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The conduction system of the heart

• Sinoatrial node
  • SA node, sinus node
  • The “pacemaker”
  • Located in the right atrium
  • Specialized cells that generate the electrical impulse which travels through the heart causing it to beat.
  • The normal rate at which the SA node will fire is between 60 and 100 times per minute.
  • Normal sinus rhythm is between 60 and 100 bpm
• Atrioventricular node
  • AV node
  • Electrically connects the atria with the ventricles.
  • The AV node will fire 40–60 times per minute if not acted upon by an external stimulant.
  • Ventricular rhythm is between 40 and 60 bpm

Arrhythmia

• Abnormal heart rhythm
• Often the result of an abnormal impulse or impulses
• Theses abnormal impulses may be generated anywhere in the heart
• Poor conduction of normal impulses through the heart may also cause an arrhythmia
  • MI is a major cause of arrhythmias. Electricity is conducted through the path of least resistance. If heart tissue is damaged the conductive activity of that tissue changes.

Supraventricular Arrhythmias

• The impulse originates above the AV node.
• The QRS complex will be narrow.

Sinus Bradycardia

• Brady = slow
  • Less than 60 beats per minute
• Normal P waves
• Narrow QRS

Sinus Tachycardia

• Tachy = fast
  • Greater than 100 bpm
• Normal p waves
• Narrow QRS

Paroxysmal supraventricular tachycardia (PSVT)

• Supraventricular
  • Above the ventricles = Narrow QRS
• Tachycardia
  • Above 100 bpm, usually 150–250
• Paroxysmal
  • Like a spams or seizure
  • A spasm of supraventricular tachycardia
  • Quick onset and may stop abruptly on its own.
• Can be a short circuit in the near the AV node that causes the electrical impulse to go through a reentrant loop and propagate itself.

Clinical Presentation

- Palpitations
- Dizzyness
- Chest discomfort

ECG

- Narrow QRS with a rate between 150-250 and the p waves usually get lost in the fast QRS
- P wave may be abnormal but are usually buried in the QRS complex

Treatment

• Vagal nerve stimulation
  • The vagus nerve signals the SA node to slow down
  • The vagus nerve slows conduction through the AV node
  • Carotid massage
    • Patient lying down
    • Right side first
    • Listen for bruits first
    • Gentle pressure of over the carotid artery at the angle of the jaw for 10–15 seconds
  • Valsalva

Study tip:

Getting a job in surgery with no experience.