Physiologic Basis for ECG Flashcards by Matt Stanton

what does ECG measure?

potential differences between recording electrodes generated by currents from the heart to body surface

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ECG measurement?

SUM of all electrical potentials

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different ECG leads

view electrical vectors of heart from different angles

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what contributes to the rate and rhythm of ECG?

1 - automaticity
2 - conduction system order and timing
3 - functional syncytium

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P wave

atrial depolarization

immediately precedes atrial contraction

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QRS complex

ventricular depolarization
atria repolarizing simultaneously

immediately precedes ventricular contraction

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T wave

ventricular repolarization

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ventricular contraction?

remain until after T wave of repolarization

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what happens during P wave

begins at SA node, spreads toward AV node

right atrium begins to depolarize before left atrium

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what happens during QRS wave?

depolarization at IV septum (Q wave)
AVERAGE current flows from base of heart to apex (R wave)
current reverses flows toward outer wall of ventricles near base (S wave)

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what is the Q wave

interventricular septum depolarization

begins at IV septum and endocardial surfaces

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what is the R wave

current flows from base of heart to apex

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what is the S wave

current reverses, flows toward outer walls of ventricle near the base

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first deflection downward?

Q wave

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first upward deflection?

R wave

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second upward deflection?

R’

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first downward deflection following an upward deflection?

S wave

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if entire configuration consists solely of one downward deflection?

QS wave

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ventricular repolarization?

T wave

begins in last area that was depolarized
travels toward base of heart in opposite direction of depolarization

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P wave

atrial depolarization

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PR interval?

atrial depolarization and AV node delay

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QRS?

ventricular depolarization

and atrial repolarization

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QT interval?

ventricular depolarization/repolarization

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ST segment?

ventricular contraction and ejection

**isoelectric line

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RR interval?

heart rate

TP interval

ventricular relaxation and filling

T wave

ventricular repolarization

Units of ECG?

1 small square = 0.04s (1mm) 1 large square = 0.2s 5 large squares = 1s 2 large squares vertically = 1mV

importance of PR interval?

atrial depolarization to ventricular depolarization -includes delay in conduction that occurs at AV node important for identifying AV blocks: primary, secondary, tertiary

what is the normal PR interval

0.12-0.2 seconds 3-5mm on EKG paper

what pathology can be found on PR interval?

AV blocks: primary secondary (Mobitz I and II) tertiary

importance of ST segment?

time from end of ventricular depolarization to start of ventricular repolarization generally horizontal or gently up-sloping in all leads

deviation from isoelectric line in ST segment?

indicates myocardial ischemia or injury ``` S-T elevation: MI acute pericarditis LVH hyperkalemia ```

importance of QT interval

time from beginning of ventricular depolarization to end of ventricular repolarization all electrical events in the ventricles heart rate dependent more time repolarization phase

long QT syndrome?

congenital: mutant Na+ failure to inactivate K+ defective repolarization acquired: electrolyte imbalance pharmacologic

normal PR interval?

0.12 - 0.2s

normal QT interval?

less than or equal to .44 s

normal QRS?

0.08 - 0.12s

normal P wave?

0.08 - 0.10s

estimation of heart rate based on number of boxes?

``` 1 - 300 2 - 150 3 - 100 4 - 75 5 - 60 6 - 50 7 - 43 8 - 38 9 - 33 10 - 30 ```

estimation of heart rate tip?

divide 300 by number of large boxes ex/ 4 large boxes: 300/4 = 75 bpm

second method for heart rate estimation?

three tick marks = 6 seconds count number of RR intervals per 6 second interval -multiply by 10

wave or depolarization towards positive electrode?

records positive voltage

wave of depolarization away from positive electrode?

negative voltage

wave of repolarization away from positive electrode?

positive voltage

wave or repolarization toward positive electrode?

negative voltage

waves perpendicular to lead axis?

no net voltage | -isoelectric

wave of depolarization perpendicular to positive electrode?

records biphasic wave (no net voltage) positive deflection precedes negative deflection

wave of repolarization perpendicular to positive electrode?

records biphasic wave negative deflection precedes positive deflection

12 leads of EKG?

bipolar standard limb (1+, 1-) leads I, II, III unipolar augmented leads (1+, 2-) leads aVL, aVR, aVF unipolar chest leads V1-V6

set up for 12 lead EKG?

2 arm electrodes and 2 leg electrodes 6 chest electrodes

what do limb leads measure?

record electrical activity moving up/down and left/right in the coronal plane

direction lead goes?

to its positive electrode

lead at 0 degrees?

lead I

lead at -30 degrees?

aVL

lead at 60 degrees?

lead II

lead at 90 degrees?

aVF

lead at 120 degrees?

lead III

lead at -150 degrees?

aVR

what is einthoven's triangle?

RA, LA, LL electrodes sets up the standard limb leads I, II, III

what makes up lead I?

LA + to RA - angle of orientation = 0

what makes up lead II?

LL + to RA - angle of orientation = 60

what makes up lead III?

LL + to LA - angle of orientation 120

set up for augmented leads?

1 positive electrode 2 negative electrodes negative electrodes averaged together to create a composite reference lead

aVL lead setup?

RA,LL - to LA + angle of orientation = -30

aVR lead setup?

LA, LL - to RA + angle of orientation = -150

aVF lead setup?

RA, LA - to LL + angle of orientation = 90

mnemonic for frontal plane leads?

Three Little Ones Ran Too Far

what leads give inferior view of heart?

Lead II Lead III Lead aVF

what gives left lateral view of heart?

Lead I | Lead aVL

what gives right-sided view of heart?

lead aVR

what do precordial leads measure?

electrical activity moving anteriorly/posteriorly in horizontal plane

placement of chest electrodes?

``` V1 - 4th intercostal, right of sternum V2 - 4th intercostal left of sternum V3 - between V2 and V4 V4 - 5th intercostal space midclavicular V5 - between V4 and V6 V6 - 5th intercostal space, midaxillary ```

V1 view of heart?

over right ventricle

V2 and V3 view of heart?

iver interventricular septum

V4 view of heart?

over apex of left ventricle

V5 and V6 view of heart?

over lateral left ventricle

orientation of right and left ventricles?

right - anterior and medial | left - posterior and lateral

anterior view of heart leads?

V2, V3, V4**

left lateral view of heart leads?

I, aVL, V5, V6**

inferior view of heart leads?

II, III, aVF**

right ventricular view of heart leads?

aVR, V1**