Lecture 8: Heart rhythmicity and normal EKG presentation

Question 1

Limb lead II is positive when

Answer 1

When the point where the right arm connects to the chest is negative with respect to the left leg

Question 2

J-point

Answer 2

Reference point for analyzing current of injury-occurs at very end of QRS wave and is the point at which all parts of the ventricle become depolarized

Question 3

T- wave represents

Answer 3

Ventricular repolarization

Question 4

AV node

Answer 4

Recieves signal from SA node .03 seconds after origin

Question 5

Limb lead III is positive when

Answer 5

When the left arm is negative with respect to the left leg

Question 6

Signal is delayed in AV node due to

Answer 6

Small size of cells
Low amplitude of action potential
Slow rate of depolarization

Question 7

When does current flow occur in an EKG

Answer 7

Only when the atria and ventricles have different potentials

Question 8

SA node threshold

Answer 8

-40

Question 9

Vector

Answer 9

An arrow that points in the direction of the electrical potential generated by the current flow, with the arrowhead in the positive direction

Question 10

No potential is recorded when the ventricle is

Answer 10

Completely polarized or

Completely depolarized

Question 11

Normal QRS lasts how long

Answer 11

.06–>.08 seconds

Question 12

Slow conduction through AV node is caused by

Answer 12

Diminished number of gap junctions along pathway resulting in an increase in the resistance to conduction

Question 13

Ventricular fiber resting potential

Answer 13

-90

Question 14

Currents of injury

Answer 14

Different cardiac abnormalities cause part of the heart to remain partially or totally depolarized all the time

Question 15

Recording limb lead III

Answer 15

Negative terminal is connected to left arm
Positive terminal is connected to left leg
Looks at heart from upper left to lower left

Question 16

Einthovens law

Answer 16

If the electrical potential of any two of the three bipolar limb EKG leads are known at any instant, the third can be determined by summing the first two

Question 17

Effect of current of injury on QRS complex

Answer 17

Abnormal negative current flows from infarcted area and spreads towards the rest of the ventricles

Question 18

Effect of vagus nerve

Answer 18

Decreases rate of rhythm of SA node
Decreases excitability of the AV junctional fibers, slowing transmission of cardiac impulses into ventricles
Increases permeability of fiber membranes to potassium

Question 19

Einthovens triangle

Answer 19

Two arms and left leg from pieces of triangle

Question 20

Hypertrophy or dilation of left/right ventricle can cause QRS to last how long

Answer 20

.09—>.12

Question 21

Sympathetic innervation distributed to which areas of heart

Answer 21

All parts of the heart, mainly ventricles

Question 22

Abnormal ventricular conditions that cause axis deviation

Answer 22

Change in position of heart in chest
Hypertrophy of one ventricle
Bundle branch block
Fluid in pericardium
Pulmonary emphysema

Question 23

Mean electrical axis

Answer 23

The direction of the electrical potential (negative to positive) from the base of the ventricles toward the apex
=59 degrees

Question 24

Limb lead I is positive when

Answer 24

When the point where the right arm connects to the chest is negative with respect to the point where the left arm connects

Question 25

Neurotransmitter in sympathetic innervation

Answer 25

Norepinephrine

Question 26

What channels open in SA depolarization, which means

Answer 26

Only slow sodium-calcium channels AP is slower to develop Repolarization is slower

Question 27

Conditions that cause bizarre complexes

Answer 27

Destruction of cardiac muscle and replacement by scar tissue | Multiple small local blocks in the conduction impulses at many points in the purkinje system

Question 28

Abnormalities causing currents of injury

Answer 28

Mechanical trauma Infectious processes Ischemia (most common)

Question 29

Neurotransmitter used in Vagus nerve

Answer 29

Ach

Question 30

Signial is delayed in AV node for how long

Answer 30

.09 seconds

Question 31

SA node

Answer 31

Composed of special cardiac muscle fibers | SA fibers connect directly to atrial fibers

Question 32

Resting potential of SA node fiber

Answer 32

-55 -60

Question 33

Recording limb lead I

Answer 33

Negative terminal connected to right arm Positive terminal connected to left arm Looks at the heart from right to left

Question 34

Final delay of how long in the penetrating bundles

Answer 34

.04 seconds

Question 35

Causes of decreased voltage in standard bipolar leads

Answer 35

Cardiac myopathies | Conditions surrounding the heart

Question 36

Q-T interval

Answer 36

0.35 seconds

Question 37

Recording limb lead II

Answer 37

Negative terminal is connected to right arm Positive terminal is connected to left leg Looks at heart from upper right to lower left

Question 38

P-wave represents

Answer 38

Atrial depolarization

Question 39

Effect of sympathetic innervation

Answer 39

Stimulates beta-1 adrenergic receptors Increases depolarization rate May increase permeability of fiber membranes to sodium and calcium

Question 40

P-Q (P-R) interval

Answer 40

Beginning of P-wave ---> beginning of QRS | ~0.16 seconds

Question 41

QRS wave represents

Answer 41

Ventricular depolarization

Question 42

Vagus nerve is sympathetic or parasympathetic- and is distributed to which areas of heart

Answer 42

Parasympathetic | Mainly to AV and SA nodes

Question 43

Most common cause of increased voltage in standard bipolar leads

Answer 43

Hypertrophy of the ventricle

Question 44

Total delay from initial origin of the signal until onset of ventricular contraction

Answer 44

0.16 seconds