Ventricular tachycardia : A potentially lethal disruption of the normal heartbeat. This arrhythmia may compromise the pumping ability of the ventricles as the ventricular rate can rise to 160 to 240 beats per minute from the normal 60 to 100. A common mechanism for ventricular tachycardia is reentry (re-stimulation of the electrical conductive pathway from a single initial stimulus), which can be produced by a three-dimensional spiral wave of electrical activity that recirculates within the ventricles with a period of about 200 to 300 ms (shown in the figure), which causes the ventricles to contract too quickly to maintain adequate blood output.
Atrioventricular dissociation, in which the sinoatrial node initiates atrial beats at a normal rate (slower than the ventricular rate), usually is present during VT. Ventricular tachycardia can occur in the absence of apparent heart disease, and in many cases it can develop very quickly into ventricular fibrillation if the initial spiral wave breaks into multiple reentrant waves. Ventricular tachycardia that lasts at least 30 seconds generally requires termination by antiarrhythmic drugs, antitachycardia pacing techniques, or electrical cardioversion.