Ventricular tachycardia

Ventricular tachycardia is defined as the occurrence of three or more consecutive ventricular premature complexes at a rate of 100 to 200 beats/min. It is considered to be sustained if the rhythm lasts for more than 30 s and non-sustained if the rhythm lasts for less than 30 s. It is occasionally difficult to differentiate ventricular tachycardia from supraventricular tachycardia with aberrancy (T.a.ble.,.2.). A wide QrS tachycardia in an older patient with heart disease is usually ventricular tachycardia. Clinical symptoms depend on the severity of the underlying cardiac disease as well as the rate of the ventricular tachycardia. It may be associated with hemodynamic deterioration, or may accelerate and degenerate into ventricular defibrillation ( Fig, 7).

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Fig. 7 Ventricular tachycardia. Criteria from Table,2, help with the diagnosis.

Torsade de pointes is a polymorphic ventricular tachycardia associated with a long QT interval. This rhythm is difficult to treat, frequently degenerates into ventricular fibrillation, and tends to recur. It may be seen in patients with inherited long QT syndrome, but may also be caused by drugs, such as class IA, IC, and III antiarrhythmics and phenothiazines, electrolyte abnormalities such as hypocalcemia, hypokalemia, and hypomagnesemia, slow heart rates, and acute brain injury. Long-acting antihistamines and erythromycin have also been associated with this arrhythmia. Torsade may be associated with a bradycardia and triggered by an early ventricular premature complex which falls on a long bizarre T wave that occurs following a pause. It is due to delayed repolarization and tends to recur if the underlying cause is not or cannot be corrected.

Ventricular flutter is an extremely rapid form of ventricular tachycardia with rates of over 200 beats/min. It may also degenerate into ventricular fibrillation which is a totally disorganized ventricular activity caused by a random pattern of re-entry circuits. This arrhythmia may be the terminal event in cardiac death.

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