Ventricular tachycardia

This is an example of a VT (click for a bigger version). There are lots of different types but if it's a broad QRS and over 120 bpm, it's a VT.

Definition

This is a broad-complex tachycardia (QRS >120ms/3 small squares) which originates in the ventricles.

Epidemiology

Really common and dangerous, particularly in coronary artery disease.

Pathophysiology

Torsades de pointes - note the changes in amplitude.

There are four different types of VT:

• Fascicular - uncommon; associated with structural heart defects; from left bundle branch; short QRS complexes (0.11-0.14s); QRS complexes look like RBBB
• Right ventricular outflow tract - right axis deviation; LBBB pattern; provoked by catecholamine release, sudden changes in heart rate, exercise; responds to alpha-blockers and calcium antagonists.
• Polymorphic - looks like Torsades de pointes (QT interval normal in sinus rhythm); similar to AF; can lead to cardiogenic shock and VF.
• Torsades de pointes - A form of VT where the amplitude of the QRS complex varies. Important as it is likely to lead to VF.

Risk Factors

• Structural heart disease or coronary heart disease
• Electrolyte disturbances: hypokalaemia, hypocalcaemia and hyponatraemia

Clinical Features

Presents with features of ischaemic heart disease or haemodynamic compromise. Chest pain, palpitations, dyspnoea, dizziness, syncope and possibly symptoms of heart failure.

Investigations

ECG

Differences between VT and SVT:

• VT more likely than SVT - AV dissociation (lack of synchronicity between atria and ventricles); fusion beat (where normal and ectopic ventricular beats coincide); QRS > 40ms; rS pattern (small rise, big fall, back to normal instead of QRS complex) in V1.
• SVT more likely than VT - RBBB pattern; varying bundle branch block; qR pattern (no initial drop in QRS complex) in V1; ectopic P wave preceding arrhythmia.

Bloods

• U+Es - particularly calcium, potassium and magnesium.
• Levels of therapeutic drugs like digoxin
• Trop T for MI
• CXR - due to possibility of heart failure

Management

• Pulseless VT - treat using advanced life support
• Unstable VT - synchronised cardioversion. May result in VF. Amiodarone is first-line for haemodynamically unstable VT. Deal with electrolyte disturbances too.
• Stable VT - treat with IV lidocaine, or other class 1b antiarrhthmic and cardioversion
• Refractory VT - amiodarone.
• Torsades de pointes
  • Acute - magnesium; then, beta 1-adrenergic agonist (isoprotenerol), temporary pacing
  • Long-term - beta-blockers (congenital, not acquired), pacing

Prognosis

Generally favourable.