Supraventricular tachycardia

Supraventricular tachycardia

Supraventricular tachycardia is identified as a narrow QRS tachycardia, often with barely discernible P waves. Common forms of SVT are atrioventricular nodal reentrant tachycardia (AVNRT) and accessory pathway mediated atrioventricular reentrant tachycardia (AVRT). Ectopic atrial tachycardia is a rarer variety of SVT. Carotid sinus massage is useful in terminating some of these tachycardias. In others, it may produce an AV block making the P waves more visible and hence the diagnosis becomes easier.

If AV block occurs and the tachycardia is continuing, it excludes AVRT and most cases of AVNRT. Ectopic atrial tachycardia usually continues with either a fixed ratio or variable AV block. If the tachycardia does not terminate with carotid sinus massage, adenosine is usually the first drug to be given. It is a short acting drug and terminates most cases of SVT. Adenosine can worsen bronchospasm in asthmatic individuals. In ectopic atrial tachycardia the transient AV block produced by adenosine makes the diagnosis more evident. The same situation may occur in atrial flutter with 1:1 conduction.