There are 5 heavy lines between 2 different QRS's. What is the heart rate?
For heavy lines the equation is 300/# of heavy lines
There are 20 thin lines on an ECG between 2 QRS waves. What is the heart rate?
The heart rate is 1500/20=75.
For the thin lines, the equation is 1500/thin lines.
T or F?
A repolarization moving toward a positive electrode produces a positive deflection
a DEPOLARIZATION moving toward a positive electrode produces a positive deflection
In which direction does a depolarization travel in relation to the heart?
It moves from right to left in a downwards motion toward the apex of the heart.
I have a lead placed at the base of the heart. In which direction will the QRS wave deflect on this lead?
negative (downward). The QRS travels in the direction of base to apex of the heart, so it would be moving away from the lead, thus resulting in a negative deflection.
How many total limb leads are there? How are they distinguished?
There are 6 total limb leads.
3 of them are bipolar leads (I,II,III) which are the standard leads.
3 of them are unipolar leads (aVR, aVL, aVF), and these are augmented limb leads.
T or F
There are 6 bipolar precordial leads
There are 6 unipolar precordial leads (V1-V6)
So there are 6 total limb leads (3 bipolar, 3 unipolar) and 6 total precordial leads (all unipolar)
Which forces are readily detected by the bipolar limb leads?
Downward forces because both of the leads are positive down there. They would be good at detecting a change in the inferior wall of the heart (See image)
What's a good conceptual way to remember where AVR, AVL, and AVF are located?
AVR=right arm (R for right)
AVL=left arm (L for left)
AVF=left foot (F for foot)
Which leads are considered inferior?
Which leads are considered lateral?
Inferior=AVF, II, III
Which precordial leads are considered right sided leads?
What about left sided?
Right sided=V1 and V2 (these can also detect septal infarcts)
Left sided=V5 and V6
What would you expect to see on an ECG in left ventricular hypertrophy compared to normal? Why?
You should see a larger R wave on the left sided leads (AVL, I, V5, V6).
This is because with more muscle there is greater voltage, resulting in increased amplitude.
A patient comes in with right ventricular hypertrophy. What would you expect to see on the ECG?
You should see a larger R wave on the right sided leads V1 and V2 (which is normally hard to see).
What are the 3 conditions in relation to the coronary artery that can be picked up by ECG?
Ischemia, Injury, and Infarct.
What are the 2 forms of ischemia and what effect do they have on the ECG?
1) Ischemia due to sudden high oxygen demand (ie exercise) with fixed coronary obstruction. Causes a depression of the ST segment (which is normally isoelectric).
2) Ischemia due to acute coronary obstruction during low oxygen demand. Causes a T wave inversion (T wave opposite direction of QRS wave)
You look at an ECG and suspect someone to have some sort of myocardial injury. What ECG finding would make you expect this?
T or F?
Both Ischemia due to exercise and Injury will show ST elevation as a sign on ECG.
Ischemia will have ST depression, injury will show ST elevation.
T or F?
A transmural infarct produces Q waves.
What's the difference between elevated ST waves and a present Q wave in regards to transmural infarct?
ST wave may be reversible.
Q wave isn't reversible, it represents necrosis.
List the 3 criteria for establishing a Q wave as significant
1) the wave is at least 1/4 the amplitude of the R wave
2) the wave is at least .04 seconds wide (at least one little box on the ECG)
3) At least 2 leads detect the same Q wave in the same area of the left ventricle (Most important!)
What is the most common type of infarct and what does that mean?
This means that the entire portion of the ventricle is blocked (all the way through the wall, from the ventricle out to the outside of the heart in that portion of the heart)
How do the findings of a transmural and a subendocardial infarct differ on ECG findings?
Transmural: Elevated ST, significant Q wave.
Subendocardial: ST depression, no Q wave. (this one looks just like an exercise ischemia)
Name which area of the heart each group of leads looks at:
I,AVL=High lateral wall
Generally, which is larger and more serious, an anterior or inferior infarct?
Anterior infarcts are generally larger and more serious.
If the QT interval is more than half of the R-R interval, what does that mean?
It means you have a prolonged QT interval.
This is a major risk factor for arrythmias.
Causes: electrolyte imbalances, anti-arrhythmatic drugs, Hypothermia, Congenital