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Flashcards in Week 2 Deck (48)
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1

P wave characteristics

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

2

PR interval characteristics

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

3

What is the function of the AV node?

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)

4

What is associated with shortened PR intervals?

Pre-excitation syndromes (WPW) and junctional rhythms

5

What is associated with prolonged PR intervals?

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

6

Which direction does electrical activity in the septum flow?

Between bundle branches from left to right

7

What does the Q wave represent?

Septal depolarisation/repolarisation of the atria

8

What direction is septal depolarisation

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

9

What is the first downward deflection called?

Q wave

10

What is the first upward deflection called?

R wave

11

Downward deflection after R wave?

S wave

12

QRS deflection depends on what?

Whether the R or S wave is bigger

13

What dominates the deflection of the QRS complex?

The left ventricle voltage as it contains more muscle mass

14

How does the QRS complex change across the chest leads?

Transition from predominately negative to positive wave

15

What do deep/wide Q wave represent?

Previous MI

16

What is the characteristics of a pathological Q wave?

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

17

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

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

18

Why does infarcted tissue result in a Q wave?

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.

19

What is a subendocardial MI?

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

20

Characteristics of a normal QRS?

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

What does the ST segment represent?

The end of ventricular depolarisation and the beginning of ventricular repolarisation

22

What does the J-point mark?

The end of the QRS and beginning of ST segment

23

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

Positive

24

ST segment depression can be seen when?

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

25

Characteristics of normal ST segment

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

26

T wave characteristics

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

Tall and peaked T waves may indicate what?

myocardial injury, hyperkalemia.

28

Notched or pointed T waves may indicate what?

Pericarditis

29

What can hyperkalaemia lead to?

Ventricular fibrillation

30

How do R and T waves of opposite polarity occur?

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