A First look at the ECG

Question 1

What are your standard limb leads ?

Answer 1

Question 2

<p>What does an approaching wave of depolarisation cause?</p>

Answer 2

<p>Upward going blip</p>

Question 3

<p>Which events are better transmitted, fast or slow?</p>

Answer 3

<p>Fast</p>

Question 4

<p>What is the PR interval and how long does it usually last?</p>

Answer 4

<p>Time from atrial depolarisation to ventricular depolarisation -mainly due to transmission through the AV node (normally about 0.1-0.2 sec)</p>

<p></p>

<p>Should really be called P - Q interval</p>

Question 5

<p>What is the QRS interval?</p>

Answer 5

<p>Time for the whole of the ventricle to depolarise</p>

<p> (normally about 0.08 sec)</p>

Question 6

<p>What is the QT interval?</p>

Answer 6

<p>Time spent while ventricles are depolarised (varies with heart rate, but normally about 0.42 sec at 60 bpm)</p>

Question 7

<p>Why can't you see atrial repolarisation?</p>

Answer 7

<p>Because atrial repolarisation coincides with ventricular depolaristion. Ventricular depolarisation involves much more tissue depolarising much faster so it swamps any signal from atrial repolarisation.</p>

Question 8

<p>How do you explain the three stages of the QRS complex?</p>

Answer 8

<p>Different parts of the ventricle depolarise at different times and also in different directions</p>

<ol> <li> <p>The interventricular septum depolarises from left to right</p> </li> <li> <p>The bulk of the ventricle depolarises from the endocardial to</p> <p> the epicardial surface – travels towards the electrode on the left leg – hence the upwards spike</p> </li> <li> <p>The upper part of the interventricular septum depolarises</p> </li></ol>

Question 9

<p>Why is the T - wave positive?</p>

Answer 9

<p>Because the action potential is longer in endocardial cells than in epicardial cells, so the wave of repolarisation runs in the opposite direction to the wave of depolarisation. ie a wave of repolarisation moving away from the recording electrode produces another positive-going blip</p>

Question 10

<p>Why is the R-wave bigger in SLL II than in SLL I or SLL II?</p>

Answer 10

<p>Because the main vector of depolarisation is <u>in line with the axis of recording</u> from the left leg with respect to the right arm.</p>

Question 11

What are the augmented limb leads?

Answer 11

Question 12

<p>What extra information do the augmented limb leads give you?</p>

Answer 12

<p>A. By recording from one limb lead with respect to the other two combined, it gives you 3 other perspective on events in the heart</p>

<p>ie recordings from SLLs I, II, III and aVR, aVL, aVF give you 6 different</p>

<p> views of events occurring in the frontal (or vertical) plane</p>

Question 13

Can you correctly label the vectors to the correct limb leads?

Answer 13

Question 14

<p>Should AVR be positive or negative?</p>

Answer 14

<p>Negative, travels away from the heart</p>

Question 15

Which wave is:

1. aVL
2. aVF
3. aVR

Answer 15

Question 16

<p>What extra information do the precordial (chest) leads give you?</p>

Answer 16

<div>A.These are arranged in front of the heart and therefore look at the same events, but in the horizontal (or transverse) plane</div>

<div>●</div>

<p> Because the main vector of depolarisation is as shown by the arrow, it will produce a negative going blip when recorded from V1, a positive going blip from V6, and flip over somewhere around V3 or V4. “Progression”</p>

Question 17

Look

Answer 17

Question 18

<p>On which plane is the spread of depolarisation measured when using:</p>

<ol> <li>Limb leads</li> <li>Precordial leads</li></ol>

Answer 18

<ol> <li>Frontal</li> <li>Transverse</li></ol>

Question 19

<p>What does the rhythm strip tell you?</p>

Answer 19

<p>Paper should run at 25mm/sec</p>

<p>Calibrating pulse is 0.2 sec = 1 large square (5mm) (5 arge squares per second)</p>

<p>Then you can determine the heart rate:</p>

<p>Measure the R-R interval and work out how many occur in 60 sec, or better ..</p>

<p>Count the R waves in 30 large squares (= 6 sec) and multiply by 10</p>

<p> 60-100 beats per min = normal</p>

<p> Below 60 beats per minute = bradycardia</p>

<p> Above 100 beats per minute = tachycardia</p>

<p></p>

Question 20

<p>What does STEMI or NSTEMI stand for?</p>

Answer 20

<p>ST elevated myocardial infarction ornon-ST elevated myocardial infarction.</p>

<p></p>

<p>ST should be flat because the cells are in their refractory state – st elevation is an indication of how severe the heart attack is. More dead tissue means more elevation. Don’t know why it is elevated though – don’t need to know.</p>