Lecture 31: ECG Interpretation

How does an ECG work?

• ion movement in cells create electric currents → movement of these currents through cardiac tissue stimulates muscle contraction → muscle pumps the blood

• ECG = graphical representation of this electrical activity

Describe the physiology of a cardiac action potential.

sodium enters cell causing rapid depolarization → potassium leaks out causing initial repolarization → calcium enters the cell causing a prolonged plateau phase and stimulating muscle contraction → more potassium leaves the cell repolarizing the cell

What is this?

normal sinus rhythm

What is the first important question to ask when reading an ECG?

does this rhythm have a pulse associated with it

What 5 questions should be asked in the same order every time when reading an ECG?

1. Is it FAST or SLOW (Rate)?

2. Is it REGULAR or IRREGULAR (nothing to do with sick/healthy)

3. Are the QRS complexes WIDE or NARROW/NORMAL

4. Is there a P wave for every QRS wave

5. Is there a QRS wave for every P wave

What type of pattern is sinus arrhythmia?

regularly irregular

What type of ECG pattern do atrial fibrilations, VPCs, and AV blocks have?

irregularly irregular (random)

How do you identify waves on an ECG?

• Identify first the QRS complexes (bigger amplitude)

• Identify the T waves after QRS complexes

• Identify P waves by exclusion of other waves

True or false: QRS complexes can have different morphology.

true

What is the most likely origin of normal QRS complexes?

supraventricular

What is the most likely origin of abnormal or wide QRS complexes, such as this one?

ventricular

How do you interpret P wave morphology?

Can you CONSISTENTLY identify P waves?

• Yes = the rhythm starts with the word “Sinus” (tachycardia, rhythm or bradycardia)

• No = then it can be:

  • Supraventricular tachycardia

  • Atrial Fibrillation

  • Junctional Tachycardia

  • Atrial Standstill

  • Ventricular Tachycardia

How do you interpret P waves and QRS complexes together?

• Check if every P wave has a subsequent QRS

• Check if every QRS is preceeded by a P wave