ECG & arrhythmias

Question 1

Bipolar limb leads

Answer 1

I: LA + RA -
II: LL + RA -
III: LL + LA -
all in frontal plane

Question 2

Unipolar limb leads

Answer 2

aVR: RA + LA & LL -
aVL: LA + RA & LL -
aVF: LL + RA & LA -
all in frontal plane

Question 3

Precordial/chest leads

Answer 3

6 chest leads in horizontal plane
anterior –> posterior
V1-6

Question 4

Rate on ECG

Answer 4

300/# big squares btw each QRS complex

Question 5

P waves

Answer 5

reflect atrial pacemaker

also note P to QRS relationship

Question 6

PR interval

Answer 6

normal = 0.12 - 0.2 s (3-5 small squares)

from beginning of P to beginning of anything that represents QRS

Question 7

QRS complex

Answer 7

normal = 0.12 s (3 small squares)

“delta” wave - gradual incline in QR segment –> WPW

Question 8

Sinus bradycardia

Answer 8

Rate < 60

Question 9

Sinus tachycardia

Answer 9

Rate > 100

max 180-200 (except babies)

Question 10

First degree heart block

Answer 10

long PR interval
1:1 P:QRS
ischemia, fibrosis of AV node

Question 11

2nd degree heart block: Morbitz type I/Wencheback

Answer 11

PR interval increases with each beat, then missing QRS

misses QRS regularly

Question 12

2nd degree heart block: Morbitz type II

Answer 12

No pattern in missing QRS complexes
PR interval constant
most likely develop into type III block

Question 13

Third degree heart block

Answer 13

complete dissociation of P and QRS
atrial rate faster than ventricular rate
usually QRS are wide, rarely it can be low
SA node --> atrial pacemaker
ectopic --> ventricular pacemaker

Question 14

Atrial flutter

Answer 14

atrial rate 300
ventricular rate 150, 100, or 75 depending on block
rhythm is regularly irregular
atrial rate > rate at which AV node can conduct (Refractory period)
“saw-tooth” p waves
common block patterns are 2:1 (AV node blocks every 2nd atrial impulse) or 3:1
ectopic atrial pacemaker

Question 15

Atrial fibrillation

Answer 15

rhythm is irregularly irregular
no p waves, but background noise present
high amount of uncoordinated electrical activity in atria –> quivering
multiple ectopic atrial sites acting as pacemaker
can lead to embolism

Question 16

Supraventricular tachycardia

Answer 16

Any narrow tachycardia with narrow QRS and P waves are not obvious

Question 17

Orthodromic AVRT

Answer 17

anterograde impulse via AV node

retrograde via accessory pathway

Question 18

Antidromic AVRT

Answer 18

anterograde impulse via accessory pathway

retrograde via AV node

Question 19

Ventricular tachycardia

Answer 19

100-250 bpm
P waves absent
wide QRS
ventricular ectopic pacemaker
can easily cause cardiac arrest

Question 20

Ventricular fibrillation

Answer 20

Uncoordinated activity only
Multiple ventricular ectopic pacemakers
No ventricular contractions
One example of cardiac arrest
code blue & defibrillate!

Question 21

Asystole

Answer 21

has been in pulseless rhythm for a while

sustained hypoxia to heart and brain

Question 22

Automatic cause of bradycardia

Answer 22

increase parasympathetic drive
decrease slope of phase 4 (vagus + cholinergic stimulation of SA node –> reduce probability that pacemaker channels are open)
increase threshold value
RMP more negative

if SA node is slow enough, an escape rhythm can take over - ectopic pacemaker (slower rate)

Question 23

Automatic cause of tachycardia

Answer 23

Decrease parasympathetic drive
Increase slope of phase 4 (B1 stimulation)
Threshold value more negative
RMP more positive
ectopic beat formation along the conduction pathway faster than the SA node may also produce tachycardia –> overstimulation of sympathetic drive
Injury to membranes

Question 24

Re-entry circuits

Answer 24

Faster conducting, slower refractory alpha

Slower conducting, faster refractory beta

Question 25

Early after-depolarization

Answer 25

During plateau of phase 2 or phase 3 (repol)
most Na channels inactivated but become abnormally activated, self-propagating action potential
torsades de pointes

Question 26

Late after-depolarizations

Answer 26

after repolarization is complete

high intracellular calcium / excessive catecholamine stimulation

Question 27

Conduction block

Answer 27

causes: ischemia, fibrosis, inflammation, drugs
secondary to refractoriness of cells: functional block
damage: fixed block
escape rhythm = third degree heart block

Question 28

Tx of bradycardia

Answer 28

Invasive: pacemaker

Sinus node: symptomatic - pacemaker; asymptomatic - no treatment
AV node: 1st degree block: no treatment; type 2: pacemaker
3rd degree: pacemaker

Question 29

Catheter ablation

Answer 29

FR energy delivered to myocardial tissue, disrupts arrhythmia substrate

Question 30

Cardioverter/defibrillator implantation

Answer 30

cardioversion: sync shock with QRS complex; good for SVTs or organized ventricular tachycardias

Question 31

Vagal maneuvers:

Answer 31

valsalva, carotid sinus massage, diving reflex

Question 32

Valsalva maneuver

Answer 32

increase in intrathoracic pressure = increase in aortic pressure (transient baroreceptor response)
decrease in CO, no stimulation of baroreceptor response –> v/c
release of pressure at the end of the maneuver –> return CO, but SVR still high
baroceptor detects increased pressure –> reduce HR

Question 33

Preload

Answer 33

the volume (load) filling the ventricle prior to contraction; equivalent to end-diastolic volume.

When preload is increased, according to the Frank-Starling Law, there will be a compensatory increase in SV to accommodate it.

Question 34

Afterload

Answer 34

wall stress experienced by the ventricle as it contracts to produce a pressure necessary to open the aortic valve and eject blood into the systemic circulation