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23 Cards in this Set
- Front
- Back
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What do the various waves of the EKG represent?
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P wave = atrial depolarization
QRS wave = ventricular depolarization T wave = ventricular repolarization |
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How do you measure PR interval? If too long?
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Beginning of P to beginning of QRS
Too long = AV block b/c impulse not traveling fast enough thru AV fibers |
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How do you measure QT interval? Constant or variable? When a problem?
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Beginning of QRS to END of T wave
This is variable Problem if it is long with a fast HR |
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What is:
J point U wave |
J point is end of QRS
U wave is repolarization of prukinje fibers - not always present |
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How is ST segment measured?
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From end of S wave to beginning of T wave
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What does each single box represent? How many boxes = 1 second?
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1 mm
25 boxes = 1 sec |
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How many seconds is each small square? Each large square?
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Small square = .04 sec
Large square = .2 sec |
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Why are electrical events so important?
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They dictate much of what happens mechanically during cardiac cycle:
Pressure Volume Flow Valve opening/closing Heart sounds |
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Definitions:
Chronotropy Inotropy |
Heart rate
Strength of cardiac contraction |
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Definitions:
Dromotropy Lusitropy |
Conduction velocity in heart (ie. AV node has low domotropy)
Lsitropy is rate of relaxation (ie. SNS causes ventricles to relax faster) |
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Why are the Heart's Electrical events so reporducible?
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Automaticity (pacemaker activity)
Conduction system Functional Syncitium (gap junctions) |
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Different pacemaker's rhythms
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SA = 70 bmp w/ vagal tone
AV and BIS = 50-60 Purkingee and ventricular myocardium = 30-40 |
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What does SNS do to chronotropy, inotropy, and dromotropy?
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All increase
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Normal intervals:
PR QRS QT |
.12-.20 (3-5 boxes)
.08-.12 (2-3 boxes) .35 sec (~9 boxes) but varies with HR |
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How much of ventricular filling is passive vs. active
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70-80% is passive
20-30% is active via atrial systole This last 20-30% is very imporatn for Frank Starling |
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Why is coordinated contraction of the ventricular myocardium so important?
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For generating adequate pressure
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Function of gap junctions
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Electrical current is quickly spread through these intercalated disks w/ gap junctions... this allows coordinated contraction and rapid spread of electrical activity
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What is the QRS interval indicative of?
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VEntricle and Vent Cond System function (PVCs, BBB)
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What are the most life threatning arrhythmias?
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Those that cause a drop in CO, and thus arterial pressure
V-fib Sustained V-tach Third degree AV block |
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What is V-tach?
Third degree AV block? |
V-tach is 3 PVCs in a row
Third degree is when there is no association between P and QRS waves |
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What gives an EKG an upward slope?
Isoelectric |
Current flowing from negative to positive
Isoelectric is when flow of depol/repol is directly in between pos and neg |
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Mean electrical axis
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The average direction that the electrical current is flowing
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Why so many leads?
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HR and rhythm can be assesed from pretty much every lead (II, III and AVF are the best)
Certain problems are not always apparent in every lead: ischemia, infarct, signs of hypertrophy |
