CV - electrocardiogram

Question 1

the ___________ node is the typical cardiac pacemaker.

Answer 1

SA

Question 2

the SA node is the typical cardiac pacemaker because it has the ___________ spontaneous rate.

Answer 2

fastest

Question 3

the AV node has a slower spontaneous rate and delays conduction at the junction between the ___________ and ___________.

Answer 3

atria

ventricles

Question 4

purkinje cells conduct faster than ___________ cells.

Answer 4

contractile myocytes

Question 5

parking cells allow extremely rapid conduction from the AV node to the ventricles through the ___________ and their extensions into the myocardium.

Answer 5

left and right bundles

Question 6

what does the P wave of an ECG represent?

Answer 6

depolarization of the atria

Question 7

what does the QRS of an ECG represent?

Answer 7

depolarization in the ventricles

Question 8

what does the T wave of an ECG represent?

Answer 8

repolarization of the ventricles

Question 9

is repolarization of the atria appreciated on an ECG?

Answer 9

no, repolarization of the atria is not seen because it normally occurs at the same time as ventricular depolarization and is buried in the much larger QRS signal from the ventricles

Question 10

if the QRS is positive, the T wave should be ___________.

Answer 10

positive

Question 11

if the QRS is negative, the T wave should be ___________.

Answer 11

negative

Question 12

discordance between the QRS and T waves in any lead is pathological, reflecting abnormalities such as ___________ or ___________.

Answer 12

ischemia

ventricular hypertrophy

Question 13

the endocardium depolarizes ___________ the epicardium.

Answer 13

before

Question 14

epicardial cells repolarize ___________ endocardial cells.

Answer 14

before

Question 15

epicardial cells repolarize before endocardial cells because they have shorter ___________.

Answer 15

action potential duration

Question 16

the first signal on the ECG is the ___________.

Answer 16

P wave

Question 17

the P wave is generated by ___________ of first the right and then the left atrium.

Answer 17

depolarization

Question 18

describe the Q of the QRS wave on an ECG.

Answer 18

an initial negative deflection during ventricular depolarization

Question 19

describe the R of the QRS wave on an ECG.

Answer 19

the upward deflection

Question 20

describe the S of the QRS wave on an ECG.

Answer 20

a terminal negative deflection

Question 21

if the activation wave is toward the sensing electrode, a ___________ deflection will be recorded.

Answer 21

positive (upward)

Question 22

the greater the muscle mass the ___________ the voltage recorded.

Answer 22

greater

Question 23

the pattern of the deflection varies with the ___________ of the recording electrodes.

Answer 23

position

Question 24

the SA node is located high in the ___________ and the depolarization wave sweeps ___________ and ___________.

Answer 24

right atrium
downward
leftward

Question 25

a lead with a positive electrode near the right arm normally has a predominantly ___________ QRS.

Answer 25

negative

Question 26

a lead with a positive electrode near the left leg has a ___________ QRS.

Answer 26

positive

Question 27

the upper portion of the septum is depolarized from ___________ to ___________.

Answer 27

left to right

Question 28

what are the sites at which conduction can be delayed or blocked with clinical consequences? (6)

Answer 28

``` sinoatrial (SA) node atrioventricular (AV) node right bundle branch left bundle branch posterior fascicular branch anterior fascicular branch ```

Question 29

SA node abnormalities commonly cause ___________, resulting in ___________ or ___________.

Answer 29

"sick sinus syndrome" slow sinus rates takeover by other pacemakers which may be either faster or slower

Question 30

3 types of AV block

Answer 30

first degree: conduction is delayed but all P waves conduct to the ventricles second degree: some P waves conduct but others do not third degree: none of the P waves conduct and a ventricular pacemaker takes over

Question 31

how does a right bundle branch block appear on ECG?

Answer 31

QRS widening with delayed conduction to the right ventricle

Question 32

how does a left bundle branch block appear on ECG?

Answer 32

QRS widening with delayed conduction to the left ventricle

Question 33

how does a fascicle block appear on ECG?

Answer 33

shifts in direction of depolarization but no QRS widening

Question 34

what is the normal sequence of activation of the ventricles?

Answer 34

1 upper portion of the septum is depolarized from left to right 2 there is then depolarization downward int he septum to the apex 3 depolarization is from endocardium to epicardium 4 depolarization moves upward from the apex in the free walls of both ventricles 5 finally there is depolarization of the base of the ventricles

Question 35

what are the common mechanisms leading to arrhythmia?

Answer 35

reentry ectopic foci triggered activity

Question 36

describe abnormal reentry

Answer 36

abnormal reentry pathways can be present in the atria, ventricles or the junctional tissues, and occurs when there is a unidirectional block and slowed conduction through the reentry pathway reentry is the most common mechanism of serious tachycardias

Question 37

describe ectopic foci

Answer 37

ectopic foci occur when a focus of myocardium outside the conduction system acquires automaticity; if the rate of depolarization exceeds that of the SA node, an abnormal rhythm occurs ectopic foci result in isolated "ectopic beats" or sustained tachyarrhythmias

Question 38

describe triggered activity

Answer 38

abnormal "afterpolarizations" may be triggered by the preceding action potential; delayed afterpolarizations appearing after an action potential is complete can trigger arrhythmias, and afterpolarizations when action potentials have only partially depolarized triggers a tachyarrhythmia arrhythmias due to this mechanism are usually associated with a delay in repolarization seen in the ECG as a "long QT interval"

Question 39

what induces the depolarization in phase 0 of the slow cardiac action potential?

Answer 39

calcium current

Question 40

why do contractile myocytes display a more rapid depolarization during phase 0 of the fast cardiac action potential?

Answer 40

sodium current

Question 41

why do purkinje cells conduct faster than contractile myocytes?

Answer 41

they have more fast Na+ channels

Question 42

what phase of the action potential does the initial R spike on an ECG correspond to?

Answer 42

phase 0

Question 43

what phase of the action potential does the ST segment on an ECG correspond to?

Answer 43

phase 2

Question 44

what phase of the action potential does the T wave on an ECG correspond to?

Answer 44

phase 3

Question 45

what phase of the action potential does the plateau following the T wave on an ECG correspond to?

Answer 45

phase 4