ECG in the diagnosis of supraventricular tachyarrhythmias

The development of catheter ablation techniques during the last decade provided new data about the mechanism of supraventricular tachyarrhythmias and at the same time, set new requirements for their classification. An accurate diagnosis of individual SVT can usually be made during an electrophysiologic study that precedes catheter ablation. Nevertheless, clinically acceptable differential diagnosis of SVT can be based on analysis of a standard 12-lead electrocardiogram. This may prove useful especially when selecting optimum antiarrhythmic drug according to a suspected mechanism of arrhythmia. At the same time, electrocardiogram during SVT serves as a recording of clinical arrhythmia for catheter ablation. At present, SVTs are divided into 3 main categories: 1. atrial tachyarrhythmias confined solely to atrial tissue, 2. tachycardias involving the AV junction, and 3. AV reentrant tachycardias involving one or more accessory connections with an electric impulse travelling between atria and ventricles. The first category can be further subdivided into: a) macroreentrant atrial tachycardias related to the presence of macroscopic anatomical or functional barriers; b) focal atrial tachycardias arising from a focus of abnormal automaticity or microreentry in the atrium; c) the syndrome of inappropriate sinus tachycardia resulting most probably from hypersensitivity to adrenergic stimulation; d) atrial fibrillation based on the existence of multiple wandering wavelets in the atria. Electrocardiographic differential diagnosis is predominantly based on an analysis of the standard 12-lead ECG. Principal diagnostic features include the presence and timing of the P waves in relation to the QRS complex. Additional criteria comprise the presence or absence of AV block during the tachycardia, an axis orientation of the P waves and their morphology, the appearance of QRS alternans or frequency of tachycardia.