Electrocardiography Basics

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Questions and Answers

What is the normal composition of an ECG?

QRS complex and T wave only

P wave and QRS complex, excluding T wave

P wave and T wave only

P wave, QRS complex, and T wave (correct)

What causes the P wave in an ECG?

Atria repolarizing

Atria depolarizing (correct)

Ventricles repolarizing

Ventricles depolarizing

During what phase does depolarization occur in cardiac cells?

Phase 2 with Na ions leaving the cell

Phase 1 with K ions entering the cell

Phase 3 with Ca ions entering the cell

Phase 0 with Na ions entering the cell (correct)

What is the T wave in an ECG also known as?

Repolarization wave Signup and view all the answers

What happens to cardiac cells during depolarization?

They lose their internal negativity Signup and view all the answers

What causes repolarization in cardiac cells?

Outward movement of K ions Signup and view all the answers

What is the primary function of the SA node in the heart's conduction system?

To generate electrical impulses Signup and view all the answers

Which type of lead in an ECG uses two electrodes to measure differences in electrical potential?

Bipolar leads Signup and view all the answers

What does the lead aVF in augmented unipolar limb leads primarily measure?

Potential in the left foot with reference to average potential of arms Signup and view all the answers

Which structure of the heart does the impulse reach after the AV node?

Bundle of His Signup and view all the answers

What is the primary purpose of modifying the augmented unipolar limb leads?

To enhance electrical potential for better recordings Signup and view all the answers

In the conduction system, where does the impulse travel after the intraatrial tracts?

To the AV node Signup and view all the answers

Where is lead V1 placed?

Fourth intercostal space right parasternal area Signup and view all the answers

What area does lead V5 represent in the heart?

Lateral area Signup and view all the answers

Which leads are located in the anterior portion of the heart?

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

What is the placement location for lead V4?

Inframammary area Signup and view all the answers

Which lead is positioned between V2 and V4?

V3 Signup and view all the answers

What does the P wave in the ECG represent?

Atrial depolarization Signup and view all the answers

How many small squares correspond to 1 mV in amplitude on the ECG paper?

10 small squares Signup and view all the answers

What is the normal duration of the PR interval in seconds?

0.12 – 0.20 seconds Signup and view all the answers

What does the QRS wave represent in an ECG?

Ventricular depolarization Signup and view all the answers

In an ECG, what is the significance of the ST segment?

The time from ventricular depolarization to repolarization Signup and view all the answers

What is the standard speed of the ECG paper?

25 mm/sec Signup and view all the answers

What direction does the vector for ventricular depolarization typically go?

Left to right Signup and view all the answers

What is the maximum duration of the P wave in an ECG?

0.25 seconds Signup and view all the answers

What does the ST segment measure in the cardiac cycle?

The time between ventricular depolarization and repolarization Signup and view all the answers

During which phase does systole occur in the cardiac cycle?

From the start of the QRS complex to the later half of the P wave Signup and view all the answers

Which of the following correctly describes diastole?

Covers the interval from the end of the T wave to the start of QRS complex Signup and view all the answers

What does the T wave represent in the cardiac cycle?

Ventricular repolarization Signup and view all the answers

What occurs first in the cardiac cycle as indicated by the P wave?

Atrial depolarization Signup and view all the answers

Study Notes

Electrocardiography (ECG)

Records the electrical activity of the heart.
Normal ECG consists of three main components: P wave, QRS complex, and T wave.
P wave represents atrial depolarization preceding atrial contraction.
QRS complex indicates ventricular depolarization preceding ventricular contraction.
Both P wave and QRS complex are classified as depolarization waves.
T wave (repolarization wave) reflects the recovery phase of the ventricles after depolarization.

Cellular Electrophysiology

Cardiomyocytes, or cardiac cells, are electrically polarized during the resting state.
Depolarization, also known as activation, is a primary electrical event in the heart where cells lose internal negativity.
Phase 0 of action potential occurs when sodium (Na+) ions enter the cell, making it more positive and propagating action potential to neighboring cardiomyocytes.
Repolarization occurs as potassium (K+) ions move out of the cell, restoring the cell's negative charge.
Overall, during depolarization, the cell experiences a shift toward a more positive interior.

Conduction System of the Heart

Impulse generation begins at the SA node, also known as the sinus node.
Impulse travels to the atria through intraatrial tracts, causing a brief atrial contraction.
After the atria, the impulse moves through internodal pathways to the AV node.
From the AV node, the signal travels down the Bundle of His and branches into the right and left bundle branches in the ventricles.
Conduction continues to the Purkinje fibers, stimulating contraction of the ventricles.

ECG Leads

ECG leads measure the magnitude and direction of the heart's electrical impulses.
Three types of leads: Limb leads, Augmented limb leads, and Precordial leads.

Limb Leads

Bipolar leads consist of 2 electrodes at different sites, measuring the voltage difference between them.
Unipolar leads measure the electrical potential at one site compared to a reference electrode at zero potential.
Color coding for limb electrodes:
- Right arm: Red
- Left arm: Yellow
- Left foot: Blue/Green
- Right foot: Black

Augmented Unipolar Limb Leads

Lead aVR: Records potential between the right arm and the average potential of the left arm and left foot.
Lead aVL: Measures potential in the left arm relative to the average potential of the right arm and left leg.
Lead aVF: Assesses potential in the left foot with reference to the average of the left arm and right arm.
Augmentation of leads increases potential recording by 50% for improved clarity in ECG interpretation.

Precordial Lead Placements

Precordial leads, commonly used in adults, include V1 through V6.
V1 is located in the fourth intercostal space at the right parasternal area.
V2 is positioned in the fourth intercostal space at the left parasternal area.
V3 is placed between V2 and V4, completing the anterior view.
V4 is found in the inframammary area, aligning with the heart's anterior aspect.
V5 is situated in the midclavicular area at the same level as V4.
V6 is positioned in the anterior axillary line, aligned with V4 and V5.
These lead placements focus on the anterior portion of the heart.
V1 and V2 specifically monitor the septal area of the left ventricle.
V3 and V4 assess the anterior area of the heart.
V5 and V6 are associated with the lateral area of the heart.

ECG Paper

ECG paper consists of horizontal and vertical lines.
Horizontal lines indicate duration in seconds or milliseconds.
Vertical lines measure amplitude in millivolts.
Standard speed for ECG tracing is 25 mm/sec.
Standard amplitude is set at 10 mm/mV.
The smallest square on ECG paper represents 1 mV (amplitude) and 0.04 seconds (duration).
Five small squares equal 0.2 seconds, while 25 small squares equal 1 second.
One millivolt corresponds to approximately 10 small squares vertically.

Waves, Segments, and Intervals

The PQRST complex represents one complete cardiac cycle.
The P wave indicates atrial depolarization, occurring before contraction.
The QRS wave indicates ventricular depolarization just prior to ventricular contraction.
The Q wave is the first negative deflection after the P wave.
The R wave is the first positive reflection following the Q wave.
The S wave is the first negative reflection occurring after the R wave.
The T wave represents the process of ventricular repolarization.
The P wave should last no longer than 0.12 seconds and reach a maximum amplitude of 0.25 mV (2.5 small squares).
The PR interval measures the duration from the start of atrial depolarization to the onset of ventricular depolarization (0.12 – 0.20 seconds).
The QRS interval measures the duration of ventricular depolarization (0.08 – 0.10 seconds).
The ST segment reflects the time from the end of ventricular depolarization to the beginning of ventricular repolarization.
The T wave records the process of ventricular repolarization.
The vector direction for ventricular depolarization (and septal depolarization) is from left to right.
Ventricular depolarization predominantly occurs in the left ventricle, with a leftward and inferior direction.

Cardiac Cycle Components

P wave: Indicates atrial depolarization, which occurs before the atrium fills with blood.
QRS complex: Represents ventricular depolarization and occurs before the contraction of the ventricles.
T wave: Reflects ventricular repolarization, marking the end of the cardiac cycle.

ST Segment

Measures time from the end of ventricular depolarization to the beginning of ventricular repolarization.
Crucial for diagnosing heart attacks or myocardial infarction.

Phases of the Cardiac Cycle

Systole: Starts at the QRS complex and lasts until the later half of the P wave, representing ventricular contraction.
Diastole: Extends from the T wave up to the start of the QRS complex, indicating the relaxation phase of the heart.

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Description

This quiz covers the fundamental concepts of electrocardiography, including the recording of electrical activity in the heart. Key components such as the P wave, QRS complex, and T wave will be explored, along with their roles in depolarization and repolarization. Test your knowledge on how these waves contribute to heart function.