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Questions and Answers
What is the result of sympathetic stimulation on the heart?
What is the result of sympathetic stimulation on the heart?
What does the QRS complex represent in an ECG?
What does the QRS complex represent in an ECG?
What is the primary function of the R-R interval in ECG interpretation?
What is the primary function of the R-R interval in ECG interpretation?
What is the significance of the S-T segment in an ECG?
What is the significance of the S-T segment in an ECG?
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What does the P wave in an ECG represent?
What does the P wave in an ECG represent?
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What is the result of parasympathetic stimulation on the heart?
What is the result of parasympathetic stimulation on the heart?
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What is the significance of the Q-T interval in an ECG?
What is the significance of the Q-T interval in an ECG?
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What is the heart rate in beats per minute (BPM) if the interval between beats is 0.36 seconds?
What is the heart rate in beats per minute (BPM) if the interval between beats is 0.36 seconds?
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What is the main function of the atrial muscle?
What is the main function of the atrial muscle?
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What is the significance of the T wave in an ECG?
What is the significance of the T wave in an ECG?
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What is the P-R interval in an ECG?
What is the P-R interval in an ECG?
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Why is there no deflection for SA node discharge in an ECG?
Why is there no deflection for SA node discharge in an ECG?
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What is associated with an increased P-R interval in an ECG?
What is associated with an increased P-R interval in an ECG?
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Why should the interval between the P wave and the QRS complex be named P-Q instead of P-R?
Why should the interval between the P wave and the QRS complex be named P-Q instead of P-R?
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What is the term for the time length between two specific points on an ECG that are supposed to be at the baseline amplitude?
What is the term for the time length between two specific points on an ECG that are supposed to be at the baseline amplitude?
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What is the normal cardiac rhythm where depolarization begins at the SA node?
What is the normal cardiac rhythm where depolarization begins at the SA node?
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What is the direction of the electrical current when cardiac impulses pass through the heart?
What is the direction of the electrical current when cardiac impulses pass through the heart?
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What is the term for the abnormal heart rhythm?
What is the term for the abnormal heart rhythm?
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What is the term for a positive and a negative charge separated by a small distance?
What is the term for a positive and a negative charge separated by a small distance?
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What is the ultimate result of the sum of all the currents originated from the electrical activity of the heart?
What is the ultimate result of the sum of all the currents originated from the electrical activity of the heart?
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What is the location where electrodes are usually placed to record the electrical activity of the heart?
What is the location where electrodes are usually placed to record the electrical activity of the heart?
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What is the purpose of augmented unipolar leads?
What is the purpose of augmented unipolar leads?
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What is the purpose of unipolar precordial chest leads?
What is the purpose of unipolar precordial chest leads?
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What does the horizontal axis on ECG paper represent?
What does the horizontal axis on ECG paper represent?
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What happens to the complexes on ECG paper if slower variations of electrical potentials occur?
What happens to the complexes on ECG paper if slower variations of electrical potentials occur?
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What is the standard calibration paper speed for ECG recording in small animals?
What is the standard calibration paper speed for ECG recording in small animals?
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Why do more muscle cells depolarizing result in higher waves on ECG paper?
Why do more muscle cells depolarizing result in higher waves on ECG paper?
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What is the purpose of aVL lead?
What is the purpose of aVL lead?
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How is heart rate calculated on ECG paper?
How is heart rate calculated on ECG paper?
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What is the standard calibration paper speed for ECG recording in humans?
What is the standard calibration paper speed for ECG recording in humans?
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Study Notes
ECG Basics
- Heart rate (HR) calculation: HR = 60/0.36 = 166 BPM
- A single heartbeat consists of the P wave, P-R interval, QRS complex, Q-T interval, and T wave
P Wave
- Represents depolarization of atrial muscle
- Occurs due to discharge of the SA node
- No deflection for SA node discharge, as it involves a small number of cells
- No deflection for atrial repolarization
P-R Interval
- Represents the time it takes for the electrical impulse to conduct through the atria, AV node, and Bundle of His
- Mostly delayed through the AV node
- Increased P-R interval is associated with A-V blocks
- Starts from the beginning of the P wave to the first deflection of the QRS
- Sympathetic stimulation decreases P-R interval, increasing conduction velocity
- Parasympathetic stimulation increases P-R interval, decreasing conduction velocity
QRS Complex
- Generated as the impulse activates the HIS-Purkinje system and ventricular muscle
- Represents ventricular depolarization
- Faster conduction velocity compared to the P wave
- Each wave represents a specific place of the ventricle being depolarized
Q-T Interval
- Reflects the approximate duration of ventricular systole and ventricular refractory period
- Measured from the beginning of the Q wave to the end of the T wave
- The S-T segment correlates with the plateau of the ventricular AP
T Wave
- Represents ventricular repolarization
- Has a longer duration than the QRS complex due to non-synchronized propagation
- High degree of variability in dogs and cats
- Can be positive, negative, biphasic, or very low amplitude
R-R Interval
- Represents the time between one R wave and the next
- Used to evaluate the regularity of the heartbeats (rhythm)
- Used to calculate HR when the rhythm is regular
ECG Interpretation
- Heart rate: number of heartbeats per minute
- Segment: time length between two specific points on an ECG at the baseline amplitude
- Interval: time length between two specific ECG events
- Sinus rhythm: normal cardiac rhythm where depolarization begins at the SA node
- Arrhythmia: abnormal heart rhythm
- Tachycardia: increased heart rate
- Bradycardia: decreased heart rate
How ECG Works
- A positive and a negative charge separated by a small distance is a dipole, which generates local current flow and a small electrical field
- Cardiac muscle cells act like a dipole when depolarizing or repolarizing
- The electrical field generated by a single dipole is too small to be measured, but the sum of multiple dipoles can be detected
- When cardiac impulses pass through the heart, the electrical current also spreads into adjacent tissues
- A small portion of the current spreads to the surface of the body, which can be recorded by electrodes
ECG Paper
- Allows 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
- The horizontal axis represents time in milliseconds
- The vertical axis represents amplitude in millivolts
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Description
Test your knowledge of Electrocardiography basics, including heart rate calculation, P wave, and P-R interval. Learn about the electrical activity of the heart and its representations on an ECG graph.