ECG Interpretation Quiz

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Questions and Answers

What is the normal QTc interval for a male?

0.40 – 0.48s

0.36 – 0.40s

0.36 – 0.44s (correct)

0.44 – 0.50s

What is the ST segment?

A part of the QRS complex

A part of the P wave

A part of the T wave

An isoelectric line between the QRS complex and T wave (correct)

What is a cause of ST segment depression?

Myocardial ischaemia (angina pectoris) (correct)

Hypokalemia (correct)

Early repolarization

Acute myocardial infarction

What is the first step in ECG interpretation?

Standardization Signup and view all the answers

What is the normal heart rate according to the ECG parameters?

60-100 beats/min Signup and view all the answers

What is the unit of standardization in ECG?

10mm/mV Signup and view all the answers

What is the formula to estimate the heart rate, where x is the number of large squares within the RR interval?

HR = 300/x Signup and view all the answers

What is the normal range of heart rate in beats per minute?

60-100 Signup and view all the answers

What is the formula to estimate the QTc, where QTm is the measured QT and RRint is the RR interval?

QTc = QTm /RRint ½ Signup and view all the answers

What is the period from the onset of ventricular depolarization to the end of ventricular repolarization?

QT interval Signup and view all the answers

How is the QRS axis estimated?

Using the aVL and II leads Signup and view all the answers

What is the purpose of Bazzet's Formula?

To adjust the QT interval for heart rate Signup and view all the answers

What is the primary function of electrocardiography?

To record and analyze the electrical activities of the heart Signup and view all the answers

What is the time measurement represented by 1mm on an ECG graph?

0.04s Signup and view all the answers

What is the direction of the normal axis in the cardiac ventricles?

Downward and to the left Signup and view all the answers

What is the voltage measurement represented by 1mm on an ECG graph?

0.1mV Signup and view all the answers

What is the range of angle for a normal axis?

0 to +90 degrees Signup and view all the answers

What is the interval from the onset of atrial depolarization to the beginning of ventricular depolarization?

PR interval Signup and view all the answers

Which of the following is a cause of left axis deviation?

Left anterior fascicular block Signup and view all the answers

What is the wave that represents ventricular repolarization?

T wave Signup and view all the answers

How many electrodes are required to record a standard 12-lead ECG?

10 Signup and view all the answers

What is the step to estimate the QRS axis to the nearest 30 degrees?

Inspect the limb leads Signup and view all the answers

What is the term for a QRS complex with an equal positive and negative deflection?

Equiphasic QRS complex Signup and view all the answers

Which lead is perpendicular to aVF?

Lead I Signup and view all the answers

What is the classification of lead V4 based on heart regions?

Anterior lead Signup and view all the answers

Which of the following is a cause of extreme axis deviation?

Artificial cardiac pacing Signup and view all the answers

What is the angle of orientation of lead aVR?

+300, -1500 Signup and view all the answers

What is the first step in determining the QRS axis?

Inspect leads I and aVF Signup and view all the answers

What is the range of angle for a right axis deviation?

+90 to 180 degrees Signup and view all the answers

What is the purpose of the QRS axis?

To determine the average direction of ventricular depolarization Signup and view all the answers

Which of the following is a cause of right axis deviation?

Left posterior fascicular block Signup and view all the answers

What is the purpose of identifying lead Y in Step II?

To get the angles of orientation of Y Signup and view all the answers

Study Notes

Electrocardiography

Electrocardiography is the study of the recording and analysis of the electrical activities of the heart.
The heart generates electrical impulses that are propagated as waves of depolarization and repolarization.
These electrical impulses are recordable on a graph for visual analysis and interpretation.

ECG Paper

The graph paper consists of horizontal and vertical lines at 1mm apart, forming small (1mm) and large (5mm) squares.
Time measurement is done horizontally, with 1mm representing 0.04s (40ms).
Voltage measurement is done vertically, with 1mm representing 0.1mV.

Standardization

Paper speed: 25mm/s.
Calibration signal or amplitude indicator: 10mm/mV.

ECG Denotations

P wave: atrial depolarization.
QRS complex: ventricular depolarization.
Q wave: first negative deflection in ventricular depolarization.
R wave: first positive deflection in ventricular depolarization.
S wave: second negative deflection in ventricular depolarization or the first negative deflection after R wave.
T wave: ventricular repolarization.

Intervals in ECG

PR interval: period from the onset of atrial depolarization to the beginning of ventricular depolarization.
QT interval: period from the onset of ventricular depolarization to the end of ventricular repolarization.
RR interval: period from the peak of R wave to the next.

Other Denotations

PR segment: isoelectric line from the end of atrial depolarization to the beginning of ventricular depolarization.
ST segment: isoelectric line from the end of ventricular depolarization to the beginning of ventricular repolarization.
J-Junction: the junction between the end of ventricular depolarization and the beginning of ST segment.
U wave: any wave between T and P waves.

U Wave

An inconstant wave.
Exact mechanism of its genesis is still controversial.
Suggested mechanisms include:
- Repolarization of papillary muscle and neighboring structures (old concept).
- Repolarization of mid-myocardial cells (M-cells).
- Afterpotentials.

Standard 12-Lead ECG

Recorded by the aid of 10 electrodes arranged on specific locations on the body surface.
One electrode is attached to each limb to produce 6 limb leads.
6 electrodes are attached to the chest to produce 6 chest or precordial leads.

Classifications of Standard 12 Leads

Types of leads: bipolar limb leads, augmented limb leads, and chest or precordial leads.
Bipolar limb leads: I, II, III.
Augmented limb leads: aVF, aVL, aVR.
Chest or precordial leads: V1, V2, V3, V4, V5, V6.

Chest Electrode Placement

V1: 4th intercostal space, right sternal edge.
V2: 4th intercostal space, left sternal edge.
V3: midway between V2 and V4.
V4: 5th intercostal space, left midclavicular line.
V5: 5th intercostal space, left anterior axillary line.
V6: 5th intercostal space, left mid-axillary line.

Classification Based on Planes of Location

Frontal plane leads: I, II, III, aVL, aVF, aVR.
Horizontal/transverse plane leads: V1, V2, V3, V4, V5, V6.

Lead Classification Based on Heart Regions

Left lateral leads: I, aVL, V5, V6.
Inferior leads: II, III, aVF.
Septal leads: V3, V4.
Anterior leads: V1, V2, V3, V4, V5, V6.
Right ventricular cavity leads: aVR, V1, V2.

QRS Axis

QRS axis is the average direction of the ventricular depolarization (QRS) current.
Normal axis points mostly downward and to the left because the more muscular left ventricle generates a stronger depolarizing current than the less muscular right ventricle.

Classification of QRS Axis

Normal axis: 0 to +90 degrees.
Left axis deviation: 0 to -90 degrees.
Right axis deviation: +90 to +180 degrees.
Extreme axis: -90 to 180 degrees.

Causes of Axis Deviation

Left axis deviation: left anterior fascicular block, left ventricular hypertrophy, inferior myocardial infarction, Wolff-Parkinson-White syndrome, artificial cardiac pacing, mechanical shift (e.g. pregnancy), and congenital heart disease (e.g. atrial septal defect).
Right axis deviation: normal variation in children and thin adults, left posterior fascicular block, left lateral wall infarction, right ventricular hypertrophy, dextrocardia, pulmonary embolism, and congenital heart disease (e.g. atrial septal defect).
Extreme axis deviation: emphysema, artificial cardiac pacing, and lead misplacement.

QRS Axis Estimation

Step I: Locate the class of the QRS axis by inspecting leads I and aVF.
Step II: Estimate the QRS axis to the nearest 30 degrees by inspecting the limb leads, finding the equiphasic QRS complex, and identifying the angles of orientation of the lead perpendicular to it.

Estimation of Heart Rate

Heart rate can be estimated using the following formulae:
1. HR = 300/x, where x is the number of large (5mm) squares within the RR interval.
2. HR = 1500/y, where y is the number of small (1mm) squares within the RR interval.
3. HR = 60/RR interval.
Normal heart rate: 60-100 beats per minute.

Estimation of QTc

QT interval: period from the onset of ventricular depolarization to the end of ventricular repolarization.
QT interval varies with heart rate.
QTc can be calculated using Bazzet's formula: QTc = QTm / RRint ½.
Normal QTc: 0.36-0.44s for males.

ST Segment

ST segment: isoelectric line between the end of ventricular depolarization and the beginning of ventricular repolarization.
ST segment begins at the J junction and ends at the K junction.
ST segment can be elevated or depressed in some cardiac disorders.

ST Segment Changes

ST segment elevation: early repolarization, acute myocardial infarction, and acute pericarditis.
ST segment depression: myocardial ischaemia (angina pectoris) and hypokalaemia.

14 Steps in ECG Interpretation

1. Standardization.
1. Rhythm.
1. Rate.
1. P wave.
1. PR interval.
1. Q wave.
1. QRS complex.
1. J-junction.
1. ST segment.
1. T wave.
1. QT interval.
1. Miscellaneous.
1. Summary.
1. Conclusion.

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Description

Test your knowledge of ECG interpretation with these questions on QTc interval, ST segment, and heart rate. Learn about ECG parameters and analysis.