Bradycardia & Tachycardia
For patients WITH a pulse, the central question is whether they are stable or unstable — that judgment drives everything from drugs to electricity. This chapter covers the adult bradycardia and tachycardia algorithms.
Symptomatic bradycardia
Bradycardia becomes an emergency when it causes symptoms — hypotension, acutely altered mental status, signs of shock, ischemic chest discomfort, or acute heart failure. First-line treatment is atropine 1 mg IV, repeated every 3-5 minutes to a maximum of 3 mg. If atropine fails or the block is high-grade (Mobitz II or complete heart block), escalate to transcutaneous pacing and/or a dopamine or epinephrine infusion, and seek expert consultation. An asymptomatic bradycardia generally needs monitoring, not immediate drugs.
Stable vs. unstable tachycardia
The pivotal question in tachycardia is stability. An UNSTABLE tachycardia with a pulse (hypotension, altered mental status, shock, ischemic chest pain, or acute heart failure) is treated with immediate synchronized cardioversion — the shock is timed to the R wave to avoid the vulnerable T-wave period that could induce VF. A STABLE tachycardia allows time for a 12-lead ECG and drugs: vagal maneuvers then adenosine for regular narrow-complex SVT, and antiarrhythmics (e.g., amiodarone, procainamide, or sotalol) for stable wide-complex tachycardia. Remember: synchronized cardioversion is for the unstable patient with a pulse, while unsynchronized defibrillation is only for pulseless VF/pVT.