HARD QUIZ ECG

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Questions and Answers

What primary function does an electrocardiogram (ECG) serve?

To directly measure the mechanical force of heart muscle contractions.

To assess the efficiency of oxygen exchange in cardiac tissue.

To measure the blood flow through the heart chambers.

To record potential differences caused by electrical currents in the heart. (correct)

Why are electrodes for ECG measurements placed at standardized locations on the body?

To provide a clear view of oxygenated blood flow from various angles.

To minimize the risk of skin irritation during the recording.

To ensure that the recorded data are comparable across different patients and tests. (correct)

To facilitate easier integration of ECG with other body scans.

How do different ECG leads enhance the diagnostic value of an ECG?

By providing views of the heart's electrical activity from different orientation angles. (correct)

By specifically measuring the concentration of ions in heart muscle tissue.

By measuring the speed of electrical signals in various body tissues.

By averaging out random electrical noise from the body.

Which of the following best describes the typical relationship between ventricular depolarization and repolarization as reflected in the ECG?

The T wave is normally upright because the wave of repolarization is moving away from the overlying recording electrode. (C) Signup and view all the answers

A patient's ECG shows a QRS complex with a duration of 0.14 seconds. This finding is most likely indicative of which of the following conditions?

Altered conduction within the ventricles. (C) Signup and view all the answers

What is the main purpose of using multiple leads in an ECG?

To provide a complete view of the electrical activity in various regions of the heart. (A) Signup and view all the answers

A negative deflection is seen before any positive deflection on an ECG, what is the most accurate way to characterize that part of the QRS complex?

Q wave (C) Signup and view all the answers

In the context of an ECG, what is meant by 'electrical vectors'?

The direction and magnitude of electrical activity generated by cardiac cells. (D) Signup and view all the answers

Given an ECG tracing with a Q-T interval of 0.40 seconds and an R-R interval of 1.0 second, what is the corrected Q-T interval (QTc)?

0.40 seconds (A) Signup and view all the answers

Which of the following is NOT a primary goal for the typical placement of ECG electrodes?

To accurately map heart's mechanical performance. (A) Signup and view all the answers

A patient's ECG shows that the mean electrical vector of the heart is moving away from the positive electrode in lead II during ventricular depolarization. Which of the following would be true regarding the shape of the QRS complex in Lead II?

The QRS complex would have a large negative amplitude. (C) Signup and view all the answers

What forms the basis of potential differences measured by the ECG?

Electric currents spreading during depolarization and repolarization. (B) Signup and view all the answers

What information does an ECG primarily provide?

Cardiac rhythm, conduction, injury, and muscle mass (C) Signup and view all the answers

According to the conventional principles of volume conduction, how is a wave of repolarization moving toward a positive electrode recorded?

As a negative voltage deflection (D) Signup and view all the answers

What is the expected recording when electrical activity moves perpendicular to the lead axis?

No net voltage is recorded. (D) Signup and view all the answers

How is the magnitude of the recorded voltage related to the tissue mass?

The magnitude of the voltage is directly related to the tissue mass (A) Signup and view all the answers

Given an instantaneous mean electrical vector pointing from a negative to a positive region, what happens with a positive recording electrode placed to the right hand side of that activity?

It will record a positive voltage. (C) Signup and view all the answers

If a wave of depolarization is moving away from a positive electrode, how does this manifest in the recording?

It will record a negative voltage (A) Signup and view all the answers

Which of the following does not directly affect the voltage recorded by an ECG electrode?

The level of oxygen saturation in the heart muscle. (B) Signup and view all the answers

What does an 'instantaneous mean electrical vector' represent in the context of ECG?

The net sum of all the electrical activity at a given moment. (A) Signup and view all the answers

If both depolarization and repolarization activity occur in the heart at the same time, how would an ECG recording electrode detect them?

The electrode will register both activities, with each one leading to a change in voltage based on the direction and type of the activity. (C) Signup and view all the answers

According to conventions, what will happen when a repolarisation wave moves away from a positive electrode?

A positive voltage will be recorded. (C) Signup and view all the answers

Study Notes

Electrocardiogram Lecture Notes

The electrocardiogram (ECG) measures potential differences between electrodes placed on the body's surface.
These differences are generated by electrical currents spreading from the heart during depolarization and repolarization.
Electrodes are placed in standardized locations on the body's surface.
Different ECG leads "view" electrical vectors from various angles, providing information about electrical activity in different heart regions.
ECG primarily shows: rhythm (rate and synchrony), conduction, injury currents, and muscle mass (e.g., ventricular hypertrophy).
The QRS complex shape depends on the depolarization sequence and timing, as well as ventricular mass and conduction abnormalities. A prolonged QRS duration often suggests intraventricular conduction problems.

Volume Conductor Principles (Vectors)

Depolarization toward a positive electrode creates a positive voltage.
Repolarization toward a positive electrode creates a negative voltage. If the movement is away from a positive electrode then the voltage will be negative.
Waves perpendicular to the lead axis produce no net voltage.
The voltage's magnitude relates directly to the tissue mass.
The potential amplitude depends on the instantaneous mean electrical vector's direction relative to the recording electrode.

Sequence of Ventricular Depolarization

The instantaneous voltage is determined by the direction and magnitude of the mean electrical vector related to the positive electrode within a specific lead axis.
Examples using lead A, B, C, and D illustrate how the vector moves relative to certain lead axes.
The depolarization sequence takes about 100 milliseconds (the QRS duration).

The QRS Complex and Mean Electrical Axis

The QRS complex's shape depends on the sequence and timing of ventricular depolarization.
Ventricular mass and hypertrophy influence the voltage.
Recording electrode placement is relevant.
Mean electrical axis is the net vector of the entire ventricular depolarization sequence.

Ventricular Repolarization- The T Wave

Ventricular repolarization is represented by the T wave, following the QRS complex.
The T wave is normally upright because of how the repolarization wave moves from the subepicardial cells.
The subepicardial cells repolarize first, even though they were the last to depolarize.

ECG Tracing - Definitions

P wave = atrial depolarization (the depolarization in the atria)
PR interval = atrial depolarization + AV nodal delay
QRS complex = ventricular depolarization, sequence
QT interval = time from initial depolarization until complete repolarization.
ST segment = depolarized ventricle (isoelectric)
T wave = ventricular repolarization

QRS Morphology: Naming Convention

Not all QRS complexes have Q, R, and S components.
The first positive deflection is an R wave, a negative deflection following an R wave is an S wave, a negative deflection without preceding an R wave is a Q or QS wave. A subsequent positive deflection is designated as R'.

ECG Tracing- Normal Wave Durations and Intervals

Provides typical duration ranges for P wave, PR interval, QRS complex, QTc interval (QT corrected, accounting for heart rate).
Includes conversion from mm to seconds based on typical ECG recording speeds.

Abnormally Long PR Intervals

Prolonged PR intervals usually suggest impaired conduction within the AV node.
It can be caused by first degree av block, excessive vagal stimulation, and certain medications or conditions affecting the AV node.

Altered Shape and Increased Duration of the QRS Complex

Altered QRS shapes and durations often point to intraventricular conduction block (e.g., bundle branch block).
The process of ventricular depolarization is changed and takes longer than normal because the conduction pathways are altered.
Premature ventricular complexes (PVCs) typically have elongated QRS durations due to altered conduction pathways.

Heart Rate Determination

A standard ECG machine recording runs at 25 mm/sec, providing a basis for counting large boxes in the ECG tracing.
Heart rates that are slow (less than 60 beats per minute) or fast (over 100 beats per minute) are deviations from the normal range.
The standard for determining the normal rate on an ECG involves counting boxes between QRS complexes.

Sequence of ECG Interpretation

The ECG is interpreted looking at rhythm (e.g., sinus rhythm), rate (how fast), the intervals (PR, QRS, QT intervals).
Also mean electrical axis (QRS), P-wave and QRS abnormalities and ST segment/T wave abnormalities.

12-Lead ECG

Different ECG leads offer various perspectives of the heart's electrical activity.
Various electrodes, either standard bi-polar leads (I, II, III) or unipolar augmented leads (aVR, aVL, aVF), provide different views of the heart.
The bipolar leads measure potential differences between two electrodes in the limbs, while the unipolar leads measure the potential difference between one electrode and an average of the other electrodes.
Unipolar chest leads (V1 through V6) capture electrical activity from the chest.

Axial Reference System

Shows the relationship between electrode placement to a rotational reference frame.
Crucial for understanding how the electrical forces of the heart move relative to the different electrode locations.

Estimating the Mean Electrical Axis

Finding the lead that is equally biphasic and calculating an angle ~90 degrees from that lead in the direction of the lead with the strongest positive QRS amplitude helps to determine the mean electrical axis.

Normal Sinus Rhythm (NSR)

NSR typically shows a heart rate of 60-100 beats per minute. The rate, intervals and shapes relate to the heart's normal electrical conduction and activity.
ECG characteristics include specific features (P waves, PR intervals, QRS complexes) and regular rhythm.

Summary of ECG Concepts

Electrical depolarization and repolarization spread throughout the heart using specialized pathways and are recorded and measured as time-dependent electrical potentials (electrical dipoles).
The instantaneous mean electrical vectors reflect the direction and strength of these dipoles in time. The mean electrical axis is the average vector during depolarization.

Different ECG Leads

Different ECG leads provide information about electrical activity in various heart regions because they are placed at various angles around the heart.

Questions: Q1 to Q4

These include questions about normal ECG characteristics.
Specific answers given in related sections.

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Description

Explore the essential concepts of electrocardiograms (ECG) through this quiz. Learn about the ECG's ability to measure electrical activity in the heart, including depolarization, repolarization, and the significance of various ECG leads. Test your understanding of how these principles apply to cardiac function and health.