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Questions and Answers
What is the primary mechanism underlying re-entry?
What is the primary mechanism underlying re-entry?
Which type of afterdepolarisation occurs during phase 4 and is associated with elevated Ca2+ levels?
Which type of afterdepolarisation occurs during phase 4 and is associated with elevated Ca2+ levels?
What is the term for the abnormal automaticity of pacemaker cells, leading to tachycardia?
What is the term for the abnormal automaticity of pacemaker cells, leading to tachycardia?
Which syndrome is an example of re-entry due to an accessory electrical pathway bypassing the AV node?
Which syndrome is an example of re-entry due to an accessory electrical pathway bypassing the AV node?
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What is the effect of decreased AP threshold on pacemaker cells?
What is the effect of decreased AP threshold on pacemaker cells?
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What is the term for the re-entry of electrical impulses from the ventricles back to the atria?
What is the term for the re-entry of electrical impulses from the ventricles back to the atria?
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Which class of antiarrhythmic drugs primarily affects the slow depolarization phase of action potentials, particularly in the sinoatrial and atrioventricular nodes?
Which class of antiarrhythmic drugs primarily affects the slow depolarization phase of action potentials, particularly in the sinoatrial and atrioventricular nodes?
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What is the primary mechanism of action for Class 1 antiarrhythmic drugs?
What is the primary mechanism of action for Class 1 antiarrhythmic drugs?
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Which of the following effects is NOT a general effect of antiarrhythmic drugs?
Which of the following effects is NOT a general effect of antiarrhythmic drugs?
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Which class of antiarrhythmic drugs primarily targets calcium channels?
Which class of antiarrhythmic drugs primarily targets calcium channels?
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Which of the following is NOT a characteristic of ectopic beats?
Which of the following is NOT a characteristic of ectopic beats?
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What is the primary mechanism of action for digoxin?
What is the primary mechanism of action for digoxin?
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Which of the following statements accurately describes the action of Class 3 antiarrhythmic drugs?
Which of the following statements accurately describes the action of Class 3 antiarrhythmic drugs?
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What is the term used to describe the property of heart cells to generate spontaneous action potentials?
What is the term used to describe the property of heart cells to generate spontaneous action potentials?
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What ion primarily causes rapid depolarization in cardiac myocytes?
What ion primarily causes rapid depolarization in cardiac myocytes?
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Which phase of the cardiac action potential is characterized by a plateau due to calcium and potassium ion movements?
Which phase of the cardiac action potential is characterized by a plateau due to calcium and potassium ion movements?
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What is the role of the atrio-ventricular (AV) node in cardiac physiology?
What is the role of the atrio-ventricular (AV) node in cardiac physiology?
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What type of channels are primarily involved during the repolarization phase of the cardiac action potential?
What type of channels are primarily involved during the repolarization phase of the cardiac action potential?
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In general, what effect do antiarrhythmic drugs have on ion flux in heart cells?
In general, what effect do antiarrhythmic drugs have on ion flux in heart cells?
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What is the effective refractory period (ERP) in cardiac action potential physiology?
What is the effective refractory period (ERP) in cardiac action potential physiology?
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What is the predominant ion responsible for maintaining resting membrane potential in cardiac myocytes?
What is the predominant ion responsible for maintaining resting membrane potential in cardiac myocytes?
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Which node of the heart is known as the primary pacemaker?
Which node of the heart is known as the primary pacemaker?
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Study Notes
Cardiac Electrical Activity
- The sino-atrial node, atrio-ventricular node, and Purkinje fibres are responsible for cardiac electrical activity.
Cardiac Action Potential
- The cardiac action potential has five phases: rapid depolarisation, partial repolarisation, plateau, repolarisation, and resting potential.
- Phase 1: rapid depolarisation ( VG Na+ )
- Phase 2: partial repolarisation ( VG K+ )
- Phase 3: plateau ( L-type VG Ca2+ vs. K+ )
- Phase 4: repolarisation ( VG K+ )
- Phase 5: resting potential
Abnormal Electrical Activity
- Re-entry: a type of abnormal electrical activity that occurs when an impulse re-excites previously active tissue, often associated with damaged heart tissue.
- Ectopic pacemaker activity: excessive automaticity or overactivity of nodes or ectopic activity outside nodes.
- Triggered activity:
- Early afterdepolarisations: occur during phase 2/3, elevated Ca2+
- Delayed afterdepolarisations: occur during phase 4, elevated Ca2+
Re-entry
- Re-entry occurs when there is a conduction delay in one pathway, causing the action potential to re-enter the cycle and cause additional beats.
- Example: Wolfe-Parkinson-White syndrome, which involves an accessory electrical pathway that bypasses the AV node.
Abnormal Automaticity
- Abnormal automaticity occurs when pacemaker cells are excessively active.
- Common in nodes and usually caused by increased phase 4 depolarisation or a decrease in AP threshold.
Arrhythmias
- Arrhythmias are abnormal heart rhythms that can be caused by re-entry, ectopic pacemaker activity, or triggered activity.
CV Pharmacology: Anti-arrhythmics
- Anti-arrhythmic drugs work by altering the characteristics of cardiac action potentials.
- Classes of anti-arrhythmic drugs:
- Class 1: lengthens rapid depolarisation (myocytes)
- Class 2: lengthens slow depolarisation (mostly nodes)
- Class 3: delays repolarisation
- Class 4: lengthens nodal AP
- Digoxin and Adenosine: special classes
Mechanisms of Anti-arrhythmic Drugs
- Anti-arrhythmic drugs increase the refractory period and decrease the likelihood of action potential generation.
Sicilian Gambit
- The Sicilian Gambit is a more complex anti-arrhythmic drug classification, including clinical and ECG effects, developed in the 1990s.
Learning Objectives
- MBBS Learning Objectives: outline the mechanisms of action and therapeutic use of drugs that target the heart and vascular system.
Additional Info
- Chronotropic: altering the rate of the heart
- Inotropic: altering the strength of heart contraction
- Automaticity: the property of heart cells to generate spontaneous action potentials
- Ectopic beats: action potentials generated in the wrong place (e.g. in myocytes, out of phase with the nodes)
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Description
Learn about the mechanisms of ectopic beats, re-entry, and types of pacemaker activity in the heart, including triggered and automatic activity. Understand the role of calcium ions and phases of the action potential.
