Questions and Answers
What is the primary mechanism underlying re-entry?
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?
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?
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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?
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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?
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Which class of antiarrhythmic drugs primarily targets calcium channels?
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Which of the following is NOT a characteristic of ectopic beats?
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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?
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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?
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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?
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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?
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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?
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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.
