EKGs

NSR - HR 75 bpm

NSR - HR 50 bpm (sinus brady)

NSR - HR 140 (sinus tach)

PVC

PAC

1st degree AV block

2nd degree AV block type I (Mobitz I/Wenckebach)

2nd degree AV block type II (Mobitz II)

3rd degree heart block

2nd degree heart block type I (mobitz I/wenckeback)

1st degree heart block

2:1 AV block (type of 2nd degree) - treated like CHB

RBBB

• RR’ in V1/V2

• broad S wave in V6

LBBB

• rS in V1/V2 (negative)

• R in V6 (positive)

LAFB

• LAD

• inferior leads: rS (negative)

• lateral leads: qR (positive)

LPFB

• RAD

• inferior leads qR (positive)

• lateral leads rS (negative)

P wave represents…

atrial depolarization

QRS represents…

ventricular depolarization

ST and T wave represents…

ventricular repolarization

phase 0 action potential

sodium channels open → rapid upstroke

phase 1 action potential

(initial) potassium efflux

phase 2 action potential

calcium channels open → calcium in matches potassium out

phase 3 action potential

potassium efflux predominates → repolarization

relative refractory period corresponds to which part of the EKG?

T wave (ventricular repolarization)

size of 1 large box (ms or s)

200 ms (0.2 s)

size of 1 small box

40 ms (0.04 s)

PR interval is from the beginning of the P wave to the start of __

QRS

PR interval represents the spread of electricity from ___ to ___

sinus node to AV node

normal PR interval (length)

120-200 ms (3-5 small boxes = <1 large box)

PR interval >0.2 seconds indicates…

1st degree AV block

if PR interval is depressed below baseline, think…

pericarditis

normal QRS length

80-120 ms (<3 small boxes)

**measure the end by the end of the S wave (when it returns back to baseline)

Q wave =

first downward deflection

R wave =

first upward deflection

S wave =

first downward deflection after an R wave

when to use capital vs. lowercase letters for QRS?

capital letter if the wave is 2+ small boxes in height

lowercase if <2 small boxes

pathologic ST segment looks like…

1-2mm above or below baseline in consecutive leads

**not J point elevation (J point = swooping up, ST elevation = immediate rise)

T wave inversion =

ischemia (first stage)

peaked T waves =

hyperkalemia

normal QT interval length

less than ½ of R-R interval

<500 ms/ 2.5 large boxes

as HR increases, QT (increases/decreases)

decreases

bipolar leads (list)

I, II, III

unipolar leads (list)

aVR, aVL, avF

lead I positive and negative

+: LA

-: RA

lead II positive and negative

+: LL

-: RA

lead III positive and negative

+: LL

-: LA

aVR combines leads:

I and II

aVL combines leads:

I and III

aVF combines leads:

II and III

V1 lead location

R 4th intercostal, sternal border

V2 lead location

L 4th intercostal, sternal border

V3 lead location

L, between V2 and V4

V4 lead location

L 5th intercostal, MCL

V5 lead location

even with V4 at anterior axillary line

V6 lead location

even with V4 and V5 at midaxillary line

which leads should have a deep S wave in a normal R wave progression?

V1 and V2

where should R and S waves be equal height in normal R wave progression?

V3

where should R wave be larger than S wave with normal R wave progression?

V4-V6

causes of poor R wave progression

anything that changes depolarization in either ventricle:

• block

• hypertrophy

• infarct

300 rule for determining HR

300, 150, 100, 75, 60, 50

only use if regular rhythm, >40 bpm

count & multiply method for HR

count number of QRS complexes in the rhythm strip and multiply by 6

use for irregular rhythms, bradycardia

characteristics of low atrial focus escape rhythm (P wave, HR)

inverted P wave - because electricity has to move up the atrial walls (normally SA node is at the top)

HR 50-60 bpm

characteristics of AV junctional focus escape rhythm (P wave, HR)

no P wave (not originating in atria)

HR 40-60 bpm

characteristics of ventricular focus escape rhythm (P wave, HR)

no P wave

wide QRS

HR 20-40 bpm

key to determining diagnosing irregular rhythm:

relationship between P and QRS

PACs (do/do not) have a P wave before every QRS

they DO but usually it has a different morphology

can be visible or buried in the previous QRS

PVCs (do/do not) have a P wave before every QRS

do NOT - P waves will come at a regular interval but QRS is irregular

PVCs have a distinctly different appearance from sinus beats (wide QRS)

normal axis degrees

-30 (0) to 90

LAD degrees

-30 to -90

RAD degrees

90 to 180

indeterminate axis degrees

-90 to 180

which leads do you look at to determine axis?

lead I, aVF

lead I positive, aVF positive: axis?

normal

lead I positive, aVF negative: axis?

left axis deviation

lead I negative, aVF positive: axis?

right axis deviation

causes of LAD

• left BBB

• LVH

• LAFB

• obesity

• inferior wall MI

causes of RAD

• COPD

• tall, thin frame

• right BBB

• RVH

• LPFB

• lateral wall MI

criteria for 1st degree AV block

PRi prolonged >200 ms (>1 big box) with normal QRS

technically a delay not a block

criteria for Type 1 2nd degree block (Mobitz 1)

PR interval progressively lengthening prior to a dropped QRS
→ the PRi of the beat after the dropped QRS will be significantly shortly than the PRi of the beat before the nonconducted P wave

dropped beat occurs when AVN is no longer able to conduct a stimulus from above

criteria for Type 2 2nd Degree block (Mobitz II)

fixed PRi with a P wave that is not followed by a QRS (dropped beat)

why is Mobitz II worse than Mobitz I?

mobitz II is infrahisian (block occurs in the bundle of His (lower than the AV node)) so it is a more unstable rhythm

mobitz I block occurs in AV node

criteria for 3rd degree/complete heart block

atrioventricular dissociation

regular atrial & ventricular rhythms but they are not associated with each other

• no atrial depolarizations are able to penetrate AVN → junctional escape rhythm takes over in ventricles

which leads are better for seeing P waves?

V1 and V2

main criteria for bundle branch block

wide QRS

morphology will also be distinct (leads V1/V6)

QRSd in bundle branch block

>120 ms

hemiblock = 100-120 ms

right chest leads in RBBB

“bunny ear” - RR’, rSR (V1 and/or V2)

• due to LV contracting before RV → joined but out-of-sync QRS complexes

left chest leads in RBBB

broad S wave (V6)

• due to slow diffusion of electricity away from LV towards RV

should you be concerned about RBBB?

not necessarily - be concerned if it is a new finding

right chest leads in LBBB

QS (single negative deflection) or rS (V1)

• may see inverted T

• due to electricity moving away to passively depolarize the left

left chest leads in LBBB

tall R wave (often RR’ with no Q)

• positive because all electricity is moving towards the left

should you be concerned about a LBBB?

yes - always investigate

LAFB:

1. axis deviation?

2. inferior leads?

3. lateral leads?

1. LAD

2. negative (II, III, aVF)

3. positive (I, aVL)

LPFB

1. axis deviation?

2. inferior leads?

3. lateral leads?

1. RAD

2. positive (II, III, aVF)

3. negative (I, aVL)

inverted T waves indicates (ischemia/injury/infarction)

ischemia

ST segement elevation indicates (ischemia/injury/infarction)

injury (early stages of infarction)

• infarction is ongoing or imminent

clinically significant ST segment elevation/depression = at least __ mm from baseline

2

Q waves represent (ischemia/injury/infarction)

infarction (scar tissue does not depolarize properly)

__ is often seen with Q waves

inverted T waves

• issue with depolarization ←→ issue with repolarization

which vessel supplies the AV node? what can happen if there is an MI in this vessel?

RCA (supplies the inferior wall)

inferior wall MI can lead to complete heart block