4 EKG intro

Question 1

What part of the EKG corresponds to signal in the SA node?

Answer 1

P wave (atrial depolarization/contraction)

Question 2

What part of the EKG corresponds to signal in the AV node?

Answer 2

PR segment (conduction pause to allow blood passage through AV valves)

Question 3

What part of the EKG corresponds to signal in the bundle of His?

Answer 3

QRS complex (ventricular depolarization)

Question 4

What part of the EKG corresponds to ventricular repolzation?

Answer 4

T wave

Question 5

What part of the EKG corresponds to the plateau phase of the action potential?

Answer 5

ST segment

Question 6

What part of the EKG corresponds to ventricular contraction?

Answer 6

QT interval (muscle contraction begins at depolarization and continues through repolarization)

Question 7

Horizontally, how many seconds is one “big box” on an EKG?

Answer 7

0.2 seconds (one small box= 0.04 s)

Question 8

Vertically, how many mV is one small box on an EKG?

Answer 8

1mm= 0.1 mV

Question 9

Where are the limb leads placed?

Answer 9

• I= Right arm to left arm
• II= Right arm to left leg
• III= Left arm to left leg

Question 10

Explain the augmented limb leads

Answer 10

• avR= lead III to right arm
• avL= lead II to left arm
• avF= lead I to left foot

Question 11

What are the precordial leads?

Answer 11

Placed directly on chest around heart (V1-V6)

Question 12

What is the normal morphology of the limb leads?

Answer 12

All positive QRS

**Lead II runs parallel to SA -> AV node conduction pathway

Question 13

What is the normal morphology of the augmented limb leads?

Answer 13

avR= negative QRS

avL and avF= positive QRS

Question 14

What is the normal morphology of the precordial leads?

Answer 14

V4,5,6= very positive QRS

V3= mostly positive QRS

V1,2= mostly negative QRS

**very downward in V1 progressing to very upward in V6

Question 15

Define brady and tachycardia

Answer 15

• Brady= <60 bpm
  
  • parasympathetic excess
  • young/athletes
  • vagal maneuvers
• Tachy= >100 bpm
  
  • sympathetic stimulation of SA node
  • exercise/stress

Question 16

What are the rates of atrial, junctional, and ventricular automaticity?

Answer 16

• atrial= 60-80 bpm
• junctional (middle/distal regions of AV node)= 40-60 bpm
• ventricular (purkinje fibers)= 20-40 bpm

**overdrive suppression (fastest signal wins, SA>>Atrial>junctional>ventricular)

Question 17

Define sinus rhythm

Answer 17

Coming from the SA node (regular, constant, cycles of equal length)

**best visualized in lead II (running parallel to conduction)

Question 18

How does respiration affect HR?

Answer 18

• There’s normal variation in HR with respiration;
• inspiration= increased HR (decreased vagal tone -> sympathetic stimulation of SA node)
• expiration= decreased HR (increased vagal tone -> parasympathetic inhibition of SA node)

Question 19

How do you determine the heart axis?

Answer 19

1. Look at leads I and avF
   
   1. I +, avF + = Normal
   2. I -, avF + = RAD
   3. I -, avF - = Far RAD
2. Sometimes need to look at lead II
   
   1. I +, avF - … look at II (+ = normal, - = LAD)

Question 20

What is a normal PR interval?

Answer 20

0.12-0.2 seconds (3-5 little boxes)

Question 21

What are some reasons for a short or long PR interval?

Answer 21

Short= WPW

Long= 1st degree AV block

Question 22

What is a normal QRS interval? What are 2 reasons it could be widened?

Answer 22

<0.12 seconds (3 little boxes)

**widened in BBB and V tach

Question 23

What is a normal QT interval? What is a good rule of thumb and how would you calculate the corrected QT?

Answer 23

<0.44 (M) <0.46 (F)

**T wave should end before halfway between R-R

**correct for heart rate: QTc= QT/√R-R

Question 24

What is the main risk of long QT?

Answer 24

Prolonged QT can lead to V tach (familial, medication, electrolyte imbalance)

**VT can lead to shock, V fib, and cardiac arrest

Question 25

Describe a normal ST segment and T wave

Answer 25

**ST segment should be at the baseline with the PR interval (not elevated or depressed)

**T waves are typically upright (repolarization traveling away from electrode)

Question 26

What are the effects of hypo/hyperkalemia?

Answer 26

• Hypokalemia
  
  • increases myocardial excitability
  • risk for ventricular tachyarrhythmias
• Hyperkalemia
  
  • reduces myocardial excitability
  • risk for bradycardia, conduction blocks, and cardiac arrest

**Both lead to changes in the EKG