Mahaim Tachycardia Mimicking Ventricular Tachycardia

Atypical accessory pathways can closely mimic the electrocardiographic features of idiopathic ventricular tachycardia from the tricuspid annulus.

A 39-year-old man with a history of previous unsuccessful radiofrequency ablation for a presumed diagnosis of idiopathic ventricular tachycardia presented with symptomatic wide QRS complex tachycardia. A subsequent redo procedure using high-density mapping revealed the true arrhythmia mechanism to be an atypical Mahaim pathway with no discernible atrial insertion.

The misdiagnosis of wide QRS complex tachycardia often results in failed ablation attempts. High-density mapping plays a pivotal role in redefining the arrhythmia substrate, uncovering the true mechanism, and guiding effective ablation; it should be recommended, especially in redo procedures.

The origin of some atypical Mahaim pathways can be distinctly subvalvular, rather than purely annular. High-density mapping is essential for a comprehensive evaluation of the subvalvular apparatus. Identification of a broad earliest activation site at specific anatomical locations should prompt a more rigorous investigation into the underlying electrophysiologic mechanism.