L10 (+ old physio notes) - EKG basics

Question 1

Very broadly speaking, what is the goal of using an EKG?

Answer 1

Visualize the electrical activity of the heart

Question 2

What does EKG stand for? What is another abbreviation?

Answer 2

Electrocardiogram, K is from Greek word for heart

ECG

Question 3

What does the P wave represent?

Answer 3

Atrial depolarization (contraction)

Question 4

What are the different named waves on an EKC? (Name in order that they appear)

Answer 4

P Waves
QRS Complex
T Waves

Question 5

What does the QRS complex represent?

Answer 5

Ventricular depolarization (contraction) as electrical impulse travels through the purkinje fibers

Question 6

What does the T wave represent?

Answer 6

Ventricular repolarization

Question 7

What wave represents the atrial repolarization?

Answer 7

It doesn’t have it’s own wave. It is hidden in the QRS complex

Question 8

Why is the magnitude (height) of the QRS higher than T or P?

Answer 8

Ventricle has more cells depolarizing than the atria

Ventricular depolarization is more synchronized than ventricular repolarization (Why T is broader wave)

Net Dipole determine by how many cells have a dipole at that instant & how consistently those dipole are oriented (same direction reinforce each other)

Question 9

What is another way of expressing HR?

Answer 9

60 seconds / RR interval

Question 10

What does the P-R interval represent?

Answer 10

Time it takes for impulse to travel through the atria & AV node

Question 11

What does the Q-T interval represent?

Answer 11

Beginning of Q to end of T

Length of ventricular depolarization & repolarization (but contraction is relatively short period that does not change much, so really you are only measuring the repolarization)

Question 12

Why is the space between the S & T flat?

Answer 12

Atria cells have already returned to resting potential & ventricular cells are in their plateau phase

Question 13

Why is the space between the P & Q flat?

Answer 13

Depolarization is only present in the AV node which has so few cells it cannot be detected

Question 14

On a microscopic scale, what is represented by the flat line portions of an EKG?

Answer 14

Resting cell has more K on the inside but relatively high K permeability –> positively charged K flows out of the cells creating a negative charge on the interior of the cells and cell membrane & a positive charge on the outside of the cell

At rest, electrodes of the ECG do not detect any activity because there is no electrical potential difference between adjacent cells. Both are negative on the inside and positive on the outside –> flat line

Question 15

On a microscopic scale, what is represented by a spike on an EKG?

Answer 15

When a cell depolarizes, Na permeability increases allowing positively charged Na to flow into the cell creating a positive charge inside the cell and a negative charge on the outside of the cell

Dipole created at intersection of adjacent cells of opposite charge, because for a split second 1 cell has not yet depolarized

Question 16

What causes upwards spikes on an EKG? Downward?

Answer 16

If the action potential is heading towards the + electrode it creates a positive/upward peak (If the resting cell is closer to the electrode than the depolarizing cell = upward spike)

If action potential is moving away from the electrode it creates a negative/downward peak (If the resting cell is farther away from the electrode –> downward spike)

Question 17

Why is the T wave an upward spike if the “wavefront” is heading in the opposite direction than depolarization?

Answer 17

Repolarization proceeds from the apex backwards towards the atria. The last cells to depolarize are the first cells to repolarize = retraces steps backwards

Looks the same to the electrode because negative cell is still away from the electrode & positive is closer even though it is heading in the opposite direction

Works almost like a double negative as direction is opposite & charge is opposite

Question 18

What are the standard Limb leads and where are they placed?

Answer 18

1 = Negative at right arm, positive at left arm forming a 0 degree axis [Think lead 1 has 1 L in it (R arm, L arm)]

2 = Negative at right arm, positive to left leg forming 60 degree angle [Think lead 2 has 2 L (R arm, L leg)]

3 = Negative at left arm, positive to left leg forming 120 degree angle [Think lead 3 has 3 Ls (L arm, L leg)]

Question 19

What gives the QRS complex its down-up-down shape?

Answer 19

1. Depolarization first occurs from L to R across the interventricual septum –> slight initial downward Q wave
2. Next depolarization travels down the length of the interventricular septum towards the apex –> bulk of peak = R wave
3. End of depolarization phase travels up the sides of the ventricular wall away from the apex –> slight downward peak = S Wave

Question 20

What are the augmented limb leads & where are they placed?

Answer 20

aVR – negative is the middle of heart, positive to right arm forming -150 degrees

aVL – negative is the middle of heart, positive to left arm forming -30 degrees

aVF – negative is the middle of heart, positive is to left leg forming +90 degrees (think F for foot)

Question 21

What planes are the leads in?

Answer 21

Frontal/vertical = standard (1,2,3) & augmented (AVL,AVR & AVF)

Horizontal = Precordial Leads

Question 22

What are the precordial leads & where are they placed?

Answer 22

All 6 placed at level at 4th/5th intercoastal space

V1: fourth intercostal space to the right of the sternum

V2: fourth intercostal space to the left of the sternum

V3 : halfway between V2 and V4

V4: fifth intercostal space at the midclavicular line

V5 : halfway between V4 and V6

V6 : fifth intercostal space at the midaxillary line

Question 23

What leads do you need to look at when analyzing an EKG?

Answer 23

In a standard 12 lead EKG you need to look at all 12

Question 24

How do you determine rate from an EKG?

Answer 24

Count boxes in between R waves

1 big box in between = 300 bpm (5 big boxes per second means 5 beats per second * 60 = 300)

2 = 150 bpm
3 = 100 bpm
4 = 75 bpm
5 = 60 bpm

If in between 2 boxes guesstimate

Question 25

Converting 200 ms to s?

Answer 25

= .2 s

Brian, don’t F this up & lose dumb points for a conversion

Question 26

How many boxes on EKG paper represent 1 s?

Answer 26

5 big boxes

25 small boxes

Question 27

How much time does 1 small box represent on EKG paper? Big box?

Answer 27

.04 s or 40ms (1s/25)

.2s or 200ms (1s/5)

Question 28

When determining rhythm from an EKG, what different options are there? Definitions?

Answer 28

Sinus bradycardia = 100 bpm

Question 29

How is corrected QT interval (cQT) calculated? Why is this necessary?

Answer 29

QT interval in ms or s, divided by square root of RR interval in seconds

Puts QT interval in perspective of HR, because higher HR obviously shortens QT interval

Question 30

If HR is 60 & QT interval is 600 ms, what is the corrected QT interval?

Answer 30

HR of 60 –> RR interval of 1 second

Square root of 1 = 1

cQT = 600ms

Question 31

What do you look at to determine axis? What do the results tell you?

Answer 31

only QRS of 1 & AVF

Both + = nl
1 - & AVF + = Left
1 + & AVF - = Right
Both - = Indeterminate

Question 32

When measuring height of a peak, what length is associated with a small box & big box?

Answer 32

Small = 1 mm

Big = 5 mm

Question 33

How do you diagnose LVH from EKG?

Answer 33

If sum of S in 1 & R in V5 or V6 is > 35mm

If R in AVL > 11 mm