ECG 1

Question 1

What does each small box on ECG paper represent in time?

Answer 1

Each small box represents 0.04 seconds.

Question 2

What does each large box on ECG paper represent in time?

Answer 2

Each large box represents 0.20 seconds (5 small boxes).

Question 3

What does each small box on ECG paper represent in voltage?

Answer 3

Each small box represents 0.1 millivolts (mV).

Question 4

What is the P wave?

Answer 4

The P wave represents atrial depolarization (contraction of atria).

Question 5

What is the QRS complex?

Answer 5

The QRS complex represents ventricular depolarization (contraction of ventricles).

Question 6

What is the T wave?

Answer 6

The T wave represents ventricular repolarization (relaxation of ventricles).

Question 7

What is the U wave?

Answer 7

The U wave is a small wave that may follow the T wave and is thought to represent repolarization of Purkinje fibers or papillary muscles.

Question 8

What is the PR interval?

Answer 8

The PR interval is the time from the beginning of the P wave to the beginning of the QRS complex, showing conduction from atria to ventricles.

Question 9

What is the ST segment?

Answer 9

The ST segment is the flat section between the end of the QRS complex and the start of the T wave; it should be isoelectric.

Question 10

What is the QT interval?

Answer 10

The QT interval extends from the start of the QRS complex to the end of the T wave and represents the total time for ventricular depolarization and repolarization.

Question 11

What is a ‘lead’ in ECG?

Answer 11

A lead is a specific angle or viewpoint from which the heart’s electrical activity is recorded, based on the voltage difference between two electrodes.

Question 12

How many leads are in a standard ECG?

Answer 12

There are 12 leads in a standard ECG: 6 limb leads and 6 chest (precordial) leads.

Question 13

What are the bipolar limb leads?

Answer 13

Leads I, II, and III are bipolar limb leads that record the voltage difference between two limbs.

Question 14

What does Lead I measure?

Answer 14

Lead I measures the voltage from the right arm to the left arm.

Question 15

What does Lead II measure?

Answer 15

Lead II measures the voltage from the right arm to the left leg.

Question 16

What does Lead III measure?

Answer 16

Lead III measures the voltage from the left arm to the left leg.

Question 17

What are the augmented limb leads?

Answer 17

aVR, aVL, and aVF are augmented leads that measure the voltage at one limb compared to a combination of the other two.

Question 18

What does aVR look at?

Answer 18

aVR looks at the heart from the right arm.

Question 19

What does aVL look at?

Answer 19

aVL looks at the heart from the left arm.

Question 20

What does aVF look at?

Answer 20

aVF looks at the heart from the left leg.

Question 21

What are the chest (precordial) leads?

Answer 21

The chest leads are V1 to V6, placed on the chest to give a horizontal view of the heart.

Question 22

What does V1 and V2 look at?

Answer 22

V1 and V2 look at the septal and right anterior part of the heart.

Question 23

What does V3 and V4 look at?

Answer 23

V3 and V4 look at the anterior wall of the left ventricle.

Question 24

What does V5 and V6 look at?

Answer 24

V5 and V6 look at the lateral wall of the left ventricle.

Question 25

What is the first step before interpreting an ECG?

Answer 25

Check the patient information and make sure the ECG belongs to the correct patient.

Question 26

What should you check about the ECG quality?

Answer 26

Check for artifacts, correct paper speed (25 mm/s), and standard calibration (1 mV = 10 mm).

Question 27

How do you calculate heart rate on a regular ECG?

Answer 27

Divide 300 by the number of large squares between two R waves.

Question 28

How do you calculate heart rate in an irregular rhythm?

Answer 28

Count the number of QRS complexes in 10 seconds and multiply by 6.

Question 29

What does it mean if the rhythm is regular?

Answer 29

The R-R intervals are consistent and P waves are present in a predictable pattern.

Question 30

What is the normal duration of a P wave?

Answer 30

Less than 0.12 seconds (3 small boxes).

Question 31

What is the normal PR interval duration?

Answer 31

Between 0.12 and 0.20 seconds (3 to 5 small boxes).

Question 32

What is the normal duration of the QRS complex?

Answer 32

Less than 0.12 seconds (3 small boxes).

Question 33

What is the ST segment?

Answer 33

The ST segment represents the period between ventricular depolarization and repolarization; it should be isoelectric (flat).

Question 34

What is the T wave?

Answer 34

The T wave represents ventricular repolarization and should be upright in most leads.

Question 35

What is the QT interval?

Answer 35

The QT interval represents the time from ventricular depolarization to repolarization and should be less than half of the R-R interval.

Question 36

How do you estimate the axis using ECG?

Answer 36

Use Leads I and aVF to determine if the axis is normal, left, or right shifted.

Question 37

What should be included in the final ECG impression?

Answer 37

Rhythm, rate, axis, intervals, signs of hypertrophy, and any ischemic changes.

Question 38

What is the cardiac axis?

Answer 38

It is the average direction of electrical activity during ventricular depolarization, shown by the QRS complex.

Question 39

What is the normal range of cardiac axis?

Answer 39

From –30° to +90°.

Question 40

What is left axis deviation (LAD)?

Answer 40

An axis between –30° and –90°, often due to left ventricular hypertrophy or conduction issues.

Question 41

What is right axis deviation (RAD)?

Answer 41

An axis between +90° and +180°, commonly caused by right ventricular strain or block.

Question 42

What is extreme axis deviation?

Answer 42

An axis between –90° and –180°, also called 'northwest axis', and is rare.

Question 43

How do you determine the axis using two leads?

Answer 43

Check if QRS is positive or negative in Lead I and aVF.

Question 44

What does it mean if QRS is positive in Lead I and aVF?

Answer 44

It indicates a normal axis.

Question 45

What does it mean if QRS is positive in Lead I but negative in aVF?

Answer 45

It suggests left axis deviation.

Question 46

What does it mean if QRS is negative in Lead I but positive in aVF?

Answer 46

It suggests right axis deviation.

Question 47

What does it mean if QRS is negative in both Lead I and aVF?

Answer 47

It indicates extreme axis deviation.

Question 48

What is the thumbs rule for cardiac axis?

Answer 48

Thumbs up in both Lead I and aVF = normal, mixed thumbs = axis deviation, both down = extreme axis.

Question 49

What are common causes of left axis deviation?

Answer 49

Left ventricular hypertrophy, inferior MI, left anterior fascicular block.

Question 50

What are common causes of right axis deviation?

Answer 50

Right ventricular hypertrophy, pulmonary embolism, right bundle branch block.