Exam #2: Electrocardiography

Question 1

What is depolarization?

Answer 1

Switching of charges on the cell membrane; positive outside relative to negative inside

Question 2

How is current related to depolarization & repolarization? How is this related to the ECG tracing?

Answer 2

• Current only flows when there is a depolarization or repolarization event
• The ECG electrode can only detect current

Question 3

By convention, flow of a positive ion away from the positive pole of an electrode appears as what? What about the opposite?

Answer 3

• Away= negative deflection
• Toward= positive deflection

Away= down 
Toward= up

Question 4

What is the electrocardiogram?

Answer 4

A summation of all the depolarizations and repolarizations occurring in cardiac cells

Question 5

What is the p-wave? What is the normal duration of the p-wave?

Answer 5

• A summation of atrial myocyte depolarization

- 0.06-0.11 sec

Question 6

What step theoretically comes before atrial depolarization?

Answer 6

SA node generation of impulse that CANNOT be seen on ECG

Question 7

What does the PR interval correspond to? What is the normal duration of a PR interval?

Answer 7

• Atrial myocyte plateau phase (Ca++ IN & K+ OUT)

- 0.12-0.2 sec

Question 8

What causes the QRS complex? What is the normal duration of a QRS complex?

Answer 8

• Ventricular depolarization

- 0.03-0.12 sec

Question 9

What is the Q of the QRS? Define Q-wave.

Answer 9

Septal depolarization, which is positive current moving away from the positive electrode

Any negative defection before the R-wave is a Q-wave

Question 10

What is the R of the QRS?

Answer 10

Ventricular muscle depolarization spreading toward electrode

Question 11

What is the S of the QRS?

Answer 11

Ventricular muscle depolarization spreading away from the electrode

Question 12

What is the ST segment?

Answer 12

Plateau phase of the ventricular myocyte

Question 13

What is the T-wave?

Answer 13

Ventricular myocyte repolarization

Question 14

Is atrial repolarization viewed?

Answer 14

NO, it is buried in the QRS

Question 15

What is the chart speed of an ECG tracing?

Answer 15

25 mm/sec

Question 16

How much time passes between 5mm?

Answer 16

0.2 sec (1 large box)

Question 17

How much time passes between 1mm?

Answer 17

0.04 sec (1 small box)

Question 18

What corresponds to 1.0 mV?

Answer 18

10mm (2x large boxes vertically)

Question 19

Where is lead I?

Answer 19

+ left arm to - right arm

Question 20

Where is lead II?

Answer 20

+ left foot to - right arm

Question 21

Where is lead III?

Answer 21

+ left foot to - left arm

Question 22

Where the standard limb leads bipolar or unipolar? What about the augmented limb leads?

Answer 22

Standard= bipolar
Augmented= unipolar

Question 23

Where is aVR?

Answer 23

+ right arm

Question 24

Where is aVL?

Answer 24

+ left arm

Question 25

Where is aVF?

Answer 25

+ left foot

Question 26

Draw the hexaxial lead system.

Answer 26

N/A

Question 27

List the placement of the precordial leads.

Answer 27

``` V1= R. sternal border 4th intercostal space V2= L. sternal border, 4th intercostal space V4= Midclavicular, left 5th intercostal space V3= between V2 & V4 V5= anterior axillary line, in line with V4 V6= in line with V4 & V5, midclavicular ```

Question 28

List the R-R rate as determined by counting "large boxes."

Answer 28

``` 1= 300 2= 150 3= 100 4= 75 5= 60 6= 50 7= 42 ```

Question 29

What causes left axis deviation?

Answer 29

``` End of deep expiration Supine Obesity Hypertrophy (systemic, valvular disease, congenital) LBBB (occurs with wide QRS) ```

Question 30

What causes right axis deviation?

Answer 30

``` End of deep inspiration Moving to standing Tall Hypertrophy (pulmonary valve stenosis, pulmonary HTN, congenital) RBBB (with wide QRS) ```

Question 31

What is the normal PR-interval?

Answer 31

0.12-0.2 seconds | 3-5 small boxes

Question 32

What is the normal QRS duration?

Answer 32

0.03-0.12 seconds | <1-3 small boxes

Question 33

What is the normal QT interval?

Answer 33

asdf

Question 34

What causes increased voltage of QRS?

Answer 34

Hypertrophy | Thin chest

Question 35

What causes decreased voltage of QRS?

Answer 35

Previous MI Fluid in pericardium or pleural space Large chest

Question 36

What are the clinical manifestations of hyperkalemia on ECG?

Answer 36

Tall, peaked T-waves

Question 37

What are the clinical manifestations of hypokalemia on ECG?

Answer 37

Decreased T-wave amplitude Inverted T-wave U-waves

Question 38

What is the pathophysiology underlying a PR interval that is longer than normal?

Answer 38

1st degree AV block

Question 39

What is the pathophysiology underlying a PR interval that is shorter than normal?

Answer 39

Junctional rhythm or accessory pathway between the atria & ventricles

Question 40

What is the pathophysiology underlying a few very large & wide QRS complexes appearing in a lead with mostly normal QRS complexes?

Answer 40

PVCs

Question 41

What is the pathophysiology underlying all very large & wide QRS complexes?

Answer 41

Ventricular rhythm | Extreme hyperkalemia

Question 42

What is the pathophysiology underlying a p-wave that occurs without a subsequent QRS complex?

Answer 42

AV Block