ABSTRACT
Idiopathic monomorphic ventricular tachycardia (IVT) represents 10% of all cases of VT and is usually observed in young subjects. The origin of the VT may be right ventricular, especially in the infundibulum, giving rise to runs of VT with inter-critical ventricular extrasystoles of the same morphology, or to paroxysmal sustained exercise-induced VT; they usually show left bundle branch block with right axis deviation: the triggering mechanism is probably a parasystole incompletely protected from the sinus rhythm (for the runs of VT) whereas the mechanism of maintenance is probably that of triggered repetitive activity (for the runs and paroxysmal forms of VT). When the origin is in the left ventricle, the VT shows right bundle branch block and left axis deviation and is typically paroxysmal and sustained, triggered by coupled atrial stimulation and followed by a post-tachycardial syndrome; these forms are probably due to reentry into or near to the left posterior hemibranch. These forms of IVT are unique by: 1) their triggering by acceleration of the heart rate, especially during the day, on effort or during an emotion; 2) the usual absence of late ventricular potentials on surface recordings; 3) their capricious outcome, usually good with 92% survival at 10 years; 4) their response to drugs (verapamil, betablockers and/or adenosine) which are relatively ineffective against other forms of VT; 5) their tendency to recur often leading to radiofrequency ablation procedures (80% success rate). The exclusion of underlying inapparent cardiac disease (especially arrhythmogenic right ventricular dysplasia) is an essential part of diagnosis.
