Adenosine is the 1st-line drug for supraventricular tachycardia (SVT). It briefly blocks conduction through the AV node, interrupting the reentry circuit that's causing the fast rhythm. It works so well it can stop the heart for a few seconds — which is the plan, not a complication.
〰️ A few seconds of asystoleEXPECTED on the monitor — not a code.
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WHAT IT DOES
STEP 1 · INTERRUPT THE CIRCUIT
SVT is an electrical loop running through the AV node — adenosine breaks the loop for a moment.
🚦 Mechanism: transiently blocks the AV node
SVT is often caused by a re-entry circuit that keeps racing back through the AV node. Adenosine slows/briefly blocks conduction through the AV node, which interrupts the loop and lets the heart's normal pacemaker (the SA node) take back over in normal sinus rhythm.
🧠 “aDENosine hits the DEN.” The AV node is the “den” where the reentry signal keeps circling — adenosine plugs the den for a moment and the loop can't continue.
🎯 Why we give it — “Indication”
1st-line drug for supraventricular tachycardia (SVT) — a common test question is simply: “Which drug does the nurse anticipate the provider will order?” Answer: adenosine.
🪜 SVT order of treatment
1
🫃 Vagal maneuver first — bearing down like a bowel movement (Valsalva)
2
💉 Adenosine — IV push, fast
3
⚡ Synchronized cardioversion if the rhythm doesn't convert or the patient is unstable
🧠 Try the body first, then the drug, then the shock.
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WATCH FOR
STEP 2 · EXPECTED VS. DANGEROUS
Most of what happens after this drug is supposed to happen — knowing which is which is the whole skill.
〰️ A few seconds of asystole on the monitor — EXPECTED, not an emergency
Because adenosine briefly blocks the AV node, a short pause — even a few seconds of asystole — on the monitor is the drug working as intended. Don't call a code for it; stay calm, keep watching, sinus rhythm typically follows.
🧠 “The flat line is the point.” That pause IS the therapy interrupting the SVT loop.
😱 Warn the patient first
Before pushing the dose, tell the patient they may briefly feel:
😰 A sense of impending doom
💢 Chest pressure/tightness
🔥 Flushing
😮💨 Shortness of breath
These pass within seconds because the drug's half-life is so short.
🚫 Contraindicated in certain heart blocks
Avoid in patients with 2nd- or 3rd-degree AV block or sick sinus syndrome (unless they have a functioning pacemaker) — the AV node is already struggling to conduct, and adenosine would block it further.
🧠 Don't block a door that's already stuck shut.
🧑🏫
TEACH
STEP 3 · HOW IT'S ACTUALLY GIVEN
Technique matters here more than almost any other IV push drug.
💨 Flush IV fast, push fast — and why
Adenosine is metabolized almost instantly, so it's given as a rapid IV push over 1–2 seconds through a proximal IV site, immediately followed by a fast saline flush to chase the dose into central circulation before it's gone.
🧠 “Push it like it's disappearing — because it is.” A slow push means the drug breaks down in the tubing before it ever reaches the AV node.
🗣️ What to tell the patient before you push it
"You may feel a sense of doom, chest pressure, or flushing for a few seconds — that's the medicine working, and it passes quickly. You might also notice the monitor pause briefly — that's expected too."
If adenosine doesn't convert it, synchronized cardioversion is next
🧠 “SUPER tachy” = SVT. Super fast, narrow-complex, and it's the AV node driving the loop.
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QUICK RECALL
SAY IT OUT LOUD
🚦 Blocks the AV nodebreaks the SVT reentry loop
💨 Push fast, flush fasthalf-life is only seconds
😱 Doom, pressure, flushingbrief — warn the patient first
〰️ Brief asystole = expectednot a code — stay calm
🎯 Cover & check — 4 rapid-fire questions
Q1: How does adenosine break SVT?
It transiently blocks conduction through the AV node, interrupting the reentry circuit driving the tachycardia so the SA node can resume normal sinus rhythm.
Q2: Why must adenosine be given as a fast IV push with an immediate flush?
Its half-life is only seconds — a slow push lets it break down before reaching the heart, so it's pushed rapidly through a proximal site and chased with a fast saline flush.
Q3: The monitor shows a few seconds of flatline right after adenosine is given. What do you do?
Stay calm and keep watching — a brief pause/asystole is an expected effect of blocking the AV node, not a code situation. Sinus rhythm typically follows.
Q4: What should the nurse tell the patient before pushing adenosine?
Warn them they may briefly feel a sense of impending doom, chest pressure, and flushing, and that these sensations pass quickly because the drug is broken down almost immediately.