodromic and Antidromic Orthodromic means there is conduction down the normal pathway, and back up the accessory pathway causing a NARROW QRS complex Antidromic means there is conduction up the abnormal accessory pathway and back into the node, causing a WIDE QRS complex as the signal has longer to travel Rate usually 200-300 bpm Retrograde P waves are usually visible, with a long RP interval QRS < 120ms unless pre-existing bundle branch block, or rate-related aberrant conduction QRS alternans: phasic variation in QRS amplitude associated with AVNT and AVRT, distinguished from electrical alternans by a normal QRS amplitude Rate-related ischaemia is common

Progressively lengthening PR interval that presents as a missed beat on ECG. the interval after a missed beat is shorter than the PR interval preceeding the missed beat Type 1 blocks are typically associated with diseased states of the AV node

Mobitz type II A constant PR interval that may be normal or prolonged with periodic abrupt failure of the atrial impluses to conduct to the ventricles. Usually associated with diseases at the level of the bundle of His MORE worrisome than type 1 as the pacemaker cells are located above the bundle of his, so there is a risk of not propagating entirely.