Nursing Field Notes / Cardio · Series: Antidysrhythmics 1 of 4

Antidysrhythmics series 1 · The 4 classes 2 · ABCDs — atrial → 3 → 4 →

Antidysrhythmics I ⚡

The Vaughan-Williams map · four classes, four channels, one heartbeat

NG-019 CARDIO ADHD-friendly visual edition

An antidysrhythmic never adds a beat — it changes ion traffic inside cardiac cells so the electrical signal starts, travels and resets differently. Vaughan-Williams sorts them by which door they slam shut: sodium, beta, potassium, calcium. Learn the door and you already know the ECG change, the side effect, and the rhythm it treats.

📄 Simple Nursing original — opens in Drive →

🔤 Some Block Potassium ChannelsI=Sodium · II=Beta · III=Potassium · IV=Calcium. Four words, whole classification.

⚡ Class = a phaseI hits phase 0 · II hits phase 4 · III hits phase 3 · IV hits the Ca²⁺ plateau & the nodes.

🚨 Every one is proarrhythmicThe drug that treats a rhythm can cause one. Ia & III prolong QT → torsades.

🩺 Same 3 checks, every timeApical HR & BP before · continuous ECG during · K⁺ and Mg²⁺ always.

🗺️

THE FOUR CLASSES

STEP 1 · THE MAP

Don't memorize 30 drugs. Memorize four doors — then hang the drugs on the door they close.

🧠 Meet your study buddy — she only knows one sentence, and it's the whole classification

🧠 “Some Block Potassium Channels.” Say it four times out loud. Sodium → Beta → Potassium → Calcium, in order I · II · III · IV. If you can say the sentence you can rebuild the entire Vaughan-Williams table from scratch.

1️⃣ Class I — sodium channel blockers

Answer first: they slow how fast the impulse fires and travels → the QRS gets wider.

Ia — quinidine, procainamide, disopyramide · moderate block, also blocks K⁺ → QT ⬆
Ib — lidocaine, mexiletine · weak block, shortens the action potential · ventricles only
Ic — flecainide, propafenone · strongest block · QRS ⬆⬆, no QT change

🧠 “Double Quarter Pounder, Lettuce More, Fries Please.” Ia = Disopyramide · Quinidine · Procainamide · Ib = Lidocaine · Mexiletine · Ic = Flecainide · Propafenone.

2️⃣ Class II — beta blockers SEE NG-176

Answer first: they take the epinephrine foot off the pedal at the SA and AV node → slower rate, slower AV conduction, PR ⬆.

Names end in -olol / -lol — metoprolol, atenolol, propranolol, esmolol
The workhorse for rate control in A-fib & A-flutter and for SVT
Only antidysrhythmic class with proven mortality benefit after MI and in heart failure

Full drug page: NG-176 · Beta blockers

🧠 “-LOL lowers the two L's” — Low heart rate, Low blood pressure. Nothing funny about it.

3️⃣ Class III — potassium channel blockers

Answer first: they block the K⁺ exit doors, so the cell takes longer to reset → refractory period ⬆ and QT gets long.

Amiodarone — the "everything" drug; blocks Na⁺, K⁺, Ca²⁺ and beta receptors
Sotalol — Class III plus a beta blocker (that's why it slows the rate too)
Dofetilide, ibutilide, dronedarone — started with the client on a monitor

🧠 “AmIODarone, sotALOL, dofetILIDE, ibutILIDE.” Class III names have that long, drawn-out sound — just like the long QT they cause.

4️⃣ Class IV — calcium channel blockers SEE NG-195

Answer first: the SA and AV nodes run on calcium, not sodium — block Ca²⁺ and you slow the top of the heart.

Only the non-dihydropyridines count here: diltiazem and verapamil
The -dipine drugs (amlodipine, nifedipine) work on vessels, not rhythm
Uses: rate control in A-fib / A-flutter, and SVT

Full drug page: NG-195 · Calcium channel blockers

🧠 “Diltiazem & Verapamil = the heart's CCBs. -dipine = the vessels' CCBs.” If the question is about a rhythm, it is never amlodipine.

📋 The one table to photograph before the exam

Class	Door it blocks	Phase	ECG fingerprint	Signature drugs
Ia	Na⁺ (moderate) + K⁺	0 & 3	QRS ⬆ and QT ⬆	quinidine · procainamide · disopyramide
Ib	Na⁺ (weak)	0	little change · shortens AP	lidocaine · mexiletine
Ic	Na⁺ (strong)	0	QRS ⬆⬆	flecainide · propafenone
II	β₁ receptors	4	HR ⬇ · PR ⬆	metoprolol · atenolol · esmolol · propranolol
III	K⁺	3	QT ⬆	amiodarone · sotalol · dofetilide · ibutilide
IV	Ca²⁺ (L-type)	2 & nodal	HR ⬇ · PR ⬆	diltiazem · verapamil
“Other”	doesn't fit the 4	—	varies	adenosine · digoxin · magnesium · atropine

EXAM TIP Class II and IV both slow the node — so both lengthen PR and both cause bradycardia. That is why IV beta blocker + IV verapamil/diltiazem together is a classic wrong answer: profound bradycardia and heart block.

🧠 Wide QRS = sodium. Long QT = potassium. Long PR = the node (II & IV). Three sentences, and you can read the class off an ECG.

⚡

HOW THEY WORK

STEP 2 · THE ACTION POTENTIAL

One curve explains every class. Find the phase, and you have found the drug.

📈 The cardiac action potential — with every class parked on its phase

🧠 Read the curve left to right and count off the classes: “Up · notch · plateau · down · drift.” The up is sodium (I), the plateau is calcium (IV), the down is potassium (III), the drift is the pacemaker that beta blockers (II) flatten.

🫀 Two kinds of heart tissue — and each class only likes one

🧠 “Nodes run on calcium, muscle runs on sodium.” That single fact is why verapamil slows a rate but never converts VT, and why lidocaine converts VT but does nothing for A-fib.

🔬 Class I split three ways — same door, different grip

EXAM TIP Dashed gray line = the normal action potential. The colored line is what the drug does to it.

🧠 “A-lengthens, B-shortens, C-stays the same.” Ia = Adds length (QT ⬆) · Ib = Brief (shortens) · Ic = Constant length but the Complex (QRS) is huge.

🎯

RHYTHM → DRUG

STEP 3 · WHO GETS WHAT

The exam rarely asks "what class is amiodarone." It asks "the client is in this rhythm — what do you expect the provider to order?"

🗂️ The matching table

Rhythm	Usual first move	Class
Symptomatic bradycardia HR <60	Atropine — then pacing / dopamine / epinephrine if it fails	“Other”
Stable SVT	Vagal maneuvers → adenosine → beta blocker or diltiazem	“Other” → II / IV
A-fib / A-flutter — rate control	Beta blocker or diltiazem / verapamil (digoxin as an add-on)	II / IV
A-fib / A-flutter — rhythm control	Amiodarone, sotalol, dofetilide, flecainide, propafenone	III / Ic
Stable ventricular tachycardia	Amiodarone, procainamide or sotalol · lidocaine as an alternative	III / Ia / Ib
Pulseless VT / V-fib	Defibrillate FIRST — CPR, shock, epinephrine, then amiodarone or lidocaine	III / Ib
Torsades de pointes	IV magnesium sulfate — and STOP the QT-prolonging drug	“Other”

No antidysrhythmic beats electricity in an unstable client. Unstable + a pulse → synchronized cardioversion. Pulseless VT/VF → defibrillation. Symptomatic brady that won't budge → transcutaneous pacing. Drugs come after.

🧠 “Stable? Sedate & medicate. Unstable? Electricity, immediately.” If the stem says hypotensive, altered, chest pain or shock — stop looking for a drug in the answer choices.

⚖️ Rate control vs. rhythm control

🐢 RATE control	🎵 RHYTHM control
Leave A-fib in place — just slow the ventricles	Try to force it back to normal sinus
Class II beta blockers · Class IV diltiazem/verapamil · digoxin	Class III amiodarone/sotalol/dofetilide · Class Ic flecainide/propafenone
Safer, easier, usually first	More proarrhythmic — needs monitoring & anticoagulation planning

🧠 “Rate = the node. Rhythm = the muscle.” Slowing the ventricular response is a node job (II, IV). Changing the actual rhythm is a muscle job (I, III).

🔗 The four "doesn't-fit-a-class" drugs already have their own pages

Adenosine — the 6-second reset button for SVT → NG-094
Digoxin — slows AV conduction and strengthens the squeeze → NG-208
Beta blockers in full detail → NG-176
Calcium channel blockers in full detail → NG-195

The ABCD bedside shortcut — Atropine, Adenosine, Beta blockers, Calcium channel blockers, Digoxin — is the whole of part 2 of this series.

🧠 Vaughan-Williams is the classroom map. ABCD is the bedside map. You need both, and they overlap on purpose.

🧪 The labs that decide whether any of this works

K⁺ 3.5–5.0 mEq/L
Low K⁺ = every antidysrhythmic misbehaves & digoxin turns toxic.

Mg²⁺ 1.3–2.1 mEq/L
Low Mg²⁺ is the setup for torsades — replace it before blaming the drug.

QTc >500 ms
High torsades risk. Prolonged is >450 (men) / >470 (women).

Digoxin 0.5–2.0 ng/mL
Narrow window — always check with the apical pulse.

Standard adult reference ranges — always confirm against your own facility's lab sheet, they vary slightly.

🧠 “Potassium and magnesium are the two batteries.” Put a rhythm drug into a client with a dead battery and you get a new, worse rhythm.

🚨

WATCH FOR

STEP 4 · THE DANGER LIST

The one sentence that shows up on every antidysrhythmic exam: the treatment can become the disease.

🚨 Proarrhythmia — and the QT interval that predicts it

Who prolongs the QT? Class Ia and Class III — plus a long list of non-cardiac drugs (many antipsychotics, methadone, ondansetron, some antibiotics and antifungals). Stacking two of them is the classic hidden trap.

What you do about it: baseline & follow-up 12-lead ECG with a QTc, keep K⁺ and Mg²⁺ replete, and hold the drug and call the provider if the QTc exceeds 500 ms or grows more than about 60 ms from baseline.

🧠 “Long QT = a long fuse.” The longer the reset takes, the more time a stray beat has to land in the wrong place and light the fuse — that stray beat is torsades.

💊 Amiodarone — the most effective and the most toxic

Answer first: it works on almost every rhythm, and it damages almost every organ. Long half-life measured in weeks, so side effects linger after you stop it.

🫁 Pulmonary fibrosis — new dry cough, dyspnea → baseline & periodic chest X-ray + PFTs
🦋 Thyroid — it is iodine-rich; causes hypo or hyper → check TSH
🫀 Liver — monitor LFTs
👁️ Corneal microdeposits — halos, blurred vision → yearly eye exam
🌞 Photosensitivity & a blue-gray skin discoloration — sunscreen, cover up
💓 Bradycardia, hypotension, QT ⬆ — continuous ECG when given IV

🧠 “AMIODARONE ruins your LUNGS, THYROID, LIVER, EYES and SKIN.” Picture a blue-gray patient coughing at the eye doctor. Five organs, one drug.

⚠️ One booby-trap per class

Ia · procainamide — a lupus-like syndrome (joint pain, rash, fever, positive ANA). Also blood dyscrasias → CBC.
Ib · lidocaine — toxicity is neuro first: perioral tingling, metallic taste, tinnitus, confusion, twitching → seizures. Never use the lidocaine with epinephrine for IV cardiac use.
Ic · flecainide — contraindicated with structural heart disease or prior MI; it raised mortality in that group.
II · beta blockers — bradycardia, bronchospasm in asthma/COPD, masks hypoglycemia (the tachycardia warning disappears; sweating remains). Never stop abruptly — rebound tachycardia, hypertension, angina.
III · sotalol/dofetilide — started in the hospital on telemetry because of torsades risk; renally cleared, so watch creatinine.
IV · verapamil/diltiazem — negative inotrope: avoid in reduced-EF heart failure. Verapamil famously causes constipation. Avoid in A-fib with WPW.

🧠 “PROCAINamide gives you a PORCELAIN face (lupus butterfly rash). LIDOcaine talks to your LID (brain). FLECainide FLEES from a scarred heart.”

✅ The nursing priority ladder — works for every drug in this chapter

Apical pulse for a full minute + BP before every dose. Common hold parameters: HR <60 or SBP <90 — but always follow the provider's written parameters.

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Continuous ECG for anything IV. Look at PR, QRS width and QTc, not just the rate.

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Replace the batteries. Check and correct K⁺ and Mg²⁺ — and renal function, since most of these drugs are cleared renally or hepatically.

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Assess the client, not the monitor. Level of consciousness, chest pain, dizziness, skin color, urine output. Treat the client, not the strip.

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Teach before discharge: take the pulse daily, change position slowly, never stop abruptly, report syncope/palpitations/new shortness of breath, and check every new drug — even OTC — for QT interaction.

🧠 “PACER” — Pulse & pressure first · Attach the monitor · Check K⁺ & Mg²⁺ · Evaluate the client · Reinforce teaching. Every antidysrhythmic, every time.

⚡

QUICK RECALL

SAY IT OUT LOUD

🔤 Some Block Potassium ChannelsI sodium · II beta · III potassium · IV calcium

📐 Read it off the ECGWide QRS = Class I · long QT = Class III (or Ia) · long PR = Class II or IV

🚨 Long QT = torsadesQTc >500 ms → hold & call. Treat torsades with IV magnesium.

⚡ Unstable = electricityCardiovert (with a pulse) or defibrillate (pulseless) before any drug.

🎯 Cover & check — 6 rapid-fire questions

Q1: Name the four Vaughan-Williams classes and their channel — in order.

“Some Block Potassium Channels.” I = sodium channel blockers · II = beta blockers · III = potassium channel blockers · IV = calcium channel blockers.

Q2: A client on quinidine has a QTc of 520 ms. What do you do?

Hold the dose and notify the provider — QTc over 500 ms is high torsades risk. Check and replace K⁺ and Mg²⁺, keep the client on continuous ECG, and review every other QT-prolonging drug on the MAR.

Q3: Why is lidocaine useless in atrial fibrillation?

Class Ib binds preferentially to ventricular tissue and to depolarized/ischemic cells — it is a ventricular drug. Atrial rate problems are treated at the node (Class II or IV) or with a Class III/Ic agent.

Q4: Which two classes both prolong the PR interval, and why is combining them IV a red flag?

Class II (beta blockers) and Class IV (diltiazem, verapamil) — both slow AV nodal conduction. Given IV together they can cause profound bradycardia, heart block and hypotension.

Q5: New dry cough and dyspnea in a client who has taken amiodarone for months — priority concern?

Pulmonary toxicity / fibrosis. Report it; expect a chest X-ray and pulmonary function tests. Also monitor TSH, LFTs, vision and skin color.

Q6: The client with VT is now unresponsive with no pulse. First action?

Start CPR and defibrillate — electricity first. Amiodarone or lidocaine come after the shock and epinephrine, never instead of it.