Sustained Ventricular Tachycardia

Question 1

What is sustained ventricular tachycardia?

Answer 1

Sustained ventricular tachycardia (VT) is a ventricular rhythm faster than 100 bpm lasting at least 30 seconds or requiring termination earlier due to haemodynamic instability.

Question 2

What is ventricular tachycardia (VT)?

Answer 2

VT is defined as a wide complex tachycardia (QRS 120 milliseconds or greater) that originates from one of the ventricles, and is not due to aberrant conduction (e.g., from bundle branch block), at a rate of 100 bpm or greater.

Question 3

What is idiopathic VT?

Answer 3

‘Idiopathic’ VT occurs in the absence of:

• Apparent structural heart disease (e.g., prior myocardial infarction, active ischaemia, cardiomyopathy, valvular disease, arrhythmogenic right ventricular cardiomyopathy, left ventricular non-compaction, or other disorders of the myocardium)
• Known channelopathy (e.g., long QT syndrome, Brugada syndrome, catecholaminergic polymorphic VT, short QT syndrome)
• Drug toxicity
• Electrolyte imbalance

Question 4

Briefly differentiate between monomorphic and polymophic VT

Answer 4

Monomorphic: tachyarrhythmia with an organised, single-morphology QRS complex arising from one of the ventricles.

Polymorhic: tachyarrhythmia with multiple different wide QRS complex (>120 milliseconds) morphologies arising from the ventricles.

Question 5

Briefly differentiate between haemodynamically stable and unstable VT

Answer 5

Stable: VT associated with a normal blood pressure and no symptoms due to haemodynamic compromise.

Unstable: VT associated with hypotension, signs of diminished cerebral perfusion (e.g., confusion, dizziness, syncope), or signs of diminished coronary perfusion (e.g., angina, dyspnoea).

Question 6

What is Torsades de pointes (TdP)?

Answer 6

A form of polymorphic VT with a characteristic twisting morphology occurring in the setting of QT interval prolongation. TdP is initiated by an early after-depolarisation and perpetuated by re-entry.

Question 7

What are the risk factors for sustained VT?

Answer 7

• Coronary artery disease
• Acute myocardial infarction
• Left ventricular systolic dysfunction
• Hypertrophic cardiomyopathy
• Long QT syndrome
• Short QT syndrome
• Electrolyte imbalance
• Drug toxicity

Question 8

What are the signs of sustained VT?

Answer 8

• Tachycardia
• Hypotension
• Weak pulse

Question 9

What are the symptoms of sustained VT?

Answer 9

• Pre-syncope and sycope
• Impaired consciousness
• Light-headedness
• Dizziness

Question 10

Why is coronary artery disease a risk factor for sustained VT?

Answer 10

Ventricular fibrillation is common during active ischaemia; chronic coronary disease leads to scar formation, which increases risk of ventricular tachycardia.

Question 11

What investigations should be ordered for sustained VT?

Answer 11

• ECG
• Electrolytes
• Troponin-I
• Creatine kinase-MB

Question 12

Why investigate using ECG? And what may this show?

Answer 12

• Required to establish diagnosis of ventricular tachycardia.
• Wide complex tachycardia (QRS 120 milliseconds or greater) at a rate of 100 bpm or greater; may show presence of atrioventricular dissociation, previous myocardial infarction; QRS duration: >140 milliseconds with right bundle branch block morphology, or QRS duration >160 milliseconds with left bundle branch block morphology.

Question 13

Why investigate electrolytes? And what may this show?

Answer 13

• Serves as baseline measurement and may reveal contributory factors to arrhythmia.
• Hypokalaemia and hypomagnesaemia frequently associated with torsades de pointes.

Question 14

Why investigate troponin-I? And what may this show?

Answer 14

• Ischaemia is a reversible cause of ventricular tachycardia and should be sought promptly to allow for revascularisation.
• Elevated in myocardial infarction.

Question 15

Why investigate creatine kinase-MB? And what may this show?

Answer 15

• Ischaemia is a reversible cause of ventricular tachycardia and should be sought promptly to allow for revascularisation.
• Elevated in myocardial infarction.

Question 16

Briefly describe the treatment for haemodynamically unstable sustained VT

Answer 16

• Synchronised cardioversion according to advanced cardiac life support protocol and treatment of any underlying cause (if appropriate).
• Anti-arrhythmic medications amiodarone and lidocaine can be used as adjunctive therapy.

Question 17

Briefly describe the treatment for torsades de pointes

Answer 17

• Torsades de pointes should be treated as any other form of VT according to the advanced cardiac life support protocol, with special recognition of the fact that hypokalaemia and hypomagnesaemia are frequently associated with torsades.
  
  • Intravenous magnesium sulfate, withdraw offending drugs and correct electrolyte abnormalities if appropriate.
• Recurrent torsades de pointes after initial acute therapy can be treated with:
  
  • Isoprenaline infusion
  • Temporary or permanent pacing

Question 18

Briefly descirbe the treatment for haemodynamically stable non-idiopathic VT

Answer 18

• Anti-arrhythmic medications are useful in the acute management of VT that is asymptomatic and associated with normal blood pressure (BP). Amiodarone, lidocaine and procainamide may be used as anti-arrthymics.
• Synchronised cardioversion should be considered before attempting anti-arrhythmic drug therapy in patients who are highly symptomatic (particularly those with symptoms of diminished cerebral perfusion), even if they have apparently stable haemodynamics.

Question 19

Briefly describe the treatment for haemodynamically stable idiopathic VT

Answer 19

• Specific types of idiopathic VT characteristically respond to specific medications. Anti-arrythmics drugs such as adenosine, verapamil, metoprolol, amiodarone and lidocaine can be used.
• Earlier use of cardioversion may be warranted in patients who are highly symptomatic (particularly with symptoms of diminished cerebral perfusion) despite apparently stable haemodynamics.

Question 20

What is an implantable cardioverter defibrillatory (ICD)?

Answer 20

A device implanted into the upper chest below the left shoulder, with leads into the heart to pace, sense and defibrillate.

Question 21

In which patients should ICD be used or considered?

Answer 21

• Treating people with previous serious ventricular arrhythmia, that is, people who, without a treatable cause:
  
  • Have survived a cardiac arrest caused by either ventricular tachycardia (VT) or ventricular fibrillation or
  • Have spontaneous sustained VT causing syncope or significant haemodynamic compromise or
  • Have sustained VT without syncope or cardiac arrest, and also have an associated reduction in left ventricular ejection fraction (LVEF) of 35% or less but their symptoms are no worse than class III of the New York Heart Association (NYHA) functional classification of heart failure.
• Treating people who:
  
  • Have a familial cardiac condition with a high risk of sudden death, such as long QT syndrome, hypertrophic cardiomyopathy, Brugada syndrome or arrhythmogenic right ventricular dysplasia or
  • Have undergone surgical repair of congenital heart disease.

Question 22

What complications are associated with sustained VT?

Answer 22

• Ventricular fibrillation
• Sudden cardiac death

Question 23

What differentials should be considered for sustained VT?

Answer 23

1. Supraventricular tachycardia with aberrancy
2. Supraventricular tachycardia with pre-excitation

Question 24

How does sustained VT differ from supraventricular tachycardia with pre-excitation?

Answer 24

• Differentiating signs and symptoms: none.
• Differentiating investigations: ECG; electrophysiological study: failure to meet criteria for ventricular tachycardia; absence of fusion or capture beats; absence of atrioventricular dissociation.

Question 25

How does sustained VT differ from supraventricular tachycardia with aberrancy?

Answer 25

• Differentiating signs and symptoms: none.
• Differentiating investigations: ECG; electrophysiological study: failure to meet criteria for ventricular tachycardia; absence of fusion or capture beats; absence of atrioventricular dissociation.