Interpreting ECG

Question 1

What does the p wave in an ECG represent?

Answer 1

Represents Atrial Depolarisation

Question 2

What is the relationship between ECG P-wave and cardiac anatomy and Physiology?

Answer 2

A normal P-wave indicates normale atrial depolarisation.
Depolarization of the atria begins near the SA node and progresses across the atria from right to left and downwards.
The first part of the P-wave represents depolarization of the right atrium; the second part represents depolarization of the left atrium.

Question 3

What does the QRS complex in an ECG represent?

Answer 3

Represents Ventricular Depolarization

Question 4

What does the T-wave in an ECG represent?

Answer 4

Represents Ventricular Repolarisation

Question 5

What is the relationship between ECG QRS complex and cardiac anatomy and Physiology?

Answer 5

A normal QRS represents normal depolarization of the ventricles.
The first part of the QRS complex, usually the Q wave represents depolarization of the interventricular septum; the rest of the QRS represents the simultaneous depolarization of the right and left ventricles

Question 6

What is the relationship between ECG T-wave and cardiac anatomy and Physiology?

Answer 6

A normal T-wave represents normal repolarization of the ventricles; beginning at the epicardial surface of the ventricles and progress inwardly through the ventricular walls to the endocardial surface

Question 7

What is the normal duration of a P-wave?

Answer 7

0.06 - 0.12 secs

Question 8

What does the PR interval in an ECG represent?

Answer 8

Represents atrioventricular conduction time

Normal PR interval represents the onset of atrial depolarization and the onset of ventricular depolarisation

Question 9

What is the normal duration of PR interval?

Answer 9

0.12 - 0.20 secs

Question 10

What is the relationship between ECG PR interval and cardiac anatomy and Physiology?

Answer 10

Indicates that the electrical impulse originated in the SA node has progressed normally through the electrical conduction system and through the AV node and bundle of His without delay

Question 11

What is the normal duration of QRS Complex?

Answer 11

0.04 - 0.12 secs

Question 12

What does an Abnormal PR interval indicate?

Answer 12

Longer than 0.20 secs - represents delayed progression of the electrical impulse through the AV node

Less than 0.12 secs - may represent that the electrical impulse originated closer to the AV node (may be an ectopic pacemaker or escape pacemaker)

Question 13

What does an Abnormal QRS Complex indicate?

Answer 13

Represents abnormal depolarization of the ventricles

May be due to:

• Interventricular Conduction Disturbances (BBB)
• Aberrant Ventricular Conduction
• Ventricular Ectopic or Escape Pacemaker

Question 14

What does the ST segment in an ECG represent?

Answer 14

Represents the end of ventricular depolarization and the beginning of ventricular repolarization

Question 15

What does an Abnormal ST Segment indicate?

Answer 15

If the ST segment appears depressed or elevated it indicates early T-wave repolarization

If Depressed - Significant =2mm in 2 continuous leads
If Elevated - Significant = 1mm

Question 16

What does a Normal ST segment look like?

Answer 16

Isoelectric in all three views of the heart:
Inferiorly
Anteriorly
Laterally

Question 17

What is the normal duration of QTc?

Answer 17

Less than 0.44 secs

Question 18

What is Bazett’s Formula?

Answer 18

QTc = QT/sqrt RR

Question 19

What does the QT interval in an ECG represent?

Answer 19

Represents the refractory period of the ventricles, during which they depolarize and repolarize

Question 20

Describe the Refractory Period?

Answer 20

The time between the onset of depolarization and the end or repolarization
Divided into Absolute Refractory and Relative Refractory

Question 21

Describe where the Absolute Refractory takes place and what it represents?

Answer 21

It is from the beginning of the QRS to the peak of the T-wave.

Cardiac cells cannot be stimulated to depolarize

Question 22

Describe where the Relative Refractory takes place and what it represents?

Answer 22

It is from the peak of the T-wave to the end of the T-wave.

Cardiac cells can be stimulated if the stimulus is strong enough

Question 23

What is the Cardiac Axis??

Answer 23

The cardiac axis is the average direction the depolarization wave spreads through the heart
The left ventricle has a greater influence than the right on the cardiac axis as it has more muscle mass
The QRS will be positive in a lead when the depolarization wave is moving towards that lead

Question 24

Describe the Normal Cardiac Axis?

Answer 24

This occurs when the average spread of depolarization moves from high in the right atrium to the apex of the ventricles (Imagine 11 o’clock to 5 o’clock)

Question 25

Which leads should be analyzed when determining the Cardiac Axis?

Answer 25

Lead I followed by aVF

Lead II may be necessary if one of the above are negative