Tachycardia: Difference between revisions

Atrial tachycardia (AT) is a tachycardia resulting from fast firing in an ectopic focus or micro-reentry circuit in the atria. It has a frequency of above the 100bpm. In some patients the tachycardia has multiple foci (multifocal atrial tachycardia). This results in different P-wave morphologies on the ECG during the arrhythmia. Atrial tachycardia can be caused by all the mechanisms of arrhythmia formation. Patient after earlier surgery or catheter ablation usually present with macro-reentry AT located around functional or anatomical sides of block. The atrial flutter is a type of AT, but due to its unique mechanism it is discussed separately.

ATs have a wide range clinical presentation. They can occur in paroxysms or can be the permanent underlying rhythm. Complaints of palpitation and a fast regular heart rate are common and as a result of the tachycardia complaints of dizziness, dyspnoea and syncope can be experienced. Focal AT that with a progressive increase at onset and decrease before termination are likely based on abnormal automaticity. Digoxine intoxication is a common cause for ATs. On the ECG an atrial tachycardia can be detected through the P-wave morphology. The P-wave has an other morphology depending on the foci of the atrial tachycardia. A ECG in resting condition of sinus rhythm can help distinguish different morphologies and help in localization of the source of the atrial tachycardia. Vagal maneuvers or administration of adenosine can block the AV-conduction and reveal firing from the atrium, thereby clearly identifying the atrial source of the tachycardia. Some ATs are sensitive to adenosine and will terminate after administration of adenosine. However sometimes only a electrophysiological study can differentiate between the different SVT and localize the precise location or circuit of the AT.  

Vagal maneuvers or adenosine can be effective in terminating focal AT. If AT persist and is drug-resistant DC cardioversion can be indicated. Recurrent episodes of AT can be prevented with anti-arrhythmic medication, for instance with beta-blockers or calcium antagonists. However not all AT are sensitive to medication and success rate of medication is usually low. If these drugs are unsuccessful Class Ic in combination with AV-nodal-blocking agents or Class III drugs can be tried. The treatment of choice for symptomatic AT is catheter ablation. In an experienced center up to 90% of the AT can be ablated. Multifocal atrial tachyardia is difficult therapy is usually directed at the management of underlying disease.