ECG Interpretation Flashcards
What electrical event is associated with:
a. P wave
b. QRS complex
c. Pause btw the P wave and the QRS
d. T wave
a) atrial depolarization (associated with atrial contraction) (remember, atria are thin walled: does not take long for depolarization to spread from the right to the left)
b) Ventricular depolarization, followed closely by ventricular contraction
c) Impulse reaches the AV node (from the SA node), which delays the conduction for a tenth of a second (depolarization is spreading from the atrium to these four structures, to the conducting system for the ventricule)
d) Ventricular repolarization
* ST = initiation of repolarization
What 4 structures make up
the ventricular conduction system?
Bundle of His, left and right bundle branches, and Purkinje fibers
SA node fires, signal sent to AV node.
Depolarization spreads rapidly to both ventricles at the same time so that they contract at the same time (synchronous).
Bundle branches and the to bundle of HIS. You can have a bundle branch block - makes the whole depolarization much slower.
How do we assess the rate (x and y-axis)?
x axis = time, y axis = voltage
Give the primary method.
Primary method: we have to know that sequence of numbers: 300, 150, 100, 75, 60, 50
You want a reproducible part of the ECG waveform, typically the R (QRS) wave, and you want it to land on a heavy line. There’s no point in counting the rate if it isn’t regular. If it’s not regular, then you move on to trying to find the reason as to why it’s not regular
Give the secondary method.
Use a 6 second strip
Multiple the number of QRS complexes in the 6 second period by 10
How do you detect a sinus arrhythmia?
First thing you look for is a p wave (depolarization started at the SA node in the atrium).
If there’s a p wave, the depolarization started in the atrium. If the p waves all look alike, then the depolarization started from the same place.
More or less, the p waves in this graph look alike which means atrial depolarization is happening in the same place. If the p waves look different, then other parts of the atrium are taking control of that.
Sinus arrhythmias - most common in highly trained athletes. The rate is not consistent. The heart rate increases with inspiration. The fact that it says “sinus” means that the SA node is still pacing the heart.
What is this condition?
Sinus arrhythmia
How do you detect a wandering pacemaker?
The p waves don’t all look alike here. We have a p wave in each case but they’re not similar. The depolarization is starting in the atrium, but its not paced from the same place because the p waves look different.
What is this condition?
Wandering pacemaker
What is ectopic foci? What are the three kind of ectopic foci and how do you differentiate them?
Foci – origin of the electrical stimulus
Ectopic – abnormal location
Characteristics
Atrial: 60-80 bpm
A-V junction: 40-60 bpm
Ventricular: 20-40 bpm
When the origin of the electrical stimulus isn’t happening at its normal place (outside the SA node).
“ectopic” - not normal, like an ectopic pregnancy
If the SA node is not pacing the heart, but somewhere else in the atrium is, the HR will drop (between 60 and 80 bpm)
When the origin of the electrical stimulus becomes lower in the heart (as we move towards the ventricle), the HR becomes lower as we go down further and further towards the apex of the heart.
Where’s the pacemaker located in this tracing?
No p wave - means that the pacemaker is not in the atrium.
Tight QRS - means that the depol went through the rapid conducting sys for the ventricle - you’re getting a rapid contraction of the ventricle.
The rate is 60 beats per min
—> JUNCTIONAL RHYTHM
What are Escape and Premature Beats?
Escape
response to a pause in the normal pacing rate
Premature
ectopic focus spontaneously fires Too Early
What is this condition?
Atrial Escape Beat
Not all p waves look alike. There are p waves for each QRS - means depol started in the atrium. But since the last p wave doesn’t look alike, suggests that another part of the atrium jumped in to stimulate the heart.
What is this condition?
Junctional Escape Beat
No p wave - not happening in the atrium.
Is it junctional or ventricular?
It is junctional - if it’s junctional, you have a tight QRS. If it’s from the ventricle, you have a wide looking QRS because the depol didn’t access that rapid conducting system.
What condition is this?
Ventricular Escape Beat
This is a ventricular beat - it is wide and bizarre looking.
Ventricular beats are always easy to identify since they are big and wide.
Ventricular:
Meaning that part of the ventricle took over the role of depolarization and now has to spread in a wave-like manner through both of the ventricles, takes times to do that which is why the wave is wide
What is this condition?
Premature Atrial Contraction (PAC)
this p wave doesn’t look alike and it’s happening too early - premature atrial contraction. Atrial - because you have a p wave present.
What is this condition?
Premature Junctional Contraction
No p wave, early beat, tight QRS because its coming from the junction (so the depol travelled down the bundle of HIS, bundle branches, and got to the pukinje fibers and caused ventricular contraction)
What is this condition?
Premature Ventricular Contraction (PVC)
Very wide, bizarre QRS complex
Associated with hypoxemia Followed by a compensatory pause
> 6 PVCs per minute is Pathological
Big and wide QRS - started in the ventricle. Whenever you see something big and wide like this, there’s no p wave even if it looks like there might be a p wave in front.
Older people tend to have more PVCs. Normally they happen every now and then and it’s not a big deal because the rest of the beats are normal and give an adequate cardiac output. More than 6/min - we start getting concerned.
What condition is this?
Unifocal Premature Ventricular Contraction
2 PVCs look alike - suggest that the depol came from the same spot in the ventricle.
Unifocal - origin of depol is the same, all come from the same spot
What condition is this?
Multifocal Premature Ventricular Contraction
All these PVCs look different - means that diff spots in the ventricle are taking over depolarization.
Multifocal - origin of depol coming from diff areas of ventricle
What condition is this? Describe it.
Paroxysmal atrial/supraventricular tachycardia: Sudden firing from an atrial ectopic focus
What condition is this?
Ventricular (paroxysmal) tachycardia
Identify these four conditions.
Atrial fibrillation
Atrial flutter
Ventricular flutter
Ventricular fibrillation
How do you detect myocardial ischemia?
Look to the ST segment
In order to identify ischemia, we are looking for a change in the ST segment.
ST segment should be at the same level as the PR interval. If ST is depressed - sign of ischemia. If elevated - sign of infarction.
Isoelectric blind - the baseline of the diagram, should be the same throughout
How do you detect myocardial infarction?
ST segment is elevated - this is a sign of infarction and does not normally go away. Depends on how close the electrode is to the primary area of infarction in order for elevation to be picked up. We distinguish ischemia from infarction based on the ST segment.
What is a second characteristic of myocardial infarction that doesn’t go away with time?
This never goes away after the heart attack, and sometimes is present if you’ve had a heart attack and didn’t even know it.
Having a Q wave more than 1mm wide, or 1/3 or more of the whole QRS complex = significant Q wave
What are the differences on ECG between myocardial ischemia, injury and infarction?
Describe the Recovery Stages Post-Infarction.
