Cardiac Arrhythmia Nursing Guide

Classification of Arrhythmias

Key Principle: Is the patient STABLE or UNSTABLE?

Adverse features (UNSTABLE) = IMMEDIATE action:

Shock (SBP <90 mmHg, cold clammy peripheries, pallor)
Syncope / impaired consciousness
Myocardial ischaemia (chest pain, ST changes)
Heart failure (pulmonary oedema)

ANY of these = cardiovert immediately (do NOT delay for drugs).

Classification by Rate

Category	Rate	Examples
Tachyarrhythmia	> 100 bpm	SVT, AF, AFL, VT, VF
Bradyarrhythmia	< 60 bpm	Sinus bradycardia, AV blocks, SSS

Classification by QRS Width

Type	QRS Width	Origin
Narrow complex tachycardia	< 120 ms (3 small squares)	Supraventricular (above bundle of His)
Broad complex tachycardia	≥ 120 ms	Ventricular OR SVT with aberrant conduction (LBBB, WPW)

Treat ALL broad complex tachycardia as VT until proven otherwise — safer than assuming SVT with aberrancy and giving verapamil (which is dangerous in VT).

Tachyarrhythmias

SVT — Supraventricular Tachycardia

Rate: 150–250 bpm | QRS: Narrow (unless aberrant) | P waves: Hidden in T wave or retrograde

Causes: AVNRT (most common), AVRT (WPW), atrial tachycardia, caffeine, alcohol, electrolyte disturbance, thyrotoxicosis

Symptoms: Sudden onset palpitations, dyspnoea, chest discomfort, pre-syncope

Treatment (stable): Vagal manoeuvres → Adenosine 6mg rapid IV bolus → 12mg if needed → DC cardioversion if haemodynamically unstable

VT — Ventricular Tachycardia

Rate: 100–250 bpm | QRS: BROAD ≥120ms | P waves: Dissociated from QRS (AV dissociation)

Monomorphic VT: Regular, uniform QRS — ischaemia, cardiomyopathy

Polymorphic VT (Torsades de Pointes): Twisting QRS around baseline; caused by prolonged QT (hypokalaemia, hypomagnesaemia, drugs — amiodarone, antipsychotics, antibiotics)

Treatment: Pulseless VT → CPR + defibrillation. Stable VT → amiodarone 300mg IV over 20–60 min. Torsades → IV magnesium sulphate 2g IV.

VF — Ventricular Fibrillation

Rate: 300–400 disorganised | QRS: No discernible complexes — chaotic waveform

Always pulseless — CARDIAC ARREST

Treatment: Immediate CPR + defibrillation (unsynchronised shock). Early defibrillation = highest priority. AED if available.

AFL — Atrial Flutter

Rate: Atrial rate 300 bpm / Ventricular rate typically 150 bpm (2:1 block) | QRS: Narrow

ECG: "Sawtooth" flutter waves in II, III, aVF

Treatment: Rate control (beta-blocker, digoxin) or cardioversion to sinus rhythm. Anticoagulation if >48 hours (same as AF).

Vagal Manoeuvres for SVT

Valsalva manoeuvre — bear down hard for 15 seconds (increases intrathoracic pressure → vagal stimulation). Modified Valsalva (supine with legs elevated 45° after straining) — more effective.
Carotid sinus massage — doctor performs; unilateral gentle massage for 5–10 seconds; CI: carotid bruits, recent stroke/TIA, digitalis toxicity
Ice-cold water facial immersion — particularly effective in children (diving reflex)

Adenosine — Key Drug Facts

Adenosine: 6mg rapid IV bolus into large peripheral vein (antecubital), followed by 10–20 mL saline flush. Wait 1–2 min — repeat with 12mg if no effect; then 12mg again if still no effect (max 18mg). Warning the patient: "You will feel a brief unpleasant sensation — chest tightness, flushing, anxiety — for about 10 seconds." Document pre-administration. CI: asthma (causes bronchospasm), 2nd/3rd degree heart block, WPW with AF (can cause VF). Dipyridamole potentiates adenosine — reduce dose.

Bradyarrhythmias & Heart Blocks

Type	ECG Features	Clinical Significance
1st Degree AV Block	PR interval >200ms (5 small squares); all P waves conducted	Usually benign; no treatment needed
2nd Degree Mobitz Type I (Wenckebach)	Progressive PR lengthening → dropped QRS; cyclical pattern	Usually benign; may occur in inferior MI
2nd Degree Mobitz Type II	Fixed PR interval; intermittent non-conducted P waves	Risk of complete heart block; often needs pacing
3rd Degree (Complete) Heart Block	Complete AV dissociation — P waves and QRS complexes independent	Haemodynamic compromise; requires pacing

Mobitz Type II and Complete Heart Block require urgent cardiology review and often temporary/permanent pacemaker implantation. Can progress to asystole without warning.

Management of Bradycardia (ALS 2021)

Stable bradycardia + no adverse features: observe, treat reversible causes (electrolytes, ischaemia, drugs)
Adverse features (shock, syncope, heart failure, ischaemia):
- First-line: Atropine 500 mcg IV (repeat to max 3 mg)
- If atropine fails: transcutaneous pacing or adrenaline infusion (2–10 mcg/min) as bridge
- Transvenous pacing for persistent high-degree block

Atropine is INEFFECTIVE in 2nd degree Mobitz Type II and 3rd degree complete heart block — may paradoxically worsen. Proceed to pacing.

DC Cardioversion — Nursing Role

Synchronised vs Unsynchronised

Type	When Used	Rhythm
Synchronised DC cardioversion	Unstable SVT, AF, AFL, stable VT with pulse	Shock delivered on R wave (avoids T wave — VF risk)
Unsynchronised defibrillation	VF, pulseless VT, polymorphic VT (chaotic — no R wave to sync)	Delivered when button pressed

Nursing Role in Cardioversion

Ensure consent obtained (elective) or document emergency rationale
IV access confirmed and patent
Ensure anticoagulation for AF >48 hours (3 weeks warfarin/DOAC or TOE to exclude clot before cardioversion)
Anaesthetist present for conscious sedation (elective cardioversion)
Ensure oxygen therapy; defibrillator pads/paddles applied
Resuscitation equipment available (intubation kit, suction, drugs)
Stand clear: "Stand clear — charging — stand clear — all clear — shock"
Post-cardioversion: monitor rhythm, vital signs, SpO₂; document

ALWAYS stand clear before delivering shock. Anyone in contact with the patient or bed will receive the shock. Remove oxygen mask/nasal cannula before shock delivery (fire risk from electrical spark).

Key Antiarrhythmic Drugs

Drug	Use	Key Points / Side Effects
Adenosine	SVT termination	6mg → 12mg → 12mg rapid IV; causes transient heart block; CI in asthma, WPW+AF
Amiodarone	VT, AF rate/rhythm, wide complex tachycardia	300mg over 20–60 min IV (pulseless VT: 300mg bolus); contains 37% iodine — thyroid, lung, liver toxicity; QT prolongation
Atropine	Symptomatic bradycardia	500 mcg IV; max 3mg; ineffective in Mobitz II/CHB
Beta-blockers (metoprolol, bisoprolol)	Rate control in AF, VT prevention	Bradycardia, hypotension, bronchospasm (CI in asthma)
Diltiazem / Verapamil	Rate control in AF (non-WPW)	NEVER give verapamil in broad complex tachycardia (fatal in VT); CI in heart failure, WPW
Digoxin	Rate control AF (especially in heart failure)	Narrow therapeutic window; toxicity: xanthopsia (yellow vision), nausea, VT, heart block; toxicity worsened by hypokalaemia
Magnesium sulphate 2g IV	Torsades de Pointes, refractory VF	First-line for Torsades; also useful in hypomagnesaemia-associated VT
Flecainide	AF cardioversion (pill-in-pocket), SVT prevention	CI in structural/ischaemic heart disease — pro-arrhythmic; CAST trial showed increased mortality post-MI

MCQ Practice — Cardiac Arrhythmias

Q1. A patient develops a regular narrow complex tachycardia at 180 bpm with sudden onset palpitations. BP 110/70. Adenosine 6mg IV is given with no effect. What is the next dose?

A) Adenosine 3mg (reduce dose if first was ineffective)

B) Amiodarone 300mg IV bolus

C) Adenosine 12mg rapid IV bolus

D) Verapamil 5mg IV

✅ C — Adenosine escalation: 6mg → 12mg → 12mg (max 18mg total). If all three doses fail, consider cardioversion or other drugs. Adenosine must be given as a rapid IV bolus in the antecubital fossa followed by saline flush.

Q2. A patient has a broad complex tachycardia at 160 bpm. The clinical team is debating whether this is SVT with aberrancy or VT. What is the safest initial approach?

A) Give verapamil 5mg IV — it terminates both SVT and VT

B) Treat as VT — give amiodarone 300mg IV. Never give verapamil to broad complex tachycardia

C) Give adenosine 6mg — adenosine is safe in both SVT and VT

D) Perform carotid sinus massage before any drug treatment

✅ B — Treat ALL broad complex tachycardia as VT until proven otherwise. Verapamil given to VT can cause profound hypotension and cardiac arrest. Amiodarone is safe in both VT and SVT with aberrancy. Adenosine is sometimes used diagnostically in stable patients under specialist supervision.

Q3. A patient develops polymorphic VT (Torsades de Pointes) in the context of a QTc of 560ms. What is the treatment of choice?

A) Amiodarone 300mg IV (further prolongs QT)

B) DC cardioversion only

C) IV magnesium sulphate 2g over 10 minutes

D) Sotalol IV infusion

✅ C — IV magnesium sulphate 2g is the first-line treatment for Torsades de Pointes. Amiodarone is CONTRAINDICATED as it further prolongs QT interval. Stop QT-prolonging drugs. Correct hypokalaemia and hypomagnesaemia. Overdrive pacing may be needed for refractory cases.

Q4. Which ECG finding characterises Complete (3rd Degree) Heart Block?

A) Progressive PR interval lengthening with occasional dropped QRS complex

B) Fixed prolonged PR interval on every beat

C) Complete dissociation between P waves and QRS complexes — each at their own independent rate

D) Absent P waves with regular narrow QRS complexes

✅ C — 3rd degree (complete) heart block: no relationship between P waves and QRS complexes. P waves march at their own rate (~60–100 bpm); QRS complexes march at their own escape rate (~30–40 bpm broad/junctional or ~40–60 bpm narrow). Requires urgent pacing. Progressive PR lengthening = Wenckebach (Mobitz I).

Cardiac Arrhythmia — Nursing Guide