Basic Concepts Of Electrocardiography

Question 1

Magnitude of the potential depends on

Answer 1

Strength of the source
Distance from the electrode to the dipole
Angle of a line form the electrode to the midpoint of the dipole therefore largest deflection when parallel

Question 2

Lead avR

Answer 2

Right arm is positive

Question 3

Lead avL

Answer 3

Left arm is positive

Question 4

Lead avF

Answer 4

Left foot is positive

Question 5

Electrocardiogram sensitivity and specificity for chamber enlargement

Answer 5

60% sensitivity

90% specificity

Question 6

Limitations of the ECG

Answer 6

Low sensitivity for chamber enlargement
Intermittent nature of some arrhythmias
- the routine ECG only records about 0.1% of the heart beats in a 24 hour period

Question 7

Position when recording ECG

Answer 7

Right lateral recumbency

Question 8

Electrode attachment

Answer 8

Just below elbows or stifles

Question 9

Standard sensitivity

Answer 9

1 mV = 10 mm

Question 10

Double sensitivity

Answer 10

1 mV = 20 mm

Question 11

Half sensitivity

Answer 11

1 mV = 5 mm

Question 12

Which electrocardiograph paper speed is best for measurements

Answer 12

50 mm/sec

Question 13

Which electrocardiogram paper speed is best for rhythm analysis (saves paper)

Answer 13

25 mm/sec

Question 14

Artifacts

Answer 14

ECG abnormalities not due to cardiac disorders

Question 15

Electrical interference

Answer 15

“60 cycle” due to A/C in electrical wires in ECG machine and room

Question 16

Most common patent movement and how to correct it

Answer 16

Respirtory

Correct by holding mouth closed for 3 to 4 seconds or by placing leads down on leg farther from chest wall

Question 17

Things to do first in ECG analysis

Answer 17

Evaluate for artifacts
Try to identify normal vs abnormal complexes
Identify the P QRS and T waves in all leads
Caliper

Question 18

Four basic determinations from ECG

Answer 18

Heart rate
Rhythm analysis
Measurements for analysis of cardiac size
Mean electrical axis determination (MEA)

Question 19

A 25 mm/sec 3 sec region is

Answer 19

75 mm

Question 20

At 50 mm/sec 3 seconds is

Answer 20

150 mm

Question 21

How to determine instantaneous heart rate

Answer 21

Method 1 - determine the time (in seconds)for a RR interval; divide this number 60 sec /min to get bpm
Method 2 -count the number of small boxes for a RR interval ; divide this number by 1500 if paper speed is 25 mm/sec and 3000 if paper speed is 50 mm/sec

Question 22

Supraventricular rhythm

Answer 22

Narrow, upright in lead II +/- related P wave >90% like “normal”; rapid conduction system

Question 23

Ventricular rhythm

Answer 23

Wide, bizarre, no related P wave

Question 24

Premature beats

Answer 24

Supra ventricular premature complex

Ventricular premature complex

Question 25

ST segment

Answer 25

Look for depression or elevation relative to baseline

Question 26

QT interval

Answer 26

Varies inversely with heart rate

Important in people, less so in animals

Question 27

T wave

Answer 27

Normal variability

Hyperkalemia

Question 28

Mean electrical axis (MEA)

Answer 28

The average direction that a wavelength of dipoles is moving in the heart
Applied to the QRS complex
Goal is to determine MEA to within 30 degrees ( is the axis normal or shifted right or left)
Several methods

Question 29

Methods to determine mean electrical axis

Answer 29

The major deflection method

The isoelectric lead method

Question 30

Isoelectric lead method

Answer 30

Find the most isoelectric lead (net voltage closest to zero)
Find the lead that is perpendicular to this lead
Determine the net valve for this lead - this is the MEA