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Lesson

SVT & Adenosine Framing

12 min Cardiac & ECG

Objective: Treat regular narrow-complex SVT as a perfusion problem first — vagal and adenosine when stable and authorized, synchronized cardioversion when the rate is the reason they are crashing.

Why This Is Hard

Everything fast and narrow gets called “SVT.” Some of it is sinus tach from sepsis or volume loss. Some of it is AF. Adenosine in the wrong rhythm is at best theater and at worst dangerous (pre-excited AF). Your job: regular vs irregular, narrow vs wide, stable vs unstable — then the protocol path. See also stable vs unstable tachycardia.

Say out loud
  • Pulse? If none, this is arrest — not SVT
  • Regular and narrow? SVT pathway may fit
  • Irregular? Think AF — adenosine is not the treatment
  • Unstable from the rate → pads on, synchronized cardioversion

What This Lesson Means by SVT

Here, SVT means a regular, narrow-complex tachycardia that is likely AVNRT or AVRT — not sinus tach, not AF, not atrial flutter with variable block, not wide-complex VT. If you cannot tell, do not invent a drug.

Street Sequence (Education)

  1. ABCs, oxygen as indicated, IV, 12-lead when it will not delay a crashing patient, pads on early.
  2. Name regularity and QRS width with your systematic approach.
  3. Unstable (hypotension, shock, severe AMS, ischemic pain, acute failure caused by the rate): synchronized cardioversion per protocol. AHA 2025 allows a brief adenosine trial for regular monomorphic narrow-complex while pads are going on — that is not permission to delay a shock in a crashing patient.
  4. Stable: vagal maneuvers (Valsalva / modified Valsalva where trained). Then adenosine if protocol includes it — rapid IV push with a flush, in a monitored patient, with defibrillator pads already on.

Adenosine Framing (Not a Formulary)

  • Works on the AV node. That is why it can terminate AVNRT/AVRT and why it is the wrong “treatment” for AF (you may see flutter waves briefly; you did not convert AF as a plan).
  • Do not give AV-nodal blockers (adenosine, diltiazem, verapamil, beta-blockers, digoxin) in suspected pre-excited AF (WPW) — you can accelerate accessory-pathway conduction into VF. Irregular, very fast, wide or changing QRS is a warning. Cardiovert if unstable; expert/protocol path if stable.
  • Warn the patient they will feel awful for a few seconds. Record a strip through the push.
  • This site does not publish milligrams. Protocol owns dose, repeat, and reduced-dose situations (central line, transplant, dipyridamole/carbamazepine teaching lists).

Field Pitfalls

  • Adenosine for sinus tach at 130 from fever or bleed.
  • Calling irregular narrow-complex “SVT.”
  • No pads on when you push adenosine.

Practice

60-second drill

In CardioStrip, pick a regular narrow tachycardia and an irregular narrow tachycardia. For each, say: vagal/adenosine path, rate-control path, or cardioversion path — and why.

Related: AF with RVR, WCT.

Sources & Further Study

Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.

Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.

Check Your Understanding

Street decisions from this lesson only. After you check, the key is highlighted. Education practice — not a certification exam.

1. The SVT pathway in this lesson is for:
2. A crashing patient whose instability is from a regular narrow tachyarrhythmia:
3. Adenosine (and other AV-nodal blockers) are the wrong move in:
4. Irregular narrow-complex tachycardia at 160 is best framed as:
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