A 32-year-old man with no past medical problems presents to the ED with palpitations. For the past 2 days he has been feeling weak and over the last 6 hours he has noticed that his heart is racing. He has no chest pain or shortness of breath. He has never felt this way before. His temperature is 98.9°F, BP is 140/82 mm Hg, HR is 180 beats per minute, and RR is 14 breaths per minute. His physical examination is normal. You obtain the following rhythm strip. What is your first-line treatment for this patient?
Synchronized cardioversion at 100 J
Adenosine 6-mg intravenous (IV) push
Adenosine 12-mg IV push
Valsalva maneuver
Verapamil 3-mg IV push
(Tintinalli, pp 136-143.) This patient has supraventricular tachycardia (SVT), a narrow complex, regular tachycardia. It is caused by a reentry or an ectopic pacemaker in areas of the heart above the bundle of His, usually the atria. Regular P waves will be present but may be difficult to discern owing to the very fast rate. The patient in this case has normal vital signs and examination, and is therefore stable. First-line treatment for a patient with stable SVT is vagal maneuvers to slow conduction and prolong the refractory period in the AV node. The Valsalva maneuver can be accomplished by asking the patient to bear down as if they are having a bowel movement and hold the strain for at least 10 seconds. Other vagal maneuvers include carotid sinus massage (after auscultating for carotid bruits) and facial immersion in cold water.
If vagal maneuvers fail, the next step is adenosine, a very short-acting AV nodal blocking medication. Initially, adenosine 6 mg (b) is rapidly pushed through the IV in a site as close to the heart as possible. Patients may experience a few seconds of discomfort, including chest pain and facial flushing on receiving the adenosine. If the patient remains in SVT 2 minutes after receiving adenosine, a second dose of adenosine at 12 mg (c) is administered. If the second dose of adenosine fails and the patient remains stable, short-acting calcium channel blockers (eg, verapamil), (e) β-blockers, or digoxin can be administered. If at any time the patient is considered unstable (hypotension, pulmonary edema, severe chest pain, altered mental status, or other life-threatening concerns), synchronized cardioversion (a) should be performed immediately.