ECG Flashcards
P-R Interval
The time from the beginning of atrial activation to the beginning of ventricular activation
Measured from the point where the P wave leaves the baseline to the beginning of the QRS complex.
P Wave
Atrial depolarization and the spread of electrical impulses throughout the L and R atria
This precedes each QRS complex
P wave
Why is a waveform representing atrial repolatization not seen on the ECG
It is buried in the QRS complex
QRS Complex
Spread of the electrical impulse through the ventricles= ventricular depolarization, triggering contraction of the ventricles
Why is the QRS complex bigger then the P wave?
QRS is significantly larger than the P wave b/c depolarization of the vents involves a considerably greater muscle mass
T wave
Ventricular Repolarization, the absolute refractory period is still present during the beginning of the T wave, the normal T wave is slightly asymmetric, return of K inward and Na outward (change in polarization of the cell)
What is an interval
It includes the waveform and the segment
Time in between small squares (1mm) on the ECG paper
.04 sec
Time in between each large square (5mm) on the ECG paper
.2 sec
15 boxes = how many seconds
3 seconds
Normal time and box count for PR interval
.12-.2 seconds or 3-5 little boxes
Normal time and box count for QRS Complex
.06-.10 seconds or 1.5-2.5 little boxes
ST segment
Slight pause after QRS complex, between QRS and T wave, normally flat segment of isoelectic line
What is abnormal deviation of the ST segment
.5mm from baseline
QT interval
Measure from the begining of the Q wave to the end of the T wave
Normally about .32-.40 seconds or 8-10 little boxes
Longer the QT interval the increased risk for what?
arrhythmia
What is the one abnormal factor about sinus bradycardia?
HR is less than 60 beats/min
Pain, fear, exercise, artificial stimulants (caffeine, nicotine, amphetamines), CHF, infection, anemia, hemorrhage, MI and hyperthyroidism are all causes for what?
Sinus Tachycardia
What is the difference between sinus arrhythmia and sinus block/pause?
- Sinus arrhythmia has a HR of 40-100, there is an irregular rhythm due to the R-R interval varying throughout
- Sinus pause/block has a HR 60-100 but the R-R is regular except for occasional pauses (usually see 1 pause in a 6 second segment)
Delay or interruption in impulse conduction occurs within the AV node, bundle of His or Purkinje system the resulting dysrhythmia is called…
AV block
PR interval reflects what?
depolarization of the R and L atria (p wave) and the spread of the impulse through the AV node, bundle of his, R and L bundle branches and the Prukinje fibers
What is key when determining the type of AV block?
PR interval
Impulses from the SA node to the ventricle are delayed (not blocked), usually occurs at the AV node…what degree of block is this?
First Degree
PR Interval > .20 seconds (>3-5 little boxes)
The site of block in 2nd degree AV block type 1 is typically where?
At the AV node (above the bundle of his)
The site of block in the 2nd degree AV type 2 is typically where?
The bundle of His or the bundle branches (below the AV node)
3rd degree block there is what type of block?
Complete block in conduction of impulses between the atria and ventricles. The site may be at the AV node, but more commonly at the bundle of His or bundle branches
All components of the ECG tracing are usually w/in normal limits with the exception of the PR interval..what degree block is this?
1st Degree AV Block, because all electrical impulses travel normally from the SA node though the atria but there is a delay in impulse conduction, usually at the level of the AV node
What should you do if a 1st degree block is found?
Usually nothing, more than likely the block is asymptomatic. However, if sx can lead to higher degrees of AV block.
When some but not all atrial impulses are blocked from reaching the ventricles because the SA node is generating impulses in a normal manner each P wave will occur at a regular interval across the strip but not every P wave will be followed by QRS–atria a depol normally but not every impulse is conducted to vents
Second Degree AC Block
What blocks are the RR interval irregular
Second Degree AV block type 1 and 2
In what block do the PR interval get longer and longer until you see a P wave with lack of a QRS complex?
Second Degree AV block Type 2 (Wenckebach)
In this AV block the QRS complexes are wider then normal, not every P wave is followed by a QRS complex (see multiple P waves w/o QRS) and PR interval is usually within normal limits. May also see ST segment elevation.
2nd degree Type 2 (Mobitz II)
*Remember, in Type 1 the QRS complexes are more narrow than usual b/c block is occurs at the level of the AV node and the PR intervals increase in length
Second degree blocks are types of incomplete blocks because the AV junction conducts at least some impulses to the ventricles. In third degree AV blocks what happens to the impulses?
Impulses generated by the SA node are blocked before reaching the ventricles so no P waves are conducted. The atria and ventricles beat independently of each other. This is a COMPLETE block. A secondary pacemaker (either junction or ventricular) stimulates the ventricles; therefore, the QRS may be narrow or wide, depending on location of the escape pacemaker and the condition of the intraventriular conduction system.
Where can a complete block occur? (3rd degree)
AV node, bundle of His, bundle branches
What is the heart’s least efficient pacemaker?
Ventricles–if they function as the heart’s pacemaker the rate is usually 20-40 beats/min. This happens if SA node fails to discharge, SA node impulses are blocked, rate of discharge from SA is slower then vents, irritable site in either vent produces an early beat or rapid rhythm
If an area of either ventricle becomes ischemic or injured, it can become irritable. This affects the manner in which impulses are conducted. When an ectopic site within vent assumes responsibility for pacing the heart, electrical impulse bypasses the normal intraventricualr conduction pathway. This results in stimulation of the ventricles at slightly different times. As a result, ventricular beats and rhythms usually have QRS complexes that are abnormally shaped and longer than normal.
Sorry….just a note.
On a strip you see wide QRS w/o P wave, and T wave in the opposite direction of the QRS complex. What is this?
Premature Ventricular Complexes
What do you call a PVC every other beat?
Bigeminy
What do you call a PVC every third beat?
Trigeminy
What do you call PVCs that are all identical?
Unifocal
What if no two PVC appear similar in configuration?
Multifocal
3 PVC’s is what?
Ventricular Tachycardia
*When 3 PVC’s occur in a row at a rate greater than 100 beats/min (No P waves, QRS is wide and bizarre)
When you have a strip where the QRS complex varies in shape/amplitude beat to beat, looks as if the QRS is twisting around the isoelectric line
Tordade De Pointes
