Lecture 7 - Exam #2 material - ECG

Question 1

In regard to a reference lead, when will a vector have the highest amplitude?

Answer 1

When the vector is very close to the direction of the reference lead.

Question 2

When will a vector, in regard to a reference lead, have the smallest amplitude?

Answer 2

When the vector is perpendicular to the reference lead.

Question 3

The sum of all vectors at a given instant

Answer 3

Instantaneous mean vector

Question 4

Mean electrical axis of the heart

Answer 4

59*

Question 5

Repolarization of the heart is in the direction of the (base/apex)

Answer 5

Apex

Question 6

Repolarization of the ventricles begins on what region of the heart (endocardium or heart surface)?

Answer 6

heart surface

Question 7

What region of the heart begins to repolarize first during the atrial Twave?

Answer 7

area around the sinus node (repolarization essentially follows depolarization)

Question 8

Explain the pathophysiology of axis deviation in ventricular hypertrophy.

Answer 8

Larger muscle mass causes increased electrical activity. Depending on the area of hypertrophy, the mean electrical axis may shift.

Question 9

Why does fluid in the pericardium cause an shift in electrical axis?

Answer 9

Fluid acts as an insulator. As a result, only certain currents may get through, which will shift the axis.

Question 10

What is the criteria for determining a “High voltage ECG?”

Answer 10

When the sum of the QRS complexes in Leads I, II, and III are > 4 mV

Question 11

Explain why conditions around the heart are responsible for low-voltage ECGs

Answer 11

Conditions (such as pleural effusion or tamponade) act to insulate the heart’s electrical activity from conduction to the skin. This results in less electron flow, and a lower ECG recording.

Question 12

Normal QRS duration?

Answer 12

0.06 sec to 0.12 sec

Question 13

Currents that flow between normal areas and damaged areas of conduction

Answer 13

Current of injury

Question 14

The reference point in determining cardiac damage

Answer 14

J point

Question 15

The voltage of the J-point

Answer 15

0 mV

Question 16

A line with both magnitude and direction

Answer 16

vector

Question 17

The J-point is an indicator of what “polarization state” of the ventricles?

Answer 17

Completely depolarized or completely repolarized (J-point=0mV)

Question 18

Tachycardia that begins and ends suddenly

Answer 18

paroxysmal tachycardia

Question 19

What three physiologic conditions cause “circus movements” in cardiac tissue?

Answer 19

1) A conduction pathway is too long
2) A conduction velocity has been lengthened
3) A refractory period has shortened

Question 20

Explain why a lengthened conduction pathway may result in fibrillation.

Answer 20

If a conduction pathway has lengthened, the tissue where the AP originates has entered either relative refractory period or depolarization. Therefore, another AP can be fired.

Question 21

Explain why a slowed conduction velocity may result in fibrillation.

Answer 21

If an AP has slowed, by the time it arrives back at the originating tissue, that tissue is either in a relative refractory period or a repolarized state.

Question 22

Explain why a shortened refractory period may result in fibrillation.

Answer 22

If the refractory period is shortened the tissue is repolarized more rapidly. An arriving AP at the point of origin will trigger another action potential.

Question 23

Explain by what 2 mechanisms a refractory period may be shortened.

Answer 23

1) Increased Na/K/ATPase activity

2) Increased K efflux