C7: ECGs and Arrythmias Flashcards
whats a 12 lead ECG?
a measurement of the electricity produced from the heart that is sensed by 10 different electrodes on the body
what is the function of using leads?
the electricity is organized into leads which can tell the reader what area of the heart the signal is coming from
what are the 2 planes that ECGs use?
frontal: the limb leads and augmented vector leads
horizontal: the V leads (across the chest)
where are leads 1, 2 and 3 represent in the frontal plane?
What is the triangle it creates called?
lead 1: RA - , LA +
lead 2: RA - , LF +
lead 3: LA - , LF +
Einthoven’s triangle
(picture the triangle diagram on page 9 of notes)
describe what the P wave represents and where is electrical stimulation traveling at this time?
how long should it last?
represents atrial depolarization… the SA node passes the signal through the inter-nodal tracts to the LA and RA muscles
should last less then 200ms
whats the PR interval and when does it occur?
occurs from beginning of P wave to end or PR segment or begining of QRS complex.
includes atrial depolarization and contraction
whats the PR segment? What is happening electrically and mechanically at this time?
the contraction of the atria while the signal is sitting at the AV node and bundle of His
when does atrial contraction start?
@ P wave
when does ventricular contraction start?
@ QRS complex
where is electrical stimulation traveling during the QRS complex and what does the QRS complex represent?
represents ventricular depolarization
conduction through the bundle branches purkinjie fibres and ventricle muscle occur here
does each segment of the QRS complex represent a different segment of conduction?
yes
how many fascicles does the LBB and RBB have?
which is + and which is -
LBB: 2 (anterior and posterior)
- (spike will go below baseline)
RBB: 1
+
how long should the QRS complex last?
less than 100ms…. >120ms is abnormal
how does the RBB lead V1 appear?
bunny ears
what influences the hight of the QRS complex?
muscle thickness: more muscle means more QRS complex
body habits: obese- small amplitude
thin- larger amplitude
pericardium: excess pericardial fluid or thickened pericardium may lower the QRS complex
what does the ST segment represent and when does it occur?
represents gap between vetric. depolarization and repol.
the ST segment is isoelectric so should be at the same level as which other segment?
PR… we always compare these segments
what does a depression in the ST segment indicate?
myocardial ischemia
what does an elevation in the ST segment indicate?
MI
when does ventricle contraction occur?
during ST segment and T wave…. but starts in QRS complex
What does the T wave represent electrically?
Elec: ventricular repolarization
May the T wave be merged with the ST segment?
Yes
Can the T wave have + or - polarity?
Yes
What are the possible causes of a negative T wave?
Ischemia, digoxin, electrolyte imbalance
Is it normal to have a + or - T wave?
+
What does normal sinus rhythm mean and what is the NSR rate?
That the impulse travels through the normal conduction pathway of the heart
60-90 bpm
What is considered a borderline HR?
50-60 and 90-100 bpm
What are the 5 methods for diagnosing heart rhythms and what are we looking for in each?
- Heart rate
- Rhythm (reg/irregular)
- P waves (are they identical)
- PR interval (long/short)
- QRS complex (wide/normal)
When looking at HR what is normal/abnormal and what are we looking for in the waveform?
60-90 is normal
50-60 and 90-100 is borderline
Every narrrow QRS complex should have a P wave after it
What consists of bradycardia and tachycardia?
Brady: <50-60 bpm
Tacky: >90-100
What’s the avg stroke volume and bpm?
Stoke volume: 70 ml
BPM: 72
What is the R-R interval? How should they appear?
The time from one R wave to another
They should be equal distance/time apart
How should normal P waves appear?
On P wave for every QRS complex
What is a normal PR interval length?
170m/s
What can cause a long PR interval?
When the AV node holds the impulse for too long
How will a left bundle branch block look on an ECG?
The peak ill be below the baseline and will be longer than normal
If there’s a P wave before each QRS complex but the PR interval is >200 ms, what does this indicate?
First degree AV block
If you have irregular R-R intervals, no detectable P waves and the ventricles just contract when they can, what does this indicate?
Atrial fibrillation
Explain what happens when you have a
PAC?
The atrial muscle tissue produces its own impulse leading to atrial contraction and then ventricular contraction.
A benign arrhythmia that results from too much catecholamines (stress hormones, caffeine)
What is a compensatory pause with PAC?
A pause the resets the timing of the heart with the SA node taking over the rhythm again
When the HB returns to normal after a PAC, will you feel this HB more strongly?
Yes because there’s more blood volume to pump out
What causes PVC?
Catecholamines and stress or caused by a partially blocked artery which causes a zone on ischemia
Describe how a zone of ischemia can cause PVCs
The zone has altered ions within it that change the impulse formation and propagating properties which lead to a PVC.
Do PVCs have a compensatory pause?
Yes
How does the waveform for a PVC appear?
It will have no P wave, a higher voltage, an abnormal T wave and a compensatory pause
Describe atrial flutter, why does it occur?
An electrical re-entry loop through the atrial tissue that allow it to depolarize repeatedly…
Caused by an ectopic electrical focus in the atria that is competing to pace the heart.
The atrial contraction is semi organized so P waves look similar to normal P waves
How does atrial flutter effect ventricular response to atrial contraction? Give a ratio
2:1, 3:1, 4:1 (atria to ventricle)…. that means 2, 3, 4 P waves for every QRS complex
Normal ratio is 1:1
What’s the atrial heart rate with atrial flutter?
250-300 bpm
How does the waveform appear in atrial flutter?
A saw-tooth apperance
When do the ventricles contract during atrial flutter?
Whenever the bundle of His lets through the impulse…. atria and ventricles don’t communicate very well
What conditions are associated with a fib?
Congestive heart failure and atrial enlargement (almost always)
Which part of the waveform is constantly changing with a fib? And what does this effect?
R-R interval
This effects LV outflow which also constantly changes (as preload changes)
Does a fib effect early or late filling more? What valve does this commonly effect and how?
Late filling, its completely lost
The movement on the MV
Do patients lose their atrial kick with a fib?
Yes
How will the MV appear on US in PLAX with a fib?
It will bounce many times before the LV contracts
How many degrees of AV block are there?
3
First degree
Second degree
Third degree
Describe the electrical waveforms of all 3 AV block types
First degree: prolonged PR interval >200ms
Second degree: gradually lengthening PR intervals until there’s a dropped QRS complex
Third degree: no association between P waves and QRS complexes
What’s another term for 2nd degree AV block?
Wenkebach
What’s another term for 3rd degree AV block? Which lead is best for seeing this type of block?
AV dissociation
Lead II
Can you have multiple consecutive PVCs?
Yes.
How many PVCs in a row is considered ventricular tachycardia?
4-5
What are multifocal PVCs?
PVCs that occur when the impulse originates from more than 1 focus in the ventricles
What is ventricular tachycardia?
An electrical re-entry loop through the ventricles only…. causes very rapid ventricular contractions
How does the waveform of ventricular fibrillation appear?
How many bpm for VF?
no P wave and no PR interval with a fibrillatory baseline
300-600
How long should the QT interval last?
440ms
Is the waveform of ventricular tachycardia somewhat organized?
Yes
Is ventricular tachycardia or ventricular fibrillation more severe?
Ventricular fib
with a bundle branch block, is the impulse being slowed as it travels through the ventricles or as it travels from the atrial to the ventricles?
through the ventricles
How can you tell multifocal PVCs from unifocal PVCs
Unifocal PVC will appear identical, each QRS looks similar
Multifocal PVC the QRS will all appear different shapes
