Arrhythmias and conduction emergencies

Cardiac Arrhythmias: Tachyarrhythmias

Atrial Fibrillation (AF)

• Haemodynamic Instability: Patients with AF presenting with shock, acute pulmonary oedema, ongoing myocardial ischaemia, or syncope require immediate synchronized direct current cardioversion (DCCV).
• Rate vs. Rhythm Control: In stable patients, initial rate control is preferred. First-line agents include oral or intravenous beta-blockers (e.g., metoprolol, bisoprolol) or non-dihydropyridine calcium channel blockers (diltiazem, verapamil). Non-dihydropyridine CCBs are contraindicated in HFrEF due to their negative inotropic effect; beta-blockers or digoxin are utilized instead.
• AF stroke prevention: Australian guidance uses CHA2DS2-VA, without a sex-category point. Anticoagulation is recommended at a score of at least 2, considered at 1 after discussion, and generally unnecessary at 0. Assess bleeding risks and modify them; do not use a bleeding score alone to deny indicated anticoagulation.
  • Congestive HF (1), Hypertension (1), Age $\ge 75$ (2), Diabetes (1), Stroke / TIA / Thromboembolism (2), Vascular disease (1), Age 65–74 (1).
  • Threshold: Oral anticoagulation is strongly recommended for a score $\ge 2$ in men or $\ge 3$ in women, and should be considered for a score of 1 in men or 2 in women.
  • Direct Oral Anticoagulants (DOACs): Apixaban ($5\text{ mg}$ BD), rivaroxaban ($20\text{ mg}$ daily), or dabigatran ($150\text{ mg}$ BD) are preferred over warfarin due to lower rates of intracranial haemorrhage and superior convenience without routine INR monitoring. Warfarin remains mandatory exclusively for patients with mechanical prosthetic heart valves or moderate-to-severe rheumatic mitral stenosis.

Supraventricular Tachycardia (SVT)

• Narrow-complex regular tachycardia most frequently represents Atrioventricular Nodal Re-entrant Tachycardia (AVNRT) or Atrioventricular Re-entrant Tachycardia (AVRT).
• First-Line: Modified Valsalva manoeuvre (strain in semi-recumbent position for 15 seconds, followed immediately by supine repositioning with 45-degree passive leg elevation for 15 seconds), which achieves cardioversion in over 40% of cases.
• Second-Line: Rapid intravenous adenosine via a large-bore antecubital vein ($6\text{ mg}$ rapid bolus followed by immediate saline flush; if unsuccessful, administer $12\text{ mg}$, then a second $12\text{ mg}$ dose). Warn the patient of transient flushing, dyspnoea, and impending doom. Adenosine is contraindicated in severe asthma (may trigger refractory bronchospasm); intravenous verapamil is preferred in asthmatic patients.

Ventricular Arrhythmias & Resuscitation

• Pulseless VT / Ventricular Fibrillation (VF): Follow the Australian Resuscitation Council (ARC) Advanced Life Support (ALS) algorithm:
  • Immediate uninterrupted cardiopulmonary resuscitation (CPR) at a 30:2 ratio.
  • Defibrillation: Early unsynchronized high-energy biphasic shock ($200\text{ J}$). Resume CPR immediately for 2 minutes before rhythm recheck.
  • Adrenaline: $1\text{ mg}$ IV administered after the 2nd shock, and repeated every second cycle (every 3 to 5 minutes).
  • Amiodarone: $300\text{ mg}$ IV bolus administered after the 3rd shock; an additional $150\text{ mg}$ IV may be given after the 5th shock.
• Haemodynamically Stable Sustained Monomorphic VT: Administer intravenous amiodarone ($300\text{ mg}$ infusion over 20 to 60 minutes) or perform elective synchronized DCCV.

Bradyarrhythmias and Conduction Disorders

Bradyarrhythmias originate from sinus node dysfunction or impaired conduction through the atrioventricular node and infranodal His-Purkinje network.

Clinical comparison: AV Block Classification and Pacemaker Indications

• First-Degree AV Block: Anatomic Site of Block: AV Node (usually); ECG Features: Constant PR interval $> 200\text{ ms}$; all P waves conducted; Clinical Prognosis: Benign; excellent prognosis; Definitive Pacemaker Indication: No (unless PR $> 300\text{ ms}$ causing pacemaker syndrome)
• Second-Degree Mobitz I (Wenckebach): Anatomic Site of Block: AV Node; ECG Features: Progressive PR lengthening until a P wave fails to conduct; Clinical Prognosis: Low risk of progression to asystole; Definitive Pacemaker Indication: Only if symptomatic bradycardia is documented
• Second-Degree Mobitz II: Anatomic Site of Block: Infranodal (Bundle of His / Purkinje); ECG Features: Constant PR interval with intermittent non-conducted P waves; Clinical Prognosis: High risk of progression to complete heart block; Definitive Pacemaker Indication: Yes, absolute indication for permanent pacemaker
• Complete AV block: Atria and ventricles activate independently. Escape rhythm width and rate help localise the block, but not every complete block is infranodal. Unstable patients need urgent pacing support; investigate ischaemia, medicines and metabolic causes.

Acute Bradycardia Management

• Unstable Features: Hypotension, altered conscious state, syncope, diaphoresis, or heart failure.
• First-Line Pharmacotherapy: Intravenous atropine ($500\text{ mcg}$ IV every 3 to 5 minutes up to a maximum of $3\text{ mg}$). Note: Atropine is effective only for nodal blocks and is ineffective in infranodal Mobitz II or complete heart block with wide escape complexes.
• Second-Line / Bridging: Intravenous isoprenaline infusion or adrenaline infusion ($2\text{ to }10\text{ mcg/min}$). If pharmacological measures fail, initiate emergency transcutaneous pacing with appropriate sedation/analgesia as a bridge to emergency transvenous temporary pacing.

Arrhythmia review example

A stable AF patient with renal impairment needs dose-appropriate anticoagulant selection and medication review, not a standard full dose copied from a table. Explain bleeding signs, adherence and what to do before a procedure. A different patient with syncope, hypotension and complete block requires immediate pacing assessment. These decisions separate long-term stroke prevention from an unstable electrical emergency; neither a normal oxygen saturation nor a short-lived symptom resolution removes the need to assess the relevant risk.

Primary references (checked 7 October 2026): Heart Foundation AF resources.