Pathophysiology
Clinical meaning
Ventricular tachycardia (VTach) originates below the bundle of His within the ventricular myocardium or Purkinje fibers. It is defined as three or more consecutive premature ventricular complexes (PVCs) at a rate of 100โ250 bpm. The primary mechanism is reentry through scarred or diseased ventricular tissue, though enhanced automaticity and triggered activity can also cause VTach. Because the impulse does not travel through the normal His-Purkinje system, ventricular depolarization is slow and disorganized, producing wide, bizarre QRS complexes (โฅ0.12 sec). AV dissociation (atria and ventricles beat independently) is a hallmark when identifiable. VTach is classified as: (1) Sustained โ lasting >30 seconds or causing hemodynamic compromise; (2) Non-sustained (NSVT) โ 3 or more beats lasting <30 seconds, self-terminating; (3) Monomorphic โ uniform QRS morphology (single reentry circuit, often from MI scar); (4) Polymorphic โ variable QRS morphology (multiple circuits or changing substrate). Torsades de Pointes (TdP) is a specific polymorphic VTach occurring with a prolonged QT interval, characterized by a 'twisting of the points' pattern where QRS amplitude oscillates around the baseline. VTach can rapidly deteriorate to VFib and cardiac arrest....