CLASSIFICATION AND AETIOLOGY OF SUPRAVENTRICULAR ARRHYTHMIAS

Most tachycardia has a re-entry mechanism (fig 1) and the classification of most arrhythmias is based on the location of this re-entry circuit. Tachycardia can be categorised as ventricular (involving the ventricle ± the His-Purkinje system only) and supraventricular (involving the supra-hisian structures with or without ventricular tissue). They can then be subdivided into regular or irregular tachycardia. Irregular SVTs—that is, atrial fibrillation (AF)—are less amenable to catheter ablation than regular SVT, but catheter ablation may be possible in selected patients. Regular SVTs can be cured by catheter ablation with high success rates (95–99%) and low complication rates (< 1%). Regular SVTs take the form of:

• atrioventricular re-entry tachycardias (AVRT), using the ventricle as part of the circuit; these tachycardias are dependent on the presence of an accessory atrioventricular (AV) pathway (fig 2)

• atrioventricular nodal re-entry tachycardia (AVNRT), where the re-entry circuit is within the AV node and the ventricle plays no part in maintaining the arrhythmia (fig 3)

• atrial tachycardia, where the re-entry circuit does not involve any part of the AV junction. Examples are atrial flutter (fig 4) or ectopic atrial tachycardia (AT) (fig 5).