Arrhythmias – Rapid Review

Causes of Arrhythmia

• Ischaemic heart disease, drugs, rheumatic heart disease, cardiomyopathy, thyrotoxicosis
• Oxygen, fluid or electrolyte disturbance (eg $K^+$, $Mg^{2+}$)

Differentiating SVT vs VT

• SVT: narrow QRS, usually regular, no/abnormal P waves, $\Downarrow$ with adenosine
• VT: broad QRS, may be irregular, P waves dissociated, inverted QRS, no adenosine response, fusion beats possible

Ventricular Ectopics (VE)

• Unifocal (same shape) or multifocal (different shapes); pulse irregular
• Danger: R-on-T $\Rightarrow$ ventricular fibrillation
• Treat if VE:normal >1:6 OR multifocal OR new onset (may signal sepsis)
• Common precipitants: post-MI, hypoxia, hypokalaemia, hypomagnesaemia, digitalis toxicity, valvular/cardiomyopathic disease

Sinus Tachycardia

• Regular rhythm, $\le160$ bpm (lower in elderly)
• Normal P morphology, gradual onset
• Always treat underlying cause (hypovolaemia, anaemia, PE, sepsis)

Paroxysmal Supraventricular Tachycardia (PSVT)

• Origin: SA node, atria or AV node
• P waves abnormal/hidden; QRS usually narrow (may widen with BBB)
• Rate $150!\text{–}!250\,\text{bpm}$; regular
• May cause ST depression (ischaemia)
• Acute therapy: adenosine (diagnostic & therapeutic)
• Ongoing control: verapamil, digoxin or $\beta$-blocker (avoid $\beta$-blocker + verapamil)

Atrial Fibrillation (AF)

• Irregularly irregular; ventricular rate $100!\text{–}!180\,\text{bpm}$
• Post-op triggers: hypovolaemia, hypoxia, hypo$K^+$/hypo$Mg^{2+}$
• Serious adverse signs (hypotension, shock, chest pain, failure, LOC, rate >140): urgent DC cardioversion or IV amiodarone
• Without adverse signs: correct triggers ± digoxin or amiodarone
• Long-standing AF may worsen if regular meds omitted

Atrial Flutter

• Saw-tooth flutter waves at $\approx300\,\text{min}^{-1}$; QRS normal with variable AV block
• Often coexists with AF; linked to structural heart disease
• Adenosine can transiently reveal/flutter or terminate
• Management: cardioversion, digoxin, verapamil