Ventricular Paroxysmal Tachycardia
Figure 13–13 shows a typical short paroxysm of ventricular tachycardia.
The electrocardiogram of ventricular paroxysmal tachycardia has the appearance of a series of ventricular premature beats occurring one after another without any normal beats interspersed.
Ventricular paroxysmal tachycardia is usually a serious condition for two reasons. First, this type of tachycardia usually does not occur unless considerable ischemic damage is present in the ventricles. Second, ventricular tachycardia frequently initiates the lethalcondition of ventricular fibrillation because of rapidrepeated stimulation of the ventricular muscle, as we discuss in the next section.
Sometimes intoxication from the heart treatment drug digitalis causes irritable foci that lead to ventricu-lar tachycardia. Conversely, quinidine, which increases the refractory period and threshold for excitation of cardiac muscle, may be used to block irritable foci causing ventricular tachycardia.