IDIOPATHIC MONOMORPHIC VENTRICULAR-TACHYC ARDIA

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, g iving rise to runs of VT with inter-critical ventricular extrasystoles of the same morphology, or to paroxysmal sustained exercise-induced V T; they usually show left bundle branch block with right axis deviatio n : the triggering mechanism is probably a parasystole incompletely pr otected from the sinus rhythm (for the runs of VT) whereas the mechani sm of maintenance is probably that of triggered repetitive activity (f or the runs and paroxysmal forms of VT). When the origin is in the lef t ventricle, the VT shows right bundle branch block and left axis devi ation 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 o r during an emotion; 2) the usual absence of]ate ventricular potential s on surface recordings; 3) their capricious outcome, usually good wit h 92% survival at 10 years; 4) their response to drugs (verapamil, bet ablockers and/or adenosine) which are relatively ineffective against o ther forms of VT; 3) their tendency to recur often leading to radiofre quency ablation procedures (80% success rate). The exclusion of underl ying inapparent cardiac disease (especially arrhythmogenic right ventr icular dysplasia) is an essential part of diagnosis.