Questions and Answers
What is formed when a positive and a negative charge are separated by a small distance?
What is the purpose of Standard Bipolar Leads in electrocardiography?
What does the horizontal axis of an electrocardiogram represent?
What happens to the width of complexes on an electrocardiogram when slower variations of electrical potentials occur?
Signup and view all the answers
What is the standard paper speed for electrocardiography in humans?
Signup and view all the answers
What happens to the amplitude of complexes on an electrocardiogram when more tissue is depolarizing?
Signup and view all the answers
In small animals, what is the paper speed for electrocardiography if the heart rate is 120 beats/min or lower?
Signup and view all the answers
What does the P wave on an ECG represent?
Signup and view all the answers
What happens to the SA node discharge on an ECG?
Signup and view all the answers
Why is there no deflection for atrial repolarization on an ECG?
Signup and view all the answers
What is the sequence of events that occurs just before the P wave on an ECG?
Signup and view all the answers
What can be inferred about the SA node discharge from an ECG?
Signup and view all the answers
What is the primary reason for the delay in the P-R interval?
Signup and view all the answers
What is the effect of sympathetic stimulation on the P-R interval?
Signup and view all the answers
What is the effect of parasympathetic stimulation on the P-R interval?
Signup and view all the answers
What is the significance of an increased P-R interval?
Signup and view all the answers
What is measured by the P-R interval?
Signup and view all the answers
What does the QRS complex represent in an electrocardiogram?
Signup and view all the answers
What is the characteristic of the conduction velocity in the HIS-Purkinje system?
Signup and view all the answers
How many waves make up the QRS complex?
Signup and view all the answers
What is the duration of the QRS complex comparable to?
Signup and view all the answers
What does each wave of the QRS complex represent?
Signup and view all the answers
What does the Q-T interval reflect?
Signup and view all the answers
What is the S-T segment correlated with?
Signup and view all the answers
What is the Q-T interval measured from?
Signup and view all the answers
Why is the segment between the end of depolarization and the beginning of repolarization isoelectric?
Signup and view all the answers
What period corresponds to the time when all ventricular muscle is depolarized?
Signup and view all the answers
What is the T wave in an electrocardiogram associated with?
Signup and view all the answers
Why is the duration of the T wave longer than the QRS complex?
Signup and view all the answers
What is a characteristic of the T wave in dogs and cats?
Signup and view all the answers
What is possible with the polarity of the T wave?
Signup and view all the answers
What is a requirement for the T wave?
Signup and view all the answers
What is the R-R interval used to evaluate?
Signup and view all the answers
What is the R-R interval equal to?
Signup and view all the answers
Under what condition can the R-R interval be used to calculate HR?
Signup and view all the answers
What is the other name for the R-R interval?
Signup and view all the answers
What is the relationship between the R-R interval and heart rate?
Signup and view all the answers
Why is the ECG less useful for diagnosing structural abnormalities?
Signup and view all the answers
What is a characteristic of the ECG waves in large animals?
Signup and view all the answers
What is an example of a structural abnormality that the ECG is less useful for diagnosing?
Signup and view all the answers
Why do cardiac depolarization pathways affect the ECG?
Signup and view all the answers
What is a limitation of the ECG in large animals?
Signup and view all the answers
Match the ECG term to correct definition
Signup and view all the answers
An arrhythmia is an abnormal heart rhythm
Signup and view all the answers
What does an EKG evaluate?
Signup and view all the answers
An EKG can indicate if a patient has _________ and __________ disturbances
Signup and view all the answers
The QRS complex represents what portion on the ventricular AP graph?
Signup and view all the answers
The PR interval includes _________ and __________.
Signup and view all the answers
Study Notes
Electric Dipole and its Effects
- A dipole is a pair of positive and negative charges separated by a small distance, which can generate local current flow and a small electrical field.
- Cardiac muscle cells, when depolarizing or repolarizing, exhibit different charges along their membranes, behaving like a dipole.
Electrocardiogram (ECG) Leads
- Standard bipolar leads are the most commonly used leads.
- Lead I: compares the left arm (LA+) with the right arm (RA-).
- Lead II: compares the left leg (LL+) with the right arm (RA-).
- Lead III: compares the left leg (LL+) with the left arm (LA-).
ECG Waveforms and Intervals
- The ECG allows for the determination of duration and amplitude of waveforms and intervals/segments.
- Standard calibration paper speed is 25 mm/sec in humans.
- In small animals, paper speed is 50 mm/sec, but can be 25 mm/sec if the heart rate is 120 beats/min or lower.
ECG Axis Interpretation
- The horizontal axis represents time in milliseconds.
- Slower variations of electrical potentials result in wider complexes (e.g., due to fibrosis, more time is required for depolarization/repolarization).
- The vertical axis represents amplitude in millivolts.
- Increased tissue depolarization results in increased amplitude (height) of the complexes (e.g., more muscle mass results in higher waves).
ECG Deflections
- The first ECG deflection is the P wave, which represents depolarization of the atrial muscle.
- The discharge of the SA node is assumed to have occurred just before the P wave.
- The discharge of the SA node does not produce a visible deflection on the ECG, likely due to the small number of cells involved.
- Atrial repolarization also does not produce a visible deflection on the ECG.
P-R Interval
- Represents the time taken for the electrical impulse to conduct through the atria, AV node, and Bundle of His.
- The impulse is mostly delayed in the AV node, which affects the overall P-R interval length.
Measurement of P-R Interval
- Measured from the start of the P wave to the first deflection of the QRS complex.
Effects of Stimulation on P-R Interval
- Sympathetic Stimulation: • Decreases the P-R interval. • Increases conduction velocity.
- Parasympathetic Stimulation: • Increases the P-R interval. • Decreases conduction velocity.
Clinical Significance of P-R Interval
- An increased P-R interval is associated with A-V blocks.
Ventricular Depolarization
- The activation of the HIS-Purkinje system and ventricular muscle leads to the generation of a QRS complex.
- The QRS complex is a representation of ventricular depolarization, comprising three waves.
- The total duration of the QRS complex is comparable to that of the P wave.
- The conduction velocity of the QRS complex is faster.
- Each wave of the QRS complex corresponds to a specific region of the ventricle undergoing depolarization.
Q-T Interval
- Represents the approximate duration of ventricular systole and ventricular refractory period
- Marks the ending of depolarization and beginning of repolarization, making it isoelectric since all ventricular muscle is depolarized
- Measured from the beginning of the Q wave to the end of the T wave
S-T Segment
- Correlates with the plateau of the ventricular action potential (AP)
Ventricular Repolarization (T Wave)
- Represents ventricular repolarization
- Has a longer duration than the QRS wave because repolarization does not occur as a synchronized propagated wave
- Exhibits high degree of variability in dogs and cats
- Can be:
- Positive
- Negative
- Biphasic
- Very low amplitude, but should be consistent
ECG Variability in Large Animals
- In large animals, there is considerable variability in the polarity and size of the ECG waves.
- ECG waves exhibit more variation in horses and cattle compared to dogs and cats.
- Significant individual variations exist among large animals.
- Cardiac depolarization pathways are not consistent in large animals.
- ECG is primarily useful for detecting arrhythmias in large animals.
Limitations of ECG
- ECG is less useful for diagnosing structural abnormalities in large animals.
- Example of a structural abnormality that ECG is not suitable for diagnosing: Ventricular hypertrophy.
Electrophysiology
- A dipole is a positive and negative charge separated by a small distance, generating local current flow and a small electrical field.
- Cardiac muscle cells, during depolarization and repolarization, show different charges along their membranes and act like a dipole.
Electrocardiography (ECG)
- Standard bipolar leads are used to measure the electrical activity of the heart.
- Lead I compares LA (+) and RA (-), Lead II compares LL (+) and RA (-), and Lead III compares LL (+) and LA (-).
- ECGs allow for the determination of duration and amplitude of waveforms and intervals/segments.
- Standard calibration paper speed is 25 mm/sec in humans, and 50 mm/sec in small animals (or 25 mm/sec if HR is 120 beats/min or lower).
ECG Components
- The P wave represents depolarization of atrial muscle and occurs just after the discharge of the SA node.
- The P-R interval represents the time it takes for the electrical impulse to conduct through the atria, AV node, and Bundle of His (mostly through the AV node).
- The QRS complex represents ventricular depolarization and is generated as the impulse activates the His-Purkinje system and ventricular muscle.
- The Q-T interval reflects the approximate duration of ventricular systole and the ventricular refractory period.
- The S-T segment correlates with the plateau of the ventricular action potential.
- The T wave represents ventricular repolarization and has a longer duration than the QRS complex.
- The R-R interval represents the time between one R wave and the next, and is used to evaluate the regularity of heartbeats and calculate heart rate.
Variations in ECGs
- ECG waves can vary in polarity and size among individuals, particularly in large animals such as horses and cattle.
- ECGs are more useful for detecting arrhythmias than diagnosing structural abnormalities, such as ventricular hypertrophy.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Understanding electrical dipoles and their role in generating local current flow and electrical fields, particularly in cardiac muscle cells and ECG leads.