cardiac electrophysiology

Question 1

A 21 y/omale from Southeast Asia dies in his sleep. Post-mortem molecular autopsy demonstrates a loss-function-mutation in the Voltage Gated Sodium Channel (SCN5a). This will have the following effect on the action potential:

Answer 1

phase 0 and 1 since this sodium channel is responsible for phase 0

can result in long QT syndrome when overactivated –> burmuda syndrome

Question 2

what defines the plateu phase in an action potential

Answer 2

L type ca channels

ca coming in and k moving out both slowly

Question 3

what channels are key for excitatation and contraction

Answer 3

L type ca –> ca induced ca release

Question 4

what is channel and phase and responsible for LQTS 1 and 2 inherited arrhythmias syndromes

Answer 4

–IKr(rapid)

–IKs(slow)

phase 3

in KCNQ1, loss of this can cause long QT

Question 5

what phase and channel is responsible for (Torsadede Pointe) drug induced arrthymias and is tested for when developing new drugs

Answer 5

K in phase 3

Question 6

what activates phase 4 in SA nodal cells

what does phase 4 control

Answer 6

hyperpolarization

heart rate

Question 7

how does going for a run activate the slope of phase 4

Answer 7

makes it steeper- faster hr

Catecholamines

Question 8

name mechanisms to slow SA firing

Answer 8

1. Slows depolarization-
2. Lowers resting –> opens K
3. Raises threshold decreases Ca

can slow or stop AV conduction

Question 9

Blocking the HERG channel will have the following effects on the action potential AND ECG:

Answer 9

1.Prolong BOTH Phase III and QT interval

could cause Torsade de Pointe

Question 10

Anisotropy

Answer 10

ordered propogation

Question 11

what is Arrhythmogenic Right Ventricular Cardiomyopathy

Answer 11

Disruption of Desmosomes in Intercalated Disc Causes Heart to Turn into Fat!

Question 12

How can arsenic cause QTc prolongation

Answer 12

trafficking defect, preventing the HERG channel from getting to the sarcolemma (phase III)

Question 13

what can cause exercise induced tachycardia

Answer 13

leaky RyR channel

A.Ca2+influx leads to delayed-after-depolarization mediated triggered arrhythmia

Question 14

what kind of things could cause a inversion where the repolarization occurs from endo to epi (normal repolarization is epi to endo)

Answer 14

pathologic and could be thickening of the heart

Question 16

what would you estimate the rate to be if the p to p covered 5 boxes

Answer 16

60

300 150 100 75 60 50

Question 17

what are the 5 questions you ask every ecg

Answer 17

• What is the Rate?
• What is the Rhythm?
• What is the Axis?
• What are the Intervals?
• Waveform?

Question 18

what would you see in lead 1 if you had left axis deviation due to left ventricular hypertrophy

what if you had right axis deviation due to right ventricular hypertrophy

Answer 18

positive in lead 1 but isoelectric in AVR

reverse

Question 19

if the myocardium is thicker than __ mm you increase risk of sudden cardiac death

Answer 19

3

Question 20

what does the PR interval represent and how long should it be

Answer 20

start of atrial dep to ventricular depolarization

120-200

Question 21

what does the QT interval represent and how long should it be

Answer 21

start of ventricular depolarization to the end of ventricular repolarization

should be less than 440 in men and 460 in women

Question 22

what impact would testosterone have on the QT interval

Answer 22

shortens it

Question 23

what is the qrs complex and how long should it be

Answer 23

qrs –> begining to end of ventricular dep

90-100

advances is more than .12s

Question 24

what kind of things could cause an altered waveform

Answer 24

obesity

COPD

effusions

hypothyrodism

kATP and MI could cause ST elevatio

Question 25

which occlusion can be electrially silent

Answer 25

LCx

Question 26

where would you see a signal for LCx or diagnal

Answer 26

V5/V6

I

AVL

Question 27

where would you see a signal for LAD

septal?

Answer 27

V1-V4

septal (V1,V2)

Question 28

where would you see a signal for RCA

Answer 28

II, III, aVF

Question 29

why can you see Why can you see the fibrillatorywaves in the ventricle but not atria

Answer 29

mass = larger magnitude

Question 30

how do you tell R vs L BBB

Answer 30

R –> LAD V1

L –> V6