Broad complex tachycardia

Although broad complex tachycardias may be supraventricular with aberrant intraventricular conduction, the distinction from sustained ventricular tachycardia may be difficult (Fig 3). Little harm results if a supraventricular tachycardia is treated as ventricular in origin, but very serious consequences can follow from the converse assumption. The first determinant of management of a broad complex tachycardia is whether or not there is a palpable pulse. Pulseless ventricular tachycardia is a rhythm akin to ventricular fibrillation, and the patient will be unconscious due to inadequate cerebral perfusion. The treatment follows the guidelines for ventricular fibrillation (Fig 1). If a palpable pulse is found, give oxygen, establish intravenous access, and look for adverse signs ( Fig 3).

Fig. 3 Algorithm for broad complex tachycardia (sustained ventricular tachyardia): VF, ventricular fibrillation; BP, blood pressure.

With adverse signs, synchronized d.c. countershock is appropriate after sedation has been given. If this does not immediately resolve the dysrhythmia, lidocaine should be administered. If the plasma potassium concentration is known to be less than 3.6 mmol/l, particularly in the presence of recent infarction, infusions of potassium and magnesium should be administered while the patient is prepared for further cardioversion. Other pharmacological agents that might be considered for refractory cases include procainamide, flecainide, propafenone, bretylium tosylate, and amiodarone. Overdrive pacing may also be considered.

In the absence of adverse signs, lidocaine can be administered in conventional doses and, if the potassium level is known to be low, an infusion of potassium and magnesium is recommended to help prevent recurrent disturbances of rhythm. If lidocaine is ineffective, synchronized d.c. countershock should be considered, as for the symptomatic patient. For refractory cases without adverse signs, amiodarone should be given by slow intravenous injection followed by an infusion, with another attempt at synchronized cardioversion after a period of up to 1 h has elapsed to allow this antiarrhythmic drug to produce a powerful pharmacological effect.

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