An adult client is being admitted to the coronary care unit with a possible myocardial infarction (MI). The client reports feeling like they are going to "pass out." The cardiac monitor displays the rhythm shown. The client's respiratory rate is 12 to 16 breaths/minute and blood pressure is 78/52 mm Hg. The nurse auscultates clear breath sounds bilaterally and the skin is pale and diaphoretic. After administering oxygen, which action should the nurse prepare to perform?

Rationale: A. Assist the client to perform vagal maneuver or bear down: The ECG shows supraventricular tachycardia (SVT) with a very rapid, regular rhythm. While vagal maneuvers may help slow the rate in stable clients, this client’s hypotension (78/52 mm Hg) and presyncope indicate instability. B. Give an anticholinergic medication: Anticholinergic agents like atropine are used for bradyarrhythmias, not for tachycardia. Administering such a drug would further increase the heart rate and worsen myocardial oxygen demand in this client with suspected myocardial infarction. C. Administer a sedative and cardiovert the client: The rhythm and symptoms indicate unstable supraventricular tachycardia. Synchronized cardioversion is the immediate treatment for unstable tachyarrhythmias with a pulse to restore sinus rhythm and improve perfusion. Sedation is given beforehand if the client is conscious. D. Give a beta blocker medication: Beta blockers are appropriate for stable tachyarrhythmias but can dangerously lower blood pressure in an unstable patient. The client’s hypotension and near-syncope require electrical rather than pharmacologic intervention.