IntroductionSupraventricular tachycardias (SVT) arise from the atrium and atrioventricular junction. They are characterised by fast rhythms with narrow QRS complexes. The majority of sustained regular tachycardias are due to re-entry mechanisms or increased automacity.
Atrial ectopicPremature depolarisation from an atrial source.
ECG findingsPremature, abnormally shaped P wave.
Atrial tachycardiaAtrial rate of 120-250 beats per minute, usually from an ectopic source. An uncommon arrhythmia that accounts for 10% of all SVTs.
ECG findingsRegular rhythm with atrial rate >120 beats per minute. P wave morphology is abnormal.
Atrial flutterOrganised atrial rhythm with an atrial rate of 250-300 bpm. It is usually associated with atrial fibrillation and, thus, should be managed similar to it.
ECG findingsP waves have a sawtooth pattern with and atrial rate of 300 beats per minute. There is usually 2:1 atrioventricular block, so the heart rate is 150 beats per minute.
Atrial fibrillationIneffective, chaotic, irregular and rapid (300-600 beats per minute) atrial activity. This results in deterioration of mechanical function. It can be classified as paroxysmal (intermittent, recurrent and self-terminating episodes), persistent (lasts longer than 7 days and does not spontaneously terminate) or permanent.
ECG findingsNo P waves, irregular QRS complexes. There is normal, narrow QRS complex morphology and T wave shape
Atrioventricular nodal re-entry tachycardia (AVNRT)Re-entrant SVTs occur due to an additional, abnormal electrical connection between the atria and ventricles. It is the commonest cause of SVTs. The abnormal connection is found within the atrioventricular node (AVN). In AVNRT, there are 2 distinct electrical pathways in the AVN:
- Fast conduction with long refractory period pathway(normal pathway)
- Slow conduction with short refractory period pathway (abnormal pathway)