Tachycardia

Items hinge on stable vs. unstable, and the “tell” is whether the rate is causing serious signs. A stable, narrow-complex SVT (abrupt onset, rate often 150–250) gets vagal maneuvers first, then adenosine 6 mg rapid IV push followed by 12 mg if needed (unchanged in the 2025 AHA ACLS update); but the moment tachycardia produces hypotension, acute altered mental status, ischemic chest pain, or signs of shock, the answer flips to synchronized cardioversion. The classic trap is treating a sinus tachycardia (gradual, usually under ~150) with adenosine or cardioversion — wrong, because sinus tach is a symptom: fix the underlying fever, pain, hypovolemia, or hemorrhage and the rate follows.

Don’t confuse this with arrhythmia priorities: that term’s defibrillation rule applies to pulseless VT/VF, whereas a tachycardic client with a pulse never gets unsynchronized shock. And remember tachycardia is the early compensatory sign of shock, appearing well before hypotension, which is a late, ominous finding (the body sacrifices rate before it loses pressure). Hook: slow-and-steady = sinus, fast-and-sudden = SVT.