L10 (+ old physio notes) - EKG basics Flashcards
Very broadly speaking, what is the goal of using an EKG?
Visualize the electrical activity of the heart
What does EKG stand for? What is another abbreviation?
Electrocardiogram, K is from Greek word for heart
ECG
What does the P wave represent?
Atrial depolarization (contraction)
What are the different named waves on an EKC? (Name in order that they appear)
P Waves
QRS Complex
T Waves
What does the QRS complex represent?
Ventricular depolarization (contraction) as electrical impulse travels through the purkinje fibers
What does the T wave represent?
Ventricular repolarization
What wave represents the atrial repolarization?
It doesn’t have it’s own wave. It is hidden in the QRS complex
Why is the magnitude (height) of the QRS higher than T or P?
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)
What is another way of expressing HR?
60 seconds / RR interval
What does the P-R interval represent?
Time it takes for impulse to travel through the atria & AV node
What does the Q-T interval represent?
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)
Why is the space between the S & T flat?
Atria cells have already returned to resting potential & ventricular cells are in their plateau phase
Why is the space between the P & Q flat?
Depolarization is only present in the AV node which has so few cells it cannot be detected
On a microscopic scale, what is represented by the flat line portions of an EKG?
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
On a microscopic scale, what is represented by a spike on an EKG?
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
What causes upwards spikes on an EKG? Downward?
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)
Why is the T wave an upward spike if the “wavefront” is heading in the opposite direction than depolarization?
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
What are the standard Limb leads and where are they placed?
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)]
What gives the QRS complex its down-up-down shape?
- Depolarization first occurs from L to R across the interventricual septum –> slight initial downward Q wave
- Next depolarization travels down the length of the interventricular septum towards the apex –> bulk of peak = R wave
- End of depolarization phase travels up the sides of the ventricular wall away from the apex –> slight downward peak = S Wave
What are the augmented limb leads & where are they placed?
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)
What planes are the leads in?
Frontal/vertical = standard (1,2,3) & augmented (AVL,AVR & AVF)
Horizontal = Precordial Leads
What are the precordial leads & where are they placed?
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
What leads do you need to look at when analyzing an EKG?
In a standard 12 lead EKG you need to look at all 12
How do you determine rate from an EKG?
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
Converting 200 ms to s?
= .2 s
Brian, don’t F this up & lose dumb points for a conversion
How many boxes on EKG paper represent 1 s?
5 big boxes
25 small boxes
How much time does 1 small box represent on EKG paper? Big box?
.04 s or 40ms (1s/25)
.2s or 200ms (1s/5)
When determining rhythm from an EKG, what different options are there? Definitions?
Sinus bradycardia = 100 bpm
How is corrected QT interval (cQT) calculated? Why is this necessary?
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
If HR is 60 & QT interval is 600 ms, what is the corrected QT interval?
HR of 60 –> RR interval of 1 second
Square root of 1 = 1
cQT = 600ms
What do you look at to determine axis? What do the results tell you?
only QRS of 1 & AVF
Both + = nl
1 - & AVF + = Left
1 + & AVF - = Right
Both - = Indeterminate
When measuring height of a peak, what length is associated with a small box & big box?
Small = 1 mm
Big = 5 mm
How do you diagnose LVH from EKG?
If sum of S in 1 & R in V5 or V6 is > 35mm
If R in AVL > 11 mm
