ECG interpretation Flashcards
ECG strips are divided into boxes. How many small boxes in a large box
size in mm of the small boxes
25
1mm x 1mm
rate of ECG recording and therefore
how much time does a large box and a small box show
• ECG records ast 25mm/s 5 large squares covered each sec
one large square = 0.2sec; one small square = 0.04sec
t or f
100% of the time the electrical impulse stimulates muscle ontraction
f sometimes there are rare disorders that make this incoordinated
what is the ony time during cardiac cycle that L ventricle is perfused and why does tachycardia affect this
• Left ventricular muscle perfused only during diastole. As such, tachycardia = less perfusion to LV. If demand exceeds supply LV ischemia (+ poss infarc)
what does asystole or isoelectric line indicate
• Isoelectric line: no electrical signal on ECG; indicates asystole (systole absent in pt, has cardiac arrest)
if there is a rise in the line on the ECG (up from the isoelecric line what does this indicate
• Rise in line on ECG: positive deflection – means electrical act is following the same direction of flow as bipolar lead or traveling toward unipolar lead
what is an artefact
what could cause this
artefact (= anything appearing on ECG trace that is not from cardiac origin)
often looks like jagged line
could be from any electrical activity eg shivering
how can you identify artefacts/distinguish them from being cardiac in origiin
• Artefact can usually be ID’d by incongruity w other info (eg: with AFib would see jagged isoelectric line, but the QRS complex would appear normal. With artefact, see jaggedness in QRS as well)
the strenght of the plateau or absolute refractory period in the cardiac cycle is d/t what ion
o Strength of contraction d/t amount of intracellular Ca2+ and so length of plateau influences contractile strength
value of resting voltage in mv
-90mv
where are the electrodes placed for lead II
• Lead II (2) is normally being shown if not specified. Goes from R arm to L foot
how s amplitude meas or shown in the strip
Vertically(AMPLITUDE): each small box is 0.1mV, or 1mm, adding up to 0.5mV or 5mm **this will come in handy later when we discuss MIs
can you note the atria contracting partway through the P wave
no! the ECG only detects electrical activity
what to look at in P wave
in my notes from med surg and elsewhere it says it should be less than 0.11 secs on her slides it says 0.6-0.12
Represents atrial depolarization
When evaluating a P wave, look closely at its characteristics, especially its location, configuration, and deflection
how are dysrhythmias named
o Dysrhtymias are named according to site of origin of impulse and mechanism of formation or conduction involvd eg impulse that originates in SA node and at slow rate is sinus bradycardia
what aspect do you focus on with the PR interval
what does the PR interval reflect
duration
When evaluating a PR interval, look especially at its duration
From the beginning of the P wave to the beginning of the QRS complex.
The PR interval tracks the atrial impulse from the atria through the AV node, bundle of His, and right and left bundle branches. When evaluating a PR interval, look especially at its duration.
Duration: 0.12 to 0.20 second
what do changes in the PR interval reflect
Changes in the PR interval indicate an altered impulse formation or a conduction delay, as seen in AV block.
what char does a normal QRS comple have
how high can it be
what does it come after
how long is it and what can you compare its length to
Follows the PR interval
5 to 30 mm high but differs for each lead used
0.06 to 0.10 second, or half of the PR interval
Duration is measured from the beginning of the Q wave to the end of the S wave (or from the beginning of the R wave if the Q wave is absent)
consists of the Q wave (the first negative deflection after the P wave), the R wave (the first positive deflection after the P wave or the Q wave), and the S wave (the first negative deflection after the R wave
ST segment what to pay extra attn to
what does it look like
what does abn indicate
Pay special attention to the deflection of the ST segment. A normal ST segment has the following characteristics: Extends from the S wave to the beginning of the T wave Usually isoelectric (neither positive or negative
A change in the ST segment may indicate myocardial damage. An ST segment may become either elevated or depressed.
what is the point that marks the end of the QRS complex and start of the ST segment known as
The point that marks the end of the QRS complex and the beginning of the ST segment is known as the J point.
what to evaluate with a t wave
is duration significant
When evaluating a T wave, look at the amplitude, configuration, and deflection.
Duration is not measured
what are normal T wave char
what does it come after
how high is it and what shape
Normal T waves have the following characteristics:
Follows the S wave
0.5 mm in lead II configuration—typically round and smooth
deflection—usually upright in lead II
what does T wave represent
The T wave represents ventricular recovery or repolarization.
what is most imp about QT interval
duration
where does Qt interval start and stop and how long should it be
Location—extends from the beginning of the QRS complex to the end of the T wave
Duration—varies according to age, sex, and heart rate; usually lasts from 0.36 to 0.44 seconds; shouldn’t be greater than half the distance between consecutive R waves when the rhythm is regular.
what normal process will affect QT interval duration
heart rate will shorten it if increasing
what does QT interval meas
The QT interval measures ventricular depolarization and repolarization. The length of the QT interval varies according to heart rate. The faster the heart rate, the shorter the QT interval.
The QT interval shows the time needed for the ventricular depolarization-repolarization cycle.
what would short or long QT interval indicate
An abnormality in duration may indicate myocardial problems. Prolonged QT intervals indicate that the relative refractory period is longer.
Prolonged QT syndrome is a congenital conduction- system defect present in certain families. Prolonged QT intervals indicate that the relative refractory period is longer.
Short QT intervals may result from digoxin toxicity or hypercalcemia.
what is a U wave
are they always there
what is most significant about them
The U wave may not appear on an ECG
Represents the recovery period of the Purkinje or ventricular conduction fibers
The configuration is the most important characteristic of the U wave.
char of U wave
what can cause them
Location—follows the T wave
Typically upright and rounded
A prominent U wave may be due to hypercalcemia, hypokalemia, or digoxin toxicity
what are the 8 steps to ECG interpretation (just the names of the steps
- Determine the rhythm-
- Determine the rate-cant just look at VS monitor. Do p wave and R wave. If the pt has irreg heart rhythm make sure you have 6 second strip.
- Eval the P wave-
- meas PR interval-make sure they are all the same.
- meas QRS
- eval T wave
- QT interval-can be alt by brady or tachy eg from exercise. QT represents the entire ventricle cycle
- Note any abn and conclude your analysis
step 1 of ECG interpretation
how is this done
what tool do you need
1)Determine the atrial and ventricular rhythm:
Measure from P-P and R-R
Are they regular or irregularly spaced?
Using either calipers or the paper method
what is the paper method for determining the rhythm
not as easy as caliper method
take paper and meas R-R and make notes on your paper then move those little noted areas to the next R and compare and so on
then do for P-P
how to determine the rate from an ECG
this is best for regular rhythm
Various methods to determine the rate….
Most accurate is dividing by 1500, this works well for regular rhythms:
Count the small squares between two consecutive P waves and then divide 1,500 by that number to get the atrial rate. To obtain the ventricular rate, use the same method with two consecutive R waves. ie: 1500/20 = 75 BPM
determining rate for irreg rhythm how long of a strip will you need
you need 6 sec strip
det rate of irreg rhythm method
The 10 times method is helpful for irregular rhythms:
Print a 6 second strip (ECG paper is marked at 3 second intervals)
Count the number of P waves and multiply by 10, and repeat for the R waves
how many lg boxes is in between the vertical hash marks (the black lines)
how many seconds is this
15lg boxes
3 seconds
what do you look at when evaluating the P wave
Are there P waves?
How do they look? Normal? Upright? Rounded? Are they all a similar size and shape?
Is there one P wave per QRS complex?
what do you look at when eval the PR interval
how long should it be?
Count the small squares between the P wave and the beginning of the QRS complex, multiply by 0.04
Normal range = 0.12 – 0.20 seconds
Are the PRIs constant?
what do you look at when eval the QRS
what is normal range
Measure from the end of the PR interval to the end of the S wave
Count the number of small squares and multiply by 0.04
Normal range = 0.06 -0.10 seconds
Is each QRS the same? If not, measure and record each one separately
Does each QRS follow a P wave?
do you meas the legnth of T waves
what do we need to look at with them
Are there T waves?
Are they upright in lead II?
Are they all the same shape?
Does each T wave follow a QRS complex?
what kind of relationship does QT interval have with heart rate
inverse relationship
As the heart rate increases, the QT interval decreases;
as the heart rate decreases, the QT interval increases.
what to eval when looking at QT interval
Count the number of small squares between the beginning of the QRS complex and the end of the T wave, where the T wave returns to the baseline and multiply by 0.04
Normal range = 0.36 – 0.44 seconds
what is step 8 of ECG analysis and what do you do
Note any abnormalities and conclude your analysis
Are there any ectopic beats?
Anything else unusual?
Is the ST segment isoelectric? Elevated? Depressed?
Record and document your findings
how to document your analyss
1-The origin of the rate (sinus node, atria, AV node, or ventricles)
2-The rate (bradycardic, tachycardic)
3-Rhythm abnormalities (flutter, fibrillation, heart block, escape rhythm, or other arrhythmias)
