Intro to EKGs

Question 1

electrical conduction pathway through the heart

Answer 1

SA (sinus) node → atria → AV node → bundle of His → right and left bundle branches → Purkinje fibers → ventricles

note - left bundle branch divides into left anterior fascicle and left posterior fascicle

Question 2

SA node (sinus node) - general

Answer 2

*located in upper part of crista terminalis near SVC opening
*“pacemaker” inherent dominance with slow phase of upstroke
*has the fastest automaticity of all the electrically active regions of the heart

Question 3

AV node - general

Answer 3

*located in interatrial septum near coronary sinus opening
*blood supply usually from the RCA
*100msec delay allows time for ventricular filling
*has slower automaticity compared to the sinus node

Question 4

pacemaker rates in the heart (general)

Answer 4

SA > AV > bundle of His/Purkinje/ventricles

Question 5

speed of conduction in the heart (general)

Answer 5

bundle of His/Purkinje > atria > ventricles > AV node

Question 6

P wave

Answer 6

atrial depolarization

Question 7

PR interval

Answer 7

*time from start of atrial depolarization to start of ventricular depolarization
*normal: 120-200 msec

Question 8

PR segment

Answer 8

*isoelectric
*time from END of atrial depolarization, BEFORE start of ventricular depolarization
*represents the signal as it travels through the AV node

Question 9

QRS complex

Answer 9

*ventricular depolarization
*normal: ~ 100 msec

Question 10

QT interval

Answer 10

*time from the beginning of the QRS (ventricular depolarization) to the end of the T wave (end of ventricular repolarization)
*ventricular depolarization, mechanical contraction of the ventricles, and ventricular repolarization

Question 11

T wave

Answer 11

*ventricular repolarization

note - T-wave inversion may indicate ischemia or recent MI

Question 12

J point

Answer 12

*junction between end of QRS complex and start of ST segment

Question 13

ST segment

Answer 13

*isoelectric
*measured from the end of the QRS complex to the beginning of the T wave
*represents the period between ventricular depolarization and repolarization

Question 14

appearance of the QRS complex

Answer 14

*even though it is always labeled as the “QRS”, not every QRS has to have a q wave, r wave, or s wave
*R wave is ALWAYS A POSITIVE DEFLECTION (UP)
*Q wave is a negative deflection in front of the R wave
*S wave is a negative deflection after an R wave

Question 15

standard EKG speed is

Answer 15

25 mm/sec

Question 16

standard EKG records how long?

Answer 16

10 seconds

Question 17

vertical axis of EKG readout

Answer 17

*vertical axis: voltage (measured in mV)
*1 big box (composed of 5 small boxes) = 0.5 mV
*2 big boxes = 1 mV

Question 18

horizontal axis of EKG readout

Answer 18

*horizontal axis: time (measured in msec or sec)
*1 big box = 200 ms (0.2 seconds)
*5 big boxes = 1 SECOND (1000 msec)

Question 19

EKG electrodes & leads

Answer 19

*electrodes (stickers) detect electrical activity
*an ECG “lead” connects the electrodes to the ECG machine
*leads are specific to location; electrodes are not
*by placing them at specific, fixed locations, they enable us to understand how electricity flows through the heart
*integrating the information obtained from different leads can help up to piece together a diagnosis

Question 20

direction of EKG deflections, based on direction of electrical signal (relative to the leads)

Answer 20

*if electrical signal is coming TOWARDS the electrode/lead, it will cause an upward or “positive” deflection
*if electrical signal is going AWAY FROM the electrode/lead, it will cause an downward or “negative” deflection
*if electrical signal is parallel (not coming toward or going away from) the lead, it will cause positive and negative deflections to be equal, or it may even be flat; this is termed “isoelectric”

Question 21

mnemonics for placement of ECG leads

Answer 21

*WHITE to the RIGHT → white limb lead goes to the right shoulder/arm
*red to left ribs
*SMOKE OVER FIRE → black over red on the left side
*snow over grass → white over green on the right side

Question 22

EKG UNIPOLAR limb leads

Answer 22

*unipolar leads mean these leads use only a positive electrode, and measure the flow of electricity relative to that fixed point
1. lead aVR: right shoulder
2. lead aVL: left shoulder
3. lead aVF: left leg
4. note - there is a lead to the right leg, but this is just an “electrical ground”; we don’t look at it

Question 23

EKG lead: aVR

Answer 23

*unipolar limb lead
*placement: right shoulder
*lead color: WHITE (white to the right)

Question 24

EKG lead: aVL

Answer 24

*unipolar limb lead
*placement: left shoulder
*lead color: BLACK (SMOKE > fire)

Question 25

EKG lead: aVF

Answer 25

*unipolar limb lead
*placement: left leg
*lead color: RED (smoke > FIRE)

Question 26

EKG BIPOLAR limb leads

Answer 26

*bipolar: information from 2 leads is used to create a waveform
*one electrode can be taken to be positive and the other is negative
*creates Einthoven’s Triangle
*leads I, II, and III

Question 27

EKG lead: lead I

Answer 27

*right shoulder = negative
*left shoulder = positive

Question 28

EKG lead: lead II

Answer 28

*right shoulder = negative
*left leg = positive

Question 29

EKG lead: lead III

Answer 29

*left shoulder = negative
*right shoulder = positive

Question 30

EKG map

Answer 30

*NORMAL: highest QRS between -30 degrees and +90 degrees (aVL, aVF, lead I, or lead II)
*if QRS is highest from -30 to -90, then there is LEFT AXIS DEVIATION
*if QRS if highest from +90 to +180, then there is RIGHT AXIS DEVIATION

Question 31

EKG map: left axis deviation

Answer 31

*lead I positive; lead II negative
*if QRS is highest from -30 to -90 on EKG map
*causes may include: inferior wall MI, left anterior fascicular block, left ventricular hypertrophy

Question 32

EKG map: right axis deviation

Answer 32

*lead I negative; aVF positive
*if QRS is highest from +90 to +180 on EKG
*causes may include: right ventricular hypertrophy, acute right heart strain, left posterior fascicular block

Question 33

EKG map: severe right axis deviation

Answer 33

*lead I negative; aVF negative
*if QRS is highest between -90 and 180
*should never happen; leads are likely placed incorrectly

Question 34

EKG precordial leads

Answer 34

V1: lower right sternal border
V2: lower left sternal border
V3 - V5: spaced roughly equidistant from each other between V2 and V6
V6: left midaxillary line

Question 35

QRS axis based on EKG: stepwise approach

Answer 35

*start at lead 1: positive or negative?
-if POSITIVE: look at lead 2
-if NEGATIVE: look at lead aVF

Question 36

QRS axis based on EKG: if lead 1 is positive…

Answer 36

*look at lead 2:
-if POSITIVE: normal
-if NEGATIVE: LEFT axis deviation

Question 37

QRS axis based on EKG: if lead 1 is negative…

Answer 37

*look at lead aVF:
-if POSITIVE: RIGHT axis deviation
-if NEGATIVE: EXTREME right axis deviation (check your leads)

Question 38

QRS axis based on EKG: lead 1 POSITIVE, lead 2 POSITIVE

Answer 38

NORMAL QRS axis

Question 39

QRS axis based on EKG: lead 1 POSITIVE, lead 2 NEGATIVE

Answer 39

LEFT QRS axis deviation

Question 40

QRS axis based on EKG: lead 1 NEGATIVE, lead aVF POSITIVE

Answer 40

RIGHT QRS axis deviation

Question 41

QRS axis based on EKG: lead 1 NEGATIVE, lead aVF NEGATIVE

Answer 41

EXTREME RIGHT axis deviation (check your leads)

Question 42

bradycardia

Answer 42

heart rate < 60 bpm

Question 43

tachycardia

Answer 43

heart rate > 100 bpm

Question 44

how can you calculate HR based on EKG?

Answer 44

1. count # of QRS complexes, and multiply by 6 (b/c an EKG measures for 10 seconds)
2. the 300 rule: HR = 300 divided by the number of big boxes between the QRS complexes (see image)