Cardiovascular pharmacology

An ECG shows a polymorphic ventricular tachycardia with waxing and waning QRS amplitude around the baseline and a prolonged QT interval. Which therapy is most appropriate to reduce the immediate arrhythmic risk?

ECG strip with twisting polymorphic wide-complex beats around the baseline after a prolonged QT interval.
ECG pattern for interpretation in a patient with suspected drug-associated ventricular arrhythmia.