Study Questions Lab 1

Question 1

1. Define the term “electrode” w/respect to human physiological recordings

Answer 1

• Type of transducer which changes ionic current into electrical current.
• They generate their own DC voltage on which cardiac electrical signals are
  superimposed and transmitted to the ECG.
• Types include flat plate, suction cups, disposable

Question 2

2. What is the purpose of shaving, abrading, and applying ethanol at the skin where an electrode is to be place?

Answer 2

• Good skin prep essential to obtain clear ECGs
• Ethanol helps remove skin oil (lipid solvent); shaving improves contact between electrode and skin, abrading removes any dead skin cells
• Analogous to stripping the plastic insulation from an electric wire: to inc electrical conductivity
• Lowers electrode-skin impedance

Question 3

3. Explain the difference btwn “wire” or “patient cable” and “lead” w/respect to electrocardiography

Answer 3

• A cable is a bundle of wires
• The cable used in electrophysiology is called patient cable; it is a bundle of wires that transmit the electrical signals from electrode to the ECG.
• Lead is a specific combo or configuration of electrodes, that gives a view of the electrical activity of the heart from a particular angle across the body
• Difference: a wire is a component of the patient cable. The patient cable is attached to electrodes on the skin measuring electrical signals. A lead is a configuration of electrodes which can measure movement of current to determine electrical activity.

Question 4

4. How can one record a 12 lead ECG w/only 10 electrodes?

Answer 4

• A lead is a specific combination, or configuration, of electrodes that gives a view of the electrical activity of the heart from a particular angle across the body.
• Leads can share the same electrode.
• The electrodes w/in the 12 lead ECG consists of 1 reference, 3 limb, and chest electrodes.
• The 3 limb leads are calculated from the 3 limb electrodes, the 6 chest leads are calculated from the 6 chest electrodes, and the 3 augmented voltage are calculated from the 3 limb leads and do not require electrode placement.
• Thus 12 leads (points of view/perspectives) can be created using just 10 electrodes.

Question 5

5. When the pos electrode and neg electrode are at same electrical potential (i.e. voltage) does the ECG stylus defect up, down, or remain unchanged? Explain

Answer 5

The ECG stylus remains unchanged. The amplifier takes the difference between the 2 inputs and sends signal to the A/D converter. Since the ECG measures changes in potential due to depolarization or repolarization, if they’re at the same electrical potential it represents no change, thus, no deflection.

Question 6

6. When current flows toward the pos electrode, does the EKG stylus deflect up, down, or remain unchanged

Answer 6

If current flows toward positive ECG electrode, there’s an upward deflection.

Question 7

7. On which of the following - Lead I, Lead II, or Lead III- would u expect the QRS complex to have the highest pos amplitude? Explain

Answer 7

Lead II would have the highest positive QRS amplitude. Lead II has a negative electrode on the RA and positive electrode on the LL. Thus it runs in the same direction as the electrical activity of the heart (depolarization axis).

Question 8

8. What is the purpose of the reference electrode in ECG (and other electrical recordings from the body)?

Answer 8

1. Improves quality of tracing
2. Provides a baseline to allowing ECG to identify and eliminate electrical “noise” found over a large region of body. Once noise eliminated, the small differences in electrical potential btwn electrodes can be seen more clearly.
3. Quality would be degraded by 60 Hz interference w/out reference electrode
4. Grounding helps prevent electrical shock to subject by providing low resistance pathway to earth/ground for current which might reach the outer case of the ECG machine due to a fault
5. Prevents “stimulus artifact” which can distort or obliterate smaller signals recorded from nerve/muscle unless diverted into lower-resistance pathway to earth

Question 9

9. Give 3 reasons for exercise stress testing?

Answer 9

1. To diagnose an abnormal response to exercise denoting CVD
2. To assess the physical tolerance of patients w/known CVD
3. To assess physical fitness of individuals w/out known CVD

Question 10

10. What is a PAR-Q and what is it used for?

Answer 10

• Physical Activity Readiness Questionnaire
• Recommended as minimal standard for entry into low to moderate intensity exercise programs
• Designed to identify small # of adults for whom PA is inappropriate for
• 7 yes/no Q’s (7 of 19 that were shown to be the best predictors of those individuals at risk to exercise)
• A yes response to one or more means individual should consult physician

Question 11

11. In what units should P-R interval be reported?

Answer 11

milliseconds (ms)

Question 12

12. What would you do if you were trying to measure the P-R interval, and it was so small that it was hard to measure accurately?

Answer 12

• Increase chart speed of ECG e.g. from 25mm/s to 50mm/s

- Faster chart speed is more appropriate to carefully look at changes in interval durations

Question 13

13. In what units should P-wave amplitude be reported?

Answer 13

Millivolts (mV)

Question 14

14. What would u do if u were trying to measure the QRS-wave amplitude and it was so large that it went off the EKG paper?

Answer 14

• Decrease the gain on the ECG

- Gain = output voltage/input voltage; aka how much original signal amplified by

Question 15

15. Pushing the calibration button generates a 1mV square wave. What is the purpose of recording a calibration signal on the ECG?

Answer 15

1. Set baseline to provide basis for calculation of amplitudes e.g. QRS amplitude, ST segment depression; measure it on mm such that 1mV = ___ mm on the ECG

Question 16

16. In what ways does 60 Hz interference look different than skeletal muscle tremor?

Answer 16

60 Hz interference has regular electrical deflections occurring around 60 Hz vs. Skeletal muscle tremor which has noise that is irregular in height and frequency

Question 17

17. In what way does motion artifact look different than wandering baseline?

Answer 17

Motion artifact appears as sudden, large deflection upward or downward in ECG tracing as the electrode moves relative to skin surface vs. Wandering baseline which is when whole tracing moves up or down

Question 18

18. How does the MEA of the heart calculated for deep inspiration differ from the axis at rest? Explain.

Answer 18

Inspiration:

• During deep inspiration diaphragm descends which increases the space in the thorax allowing the heart to hang more vertically
• Thus MEA of the heart increases (eg. 60 to 70 degrees.)

Rest:
- At rest the apex of the heart points downwards and to the left therefore having a mean axis of ~60 degrees

• In case expiration asked*
• Air leaves the lungs causing the diaphragm to move up
• Diaphragm moving upward pushes the heart into a more horizontal position as the apex of the heart moves upward and towards the left
• Therefore MEA decreases

Question 19

19. Would an elite endurance athlete have a normal MEA, or would it be shifted? It it’s shifted, in what direction would the shift be?

Answer 19

• An elite endurance athlete would have a LV hypertrophy due to conditioning of myocardium
• This would cause a left shift of his mean electrical axis such that its between -30 and -90 degrees.

Question 20

20. If you’re administering an exercise ECG, you should stop the exercise if you see certain abnormalities. Name 3 of these.

Answer 20

1) Ventricular tachycardia (large inc in HR early on, may signify CAD)
2) Ventricular fibrillation (totally irregular ECG appearance; ventricles not contracting in coordinated manner)
3) ST segment depression (horizontal or down-sloping) greater than 2 mm
4) If more than 30% of heart beats are PVC’s (Pre Ventricular Contractions)
5) SBP>250 mmHg or DBP>115mmg

Question 21

21. During exercise testing, signs and symptoms of possible CVD may occur. List at least 4 of these other than HR or BP responses.

Answer 21

1) Claudication (cramping pain in the legs, due to peripheral atherosclerosis)
2) Dyspnea (shortness of breath)
3) Hyperpnea (laboured or rapid breathing)
4) Cyanosis (blueness) of the lips or nail beds (from poor circulation or inadequate oxygenation of the blood)
5) Clammy skin
5) Post exercise syncope (fainting), dizziness, nausea, vomiting, lightheadedness, headache

Question 22

22. If you are a kinesiologist who is administering the exercise test, what should you do and say to the client if you see these signs/symptoms?

Answer 22

You should terminate the exercise by saying “That’s enough for today” and avoid making comments that could alarm the patient/subject.

Question 23

23. Distinguish between “unipolar” leads and “bipolar” leads.

Answer 23

BIPOLAR:

• Bipolar leads utilize a single positive and a single negative electrode between which electrical potentials are measured.
• E.g. limb leads I, II, III

UNIPOLAR:

• Unipolar leads have a single positive recording electrode and utilize a combo of the other electrodes to serve as a composite negative electrode.
• E.g. aVF, aVR, aVL, V1, V2, V3, V4, V5, V6)

Question 24

24. List three desirable characteristics of an ECG electrode.

Answer 24

1) Must be designed so that it provides relatively low and stable impedance when placed on skin.
2) Is inexpensive to manufacture.
3) Conveniently manipulated by the practitioner

Question 25

25. Why is ECG bandwidth an important consideration?

Answer 25

• ECG bandwidth defines the range of frequencies that can be reproduced on ECG paper
• Important consideration because you want to filter certain frequencies that you know are associated with interference.
• Common to do a band pass where the ECG machine filters certain frequencies between say 0.5-40 Hz (it lets through all frequencies within this range). After filtering these frequencies the ECG machine will then amplify the ones (we’re interested in) let through

Question 26

26. Which phases of the cardiac cycle are represented by the Q-T interval and the T-Q segment? When comparing a pre-exercise ECG trace with an exercise ECG trace (obtained doing moderate exercise on a bicycle ergometer, heart rate = 155 BPM), how would you expect the R-T interval and the T-R segment to change? Give a physiological explanation.

Answer 26

1. Q-T interval represents the beginning of ventricular depolarization/atrial repolarization and the end of ventricular repolarization
2. The T-Q segment represents the interval btwn end of ventricular repolarization and start of ventricular depolarization of the next cycle; it also encompasses artrial depolarization
3. When comparing a pre-exercise ECG trace with a moderate exercise ECG trace:
   a) the R-T interval would shorten.
   b) the T-R interval would also shorten
   This is to accommodate the increased demand for O2 to muscles, the HR must increase to increase CO and so ventricles much depolarize and repolarize much faster.

Question 27

27. You should be able to recognize the following arrhythmias and give a physiological explanation of the cause of the arrhythmia and the shape of the resulting ECG waveform.
28. ST segment depression and elevation.
29. Premature ventricular contraction.
30. Ventricular tachycardia.
31. Ventricular fibrillation.
32. First, second, and third degree heart block.
33. Atrial fibrillation.

Answer 27

1. ST segment depression and elevation
   - Shown as 1mm or more below ECG isoelectric line, remaining horizontal or down slopping for duration of 80ms or longer from the J point (the junction btwn the end of QRS complex and the beginning of the T wave)
   - Caused by myocardial ischemia (insufficient O2 supply)
   - Magnitude of myocardial ischemia is generally proportional to amount of depression, number of leads used, and duration of ST segment depression in recovery

2) Premature ventricular contraction (PV)
- Indicates ischaemic atherosclerotic heart disease, often involving two or three major coronary vessels
- Ventricles demonstrate disorganized electrical activity. Caused by the ventricles not being stimulated by the normal passage of the wave of depolarization through the AV node. Rather portions of the ventricles become spontaneously depolarized
- Appears as abnormal, high amplitude, long duration QRS complex. PVC often lack P wave associated with atrial depolarization
- Certain medications, including common asthma medications, injury to the heart muscle from CAD, congenital heart disease, high BP can be causes

3) Ventricular tachycardia
- Seen as rapid heart rate (> 100 bpm), Broad QRS complexes (> 120 ms)
- Arises from improper electrical activity in the ventricles of the heart
- Signifies CAD, cardiomyopathy
- May degenerate to ventricular fibrillation if not corrected

4) Ventricular fibrillation
- Recognized as totally irregular appearance on ECG
- Ventricles do not contract in coordinated matter, thus CO falls dramatically.
- Commonly caused by a heart disorder such as inadequate blood flow to the heart due to CAD

5)
a) First-Degree Heart Block (Slowed block)
- Conduction through AV node slowed, increasing the time it takes to travel from atria to the ventricles
- PR interval is lengthened beyond 0.20s

b) Second Degree Heart Block
- Conduction block btwn atria and ventricles
- 1 or more (but not all) of atrial impulses fail to conduct to the ventricles due to impaired conduction
- On ECG, the pattern of QRS waves don’t follow each P wave as it normally would.

b) Third Degree Heart Block (Complete block)
- The nerve impulse generated in SA node in atrium does not propagate to ventricles
- Lack of any apparent relationship between P waves and QRS complexes

6) Atrial fibrillation
- Abnormal heart rhythm characterized by rapid and irregular beating of the atria
- High BP common risk factor

Question 28

28. Which of the following would you expect to produce a negative R-wave in a subject with a normal MEA of the heart - aVR, aVL, or aVF? Explain.

Answer 28

• aVR
• The aVR lead has its pos electrode on RA
• We can think of aVR having an imaginary negative electrode as the avg of the LA and LL
• Heart’s electrical activity (wave of depolarization) is downwards and to the left, thus it will travel away from the pos aVR electrode and cause a downward deflection on the ECG trace

Question 29

29. List at least four things (not including pathological conditions) which would produce a lower amplitude R-wave on an electrocardiogram.

Answer 29

1) Not using electrode paste.
2) Not cleaning the skin properly.
3) A higher amount of fat under subcutaneous tissue.
4) Gain setting too low
5) Type chest lead you use (further away from the heart means lower amplitude R wave)
6) Performing at rest in comparison to exercise