Ecg

Question 1

ST segment /T wave

Answer 1

St segment is the isoelectric (flAt) segment between the end of QRS and start of T wave.

Ischaemia manifests green

• Depression = ischaemia
• Elevation= myocardial infarction

Some elevation normal
Repolarisation of ventricles

Question 2

Diff heart rates

Answer 2

Normal: 60-100 bpm
Tachycardia: > 100 bpm
Bradycardia: < 60 bpm

Question 3

How to calculate HR on regular heart rhythm

Answer 3

If a patient has a regular heart rhythm their heart rate can be calculated using the following method:

Count the number of large squares present within one R-R interval.
Divide 300 by this number to calculate heart rate.

4 large squares in an R-R interval
300/4 = 75 beats per minute

Question 4

How to calculate heart rate on irregular heart rhythm?

Answer 4

If a patient’s heart rhythm is irregular the first method of heart rate calculation doesn’t work (as the R-R interval differs significantly throughout the ECG). As a result, you need to apply a different method:

Count the number of complexes on the rhythm strip (each rhythm strip is typically 10 seconds long).
Multiply the number of complexes by 6 (giving you the average number of complexes in 1 minute).
Example
10 complexes on a rhythm strip
10 x 6 = 60 beats per minute

Question 5

Irregular heart rhythms

Answer 5

A patient’s heart rhythm can be regular or irregular.

Irregular rhythms can be either:

Regularly irregular (i.e. a recurrent pattern of irregularity)
Irregularly irregular (i.e. completely disorganised)
Mark out several consecutive R-R intervals on a piece of paper, then move them along the rhythm strip to check if the subsequent intervals are similar.

Question 6

Cardiac axis

Answer 6

Cardiac axis describes the overall direction of electrical spread within the heart.

In a healthy individual, the axis should spread from 11 o’clock to 5 o’clock.

To determine the cardiac axis you need to look at leads I, II and III.

Question 7

Normal cardiac axis

Answer 7

Typical ECG findings for normal cardiac axis:

Lead II has the most positive deflection compared to leads I and III

Question 8

Right axis deviation

Answer 8

Typical ECG findings for right axis deviation:

Lead III has the most positive deflection and lead I should be negative.
Right axis deviation is associated with right ventricular hypertrophy.

Question 9

Left axis deviation

Answer 9

Typical ECG findings for left axis deviation:

Lead I has the most positive deflection.
Leads II and III are negative.
Left axis deviation is associated with heart conduction abnormalities.

Question 10

P-waves

Answer 10

The next step is to look at the P waves and answer the following questions:

Are P waves present?
If so, is each P wave followed by a QRS complex?
Do the P waves look normal? – check duration, direction and shape
If P waves are absent, is there any atrial activity?
Sawtooth baseline → flutter waves
Chaotic baseline → fibrillation waves
Flat line → no atrial activity at all
Hint
If P waves are absent and there is an irregular rhythm it may suggest a diagnosis of atrial fibrillation.

Question 11

normal PR interval

Answer 11

The PR interval should be between 120-200 ms (3-5 small squares).

Question 12

Prolonged PR interval (>0.2 seconds)

Answer 12

A prolonged PR interval suggests the presence of atrioventricular delay (AV block).

Question 13

First-degree heart block (AV block)

Answer 13

First-degree heart block involves a fixed prolonged PR interval (>200 ms).

Question 14

Second-degree heart block (type 1) Mobitz type 1 AV block or Wenckebach phenomenon

Answer 14

Typical ECG findings in Mobitz type 1 AV block include progressive prolongation of the PR interval until eventually the atrial impulse is not conducted and the QRS complex is dropped.

AV nodal conduction resumes with the next beat and the sequence of progressive PR interval prolongation and the eventual dropping of a QRS complex repeats itself.

Question 15

Second-degree heart block

Second-degree AV block (type 2) is also known as Mobitz type 2 AV block.

Answer 15

Typical ECG findings in Mobitz type 2 AV block include a consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction.

The intermittent dropping of the QRS complexes typically follows a repeating cycle of every 3rd (3:1 block) or 4th (4:1 block) P wave.

Question 16

Third-degree heart block (complete heart block)

Answer 16

Third-degree (complete) AV block occurs when there is no electrical communication between the atria and ventricles due to a complete failure of conduction.

Typical ECG findings include the presence of P waves and QRS complexes that have no association with each other, due to the atria and ventricles functioning independently.

Cardiac function is maintained by a junctional or ventricular pacemaker.

Narrow-complex escape rhythms (QRS complexes of <0.12 seconds duration) originate above the bifurcation of the bundle of His.

Broad-complex escape rhythms (QRS complexes >0.12 seconds duration) originate from below the bifurcation of the bundle of His.

Question 17

Anatomical location of the various types of AV block

Answer 17

First-degree AV block:

Occurs between the SA node and the AV node (i.e. within the atrium).
Second-degree AV block:

Mobitz I AV block (Wenckebach) occurs IN the AV node (this is the only piece of conductive tissue in the heart which exhibits the ability to conduct at different speeds).
Mobitz II AV block occurs AFTER the AV node in the bundle of His or Purkinje fibres.
Third-degree AV block:

Occurs at or after the AV node resulting in a complete blockade of distal conduction.

Question 18

Describe the electrical activity of the heart

Answer 18

1. Begins at SA node. SA node is the natural pacemaker of the heart, this is the beginning of conduction.
2. AV node: found between border of right atrium and ventricle. This is known as the gate keeper of heart, decides what impulse gets through.
3. Then we have bundle of His, a single fibre between the ventricles. T
4. Then we have left and right bundle branches, which extend within apex of heart, purkinje fibres.

Question 19

QRS complex

Answer 19

Ventricle depolarisation.

Also Represents atrial repolarisation. Ventricles are stronger than atria so tend to mask atrial repolarisation.