ECG Basics and Function

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Questions and Answers

What is the primary function of an electrocardiogram (ECG)?

To visualize heart structures

To measure blood pressure

To record the electrical activity of the heart (correct)

To assess heart valve function

Which wave in the ECG represents atrial depolarization?

QRS complex

PR segment

P wave (correct)

T wave

What occurs at the AV node during atrial depolarization?

Ventricular depolarization

Impulse delay (correct)

Ventricular contraction

Atrial contraction

What type of leads are I, II, and III classified as?

Bipolar leads Signup and view all the answers

What does the QRS complex in an ECG indicate?

Ventricular depolarization Signup and view all the answers

Which of the following is NOT a unipolar limb lead?

Lead III Signup and view all the answers

What does the augmented limb lead aVF represent?

Augmented lead toward the foot Signup and view all the answers

Which sequence accurately describes ventricular depolarization as noted in the ECG?

Depolarization begins at the septum, spreads to the apex, then ventricular muscle Signup and view all the answers

What initiates atrial depolarization in the heart?

SA node Signup and view all the answers

How many bipolar leads are typically used in a standard ECG setup?

3 Signup and view all the answers

Where does ventricular repolarization begin in the ECG cycle?

Apex of the heart Signup and view all the answers

Which electrode is positioned in the fourth intercostal space to the right of the sternum?

V1 Signup and view all the answers

What shape do the axes of the three bipolar leads (I, II, III) form around the heart?

Triangle Signup and view all the answers

Why is atrial repolarization not visible on the ECG?

It occurs simultaneously with ventricular depolarization Signup and view all the answers

What does the isoelectric PR segment represent in an ECG?

Impulse delay at the AV node Signup and view all the answers

Which lead is placed at the left anterior axillary line at the same level as V4?

V5 Signup and view all the answers

What is the amplitude range for a P wave in an ECG?

0.05-0.25 mV Signup and view all the answers

Which part of the ECG shows the completion of ventricular depolarization?

S wave Signup and view all the answers

Which lead is placed directly between leads V2 and V4?

V3 Signup and view all the answers

What does the QT interval measure in an ECG?

Time of ventricular depolarization and repolarization Signup and view all the answers

Which wave in an ECG is often small and can go unnoticed?

U Wave Signup and view all the answers

What is the function of the reference point in unipolar leads?

To provide an additional positive electrode Signup and view all the answers

What is the duration of the PR interval in an ECG?

0.12-0.20 seconds Signup and view all the answers

Where is the RA electrode positioned?

Anywhere on the right arm or right midclavicular line Signup and view all the answers

What determines the direction of waveforms in an ECG lead?

Position relative to the positive electrode Signup and view all the answers

Which part of the ECG represents the isoelectric line following the QRS complex?

ST Segment Signup and view all the answers

Which ECG leads record the flow of electrical impulses between two electrodes?

Bipolar Leads Signup and view all the answers

What is the duration of a QRS complex in an ECG?

0.06-0.10 seconds Signup and view all the answers

What does a small atrial muscle mass produce in comparison to the QRS complex?

Small potential Signup and view all the answers

During depolarization, what occurs to the outside of the cell?

Becomes more negative Signup and view all the answers

Which leads are included in the frontal plane view of the heart?

I, II, III, aVR, aVL, aVF Signup and view all the answers

What is the purpose of the precordial leads in a 12-lead ECG?

To visualize anterior and lateral views of the heart Signup and view all the answers

How is artifact in an ECG tracing defined?

Markings not related to the heart’s electrical activity Signup and view all the answers

What does each small square on the ECG paper represent in terms of time?

0.04 seconds Signup and view all the answers

What condition is indicated by the term dysrhythmias?

Abnormalities in cardiac rate and/or rhythm Signup and view all the answers

Which leads in the 12-lead ECG provide an inferior view of the heart?

II, III, aVF Signup and view all the answers

What is the function of augmented voltage leads in the 12-lead ECG?

To enhance the readings of limb leads Signup and view all the answers

In a standard 12-lead ECG, which leads give the anterior view of the heart?

V1, V2, V3, V4 Signup and view all the answers

What is the primary means by which electrodes detect the heart's electrical activity?

By placing electrodes on the skin Signup and view all the answers

What is the machine that produces an electrocardiogram called?

Electrocardiograph Signup and view all the answers

Study Notes

The Electrocardiogram (ECG)

The ECG is a recording of the electrical activity of the heart.
It is an important diagnostic tool used to evaluate heart function and identify any abnormalities.
The ECG is a graphical representation of the electrical activity of the heart, recorded using electrodes placed on the skin.

How the ECG Works

The P wave: reflects the electrical activity of the atria as they depolarize, which is initiated by the sinoatrial (SA) node.
The PR interval: represents the time it takes for the electrical impulse to travel from the SA node through the atria, the atrioventricular (AV) node, and to the ventricles.
The QRS complex: represents ventricular depolarization, the electrical activation of the ventricles which begins at the interventricular septum, the wall between the ventricles. The Q wave represents the depolarization of the septum, the R wave represents the depolarization of the ventricles, and the S wave represents the depolarization of the posterior part of the left ventricle.
The ST segment: represents the time when the ventricles are fully depolarized. It is the period between the end of ventricular depolarization and the start of ventricular repolarization.
The T wave: reflects the electrical activity of the ventricles as they repolarize (return to their resting state).
The QT interval: represents the time it takes for the ventricles to depolarize and repolarize.
The U wave: reflects the repolarization of the papillary muscles and Purkinje fibers.

ECG Components

Wave: A deflection from the isoelectric baseline.
Segment: A region between two waves.
Interval: A duration of time that includes one or more waves and a segment.

Reading the ECG

P Wave: Amplitude of 0.05-0.25 mV, duration of 0.06-0.10 seconds, waveform is upright and slightly asymmetrical.
PR Interval: Duration of 0.12-0.20 seconds.
QRS Complex: Amplitude of 0.5-3.0 mV, duration of 0.06-0.10 seconds.
ST Segment: Is the isoelectric line that follows the QRS complex.
T Wave: Is a larger, slightly asymmetrical waveform that follows the ST segment, the J point is the start of the ST segment.
QT Interval: Distance from the onset of the QRS complex to the end of the T wave, the normal duration is 0.36 to 0.44 seconds.
U Wave: Small, upright wave following the T wave, but before the next P wave.

ECG Leads & the Electrical View of the Heart

Limb Leads: Are bipolar or unipolar leads. The bipolar leads include I, II, and III. These record the flow of electrical impulses between two electrodes (one positive, one negative) and form a triangle called Einthoven's Triangle.
Bipolar Leads: Record the difference in potential between a positive and a negative electrode.
Unipolar Leads: Use only one positive electrode with a reference point calculated by the ECG machine. Unipolar leads include aVR, aVL, and aVF (augmented limb leads), and V1-V6 (chest leads).
The 12-Lead EKG: Provides a three-dimensional view of the heart by using nine electrodes (plus a ground) placed on the extremities and chest wall.
- Frontal Plane: View provided by the limb leads (I, II, III, aVR, aVL, and aVF), providing inferior, superior, and lateral views of the heart.
- Horizontal Plane: View provided by the chest leads (V1, V2, V3, V4, V5, and V6), providing anterior and lateral views.

Performing an ECG:

Electrodes: Are positioned to form leads.
Standard 12-lead ECG: - Is typically performed with the person lying supine. - Includes three bipolar limb leads (I, II, III), three augmented voltage leads (aVR, aVL, aVF), and six chest leads (V1 – V6).

Artifact

Artifact is any marking on the ECG tracing that is not a product of the heart’s electrical activity, Patient movement is one of many causes, and can mimic life-threatening dysrhythmias.

Summary

The ECG is a record of the electrical activity of the heart.
Each lead offers a different view.
Impulses traveling towards a positive electrode are recorded on the ECG as upward deflections.
Electrodes are positioned on the patient’s skin to pick up electrical activity of the heart.
Any abnormalities in the heart’s rhythm or rate – are called dysrhythmias.

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Description

This quiz covers the essential aspects of the electrocardiogram (ECG), including its function, components, and how it reflects heart activity. You'll learn about the P wave, PR interval, and QRS complex, along with their significance in diagnosing heart conditions. Test your understanding of this crucial diagnostic tool used in cardiology.