Electrocardiograms

Question 1

Depolarization of the cardiac cell.

Answer 1

Na in and K out.

Ca++ in, which causes an action potential and muscle cell contraction.

Cardiac cells respond to an electrical impulse, causing movement of ions across the cell membrane resulting in contraction.

Shows up as QRS complex on the EKG.

Question 2

Repolarization of the cardiac cell.

Answer 2

The cell changes back to a relaxed state.

Shows up as a T wave on the EKG.

Question 3

Cardiac Pacemaker

Answer 3

Power supply of the heart that initiates and transmits an electrical impulse resulting in mechanical contraction (depolarization).

Question 4

Sinoatrial Node

Answer 4

Normal (dominant) pacemaker of the heart.

Regulated by sympathetic and parasympathetic nervous systems.

Produces sinus rhythms at 60-100 bpm.

Question 5

Atrioventricular Node

Answer 5

Backup pacemaker of the heart

Respons if normal SA node fails

Responsible for rhythms 40-60 bpm.

“Junctional rhythms”

Question 6

Purkinje fibers

Answer 6

Final backup pacemaker of the heart.

Ventricular focus in the purkinje fibers.

Responsible for rhythms 20-40 bpm.

“Idioventricular rhythm”

Question 7

Overdrive Suppression

Answer 7

The pacemaker with the highest rate suppresses all other pacemakers.

Helps heart pump as single unit.

No competition between nodes.

Question 8

Describe the path of an electrical impulse through the heart.

Answer 8

SA node

Internodal pathways

AV node

Bundle of His

Left bundle

Right bundle

Purkinje fibers

Question 9

Why is the P wave comparatively small?

Answer 9

The P wave represents electrical impulses being conducted through the atria in ring-like waves, which shows up as a small and rounded deflection on the EKG.

Question 10

What centers are responsible for rapid ventricular depolarization?

Answer 10

The bundle branches and purkinje fibers carry the electrical impulses that cause the QRS complex.

Question 11

What does the T wave represent?

Answer 11

The T wave shows ventricular relaxation.

Question 12

What does the P wave represent?

Answer 12

Electrical depolarization (contraction) of the atria.

Question 13

What does the QRS complex represent?

Answer 13

The QRS complex shows ventricular depolarization.

Question 14

What is the PR interval?

Answer 14

The PR interval shows the length of time it takes for an electrical impulse to travel from the atria to the ventricles.

Remember, the AV node delays the impulse so that the atria and ventricles don’t all contract at the same time.

Question 15

What is the vertical axis on an EKG a measure of?

Answer 15

An EKG measures voltage vertically in millimeters.

Question 16

What is the horizontal axis on an EKG a measure of?

Answer 16

The EKG measures time horizontally in seconds.

One large square is 0.2 seconds, while each tiny square is 0.04 seconds.

Question 17

What is voltage?

Answer 17

Voltage is the recorded amplitude of the electrical signal generated by the heart.

Question 18

How does deflection work?

Answer 18

As depolarization moves across the myocardium, the electrical impulse is detected by the electrodes on the skin.

Electricity moving away from the electrode is negative deflection, and electricity moving towards the electrode is positive delfection.

Question 19

What is normal paper speed for an EKG?

Answer 19

An EKG runs at 25 mm/second.

Question 20

What is normal height calibration for an EKG?

Answer 20

Standard calibration is 10 mm in height.

Question 21

How many electrodes are there for a 12 lead EKG?

Can you name them?

Answer 21

10 electrodes to produce 12 leads, which are:

Limb leads: Lead I, Lead II, Lead III, aVR, aVL, aVF.

6 chest leads.

Question 23

Biphasic waveform

Answer 23

Electrical activity moves at right angles to an electrode.

Question 24

What is the measurement for a normal P wave?

Answer 24

Does not exceed 2.5 mm in amplitude.

Less than 0.12 seconds long.

Question 25

How long should the QRS be?

Answer 25

The QRS usually measures <0.12 seconds.

Question 26

How long is a normal QT interval?

Answer 26

The QT interval should measure approximately 0.44 seconds.

Question 27

What is the best way to count the heart rate for slower or irregular heart beats?

Answer 27

Count the number of QRS complexes in a six second period and multiply by 10.

Question 28

What is the best way to quickly judge someone’s heart rhythm?

Answer 28

Memorize the following sequence: 300, 150, 100, 75, 60, 50.

Find the peak of an R wave that falls on a large block.

Using the number sequence, count down the blocks until the next R wave appears.

Question 29

What is the best way to count someone’s heart rate if they’re in a rapid rhythm?

Answer 29

Take 1500 and divide it by the number of small boxes between two R waves.

Question 30

What is a 12 lead EKG used for?

Answer 30

Used to evaluate chest pain

Identifies STEMI, cardiomegaly, rate and rhythm abnormalities, conduction issues, insufficien blood flow, and location of coronary artery occlusion.

Question 31

What are the 3 types of diagnostic EKGs? What leads do they have in common?

Answer 31

12, 15, and 18 lead EKGs.

Limb lead electrode placement is the same for all 3.

Question 32

What is the purpose of an 18 lead EKG?

Answer 32

Provides a better view of the right side of the heart.

Use if ST elevation is detected in leads II, III, or aVF.

Identifies right ventricular wall MI.

Question 33

What is the purpose of a 15 lead EKG?

Answer 33

Looks at posterior wall of heart.

Use if you see ST segment depression, upright T waves, and tall, broad R waves in V1-V3.

Question 34

Where does precordial lead placement begin?

Answer 34

At the 4th intercostal space.