The ECG shows a narrow complex, regular tachycardia typical of supraventricular tachycardia. It is caused by a re-entry 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. 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 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 is administered. If the second dose of adenosine fails and the patient remains stable, short-acting calcium channel blockers (eg, verapamil), beta-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 should be performed immediately.
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