Electrocardiography

A Brief Overview of ECG Interpretation

Normal to Abnormal

• Only way to understand abnormal is to first look at the “normal”.

• First: looking at cardiac electrical conduction.

Conduction System

Sinoatrial Node

Atrioventricular Node

Bundle of His

Bundle Branches Perkinje Fibres

Conduction System

• Sinoatrial Node (60-80 bpm)

• Atrioventricular Node (40-60 bpm)

• Bundle of His (20-40 bpm)

• Bundle Branches

• Purkinje fibres

• Cardiac Cells

Normal Conduction

• SA node starts action

• Accepted by AV node, starts inferior action

• Passes to bundle of His, down Purkinje fibres

• Action potential restarts

Cardiac CellRegular Muscle cells many moreNuclei per cell, whereas cardiacMuscle cells only have one.

Much more like smooth muscle,Under involuntary control.

Cardiac Cell

Muscle Cell

Conductivity

• Contractile and Conductive cells

• Focused impulse is generated (a pacemaker of any other site) then surrounding tissue will rhythmically contract.

• Bad when not starting at node.

Normal ECG

Normal ECG

Dysrhythmias

• Look at P Wave

• Look at QRS complex

• Look at T Wave

• Look for U Waves

Rhythm Rate

• In order to tell what the rate of the heart is from the ECG:

• Count the # of QRS complexes in a six second strip and multiply by ten.

Dysrhythmias

• Rate

• P Waves (present, inverted, absent, retrograde, ratio)

• PR Interval (5 small squares)

• QRS (3 small squares)

• Rhythm (regular/irregular)

Interpret me!

Now me!

Heart Disease

• #1 killer in Canada

Blocked Coronary Artery

• depending on the amount of damage, conductive system may be impaired.

• electrical impulses do not travel across dead tissue.

Defibrillation

• Reboot the computer

Defibrillation

• Definition - the application of an external electrical shock to the heart muscle which terminates the electrical activity of the heart. This allows the natural pacemakers of the heart to restore normal rhythm.

• Time from collapse to defibrillation is critical factor to survival

Ventricular Tachycardia

Ventricular Fibrillation

Non-Shockable Rhythms

12 Lead

• Normally look at Lead II (over Left shoulder)

• Sometimes need to look at more aspects of heart

• Used to diagnose myocardial infarction, other cardiac dysrhythmias

• Looks at 12 Different aspects of the heart

12 Lead

Questions?