Accessory pathway

Accessory pathway

An accessory pathway is an additional electrical conduction pathway between the atria and ventricles of the heart. This pathway can bypass the normal conduction system, potentially leading to arrhythmias.

Anatomy and Physiology

The heart's normal electrical conduction system includes the sinoatrial node, atrioventricular node, bundle of His, and Purkinje fibers. An accessory pathway is an abnormal conduction pathway that can connect the atria and ventricles directly, bypassing the atrioventricular node.

Accessory pathways are often associated with conditions such as Wolff-Parkinson-White syndrome and Lown-Ganong-Levine syndrome. These pathways can conduct electrical impulses more rapidly than the normal conduction system, leading to pre-excitation of the ventricles.

Types of Accessory Pathways

Accessory pathways can be classified based on their location and conduction properties:

• Atrioventricular accessory pathways: These connect the atria to the ventricles and can conduct impulses in both directions. The most common type is the Kent bundle found in Wolff-Parkinson-White syndrome.

• Atriofascicular pathways: These connect the atria to the fascicles of the ventricles, such as the Mahaim fibers.

• Nodoventricular and nodofascicular pathways: These connect the atrioventricular node to the ventricles or fascicles.

Clinical Significance

Accessory pathways can lead to various types of arrhythmias, including:

• Atrioventricular reentrant tachycardia (AVRT)
• Atrial fibrillation with rapid ventricular response
• Ventricular pre-excitation

Patients with accessory pathways may experience palpitations, dizziness, syncope, or even sudden cardiac arrest in severe cases.

Diagnosis

The diagnosis of accessory pathways is often made using electrocardiography (ECG). Characteristic findings on ECG may include:

• Shortened PR interval
• Delta waves
• Wide QRS complex

Invasive electrophysiological study may be required to map the accessory pathway and assess its conduction properties.

Treatment

Treatment options for accessory pathways include:

• Medications: Antiarrhythmic drugs may be used to control heart rate and rhythm.

• Catheter ablation: A minimally invasive procedure that uses radiofrequency energy to destroy the accessory pathway.

• Surgical ablation: In rare cases, surgical intervention may be necessary to remove the accessory pathway.

Related pages

• Wolff-Parkinson-White syndrome
• Atrioventricular reentrant tachycardia
• Electrophysiology
• Cardiac arrhythmia

Gallery

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  ECG showing accessory pathway in Ebstein's anomaly

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  ECGs in Ebstein's anomaly with Mahaim accessory pathway