Arrhythmia is a disorder in which the heart beats irregularly. It may be too slow or too fast.
Bradycardia is having a heart rate of <50 beats/minute that may not affect the hemodynamic status of some patients.
Clinically significant bradycardia is having a heart rate that is inadequate for the patient's current condition and may not be able to support life.
Tachycardia is having serious signs and symptoms that are often demonstrated at ventricular rates of >150 beats/minute.
Signs and symptoms related to rapid heart rate are altered sensorium, angina, shortness of breath, myocardial infarction, hypotension and other signs of shock (eg cold clammy skin, low urine output), heart failure or pulmonary congestion.


Establish that the cause of the following is bradycardia

Signs & Symptoms of Poor Perfusion & Clinical Instability

  • Hypotension
  • Shock
  • Congestive heart failure (CHF)
  • Altered mental status
  • Chest pain
  • Seizures
  • Syncope
Atrioventricular (AV) Block
  • May be brought about by drugs, electrolyte imbalance or structural anomalies resulting from myocardial infarction (MI) or other myocardial diseases

Classification of AV blocks

1st Degree

  • Prolonged PR interval (>0.20 sec)
  • Benign

2nd Degree

  • Mobitz I
    • Block located at the AV node
    • Mostly transient
    • Patient may be asymptomatic
  • Mobitz II
    • Block is located at the Bundle of His or bundle branches
    • Patient is often symptomatic
    • May progress to 3rd degree block

3rd Degree

  • Complete AV block
  • May be permanent or transient

Risk of asystole

Indicated by:

  • Recent asystole
  • Mobitz type II AV block
  • Complete (3rd degree) heart block
  • Ventricular standstill of >3 sec
Assessment of Tachycardia
  • Establish that the signs of cardiovascular compromise are rate-related
  • Provide immediate synchronized cardioversion for unstable & deteriorating patients
  • If the patient is stable, evaluate cardiac rhythm to determine treatment options
  • Consider referral to a specialist


Interpretation of ECG

  • Identify sinus from non-sinus tachycardia
  • Determine narrow-complex (QRS <0.12s) & wide-complex (QRS ≥0.12s) tachycardia
  • Determine regularity

Regular Narrow-Complex Tachycardias

Sinus Tachycardia

  • Occurs when the sinus node discharge rate is >100 per minute in a physiological response to a variety of stimulus
  • Upper limit of sinus tachycardia is age-related
  • Uniform & upright P waves on leads I, II & aVF
  • P wave appears before every QRS complex w/ constant PR intervals

Supraventricular Tachycardia (SVT)

  • Re-entry SVT/Paroxysmal SVT (PSVT)
    • Surpasses the upper limits of sinus tachycardia at rest (>150 bpm) w/ or w/o discernible P waves
  • Regarded as ventricular in origin if the QRS complex is narrow or if the QRS complex is wide & bundle branch aberrancy is present
  • May include AV nodal re-entry tachycardia (AVNRT) or AV re-entrant tachycardia (AVRT)

Irregular Narrow-Complex Tachycardias

Atrial Fibrillation (A-fib)

  • Most common
  • W/o aberrant conduction or preexisting bundle branch block, QRS complex is narrow
  • No clear atrial activity
  • Ventricular response is irregularly irregular w/ rate ranging from 100-200 bpm

Atrial Flutter

  • Less common
  • Supraventricular rhythm caused by the re-entrant loop just above the AV node in the right atrium
  • Sawtooth pattern on inferior ECG leads

Regular Wide-Complex Tachycardia

Ventricular Tachycardia (VT)

  • Series of >3 consecutive wide complex beats
  • Rate >100 bpm
  • Likely VT when QRS complex is not observed on all precordial leads
  • There is AV dissociation

Irregular Wide-Complex Tachycardia

  • Most commonly AF w/ bundle branch block
  • Other possible causes: AF w/ ventricular pre-excitation in Wolff-Parkinson-White (WPW) syndrome, poly- morphic VT (eg, torsades de pointes)
  • Pre-excitation syndrome: Visible delta wave characteristic of WPW during normal sinus rhythm prior to the onset of A-fib

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