Electrocardiograph Basics

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Questions and Answers

Which of the following is a characteristic of a broad and bifid P wave?

Pulmonary hypertension

Left atrial hypertrophy (correct)

Tricuspid valve stenosis

Right atrial hypertrophy

What is the maximum duration of a normal QRS complex in milliseconds?

120 (correct)

100

140

What is the relationship between the ST segment and the T wave?

The ST segment follows the T wave.

The ST segment precedes the T wave. (correct)

The ST segment and T wave are independent of each other.

The ST segment and T wave form a single complex.

Which of the following conditions would lead to a peaked P wave?

Tricuspid valve stenosis (D) Signup and view all the answers

In a left ventricular lead, what is the maximum height of the R wave in millimeters?

25 (C) Signup and view all the answers

What primarily drives clinical diagnosis, according to the text?

Patient's medical history (D) Signup and view all the answers

Which ECG component directly reflects the contraction of the atria?

P wave (B) Signup and view all the answers

What does the 'T' wave on an ECG signify?

Ventricular repolarization (D) Signup and view all the answers

Within the QRS complex, if the initial deflection is downwards, how is it labeled?

Q wave (A) Signup and view all the answers

If an upward deflection occurs in the QRS complex, regardless of preceding waves, how is it identified?

R wave (B) Signup and view all the answers

On the ECG paper, how much time does one large 5 mm square represent?

0.2 seconds (C) Signup and view all the answers

What is the standard speed at which ECG machines record electrical activity?

25 mm/s (D) Signup and view all the answers

Following a standard 'T' wave, what does the appearance of a 'U' wave potentially signify?

Papillary muscle repolarization (C) Signup and view all the answers

What does a normal PR interval indicate about the conduction through the heart?

It represents delay primarily within the AV node. (C) Signup and view all the answers

What is the significance of the duration of the QRS complex?

It indicates how long excitation takes to spread through the ventricles. (B) Signup and view all the answers

How can heart rate be quickly calculated from an ECG tracing?

By counting the number of small squares between R waves. (B) Signup and view all the answers

Which characteristic is described as the 'PQ interval' in common usage?

The time from the beginning of the P wave to the QRS complex. (D) Signup and view all the answers

What does a very short PR interval suggest about atrial depolarization?

The atria depolarize from the AV node. (D) Signup and view all the answers

What is the normal range for a QRS complex duration?

90–150 ms. (D) Signup and view all the answers

Which statement is true regarding the relationship between the QRS complex and ventricular contraction?

Contraction of the ventricles follows the QRS complex. (D) Signup and view all the answers

What is the primary function of the electrodes used in an ECG?

They detect electrical signals from the heart's surface. (C) Signup and view all the answers

What causes the deflection in lead I to become negative?

Depolarization spreading away from lead I (A) Signup and view all the answers

When is left axis deviation considered significant?

When the QRS complex is predominantly negative in lead II (B) Signup and view all the answers

What angle corresponds to lead II in measuring the cardiac axis?

+60° (D) Signup and view all the answers

What is the normal range for the cardiac axis in degrees?

-30° to +90° (D) Signup and view all the answers

What does a greater S wave than R wave in lead II indicate?

Left axis deviation (C) Signup and view all the answers

Which condition is associated with right axis deviation?

Excess strain on the right side of the heart (B) Signup and view all the answers

What indicates right axis deviation in lead I?

When the S wave is greater than the R wave (D) Signup and view all the answers

What should be investigated if axis deviation is present?

Underlying conduction defects (C) Signup and view all the answers

What does a predominantly upward QRS complex in a lead indicate about the depolarization wave?

The wave is moving towards the lead. (D) Signup and view all the answers

How is the cardiac axis derived from the QRS complex?

Using leads I, II, and III. (A) Signup and view all the answers

What is the significance of the direction of the QRS complex in leads VR and II?

They reflect the normal propagation of the depolarization wave. (D) Signup and view all the answers

What does it imply if the average depolarization wave is swinging towards the right?

The right ventricle is hypertrophied. (D) Signup and view all the answers

If the R wave is greater than the S wave in the QRS complex, what does that indicate?

The depolarization is moving towards the lead. (B) Signup and view all the answers

In which situation would the QRS complex appear predominantly downward?

When the depolarization wave is moving away from the lead. (A) Signup and view all the answers

Which physical position corresponds to the normal cardiac axis during depolarization?

11 o’clock to 5 o’clock. (C) Signup and view all the answers

If R and S waves are of equal size in an ECG lead, what does this suggest about the direction of the depolarization wave?

The wave is moving at right angles to the lead. (D) Signup and view all the answers

In a right ventricular lead, the initial upward deflection (R wave) is caused by the depolarization of which structure?

The interventricular septum (A) Signup and view all the answers

Which chest lead primarily focuses on the septum?

V3 and V4 (B) Signup and view all the answers

The QRS complex in chest leads progresses from predominantly downward in V1 to predominantly upward in V6 due to:

The depolarization wave spreading from right to left across the septum (B) Signup and view all the answers

What does the 'transition point' in the QRS complex signify?

The location of the interventricular septum (B) Signup and view all the answers

In a left ventricular lead, the downward deflection (S wave) is mainly attributed to what?

Depolarization of the right ventricle (B) Signup and view all the answers

A prolonged PR interval, exceeding 220ms, indicates:

A delay in conduction from the SA node to the ventricles (A) Signup and view all the answers

What is NOT a characteristic of first-degree heart block?

There is a complete blockage of the conduction pathway (A) Signup and view all the answers

The spread of depolarization from the SA node to the ventricular muscle is represented by which ECG interval?

PR interval (D) Signup and view all the answers

Study Notes

Electrocardiograph (ECG)

ECG stands for electrocardiogram or, in some countries, EKG.
Clinical diagnosis relies primarily on patient history and, to a lesser extent, physical examination.
ECG provides supporting evidence for diagnosis, and is crucial in patient management.
ECG is essential for diagnosing and managing abnormal cardiac rhythms.
ECG aids in identifying the cause of chest pain and guiding early intervention in myocardial infarction.

ECG Parts

Atrial muscle mass is smaller than ventricular mass.
The electrical change accompanying atrial contraction is represented by the P wave.
Ventricular depolarization (contraction) is associated with the large QRS complex.
The T wave represents ventricular repolarization (return to resting electrical state).
An extra wave, called a U wave, might appear at the end of the T wave, though its origin is uncertain.
P, Q, R, S, and T are arbitrarily labeled ECG waves (deflections).
Q, R, and S waves together form a complex.

ECG Waves

A downward deflection following an R wave is termed an S wave.
An upward deflection is termed an R wave, regardless of preceding Q waves.
ECG machines measure electrical activity by recording a trace on a moving paper strip.

ECG Times and Speeds

A standard ECG recording speed is 25 mm/sec, using squares of a standard size.
One large square equals 0.2 seconds (200 milliseconds)
One small square equals 0.04 seconds (40 milliseconds)
Five large squares equal one second
There are 300 large squares per minute

ECG Interpretation: R-R interval

The time between successive R waves reflects the heart rate.
The relationship between R-R interval and heart rate is shown in a table.

ECG Intervals

PR interval is measured from the start of the P wave to the start of the QRS complex. It depicts the time taken for atrial excitation to spread to the ventricles via the AV node.
The normal PR interval is between 120–220 ms (three to five small squares).
QT interval represents the total time for ventricular depolarization and repolarization.
The normal QT interval is between 360–440 ms (nine to eleven small squares).

ECG Leads

ECG recorders compare electrical activity from different electrodes.
The comparison patterns are called leads.
The 12-lead ECG provides a comprehensive view of the heart's electrical activity.
Some leads reflect the heart from the front (chest leads), others reflect from the sides (limb leads).
Each lead provides, and is associated with, a different view of the heart or part of the heart, which helps with diagnosis and interpretation.

Cardiac Axis

The average depolarization direction through the ventricles is called the cardiac axis.
Normal cardiac axis is between −30° to +90°.
The cardiac axis can be derived from the QRS complex in leads I, II, and III.
Right or Left heart axis deviations can be associated with hypertrophy.

Abnormalities of P waves, QRS complexes, and T waves

Abnormalities in these waves can indicate a variety of problems, including atrial or ventricular hypertrophy.
Examples of P wave abnormalities: peaked P waves (right atrial hypertrophy), broad or bifid P waves (left atrial hypertrophy).
Examples of QRS complexes abnormalities: abnormally wide QRS complexes and duration (heart blockages).
Examples of T wave abnormalities: abnormal shapes or inversions can reflect underlying myocardial problems.

Conduction Problems

The time taken for depolarization from SA node to the ventricular muscle is shown by the PR interval.
Interference with conduction causes "heart block".
Heart blocks are graded into several (and increasing severity) types: first degree, second degree, and third degree.

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Description

This quiz covers the fundamental concepts of electrocardiography (ECG), including its significance in clinical diagnosis and management of cardiac conditions. It also explores the different parts of the ECG and their corresponding electrical events in the heart. Test your understanding of how ECGs help in patient care, especially in cases of abnormal cardiac rhythms and chest pain.