EKG lecture 2 part 2

Question 1

What part of the electrical system is included in the QRS complex?

Answer 1

Bundle of His, right and left bundle branches

Question 2

Septal Q waves
1) What is the first part of the Q wave to depolarize?
2) What direction does it depolarize in?
3) Is it always visible on an EKG? Explain
4) How large are normal septal Q waves?

Answer 2

1) IV septum; septal fascicle of the LBB
2) Left to right
3) Not always visible on EKG but may cause a small negative deflection in one or several of the lateral leads (1, aVL, V5-6)
4) Have amplitude of not greater than 0.1 mV (1 small box)

Question 3

1) What part of the heart dominates the QRS complex?
2) What direction is the average vector?
3) What occurs at the frontal plane?

Answer 3

1) Left ventricle
2) Toward LEFT, between 0 to +90 degrees
3) Large R wave in lateral and inferior leads, lead aVR will have deep S wave

Question 4

How long is a normal QRS interval?

Answer 4

0.06 – 0.12 seconds (1.5-2.5 small boxes) (narrow)

Question 5

Describe V1-8 during ventricular depolarization

Answer 5

V1 overlies RV: deep S
V5-6 overlies LV: tall R
V3-4 transition: biphasic; predominantly negative to positive
R wave progression

Question 6

1) What does the ST segment show up as in all leads?
2) What does it represent?

Answer 6

1) Flat or gently upsloping in all leads
2) End of ventricular depol to start of ventricular repol

Question 7

Describe the T wave

Answer 7

Represents ventricular repolarization
Requires expenditure of cellular energy to run the ion pumps to return to “resting” state, therefore susceptible to cardiac and non-cardiac influences and thus variable appearance
Generally, begins in last area of heart to depol and travels backwards

Question 8

Describe the positivity or negativity of the T wave

Answer 8

Remember: repol vectors have opposite affect on + electrodes
Toward = negative deflection
Away = positive deflection
Leads that record + deflection during depol will record + deflection during repol
Typical to find positive T waves in same leads as tall R waves
Amplitude of normal T wave is 1/3 to 2/3 of the corresponding R wave

Question 9

QT interval
1) What does the QT interval represent?
2) Is it narrower or wider than QRS?
3) What is duration dependent on? Explain.
4) QT interval constitutes ~___% of the normal cardiac cycle as measured from one R wave to the next R wave

Answer 9

1) Beginning of ventricular depol thru ventricular repol = all the electrical events that occur in the ventricle
2) T wave wider than QRS
3) Heart rate; Faster rate = faster repol, shorter QT interval
4) ~40%