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Rhythm

Ventricular tachycardia (monomorphic)

Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

Ventricular tachycardia is a rapid rhythm arising from the ventricles, with three or more consecutive wide QRS beats at a rate above 100 beats/min. It is a life-threatening arrhythmia that may degenerate into ventricular fibrillation.

ECG criteria

  • Three or more consecutive ventricular beats at over 100 beats/min (most are 140 to 220); sustained if lasting over 30 seconds or causing instability.
  • Wide QRS, usually 140 ms or more, with a regular and monotonous (same-shape) morphology in monomorphic VT.
  • AV dissociation, with P waves independent of the QRS, is the most specific sign.
  • Capture beats (narrow normally conducted beats) and fusion beats confirm the diagnosis.
  • QRS concordance across the precordial leads, extreme axis deviation, and a very wide QRS support a ventricular origin.

Mechanism

Most monomorphic VT arises from re-entry around a myocardial scar, commonly after infarction, or less often from focal automaticity or triggered activity. Activation spreads cell to cell from the ventricular focus, which accounts for the wide QRS and AV dissociation.

Common causes

  • Ischaemic heart disease: acute myocardial infarction or healed infarct scar (the commonest cause).
  • Cardiomyopathies (dilated, hypertrophic, arrhythmogenic) and structural heart disease.
  • Electrolyte disturbance (hypokalaemia, hypomagnesaemia), drug toxicity and QT-prolonging drugs.
  • Genetic channelopathies; idiopathic VT in structurally normal hearts (for example outflow tract VT).

Management principles

Pulseless VT is treated as cardiac arrest, and unstable VT with synchronised cardioversion, according to the local advanced life support protocol. Stable patients need urgent specialist input, correction of electrolytes and ischaemia, and assessment for an implantable defibrillator or ablation; follow local guidelines, for example AHA and ESC.

High-level principles for study. Treatment decisions follow local guidelines and the clinical situation.

Pitfalls and mimics

  • Assume a regular wide-complex tachycardia is VT until proven otherwise; misdiagnosis as supraventricular tachycardia with aberrancy is common and harmful, especially if haemodynamic tolerance is mistaken for a supraventricular origin.
  • Preserved blood pressure does not exclude VT, which can be well tolerated for a time.
  • Supraventricular tachycardia with bundle branch block, pre-excited tachycardia and hyperkalaemia can all mimic VT.

Practise in the ECG trainer — Recognise this pattern on generated tracings.

References

  1. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death. American Heart Association / American College of Cardiology / Heart Rhythm Society (2017) — Tier 2 (guidelines / primary literature)
  2. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. European Society of Cardiology (2015) — Tier 2 (guidelines / primary literature)
  3. Wagner GS, Strauss DG. Marriott's Practical Electrocardiography. Wolters Kluwer, 12th edition (2013) — Tier 3 (textbook)

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