Focal atrial tachycardia (AT) is a relatively uncommon cause of supraventricular tachycardia, but when present is frequently difficult to treat medically. Atrial tachycardias tend to originate from anatomically determined atrial sites. The P-wave morphology on surface electrocardiogram (ECG) together with more sophisticated contemporary mapping techniques facilitates precise localisation and ablation of these ectopic foci. Catheter ablation of focal AT is associated with high long-term success and may be viewed as a primary treatment strategy in symptomatic patients.
The least common type of supraventricular tachycardia is focal atrial tachycardia (AT), accounting for 5-15% of cases presenting to the electrophysiology (EP) laboratory for ablation.1 Focal AT is defined by the presence of a discrete atrial focus with centrifugal spread of atrial activation away from that site.2 It is generally poorly responsive to pharmacological therapy and may be responsible for the development of tachycardia-mediated cardiomyopathy3 or initiation of other atrial arrhythmias such as atrial flutter or atrial fibrillation (AF). With the advent of radiofrequency (RF) ablation this type of tachycardia can be treated with high long-term success.3-5
Electrocardiographic P-wave morphology can provide a useful indication of the likely site of focal AT origin, which are generally distributed to characteristic anatomical locations.5,6 Studies evaluating mechanism of focal AT have demonstrated electrophysiological characteristics reflecting abnormal automaticity, triggered activity and micro-re-entry in different patients.4 This article will discuss localisation of atrial tachycardia using P-wave morphology and techniques of endocardial mapping to facilitate successful ablation.
Focal AT demonstrates a characteristic anatomical distribution and does not occur randomly throughout the atria. In published series, the right atrium (RA) is the most common location for foci, accounting for approximately 75%. Within the RA they are most commonly observed along the crista terminalis (CT) (approximately 33%) particularly in the superior and mid-CT. Other common sites include the tricuspid annulus (TA), the coronary sinus (CS) ostium and within the CS, the perinodal (parahisian) region and septum, and from within the right atrial appendage (RAA). In the left atrium (LA) the majority of foci originate from the pulmonary veins (PVs), the mitral annulus (MA), left atrial appendage (LAA) and left septum being less common.6
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