Idiopathic Ventricular Tachycardia

Report:

Ventricular tachycardia 181/min

Comment:

The rate is made irregular by the presence of shorter cycles, as in the Case 2 or Case 61; this is no impediment to the diagnosis of VT. As in the Case 2, the QRS morphology is diagnostic of an ectopic ventricular origin.

The VT criteria are contained in the leads V1 and V2: the relatively broad primary R wave in V1 (Rosenbaum’s ‘normal’ pattern) and the 0.06” between the onset of the QRS and the nadir of the S wave in V21.

The idiopathic VT is usually manifest before the age of 30 and has the characteristic LBBB morphology with an ‘inferiorly directed’ (i.e., relatively rightward) axis (+76o in this case). It is precipitated by exercise, excitement and other adrenaline-releasing stimuli; therapy with beta-blockers, verapamil or adenosine is usually successful. After this episode, both beta-blockers and verapamil were used. This patient’s normal ECG is shown below.

This tachycardia originates in the right ventricular outflow tract (infundibulum). It is also known as adenosine-sensitive or RVOT VT56. A minority (about 30%) of cases have a left ventricular focus, giving rise to RBBB morphology in V1 and LAD – rarely RAD – in the limb leads; the focus appears to be in the posterior or – rarely - anterior fascicle of the left bundle branch. This variety was the original ‘verapamil-sensitive VT’57.