Questions and Answers
What is the result of sympathetic stimulation on the heart?
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 significance of the S-T segment in an ECG?
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What does the P wave in an ECG represent?
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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?
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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?
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What is the significance of the T wave in an ECG?
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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?
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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?
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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?
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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?
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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?
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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?
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What is the purpose of augmented unipolar leads?
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What is the purpose of unipolar precordial chest leads?
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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?
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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?
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What is the purpose of aVL lead?
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How is heart rate calculated on ECG paper?
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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.