ACLS Megacode 3: Narrow Complex Tachycardia

The ECG shows an irregularly irregular narrow complex tachycardia, characteristic of atrial fibrillation. In a hemodynamically stable patient (BP 140/80 mmHg), the initial goal of treatment is heart rate control using agents such as IV beta-blockers or calcium channel blockers (diltiazem).

Metoprolol is a cardioselective beta-1 blocker given intravenously for rate control in patients with atrial fibrillation. Agents such as epinephrine or dobutamine are inotropes/vasopressors that increase the heart rate, and diltiazem belongs to the class of non-dihydropyridine calcium channel blockers.

This patient is unstable with narrow complex, irregular tachycardia (in this case atrial fibrillation). The appropriate management is synchronized cardioversion. Defibrillation is not indicated for a patient with a pulse. Metoprolol would further drop blood pressure and would likely worsen the clinical scenario. IVFs may transiently help raise the blood pressure, but ultimately would unlikely help control the rate, which is the source of the hypotension.

This rhythm demonstrates sinus tachycardia. The treatment for tachycardia is to treat the underlying cause. Patient does not need to be cardioverted as she is in sinus rhythm. Metoprolol or diltiazem would potentially slow the rate, however, the heart rate may be required to maintain cardiac output and blunting this response could precipitate hypotension.

The ECG shows supraventricular tachycardia (SVT). In a hemodynamically stable patient (BP 120/70 mmHg), vagal maneuvers (such as the Valsalva maneuver) are the first-line initial intervention to try to convert the rhythm. If vagal maneuvers are ineffective, the next step is administering 6 mg of adenosine.