Left posterior fascicular tachycardia: a diagnostic and therapeutic challenge.

A wide QRS complex tachycardia with right bundle-branch block morphology and left axis deviation observed in a young patient without structural heart disease may pose a diagnostic and therapeutic challenge. The surface ECG may provide several diagnostic clues to make a correct diagnosis of left posterior fascicular tachycardia and may help to differentiate it from both a supraventricular tachycardia with aberrant conduction and a typical ventricular tachycardia related to coronary artery disease. Although this tachycardia is sensitive to verapamil, this medication may probably cause transient infertility in males. The presence of a Purkinje potential preceding the QRS complex during tachycardia and optimal pace mapping may guide radio-frequency ablation resulting in a definite cure.