4 EKG intro Flashcards
What part of the EKG corresponds to signal in the SA node?
P wave (atrial depolarization/contraction)
What part of the EKG corresponds to signal in the AV node?
PR segment (conduction pause to allow blood passage through AV valves)
What part of the EKG corresponds to signal in the bundle of His?
QRS complex (ventricular depolarization)
What part of the EKG corresponds to ventricular repolzation?
T wave
What part of the EKG corresponds to the plateau phase of the action potential?
ST segment
What part of the EKG corresponds to ventricular contraction?
QT interval (muscle contraction begins at depolarization and continues through repolarization)
Horizontally, how many seconds is one “big box” on an EKG?
0.2 seconds (one small box= 0.04 s)
Vertically, how many mV is one small box on an EKG?
1mm= 0.1 mV
Where are the limb leads placed?
- I= Right arm to left arm
- II= Right arm to left leg
- III= Left arm to left leg
Explain the augmented limb leads
- avR= lead III to right arm
- avL= lead II to left arm
- avF= lead I to left foot
What are the precordial leads?
Placed directly on chest around heart (V1-V6)
What is the normal morphology of the limb leads?
All positive QRS
**Lead II runs parallel to SA -> AV node conduction pathway
What is the normal morphology of the augmented limb leads?
avR= negative QRS
avL and avF= positive QRS
What is the normal morphology of the precordial leads?
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
Define brady and tachycardia
- Brady= <60 bpm
- parasympathetic excess
- young/athletes
- vagal maneuvers
- Tachy= >100 bpm
- sympathetic stimulation of SA node
- exercise/stress
What are the rates of atrial, junctional, and ventricular automaticity?
- 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)
Define sinus rhythm
Coming from the SA node (regular, constant, cycles of equal length)
**best visualized in lead II (running parallel to conduction)
How does respiration affect HR?
- 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)
How do you determine the heart axis?
- Look at leads I and avF
- I +, avF + = Normal
- I -, avF + = RAD
- I -, avF - = Far RAD
- Sometimes need to look at lead II
- I +, avF - … look at II (+ = normal, - = LAD)
What is a normal PR interval?
0.12-0.2 seconds (3-5 little boxes)
What are some reasons for a short or long PR interval?
Short= WPW
Long= 1st degree AV block
What is a normal QRS interval? What are 2 reasons it could be widened?
<0.12 seconds (3 little boxes)
**widened in BBB and V tach
What is a normal QT interval? What is a good rule of thumb and how would you calculate the corrected QT?
<0.44 (M) <0.46 (F)
**T wave should end before halfway between R-R
**correct for heart rate: QTc= QT/√R-R
What is the main risk of long QT?
Prolonged QT can lead to V tach (familial, medication, electrolyte imbalance)
**VT can lead to shock, V fib, and cardiac arrest
Describe a normal ST segment and T wave
**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)
What are the effects of hypo/hyperkalemia?
- 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
