p.3
Electrical Activity and Action Potentials
What initiates and organizes the contractile sequence of the heart?
An electrical signal known as Action Potential (AP) initiates and organizes the contractile sequence.
p.3
Myogenic Nature of Cardiac Muscle
What is the nature of all vertebrate hearts?
All vertebrate hearts are myogenic and will continue beating even if all nervous connections are removed.
p.18
Electrocardiography (ECG) Basics
What do ECG waveforms correspond with?
ECG waveforms correspond with the electrical activity of the heart.
p.2
Blood Flow Pathways in the Heart
What valve does blood flow through from the left atrium to the left ventricle?
Blood flows through the left AV valve to the left ventricle.
p.2
Blood Flow Pathways in the Heart
How does deoxygenated blood return to the heart?
Deoxygenated blood returns from systemic circulation to the right atrium via vena cavae.
p.26
Electrical Activity and Action Potentials
What do ECG waveforms correspond with?
ECG waveforms correspond with the electrical activity of the heart.
p.36
Disturbances in Impulse Generation and Propagation
What is sinus tachycardia and how does it appear on an ECG?
Sinus tachycardia is characterized by a normal ECG except that T waves overlap P waves, and it is probably initiated by SA node pacemaker cells. The heart rate is approximately 235 bpm, which is extremely rapid for a resting dog.
p.4
Myogenic Nature of Cardiac Muscle
What is the nature of cardiac muscle in terms of action potential initiation?
Cardiac muscle is myogenic, meaning the initiation of an action potential is spontaneous and does not require input from the nervous system.
p.8
Cardiac Conduction System Components
What is the function of the Bundle of His?
The Bundle of His penetrates the annulus fibrosis and divides into left and right bundle branches, facilitating the conduction of action potentials to the ventricles.
p.7
Cardiac Conduction System Components
What is the role of the cardiac conducting system?
It transmits depolarisation between the atria and ventricles, enabling a coordinated response.
p.7
Disturbances in Impulse Generation and Propagation
What is 'refractoriness' in cardiac cells?
It is the period during which cells cannot be depolarised again until they return to resting potential after repolarisation.
p.2
Blood Flow Pathways in the Heart
What valve does blood flow through from the right atrium to the right ventricle?
Blood flows through the right AV valve to the right ventricle.
p.5
Cardiac Conduction System Components
What structure allows rapid conduction of action potentials between cardiac muscle cells?
Intercalated discs allow rapid conduction of the depolarization between cells.
p.3
Functional Anatomy of the Mammalian Heart
How does the heart propel blood through the blood vessels?
The heart propels blood by alternately contracting and relaxing.
p.4
Role of the Sinoatrial Node (SAN)
Where does spontaneous depolarization of autorhythmic cells occur?
Spontaneous depolarization of autorhythmic cells occurs in the sinoatrial node (SAN), which contains 'pacemaker' cells.
p.17
Electrocardiography (ECG) Basics
How do I record an ECG?
2 or more electrodes are applied to the skin surface either side of the heart. Voltages recorded between a pair of electrodes (+ ve and - ve) are displayed on a video screen or printed on a strip of paper.
p.9
Cardiac Conduction System Components
How does depolarisation spread through the atrial muscle?
Depolarisation spreads rapidly through atrial muscle.
p.7
Disturbances in Impulse Generation and Propagation
What does refractoriness allow for in the heart?
It allows time for filling of the cardiac chambers and coordinated muscle contraction.
p.13
Cardiac Conduction System Components
What happens if the SAN becomes dysfunctional?
If the SAN becomes dysfunctional, the Atrioventricular Node (AVN) will take over the role of pacemaker.
p.9
Cardiac Conduction System Components
Why is the delay in depolarisation at the A-V node important?
The delay ensures adequate time for ventricular filling.
p.5
Myogenic Nature of Cardiac Muscle
What is the functional network formed by cardiac muscle cells called?
The functional network is called a syncitium, where cells contract in synchrony as a unit.
p.20
Electrocardiography (ECG) Basics
What is Einthoven's triangle?
A system of limb leads that record electrical activity reaching the body surface in the horizontal (frontal) plane, with the heart assumed to be located approximately in the center of an equilateral triangle formed by the two front limbs and the left hind limb.
p.8
Cardiac Conduction System Components
What are Purkinje fibres and their significance in the heart?
Purkinje fibres form an extensive network that branches into the ventricular myocardium, allowing rapid transmission of action potentials to both ventricles, with larger animals having thicker fibres that conduct action potentials more rapidly.
p.26
ECG Waveforms and Interpretation
What is the significance of T wave morphology in an ECG?
T wave morphology is extremely variable due to changes in the pattern of repolarisation.
p.40
Disturbances in Impulse Generation and Propagation
What factors are associated with atrial fibrillation in horses?
Atrial fibrillation is associated with large atria and high vagal tone, and may also involve mitral insufficiency.
p.23
Electrocardiography (ECG) Basics
How many leads are required for rhythm assessment in horses?
A single lead is required.
p.13
Role of the Sinoatrial Node (SAN)
Where does depolarisation occur most rapidly in the heart?
Depolarisation occurs most rapidly in the Sinoatrial Node (SAN).
p.9
Cardiac Conduction System Components
What happens to depolarisation as it enters the A-V node?
Depolarisation enters and traverses the A-V node relatively slowly.
p.30
Electrocardiography (ECG) Basics
What is the formula to calculate heart rate using R-R intervals?
HR = number of R - R intervals in 6 seconds x 10
p.6
Cardiac Conduction System Components
Why is it important to have a delay between the contraction of the atria and ventricles?
The delay is important to ensure proper filling of the ventricles before they contract.
p.34
Arrhythmias and Electrical Dysfunctions
What happens to parasympathetic activation during inspiration in respiratory sinus arrhythmia?
There is decreased parasympathetic activation during inspiration.
p.24
Electrocardiography (ECG) Basics
What alterations can an ECG indicate regarding conductivity?
Alterations in conductivity between heart and skin.
p.22
Electrocardiography (ECG) Basics
What are the six standardised ECG leads used in small animal medicine?
The six standardised ECG leads are typically the limb leads (I, II, III) and the augmented leads (aVR, aVL, aVF).
p.2
Blood Flow Pathways in the Heart
Where does oxygenated blood enter the heart?
Oxygenated blood enters the left atrium via pulmonary veins.
p.40
Disturbances in Impulse Generation and Propagation
What is atrial fibrillation and its impact on horses?
Atrial fibrillation is common in horses and results in poor performance due to reduced cardiac output.
p.9
Cardiac Conduction System Components
Where does depolarisation begin in the cardiac conduction system?
Depolarisation begins in the S-A node.
p.2
Blood Flow Pathways in the Heart
What is the pathway of blood from the right ventricle to the lungs?
The right ventricle pumps blood through the pulmonary valve to the lungs via the pulmonary trunk.
p.6
Cardiac Conduction System Components
What separates the atria and ventricles in the heart?
The annulus fibrosus separates the atria and ventricles.
p.10
Cardiac Conduction System Components
What happens to the atrial muscle during depolarisation of the ventricles?
Atrial muscle begins to repolarise nearly simultaneously as depolarisation spreads into the ventricles.
p.10
Cardiac Conduction System Components
What is the result of nearly simultaneous depolarisation of cells throughout the ventricular myocardium?
It leads to forceful ventricular contraction.
p.19
Electrocardiography (ECG) Basics
How many standardized leads are used in humans and small animals for ECG recording?
6 standardized leads: I, II, III, aVR, aVL, aVF
p.35
Arrhythmias and Electrical Dysfunctions
What are deviations from the normal regular rhythm called?
All deviations from the normal regular rhythm are termed arrhythmias.
p.32
Arrhythmias and Electrical Dysfunctions
Is there a P for every QRS?
Yes, this indicates a normal relationship between atrial and ventricular activity.
p.8
Cardiac Conduction System Components
What is the role of the Atrioventricular (A-V) node in the cardiac conduction system?
The A-V node is a collection of modified cells that conducts action potentials more slowly than ordinary muscle cells, ensuring a delay in impulse transmission between the atria and ventricles for adequate filling before contraction.
p.4
Cardiac Conduction System Components
What is the role of the sinoatrial node (SAN) in the heart?
The sinoatrial node (SAN) initiates action potentials that are transmitted throughout the contractile cells of the heart, resulting in contraction.
p.7
Cardiac Conduction System Components
What are autorhythmic cells?
Specialised conducting cells that conduct the electrical impulse from the atria to the ventricles.
p.23
Electrocardiography (ECG) Basics
What is the electrode placement configuration used in horses for rhythm assessment?
Base - Apex configuration.
p.7
Disturbances in Impulse Generation and Propagation
Why is refractoriness important for the heart?
It ensures that the heart muscle cannot develop a tetanic spasm and allows for one-way conduction.
p.10
Cardiac Conduction System Components
How does depolarisation spread in the cardiac conduction system compared to ordinary ventricular muscle?
Depolarisation spreads down the conduction system faster than it could through ordinary ventricular muscle.
p.39
Disturbances in Impulse Generation and Propagation
What is a common cause of 2nd degree AV block in resting horses?
High vagal (parasympathetic) tone.
p.34
Arrhythmias and Electrical Dysfunctions
What is respiratory sinus arrhythmia?
A naturally occurring variation in heart rate that occurs during the breathing cycle.
p.37
Disturbances in Impulse Generation and Propagation
What can happen if premature beats become persistent or continuous?
They can result in tachycardia.
p.4
Cardiac Conduction System Components
What are the two types of cardiac cells?
The two types of cardiac cells are autorhythmic cells and contractile cells.
p.15
Electrocardiography (ECG) Basics
What does the ECG detect and amplify?
The ECG detects and amplifies the tiny electrical charges on the skin caused by the depolarisation of cardiac muscle during each heartbeat.
p.2
Blood Flow Pathways in the Heart
How does the left ventricle contribute to systemic circulation?
The left ventricle pumps blood through the aortic valve to systemic circulation via the aorta.
p.14
Electrocardiography (ECG) Basics
What is electrocardiography (ECG)?
A non-invasive measurement of the electrical activity of the heart.
p.13
Myogenic Nature of Cardiac Muscle
What is the ability of autorhythmic cells?
Autorhythmic cells have the ability to spontaneously depolarise.
p.23
Electrocardiography (ECG) Basics
What is the position of the negative electrode in horse ECG placement?
The negative electrode should be above and cranial to the heart.
p.37
Disturbances in Impulse Generation and Propagation
From which sites can premature beats arise?
SAN, atrial myocardium, AVN (junctional), and ventricular myocardium.
p.39
Disturbances in Impulse Generation and Propagation
What are the types of AV block mentioned?
1st degree AV block and 2nd degree AV block.
p.41
Disturbances in Impulse Generation and Propagation
What is ventricular fibrillation?
A condition where different parts of the ventricular myocardium contract and relax at random, leading to the failure of the ventricles to pump blood.
p.34
Arrhythmias and Electrical Dysfunctions
What occurs to parasympathetic activation during expiration in respiratory sinus arrhythmia?
There is increased parasympathetic activation during expiration.
p.19
Electrocardiography (ECG) Basics
What is the purpose of different leads in an ECG?
Different leads examine the heart from different angles and help determine which area of the heart is affected.
p.14
Electrocardiography (ECG) Basics
What significant award did Dr. Willem Einthoven receive?
The Nobel Prize in Physiology/Medicine in 1924.
p.36
Disturbances in Impulse Generation and Propagation
What is sinus bradycardia and what is its heart rate?
Sinus bradycardia is characterized by a normal ECG but with a heart rate of only approximately 55 bpm, indicating that the SA node pacemaker is abnormally slow.
p.14
Electrical Activity and Action Potentials
What creates the electrical potential detected by ECG?
Cardiac cell depolarisation and repolarisation.
p.16
Electrical Activity and Action Potentials
What happens to the electrical potential in cardiac muscle during depolarization?
A difference in electrical potential is created between parts of the muscle that are depolarised and those that are not.
p.30
Electrocardiography (ECG) Basics
If the paper speed is 25mm/s, how do you measure heart rate?
Count the number of R-R intervals in 6 seconds and multiply by 10.
p.16
Electrical Activity and Action Potentials
How do ionic currents relate to the electrical activity of the heart?
The voltage difference created during depolarization sets up ionic currents in the tissues and body fluids surrounding the heart.
p.6
Cardiac Conduction System Components
Are there electrical connections (gap junctions) between the atria and ventricles?
No, there are no electrical connections (gap junctions) that cross the fibrous layer.
p.6
Cardiac Conduction System Components
What results from the electrical isolation of the atria and ventricles?
It results in two functional syncitia.
p.35
Arrhythmias and Electrical Dysfunctions
What causes arrhythmias?
Arrhythmias occur due to disturbances in impulse generation or impulse conduction.
p.32
Arrhythmias and Electrical Dysfunctions
Are they consistently and reasonably related?
Yes, consistent and reasonable relation indicates a stable rhythm.
p.32
Arrhythmias and Electrical Dysfunctions
Are P-waves and QRS complexes all the same?
Yes, uniformity in P-waves and QRS complexes suggests a normal rhythm.
p.32
Arrhythmias and Electrical Dysfunctions
Is the rhythm regular or irregular?
Determining if the rhythm is regular or irregular helps in diagnosing the type of arrhythmia.
p.28
Electrocardiography (ECG) Basics
How is the RR interval used in an ECG?
The RR interval measures the time between ventricular depolarisations and is used to calculate the ventricular rate.
p.33
Role of the Sinoatrial Node (SAN)
What is normal sinus rhythm?
Normal sinus rhythm is the heart rhythm originating from the sinoatrial node, characterized by a regular rate of 60 to 100 beats per minute and a consistent pattern of P waves preceding each QRS complex.
p.38
Arrhythmias and Electrical Dysfunctions
What is a ventricular ectopic beat?
A ventricular ectopic beat is a premature ventricular depolarisation.
p.23
Electrocardiography (ECG) Basics
Where should the positive electrode be placed in relation to the heart in horses?
The positive electrode should be below and caudal to the heart.
p.38
Arrhythmias and Electrical Dysfunctions
What is a supraventricular (atrial) ectopic beat?
A supraventricular (atrial) ectopic beat is a premature atrial depolarisation.
p.13
Disturbances in Impulse Generation and Propagation
What occurs if there is a blockage in the transmission of action potentials between the atria and ventricles?
If transmission of action potentials is blocked, action potentials will be generated in the bundle of His or Purkinje network, resulting in an escape rhythm.
p.41
Disturbances in Impulse Generation and Propagation
What are the consequences of ventricular fibrillation?
It rapidly results in death (sudden death) if not treated.
p.16
Electrocardiography (ECG) Basics
What does an ECG measure?
An ECG measures the voltage differences over time that are induced by the depolarization of cardiac muscle.
p.16
Myogenic Nature of Cardiac Muscle
Which part of the ventricular myocardium depolarises first?
The ventricular myocardium lying nearest the ventricular chambers depolarises first due to its proximity to the cardiac conduction system.
p.32
Arrhythmias and Electrical Dysfunctions
Is there a QRS for every P?
Yes, this suggests that every atrial contraction is followed by a ventricular contraction.
p.28
Electrocardiography (ECG) Basics
What is measured by the QRS duration in an ECG?
The QRS duration measures the time required for ventricular depolarisation.
p.21
Electrocardiography (ECG) Basics
What do augmented limb leads measure?
They measure voltages from one limb compared to the average of the other two.
p.28
Electrocardiography (ECG) Basics
What is the purpose of the PP interval in an ECG?
The PP interval measures the time between atrial depolarisations and is used to calculate the atrial rate.
p.27
Cardiac Conduction System Components
Which node is located between the atria and ventricles?
Atrioventricular node (AV node).
p.24
Electrocardiography (ECG) Basics
What can be determined from an ECG?
Rate, rhythm, and nature of cardiac depolarisation and repolarisation.
p.9
Cardiac Conduction System Components
What prevents depolarisation from passing into the ventricles during atrial contraction?
Depolarisation does not pass through the fibrous connective tissue layer.
p.24
Electrocardiography (ECG) Basics
What does an ECG indicate about myocardial mass?
Changes in myocardial mass.
p.35
Arrhythmias and Electrical Dysfunctions
What are the two types of heart rate changes associated with arrhythmias?
Bradycardia (slow) and Tachycardia (fast).
p.25
Electrocardiography (ECG) Basics
What are the main components of the ECG?
The main components of the ECG include the P wave, QRS complex, and T wave.
p.27
Role of the Sinoatrial Node (SAN)
Which node is responsible for initiating the electrical impulse in the heart?
Sinoatrial node (SA node).
p.27
ECG Waveforms and Interpretation
What is the significance of the P-R interval in an ECG?
It represents the time taken for the electrical impulse to travel from the SA node to the AV node.
p.27
ECG Waveforms and Interpretation
What does the QRS complex represent in an ECG?
Ventricular depolarization.
p.35
Arrhythmias and Electrical Dysfunctions
What do abnormal ECG voltages indicate?
Abnormal ECG voltages are indicative of structural or electrical abnormalities.
p.10
Disturbances in Impulse Generation and Propagation
What prevents the reactivation of the atria once the action potential reaches the ventricles?
The long refractory period prevents the reactivation of the atria.
p.41
Disturbances in Impulse Generation and Propagation
How can ventricular fibrillation be reversed?
It can only be reversed by defibrillation.
p.19
Electrocardiography (ECG) Basics
What additional leads are used in humans to detect abnormal conduction?
Additional chest leads are used to detect areas of abnormal conduction caused by infarcts.
p.29
Electrocardiography (ECG) Basics
How many major divisions on the horizontal axis equal 1 second at a chart speed of 25mm/s?
5 major divisions = 1 sec.
p.29
Electrocardiography (ECG) Basics
How many major divisions on the horizontal axis equal 1 second at a chart speed of 50mm/s?
10 major divisions = 1 sec.
p.29
Electrocardiography (ECG) Basics
Why is a faster chart speed used in ECGs?
It helps to spread out ECG events in animals with rapid heart rates.
p.28
Electrocardiography (ECG) Basics
In a normal heart, how do the PP interval and RR interval compare?
In a normal heart, the PP interval and RR interval should be equal.
p.6
Cardiac Conduction System Components
What is the role of the conducting system in relation to the fibrous layer?
The conducting system acts as an 'electrical window' through the fibrous layer.
p.13
Blood Flow Pathways in the Heart
How does the distance from the SAN affect heart rate?
The further away from the SAN, the slower the heart rate will be.
p.24
Electrocardiography (ECG) Basics
What metabolic abnormalities can be indicated by an ECG?
Metabolic abnormalities affecting the myocardium.
p.27
Electrocardiography (ECG) Basics
What do the ECG waveforms correspond with?
The electrical activity of the heart.
p.21
Electrocardiography (ECG) Basics
What are augmented limb leads?
Augmented limb leads, also known as Goldberger’s leads, include aVR, aVL, and aVF.
p.31
Electrocardiography (ECG) Basics
How do you calculate the instantaneous heart rate for a paper speed of 25 mm/s?
The formula is 1500 divided by the R-R interval.
p.31
Electrocardiography (ECG) Basics
What is the instantaneous heart rate if the R-R interval is 50 mm at a paper speed of 25 mm/s?
The instantaneous heart rate is 30 bpm.
p.31
Electrocardiography (ECG) Basics
What is the formula for calculating instantaneous heart rate at a paper speed of 50 mm/s?
The formula is 3000 divided by the R-R interval.
p.28
Electrocardiography (ECG) Basics
What does the PR interval represent in an ECG?
The PR interval is the time between the start of atrial depolarisation and the start of ventricular depolarisation, reflecting A-V node conduction velocity.
p.21
Electrocardiography (ECG) Basics
How are augmented limb leads derived?
They are derived from the same 3 electrodes as leads I, II, and III.
p.28
Electrocardiography (ECG) Basics
What does the QT interval indicate in an ECG?
The QT interval is the time from the start of ventricular depolarisation to the end of ventricular repolarisation.
p.21
Electrocardiography (ECG) Basics
What is the significance of augmented limb leads?
They provide views of the heart from different angles (vectors).
p.25
Electrocardiography (ECG) Basics
What does the Q-T interval represent in an ECG?
The Q-T interval represents the time from the beginning of the Q wave to the end of the T wave.
p.25
Electrocardiography (ECG) Basics
What does the QRS complex represent in an ECG?
The QRS complex represents the depolarization of the ventricles.
p.25
Electrocardiography (ECG) Basics
What is the significance of the P wave in an ECG?
The P wave represents the depolarization of the atria.
p.25
Electrocardiography (ECG) Basics
What does the T wave indicate in an ECG?
The T wave indicates the repolarization of the ventricles.
p.25
Electrocardiography (ECG) Basics
What is the P-R interval in an ECG?
The P-R interval is the time from the beginning of the P wave to the beginning of the QRS complex.
