Mahaim Fiber pathway related Tachycardia

 

Case of Mahaim Fiber pathway related Tachycardia:

During atrial pacing, the above tachycardia is induced.

In Differentiating wide complex tachycardia following points should be considered.

During atrial pacing (the 1st beat), the His catheter has the activation sequence proximal to distal (antegrade His activation). During the 2nd paced beat, the His deflection (on proximal His) gets buried within the ventricle (block of the AV node, maximal preexcitation) and antidromic tachycardia is induced. During tachycardia, the His activation sequence is reversed, and distal His is before proximal His. Therefore, the activation of the His bundle is retrograde during tachycardia, but still before ventricular activation. This is only possible in the presence of an extranodal pathway inserting in the fascicle just below the His bundle, most frequently the right bundle (Mahaim). Careful examination of the sequence of His bundle activation can lead to the correct diagnosis already at first glance in an otherwise highly complex diagnostic challenge.

The differential diagnosis of bundle branch re-entrant ventricular tachycardia (BBRVT) is theoretically not fully excluded by this tracing. However, the induction with a relatively long AV interval (not so different from the basic interval seen at the first RR interval) makes it highly unlikely that only the right bundle is activated and the left bundle is completely blocked and able to conduct retrogradely for the re-entry circuit. Moreover, in BBRVT, the HV interval is not expected to be so short. The shortening of HV intervals during tachycardia and the reversal of His to proximal right bundle activation further argue against BBRVT where the HV interval would be equal to or longer than in sinus.

Mahaim Fibers and Tachycardia: A Detailed Overview

Mahaim fibers are a type of accessory electrical pathway in the heart that can cause tachycardia, a rapid heart rate. These fibers are named after the French cardiologist Ivan Mahaim, who first described them.

Anatomy and Physiology

Mahaim fibers are abnormal electrical connections between the atria and ventricles. They can be found in the anteroseptal, midseptal, or posteroseptal regions of the heart. These fibers can bypass the normal electrical pathway, the atrioventricular (AV) node, and cause the ventricles to contract prematurely.

Types of Mahaim Fibers

There are two main types of Mahaim fibers:

1. Atriofascicular fibers: These fibers connect the atria to the fascicles of the ventricular conduction system.

2. Nodofascicular fibers: These fibers connect the AV node to the fascicles of the ventricular conduction system.

Tachycardia Associated with Mahaim Fibers

Mahaim fibers can cause various types of tachycardia, including:

1. Antidromic AV reentrant tachycardia (AVRT): This is the most common type of tachycardia associated with Mahaim fibers. During antidromic AVRT, the electrical impulse travels anterogradely (forward) down the Mahaim fiber and retrogradely (backward) up the AV node or another accessory pathway.

2. Orthodromic AVRT: This type of tachycardia is less common with Mahaim fibers. During orthodromic AVRT, the electrical impulse travels anterogradely down the AV node and retrogradely up the Mahaim fiber.

Clinical Presentation

Patients with Mahaim fiber-related tachycardia may experience symptoms such as:

1. Palpitations

2. Rapid heart rate

3. Shortness of breath

4. Chest pain or discomfort

5. Dizziness or lightheadedness

Diagnosis

Diagnosis of Mahaim fiber-related tachycardia typically involves:

1. Electrocardiogram (ECG): This can show a wide QRS complex tachycardia with a left bundle branch block (LBBB) pattern.

2. Electrophysiology study (EPS): This can help identify the location and properties of the Mahaim fiber.

Treatment

Treatment options for Mahaim fiber-related tachycardia include:

1. Catheter ablation: This is a minimally invasive procedure that uses radiofrequency energy to destroy the Mahaim fiber.

2. Medications: Anti-arrhythmic medications can be used to control symptoms and prevent tachycardia episodes.

In conclusion, Mahaim fibers are a rare but important cause of tachycardia. Understanding the anatomy, physiology, and clinical presentation of Mahaim fibers is crucial for accurate diagnosis and effective treatment.