Narrow QRS complex tachycardia with atrioventricular dissociation

Area of Science:

• Cardiology
• Electrophysiology
• Medical Case Reports

Background:

• Narrow QRS complex tachycardia can have various etiologies.
• Atrioventricular dissociation during tachycardia suggests supraventricular origin with block in conduction to the ventricles.
• Mahaim fibers are accessory pathways that can participate in reentrant tachycardia.

Observation:

• A 22-year-old male presented with frequent episodes of narrow QRS complex tachycardia and atrioventricular dissociation.
• Electrocardiogram (ECG) during sinus rhythm was normal, but showed a left bundle branch block pattern during atrial pacing and after verapamil administration.
• Electrophysiological study confirmed the presence of nodoventricular Mahaim fibers.

Findings:

• The narrow QRS complex tachycardia was attributed to a reentrant circuit.
• Antegrade conduction occurred via the atrioventricular nodo-His axis.
• Retrograde conduction occurred via the nodoventricular bypass tract (Mahaim fibers).

Implications:

• This case highlights the importance of electrophysiological studies in diagnosing unusual tachycardia mechanisms.
• Understanding Mahaim fiber conduction is crucial for effective management of related arrhythmias.
• Accurate diagnosis of accessory pathway involvement can guide therapeutic strategies, including ablation.