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Supraventricular tachycardia (SVT) is characterised by a rapid impulse formation, that emanates from the sinus node, from atrial tissue (focal or macro-reentrant atrial tachycardia (AT)), from the atrioventricular (AV) node, or from anomalous muscle fibres that connect the atrium with the ventricle (accessory pathways (APs)). The most frequently (90%) encountered SVTs are AV nodal reentrant tachycardia (AVNRT), AV reentrant tachycardia (AVRT) mediated by accessory pathways, and atrial flutter (AFL). The remaining SVTs are AT and non-paroxysmal, usually incessant, forms of SVT.
Paroxysmal forms of SVT (PSVT) are regular recurrent tachycardias with a sudden onset and termination. If terminated by vagal manoeuvres, a reentrant tachycardia involving the AV node is most likely. The ventricular rate during SVT is commonly between 140–250 beats/min (bpm). If vagal or pharmacologic manoeuvres (adenosine) during an SVT result in AV block with persistence of atrial tachycardia, the diagnosis is most likely AT. The A:V ratio is always 1:1 in AP mediated tachycardias. Non-paroxysmal forms of SVT are ongoing repetitive or permanent/incessant tachycardias, which if left untreated can result in systolic left ventricular dysfunction and dilation (tachycardiomyopathy). These forms of tachycardias—for example, incessant AT or AFL—may be of unknown duration and without significant symptoms. Inappropriate sinus tachycardia (IST) is another form of non-paroxysmal SVT.
General evaluation and management of SVT
In clinical decision making it is important to distinguish correctly between the different types of SVT.1 A resting 12 lead ECG may disclose the presence of preexcitation, prolonged QT interval and other disease states—such as old myocardial infarction, hypertrophy, or bundle branch block—that may affect the choice of therapy. An ECG during tachycardia may give further clues to the type of SVT (table 1).
Focal ATs are due to triggered rhythms, abnormal automaticity or microreentry activity from a discrete atrial focus, the location of which governs …