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ECG > Week 2 > Flashcards

Week 2 Flashcards

1
Q

P wave characteristics

A

Location: precedes QRS complex
Amplitude: 2-3 mV
Duration: 1.5 - 3 boxes (0.6-0.12 seconds)
Configuration: upright and rounded - except aVR

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2
Q

PR interval characteristics

A

Location: beginning P wave to beginning of QRS complex
Amplitude: isoelectric
Duration: 3 - 5 boxes (0.12 - 0.2 seconds)

Represents: time when atria are contracting

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3
Q

What is the function of the AV node?

A

It delays conduction through by 0.04 seconds to allow optimal ventricular filling. It is also acts as a safety mechanisms (prevents rapid atrial impulses from spreading to the ventricles)

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4
Q

What is associated with shortened PR intervals?

A

Pre-excitation syndromes (WPW) and junctional rhythms

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5
Q

What is associated with prolonged PR intervals?

A

Bundle branch block or impaired conduction from atria to ventricles, e.g. digoxin toxicity

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6
Q

Which direction does electrical activity in the septum flow?

A

Between bundle branches from left to right

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7
Q

What does the Q wave represent?

A

Septal depolarisation/repolarisation of the atria

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8
Q

What direction is septal depolarisation

A

Depends whether the lead is looking at the heart from the left or right (left = downward, right = upward)

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9
Q

What is the first downward deflection called?

A

Q wave

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10
Q

What is the first upward deflection called?

A

R wave

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11
Q

Downward deflection after R wave?

A

S wave

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12
Q

QRS deflection depends on what?

A

Whether the R or S wave is bigger

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13
Q

What dominates the deflection of the QRS complex?

A

The left ventricle voltage as it contains more muscle mass

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14
Q

How does the QRS complex change across the chest leads?

A

Transition from predominately negative to positive wave

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15
Q

What do deep/wide Q wave represent?

A

Previous MI

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16
Q

What is the characteristics of a pathological Q wave?

A

(1) More than 1/4 height of R-wave (2) duration longer than 0.04 seconds

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17
Q

What is a Q-wave MI called and what does it signify?

A

Transmural myocardial infarction - damage of all layers of the heart.

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18
Q

Why does infarcted tissue result in a Q wave?

A

The lead ‘looks’ through the infarcted tissue as it is no longer conductive. Since electrical activity moves from the inside to the outside of the heart, it is seen as a downward deflection on the ECG.

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19
Q

What is a subendocardial MI?

A

MI when not all layers of the heart are damaged and pathological Q waves are not evident

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20
Q

Characteristics of a normal QRS?

A
  1. Location: follows PR interval
  2. Amplitude: 5 to 30 mm high (1 large to 6 large boxes)
  3. Duration: 0.06 - 0.12 seconds (1.2 - 2.5 square)
21
Q

What does the ST segment represent?

A

The end of ventricular depolarisation and the beginning of ventricular repolarisation

22
Q

What does the J-point mark?

A

The end of the QRS and beginning of ST segment

23
Q

During the ST segment, is the intracellular membrane potential positive or negative?

A

Positive

24
Q

ST segment depression can be seen when?

A

During ischemia and angina (which is a symptom of CVD).

25
Q

Characteristics of normal ST segment

A

Deflection: isoelectric - may vary from 0.5 (DEPRESSION) to 1.0mm (ELEVATION) in some precordial leads

26
Q

T wave characteristics

A

Location: following ST segment
Amplitude: 0.5 in leads I, II and III and up to 10mm in precordial leads
Configuration: typically rounded and smooth
Deflection: usually upright in leads I, II and V3 to V6

27
Q

Tall and peaked T waves may indicate what?

A

myocardial injury, hyperkalemia.

28
Q

Notched or pointed T waves may indicate what?

A

Pericarditis

29
Q

What can hyperkalaemia lead to?

A

Ventricular fibrillation

30
Q

How do R and T waves of opposite polarity occur?

A

Results of slowing of spread of the wave of excitation through the myocardium

31
Q

What is the QT interval?

A

The entire duration of the depolarisation-repolarisation cycle through the ventricles

32
Q

What influences the QT interval?

A

heart rate dependent - increased HR shortens the QT interval

33
Q

Characteristics of normal QT?

A

Location: extends from the beginning of the QRS complex to the end of the T wave
Duration: 0.36 - 0.44 seconds (9-11 small boxes)
Shouldn’t be greater than half the distance between consecutive R waves

34
Q

QT interval duration is influenced by what?

A

Age, sex and heart rate

35
Q

What dose a prolonged QT interval indicate?

A

A longer relative refractory period

36
Q

A long QT interval increases the risk of what ventricular tachycardia?

A

Torsades de points - can deteriorate in v.fib

37
Q

What is the U wave?

A

Repolarisation of the interventricular septum or the purkinji fibres

38
Q

What leads is the U wave most clearly seen?

A

V2 - V4

39
Q

Reasons for prominent U wave?

A

Hypercalcemia, hypokalemia, digoxin toxicity

40
Q

What is a lead?

A

View of the heart’s electrical activity between a negative and positive pole

41
Q

The imaginary line between a negative and positive pole is what?

A

Lead axis

42
Q

What is a plane?

A

Cross-sectional perspective of the heart’s electrical activity

43
Q

What type of perspective does the frontal plane of the heart give?

A

Anterior-posterior view

44
Q

What type of persecptive does the horiztonal plane of the heart give?

A

Superior-inferior view

45
Q

How many views does a 12-lead ECG give of the heart

A

12 views using 10 electrodes

46
Q

What leads give information in the frontal plane?

A

the 6 limb leads - I, II, III, aVL, aVR, aVF

47
Q

What are the bipolar leads?

A

I, II, III - have both a positive and negative electrode

48
Q

Left axis deviation leads to an abnormally large R wave in which lead?

A

Lead I

ECG (8 decks)

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