ECG

Question 1

-understanding the ECG paper

• Before interpreting ECG rhythms it is important to understand the complexity of the ECG paper you read it from.

Question 2

Conduction/interval times

SA node rate = 60-100 per minute
AV delay (normal) = 0.09 seconds
P width = 0.08-0.11 seconds.
PR interval = 0.12-0.20 seconds.
QRS width = 0.08-0.12 seconds
ST segment width = <0.12 seconds
Q-T interval = o.35-0.43 seconds

Question 3

NSR features

• Regular rhythm at 94bpm
• Normal p wave morphology
• Normal QRS complex (<100ms wide)
• Each p wave is followed by a QRS complex
• The PR interval is consistent.

Question 4

ECG abnormalities and arrhythmias

• J-point
• in order to identify these abnormalities you need to be able to identify the J-point.
• The J-point is the function between the termination of the QRS complex and the beginning of the ST segment.

The J wave is a much less common long slow deflection of uncertain origin originally described in relation to hypothermia.

Question 5

ECG abnormalities and arrhythmias

S-T Segment

• The S-T segment is a flat isoelectric section of the ECG between the end of the S wave (The J point) and the beginning of the T wave.
• The S-T segment represents the interval between ventricular depolarization and repolarization.

The most important cause of S-T segment abnormality (elevation and depression) is myocardial ischemia or infarction.

How to locate this segment?

1. Identify the isoelectric segment (TP segment)
2. Compare the ST segment
3. Locate the J-point
   S-T Segment analysis
   - ST deviation of 1mm in limb leads is clinically significant
   - ST deviation of 2mm in chest leads is clinically significant
   - 2 adjacent leads.

Question 6

ECG CHANGES IN A MI

• Process the leads to death of a MI

1. Ischemia
2. injury
3. Infarct / necrosis (death)

morphological changes
- QRS complex
- ST segment
- T wave

Question 7

Diagnosing a MI on a EGC

• Recognising ST elevation consistent with an MI

is there any
- ST elevation of 1mm or more in two limb leads looking at the same area of the heart. For example I and AVL or II, III and AVF.

or

• ST elevation of 2mm or more in at least two adjacent leads. for example V2 and V3,

THEN CHECK
- Are there any reciprocal changes present?

These are diagnostics of a MI

Question 8

Reciprocal changes are created by leads that are opposite each other but within the sam plane, they see the electrically opposite view of the ST segment specifically.

Question 9

STEMI VS NON-STEMI

STEMI: Infarction is full thickness and therefore leads to ST elevation +/- T Wave inversion and eventually Q wave that represents infarction (depolarisation and repolarisation is affected).

Question 10

STEMI VS NON STEMI

NON-STEMI: Infarction is not full thickness and therefore leads to ST depression and T wave inversion (repolarisation is affected non depolarisation).