Narrow QRS ventricular tachycardia from the posterior mitral annulus without involvement of the His-Purkinje system in a patient with prior inferior myocardial infarction.

A 54-year-old man with prior inferior myocardial infarction suffered from monomorphic ventricular tachycardia (VT) with narrow QRS complex of 120 ms. During VT, a fragmented prepotential preceding QRS onset by 30 ms at the right ventricular posterior septum and a late diastolic potential preceding QRS onset by 70 ms at the infarcted posterior mitral annulus were recorded. Radiofrequency energy delivered to the late diastolic potential at the posterior mitral annulus eliminated VT. During sinus rhythm, the late diastolic potential shifted to the end of QRS complex and no Purkinje potentials were observed. Synchronized excitation of both ventricles from the posterior infarcted mitral annulus in this patient may make the QRS width during VT narrow, without involvement of the His-Purkinje system.