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Questions and Answers
Which of the following is NOT a factor that contributes to efficient blood ejection in the heart?
Which of the following is NOT a factor that contributes to efficient blood ejection in the heart?
What does the ECG record?
What does the ECG record?
What does a '0' reading on an ECG indicate?
What does a '0' reading on an ECG indicate?
Why is it important for the chambers of the heart to relax after contracting?
Why is it important for the chambers of the heart to relax after contracting?
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What is the relationship between the ECG and the cardiac contraction cycle?
What is the relationship between the ECG and the cardiac contraction cycle?
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Which ion current contributes to making the membrane charge more positive?
Which ion current contributes to making the membrane charge more positive?
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Which of these ions enters the cell during the action potential?
Which of these ions enters the cell during the action potential?
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Which of the following statements is TRUE about the Na+ channels?
Which of the following statements is TRUE about the Na+ channels?
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What is the main function of the refractory period?
What is the main function of the refractory period?
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What is the main difference between the effective refractory period and the relative refractory period?
What is the main difference between the effective refractory period and the relative refractory period?
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Which of these statements accurately describes the effect of Class 3 anti-arrhythmic drugs on the action potential?
Which of these statements accurately describes the effect of Class 3 anti-arrhythmic drugs on the action potential?
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Which of the following is NOT a characteristic of ventricular fibrillation?
Which of the following is NOT a characteristic of ventricular fibrillation?
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What is the primary mechanism of action of Class 2 anti-arrhythmic drugs?
What is the primary mechanism of action of Class 2 anti-arrhythmic drugs?
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Which class of anti-arrhythmic drugs primarily affects the sinoatrial (SA) node to reduce heart rate?
Which class of anti-arrhythmic drugs primarily affects the sinoatrial (SA) node to reduce heart rate?
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How do Class 1 anti-arrhythmic drugs reduce the chance of triggering another action potential?
How do Class 1 anti-arrhythmic drugs reduce the chance of triggering another action potential?
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What is the primary effect of class I antidysrhythmic drugs on the cardiac action potential?
What is the primary effect of class I antidysrhythmic drugs on the cardiac action potential?
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Which of the following is NOT a characteristic of fibrillation?
Which of the following is NOT a characteristic of fibrillation?
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Which of the following is a mechanism of action for class II antidysrhythmic drugs?
Which of the following is a mechanism of action for class II antidysrhythmic drugs?
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What is the primary aim of anti-arrhythmic drugs?
What is the primary aim of anti-arrhythmic drugs?
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What is the term used to describe an abnormally slow heart rate?
What is the term used to describe an abnormally slow heart rate?
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Which of the following is NOT a way in which anti-arrhythmic drugs can work to reduce dysrhythmias?
Which of the following is NOT a way in which anti-arrhythmic drugs can work to reduce dysrhythmias?
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Which class of antidysrhythmic drugs is MOST associated with the blocking of sodium channels?
Which class of antidysrhythmic drugs is MOST associated with the blocking of sodium channels?
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What type of arrhythmia is considered fatal and requires IMMEDIATE intervention?
What type of arrhythmia is considered fatal and requires IMMEDIATE intervention?
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Study Notes
Anti-arrhythmic Drugs
- Anti-arrhythmic drugs aim to restore normal sinus rhythm
- They achieve this by preventing depolarisation outside the normal sinus rhythm
- They also prevent transmission of non-sinus depolarisations
- Generally, they reduce electrical excitability of the heart
Cardiac Arrhythmias
- Arrhythmias are classified according to the origin of the problem. Examples are atrial fibrillation and ventricular ectopic beats
- They are also classified by the direction of rate change. Examples are tachycardia (increased heart rate) and bradycardia (decreased heart rate)
- Fibrillation is a lack of discernible rhythm. This is a severe concern as it can be survivable (atrial) or fatal (ventricular)
- A defibrillator is used in cases of ventricular fibrillation to resynchronise the heart
Cardiac Contraction Cycle
- Coordinated contractions are essential for efficient blood ejection
- Atrial contraction pushes blood into the ventricles
- Ventricular contraction pumps blood past the aortic valve into circulation
- Relaxation allows chambers to refill for the next contraction
- Any uncoordinated contraction reduces blood transfer efficiency
ECG and Cardiac Activity
- An ECG records changes in the cardiac membrane current
- '0' on an ECG signifies no depolarization or repolarization which indicates fibrillation (the average electrical activity is zero)
- The ECG shows the relationship between cardiac contraction and electrical activity:
- P wave corresponds to atrial systole
- QRS complex shows ventricular systole
- T wave shows ventricular repolarisation
- The intervals between the waves also have meaning and are measured in milliseconds
Action Potentials
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Cardiomyocyte action potentials are characterized by phases: (0, 1, 2, 3, 4) each with specific ion currents involved (e.g. Na+, K+, Ca2+).
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Various phases of the action potential reflect different ion channels opening/closing leading to electrical changes.
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These ion currents and channels play crucial roles for normal heart function.
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Refractory period: this is a crucial aspect of cardiac function. It is the period where the heart cannot be stimulated to contract again, naturally protecting from arrhythmias
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The refractory period has two parts:
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Effective refractory period
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Relative refractory period
Ion Currents in Cardiomyocytes
- Na+ current: Positive membrane charge activates Na+ channels; Na+ enters the cell making the membrane more positive
- K+ current: Positive membrane charge activates K+ channels; K+ exits the cell making the membrane more negative
- Ca2+ current: Positive membrane charge activates Ca2+ channels; Ca2+ enters the cell making the membrane more negative
- I current: Negative membrane charge activates I channels;cations enter the cell, making the membrane more positive
Voltage-sensitive Na+ channels
- Na+ channels rapidly switch between open and inactivated states
- The channel needs to go through a closed state before being able to reopen after reaching the inactivated state by being exposed to a negative voltage
Anti-arrhythmic Drug Classification
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Class I: Sodium channel blockers (e.g., lidocaine)
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Class II: Beta-adrenergic antagonists (e.g., propranolol) which reduce the effect of sympathetic activation
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Class III: Potassium channel blockers (e.g., amiodarone) which prolong repolarization
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Class IV: Calcium channel blockers (e.g., verapamil)
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The diagram show the effect of the drugs on the cardiac action potential
No Transmission= No Dysrhythmia
- Dysfunction with no transmission = sinus rhythm
- Dysfunction leading to transmission = arrhythmia
- This is due to failure of repolarization failing out of or within the refractory period
- Repolarisation has to be complete before an action potential can happen again
Fibrillation
- Uncoordinated contraction = no ejection
- Electrical cardioversion required to resynchronize cells
- AED (Automated External Defibrillator) and ICD (Implantable Cardioverter Defibrillator) are used to resynchronise the heart
Summary
- Ventricular fibrillation is incompatible with life
- Cardiac arrhythmias reduce heart efficiency and can lead to fibrillation
- Anti-arrhythmic drugs reduce electrical excitability to regulate cardiac activity
- Different classes of anti-arrhythmic drugs target different ion channels or receptors, affecting various aspects of the cardiac action potential.
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Description
This quiz explores the functions of anti-arrhythmic drugs and the classification of cardiac arrhythmias. It covers vital concepts like the cardiac contraction cycle and the implications of various arrhythmias. Test your knowledge on how these elements influence heart health and treatment methods.
