EKG

Question 1

What is an EKG?

Answer 1

Electricity
The EKG is simply a recording of the heart’s electrical activity
A bit about electrophysiology
Cardiac cells, in their resting state, are electrically polarized; that is, their insides are negatively charged compared to their outsides.
Cardiac cells lose their internal negativity in a process called depolarization. Pacemaker cells spontaneously depolarize, producing a wave of depolarization that is transmitted across the entire heart.
All the waves we see on an EKG are from depolarization and repolarization.

Question 2

Cardiac Conduction System

Answer 2

Pacemaker cells are located in the right atrium, called the sinoatrial node (SA node).
Each spontaneous depolarization sends a wave of depolarization that initiates one complete cardiac contraction and relaxation.

Question 3

The Cardiac Cycle

Answer 3

Depolarization of the atrial myocardial cells results in atrial contraction. (P wave)

Electrical conduction is then funneled to the atrioventricular node (AV node) and along the interventricular septum . This slows down the conduction, creating a pause in the EKG. (This lasts a fraction of a second, allowing the atria to finish contracting before the ventricles contract)

The depolarizing wave escapes the AV node and hits the ventricles, causing them to contract. (QRS complex)

The ventricles repolarize resulting in myocardial cells relaxing. (T wave)

Question 4

Cardiac Cycle

Answer 4

To clarify:
P wave= Atria contract
QRS complex= Ventricles contract
T wave= Ventricles relax
But wait…
Where is the wave for the atria relaxing?
Why is the QRS complex so much bigger?

Question 5

Heart Sounds

Answer 5

What part of the ECG is the “lubb” and what is the “dupp”?
Lubb= AV valves close
Beginning of ventricular systole
Dubb= semilunar valves close 
Beginning of ventricular diastole

Question 6

Views of the Heart

Answer 6

Electrodes placed on the surface of the body record the heart’s electrical activity
The heart is a 3-D organ, requiring multiple views which provide unique angles and more information. This is where the 12-lead EKG becomes useful.

Question 7

Reading the rhythm

Answer 7

The EKG gives us information on:
Amplitude of a wave= Force of a contraction (mv)
Duration of waves or lines= Duration (sec)
Rate= Heart Rate (bpm)
Rhythm
Sinus Rhythm (good!) vs. Arrhythmias (bad)

Question 8

Sinus Rhythm

Answer 8

Sinus Bradycardia

100 bpm

Question 9

Atrial Fibrillation

Answer 9

Non-distinguishable P waves

Question 10

Complete Heart Block (aka 3rd degree block)

Answer 10

Atrial contraction is present, but conduction is not passed to the ventricles

Question 11

Ventricular Tachycardia

Answer 11

Ventricles generate rapid and irregular hear rhythm. Cardiac arrest is possible if sustained. Shock this rhythm!

Question 12

Ventricular Fibrillation

Answer 12

Ventricles quiver instead of contract. Most lethal rhythm! Shock!