EKG Basics Flashcards
What are the primary segments and intervals of an EKG?
PR interval PR segment ST segment QT interval R-R interval.
What are the basic waveforms of an EKG?
P wave
QRS colmplex
T wave
Sometimes a U wave
What do all of the waves, segments, and intervals represent?
P wave- atrial depolarization, spread of impulse from SA node through the internodal pathways and the interatrial pathway (bachmann’s bundle)
PR interval- the time from onset of atrial depolarization to the onset of ventricular depolarization
PR segment- the short isoelectric line between the end of the p wave and the beginning of the QRS. it’s a baseline for st segment elevation. It is the AV pause before ventricular contraction.
QRS complex- depicts ventricular depolarization, is the spread of the impulse in the His-purkinje system.
ST segment- the end of ventricular depolarization and the beginning of repolarization.
T wave- the latter end of ventricular repolarization.
U wave- not always present. Is thought to represent further repolarization of the ventricles.
QT interval- represents both ventricular depolarization and repolarization.
R-R interval- is the measure of one r wave to the next can be used to assess rhythm and rate.
What is the baseline of the EKG?
The return to the flat isoelectric line between beats when electrical activity is absent.
What are positive, negative and biphasic deflections?
Positive is any EKG deflection above the isoelectric line or baseline.
Negative is any EKG deflection below the isoelectric line or baseline
Biphasic is a EKG deflection having both positive and negative components.
How are these positive, negative, and biphasic deflections created?
One monitor lead on an EKG provides a view of the heart between two poles, a positive and negative pole. An electrical current flowing towards a positive flow will cause a positive deflection on an EKG. A negative will cause a negative deflection. Current flowing away from the poles all together will cause a biphasic deflection. A biphasic deflection can be equally positive and negative, more negative then positive, or more positive then negative depending on the angle the impulse is going.
What do all the squares on EKG paper represent?
when viewing them as horizontal factors they measure time:
The small squares=0.04 seconds
A large square=0.20 seconds
When viewing them in vertical factors they represent space:
One small square= 1mm in height
A large square = 5mm of height.
What does a normal p wave look like and what does a normal P wave indicate?
Small Smooth and rounded.
Positive in lead II.
One P wave for every QRS.
No more then 2.5 mm high and no longer then 0.10 seconds
It indicates that the electrical impulse that is responsible for the P wave came from the SA node and that normal depolarization of the right and left atria has occured.
What is an abnormal P wave caused by?
Either an abnormal sinus P wave or an ectopic P wave.
What does a P wave that is tall and peaked mean?
Abnormal sinus P wave from right atrial enlargement RAE
What does a wide and notched P wave mean?
Abnormal sinus P wave resulting from left atrial enlargement LAE
How do you know you have an ectopic P wave?
Small and pointed, inverted, or absent
What is a normal PRI duration?
0.12-0.20 second
Why would the PRI be too short?
If the electrical impulse is conducted from the atria to the ventricles through an accessory pathway that bypasses the AV node, which gives the heart it’s pause for ventricular filling.
Example WPW
Could also be because the impulse originates in an ectopic site in the AV node.
Why would the PRI be too long?
This would be the case if the impulse is abnormally delayed traveling through the AV node.
Examples: first degree block, hypothyroidism, those taking digitalis, beta blockers, or calcium channel blockers, or in aging populations.
What are the parts of the QRS?
Q-1st negative deflection
R-1st positive deflection
S-a negative waveform that follows the R.
How is a QRS measured and how long should it be?
A QRS is measured from the first deflection off the isoelectric line to the j point which is where the deflection meets the isoelectric line.
It’s duration should be 0.10 seconds or less.
What is too long for a QRS?
0.12 seconds or longer
Is there always a QRS in the QRS complex?
Not always. It will always be CALLED a QRS, but the variations are as follows:
Q and an R no S
R and an S no Q
R no Q or S
If the entire complex is negative it is a QS complex because Rs are always positive.
You can also have more then one R wave the second is R prime written R’, or a second S written S’.
What is a notched wave?
In order to be called a wave the deflection must cross over the isoelectric line. A wave that changes direction and does not cross the isoelectric line is a notch.
How are waves written and why?
The waves smaller then 5mm amplitude are written in lowercase.
An example is if the R is smaller then the S it is written rS.
This so a reader can see the picture of the complex without drawing it.
What are reasons for a wide QRS?
A block in the conduction system, either the right or left bundle branch
An electrical impulse that has arrived early(as with premature beats). Early depolarization
An impulse that has skipped the AV node through an accessory pathway. Also early depolarization.
An impulse from an ectopic site in the ventricles.
What does a normal ST segment look like?
Flat
What is used as a baseline for ST segment elevation or depression?
The PR segment
How do you measure elevation of the ST segment?
Measure at 0.04 seconds past the j point on the ST segment and the PR segment. Anything higher then 1 mm in two contiguous leads is significant.
What does ST segment elevation mean?
Typically AMI, but could be; coronary vasospasm (Prinzmetal ‘s angina), pericarditis, ventricular aneurysm, hyperkalemia, and early repolarization(a normal variant).
What does ST depression mean?
Typically myocardial ischemia, but could be; left and right ventricular hypertrophy, hypokalemia, drug effects(digitalis- which causes a sagging scooped out looking ST).
What is a normal T wave?
Rounded asymmetrical (peak is closer to the end then the beginning.
No taller the 5 mm amplitude.
Positive in lead II
What’s an abnormal T wave look like and what could it mean?
Symmetrical, tall or low, flattened, biphasic, or inverted.
It could mean; MI, myocardial ischemia, pericarditis, hyperkalemia, ventricular enlargement, BBB, subarrachnoid hemorrhage, or certain drugs(quinidine or procainamide).
How do you measure a QT and how do you determine if its normal?
Measure QT from start of QRS to end of T wave
Count the small boxes in the R-R interval then divide by 2
Count the small boxes in the QT Interval
If QT is less then half the R-R then it’s probably normal, if its the same as half it’s borderline and if its longer then half it’s prolonged.
Why is a long QT bad?
It lengthens the relative refractory period allowing more time for an ectopic focus to take control of the heart and causing a life threatening dysrhythmia such as torsades de pointes.
What causes a long QTI?
Electrolyte imbalance (hypokalemia, hypomagnesemia, hypocalcemia), hypothermia, bradydysrythmia, myocardial ischemia, antiarrhythmics, psychotropic agents, hereditary and idiopathic.
What is the U waves importance?
It’s really not important although it should be understood that a very prominent U wave predisposes individuals to torsades de pointes.
What are the two types of monitoring and what is the difference between the two?
Hardwire, connects directly to the monitor
Telemetry, connects to a transmitter.
What are the precordial lead positions?
V1-4thh intercostal, right sternal border
V2-4th intercostal, left sternal border
V3-midway between V2 and V4
V4-5th intercostal, left midclavicular
V5-5th intercostal, left anterior axillary
V6-5th intercostal, left midaxillary
V7- 5th intercostal, left midscapular
V8-5th intercostal, between V7 and spine
V4R- 5th intercostal, right midclavicular
How do you know which limb lead goes where?
White-right arm Green- right leg Black-left arm Red-left leg Brown-chest
How can you look at precordial leads without 12 lead cables?
Put the brown or chest lead on the lead you want to look at in the 12 lead placement scheme.
if you dont have a brown wire you can do modified chest leads with the LL lead(red) and put that on the space of the lead you want to look at. MCL1=V1 MCL2=V2 and so on.
Where are the positive and negative poles in each lead and what do they view?
LIMB LEADS Lead I- +LA, - RA, lateral Lead II- +LL, -RA, Inferior Lead III- +LL, -LA, inferior AUGMENTED LEADS- the negative pole is the center of the chest aVR-+ RA, none aVL-+LA, lateral aVF-+LL, inferior PRECORDIAL Precordial leads- the lead itself is always positive and LA is the negative. So in V1,V1 is positive, in V2, V2 is positive and so on. V1-septum V2-septum V3-anterior V4-anterior V5-lateral V6-lateral
What is the pneumonic for knowing what the leads look at?
I See All Leads-RP INFERIOR- I, III, aVF SEPTAL-V1,V2 ANTERIOR- V3, V4 LATERAL-V5, V6, I, aVL RIGHT VENTRICLE- V4R POSTERIOR-V8, V9
What are the steps to identify the rhythm?
Determine the rate Determine the rhythm Identify and examine the P waves Measure the PRI Measure the QRS Bonus measure the QTI
How does 12 lead analysis fit into all this?
Identifying the rhythm is part of the 12 lead algorithm that will be covered in another stack.
So the rhythm identify algorithm is just an algorithm inside an algorithm.
How do you assess regularity on an EKG?
Place a piece of paper above the strip.
Mark the R waves.
If there is a difference of 0.12 seconds or 3 squares between the longest and the shortest then the rhythm is considered irregular.
How do you calculate the heart rate?
It’s usually the ventricular rate unless the atrial rate differs from the ventricular rate then get both.
If there are premature beats count the rhythm that’s underlying and say with PVCs example normal sinus rhythm of 72 with multiple PVCs.
If there are multiple rhythms count for each rhythm.
Read the monitor.
Or
If its regular:
The lines at the topic the paper mark 3 seconds so count the Rs between two of the sections and multiply by ten.
Or
Count the number of small squares and divide by 1500
If its IRREGULAR
Use the first suggestion that was used for regular- the 6 second strip x 10
How do you identify and examine P waves?
There should be one P for every QRS
Should all be identical in shape size and position.
How do you measure the PRI?
Measure from beginning of P to the beginning of the QRS.
count small squares and multiply by 0.04
How do you measure the QRS?
Measure QRS to j point
Take small squares x 0.04
