Arrhythmias

• Arrhythmias are abnormal heart rhythms resulting from an interruption to the normal electrical signals that coordinate the contraction of the heart muscle
• There are several types of arrhythmia, each with different causes and management options
• Shockable rhythms

  • Ventricular tachycardia
  • Ventricular fibrillation
• Narrow Complex Tachycardia refers to a fast heart rate with a QRS complex duration of less than 0.12 seconds
• Main differentials of a narrow complex tachycardia

  • Sinus tachycardia (treatment focuses on the underlying cause)
  • Supraventricular tachycardia (treated with vagal manoeuvres and adenosine)
  • Atrial fibrillation (treated with rate control or rhythm control)
  • Atrial flutter (treated with rate control or rhythm control, similar to atrial fibrillation)
• Cardiac Arrest Rhythms: There are four possible rhythms in a pulseless patient, either shockable or non-shockable
• Non-shockable rhythms

  • Pulseless electrical activity (all electrical activity except VF/VT, including sinus rhythm without a pulse)
  • Asystole (no significant electrical activity)
• On a normal 25 mm/sec ECG, 0.12 seconds equals 3 small squares
• Patients with life-threatening features, such as loss of consciousness (syncope), heart muscle ischaemia (e.g., chest pain), shock or severe h
• Cause of Atrial Flutter

  Re-entrant rhythm in either atrium causing a self-perpetuating loop due to an extra electrical pathway in the atria
• Atrial flutter gives a sawtooth appearance on the ECG with repeated P waves occurring at around 300 per minute and a narrow complex tachycardia
• Broad Complex Tachycardia

  A fast heart rate with a QRS complex duration of more than 0.12 seconds or 3 small squares on an ECG
• Afterdepolarisations can lead to torsades de pointes, a type of polymorphic ventricular tachycardia
• Prolonged QT Interval

  The QT interval is from the start of the QRS complex to the end of the T wave. The corrected QT interval (QTc) estimates the QT interval if the heart rate were 60 beats per minute. It is prolonged at more than 440 milliseconds in men and more than 460 milliseconds in women
• Types of Broad Complex Tachycardia

  • Ventricular tachycardia
  • Unclear cause (treated with IV amiodarone)
  • Polymorphic ventricular tachycardia, such as torsades de pointes (treated with IV magnesium)
  • Atrial fibrillation with bundle branch block (treated as AF)
  • Supraventricular tachycardia with bundle branch block (treated as SVT)
• Treatment for Atrial Flutter

  1. Rate control

  2. Rhythm control

  3. Synchronised DC cardioversion under sedation or general anaesthesia

  4. Intravenous amiodarone if initial DC shocks are unsuccessful
• Atrial flutter has an atrial rate of around 300 beats per minute and a ventricular rate of 150 beats per minute due to 2:1 conduction
• Treatment for Atrial Flutter

  1. Similar to atrial fibrillation, including anticoagulation based on the CHA2DS2-VASc score

  2. Radiofrequency ablation of the re-entrant rhythm can be a permanent solution
• A prolonged QT interval represents prolonged repolarisation of the heart muscle cells after a contraction
• Torsades de pointes


  • Appearance on ECG like standard ventricular tachycardia but with the QRS complex twisting around the baseline, with progressively smaller and larger QRS complexes
• Ventricular tachycardia can lead to

  Cardiac arrest
• Management of a prolonged QT interval

  1. Stopping and avoiding medications that prolong the QT interval

  2. Correcting electrolyte disturbances

  3. Beta blockers (not sotalol)

  4. Pacemakers or implantable cardioverter defibrillators
• When a contraction occurs before proper repolarisation, leading to recurrent contractions without normal repolarisation, it is called torsades de pointes
• Heart Block

  Impaired conduction of electrical signals in the heart
• Ventricular Ectopics

  Premature ventricular beats caused by random electrical discharges outside the atria
• Mobitz type 2


  • Intermittent failure of conduction through the atrioventricular node, with P waves not always followed by QRS complexes
• Second-degree heart block

  Some atrial impulses do not make it through the atrioventricular node to the ventricles
• Bigeminy

  Refers to when every other beat is a ventricular ectopic, alternating with a normal beat on an ECG
• First-degree heart block

  Delayed conduction through the atrioventricular node, with every atrial impulse leading to a ventricular contraction
• Causes of prolonged QT interval

  • Long QT syndrome
  • Medications such as antipsychotics, citalopram, flecainide, sotalol, amiodarone, and macrolide antibiotics
  • Electrolyte imbalances such as hypokalaemia, hypomagnesaemia, and hypocalcaemia
• Torsades de pointes

  A type of polymorphic ventricular tachycardia, translating from French as “twisting of the spikes” on an ECG
• Acute management of torsades de pointes

  1. Correcting the underlying cause (e.g., electrolyte disturbances or medications)

  2. Magnesium infusion (even if they have normal serum magnesium)

  3. Defibrillation if ventricular tachycardia occurs
• Torsades de pointes will terminate spontaneously

  Reverting to sinus rhythm or progressing to ventricular tachycardia
• Mobitz type 1 (Wenckebach phenomenon)


  • Progressively longer conduction through the atrioventricular node until it finally fails, then resets, with increasing PR interval until a P wave is not followed by a QRS complex
• Ventricular Ectopics


  • Appear as isolated, random, abnormal, broad QRS complexes on an otherwise normal ECG
• Management of Ventricular Ectopics

  1. Reassurance and no treatment in otherwise healthy people with infrequent ectopics

  2. Seeking specialist advice in patients with underlying heart disease, frequent or concerning symptoms, or a family history of heart disease or sudden death

  3. Beta blockers are sometimes used to manage symptoms
• It can be difficult to tell whether a 2:1 block is caused by Mobitz type 1 or Mobitz type 2
• Mobitz type 2


  Intermittent failure of conduction through the atrioventricular node, absence of QRS complexes following P waves, set ratio of P waves to QRS complexes (e.g., 3:1 block), normal PR interval, risk of asystole
• Third-degree heart block


  Also called complete heart block, no observable relationship between P waves and QRS complexes, significant risk of asystole
• ECG cycle

  Increasing PR interval until a P wave is not followed by a QRS complex, then PR interval returns to normal, and the cycle repeats itself