Questions and Answers
What is the primary pacemaker of the heart responsible for initiating the heartbeat?
What characterizes ventricular tachycardia?
Which phase of the action potential involves the influx of Ca2+ ions in pacemaker cells?
What is a common adverse effect associated with the antiarrhythmic drug Quinidine?
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In which situation would Class I antiarrhythmic drugs be considered appropriate?
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What is the primary action of Class II antiarrhythmic drugs?
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What is characterized by altered conduction leading to tachycardia?
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Which of the following conditions would NOT predispose to arrhythmia?
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What effect do antiarrhythmic drugs aim to achieve?
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What is the mechanism of action for the drug Lidocaine?
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What is the primary function of the S.A. node in the cardiac conduction system?
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What is the role of beta-1 receptors in the heart?
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Which section of the electrocardiogram represents the delay between atrial and ventricular depolarization?
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What effect would increased muscarinic receptor activity have on heart function?
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What is the main cause of the QRS complex in an electrocardiogram?
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Which type of supraventricular tachycardia is specifically characterized by ectopic activation from the atrium?
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Which of the following statements is true regarding the relationship between tachycardia and arrhythmia?
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What might an elevated presence of muscarinic receptors in the ventricular myocardium affect?
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What does the T wave in an electrocardiogram indicate?
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Which component in the cardiac conduction system is responsible for conducting impulses to the ventricle?
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What is a primary use of Ibutilide?
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What is a notable adverse effect associated with the use of certain antiarrhythmic medications?
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Which class of medication primarily affects the SA and AV node?
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Which of the following is a potential side effect of Ibutilide?
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Which arrhythmia is treated with calcium channel blockers?
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Which of the following is NOT an adverse effect associated with antiarrhythmic medications?
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What is a common condition that class IV medications are not effective against?
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What is the main site of action for calcium channel blockers?
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Bradycardia, heart block, and heart failure are associated with which of the following?
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Which adverse effect is characterized by tremors, headaches, and ataxia?
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Study Notes
Cardiac Conduction System
- Begins with the Sinoatrial (SA) node, which generates electrical impulses to stimulate cardiac contraction.
- SA node cells are activated by the autonomic nervous system utilizing beta-1 receptors for acceleration and muscarinic receptors.
- Inter-nodal pathways conduct the impulse from the SA node to the Atrioventricular (AV) node, which routes signals to the ventricles.
- Ventricular myocardium predominantly contains beta-1 receptors, with minimal muscarinic presence to ensure effective ejection fraction.
- Major components: SA node → Inter-nodal pathways → AV node → Bundle of His → Purkinje fibers.
Electrocardiogram (ECG) Waves
- P wave: Represents atrial depolarization due to SA node signaling.
- PR segment: Allows for ventricular filling via delayed conduction from the SA to AV node.
- QRS complex: Depolarization of ventricular muscle, key for heart contractions.
- ST segment: Marks the start of ventricular repolarization and should appear flat.
- T wave: Indicates complete ventricular repolarization.
- U wave: Residual polarization; not seen in all patients.
Supraventricular Tachycardia Types
- Paroxysmal tachycardia: Caused by ectopic activation from the atrium.
- Atrial flutter: Distinct rapid rhythm type.
- Atrial fibrillation: Chaotic electrical activity in the atria.
Tachycardia vs Arrhythmia
- Tachycardia: An increased heart rate; may be normal but potentially pathological if out of rhythm.
- Sinus tachycardia: Elevated rate without arrhythmia; risk of developing arrhythmia at extreme rates.
- Ventricular tachycardia: Abnormal fast heart rhythms originating in the ventricles.
Pacemaker Cells Action Potential
- Reflects cardiac contractility, with the slope of action potential determining heart rate.
- SA node: Normal depolarization of 60-100 beats per minute (bpm); primary pacemaker.
- AV node: Normal depolarization of 40-60 bpm.
- Three phases of action potential:
- Phase 4: Slow depolarization via Na+ influx; leads to threshold potential (-40 mV).
- Phase 0: Depolarization occurs when reaching -40 mV due to Ca2+ channel activation (+10 mV upstroke).
- Phase 3: Repolarization as K+ channels open, returning potential to -60 mV.
Myocytes Action Potential
- Exhibits five phases:
- Phase 0: Rapid depolarization via Na+ influx, reaching +20 mV.
- Phase 1: Na+ channel inactivation; slight potential drop initiates phase 2.
- Phase 2: Plateau from balanced Ca2+ influx and K+ efflux.
- Phase 3: Repolarization due to closing of Ca2+ channels and sustained K+ efflux.
- Phase 4: Resting phase without spontaneous depolarization.
Arrhythmia Overview
- Abnormalities in heart rhythm (extrasystoles like PAC, PVC) or heart rate (tachycardia, bradycardia).
- Regular rhythms (sinus tachycardia/bradycardia) are not considered arrhythmias, but extreme rates can increase risk.
Tachycardia Arrhythmia Origins
- Altered automaticity and conduction lead to various tachycardias.
- Ectopic atrial conduction results in extra beats and tachycardia episodes.
Types of Re-entrant Tachycardia
- AV nodal re-entry tachycardia (AVNRT) involves dual pathways within the AV node causing circulatory transmission.
- AV re-entry tachycardia (AVRT) can be orthodromic or antidromic, causing abnormal signal routing.
- Wolff-Parkinson-White syndrome features an abnormal conduction pathway (Bundle of Kent).
Anti-arrhythmic Drugs Overview
- Aim to restore normal heart rhythm, conduction, and rate.
- Modulate conduction velocity, cardiac cell excitability, and automaticity.
Antiarrhythmic Drug Classifications
-
Class I: Na+ channel blockers; divided into subclasses affecting action potential duration.
- Class IA: Quinidine and Procainamide; used for various arrhythmias with notable side effects including QT prolongation.
- Class IB: Lidocaine; used for ventricular arrhythmias, limited orally due to low bioavailability.
- Class IC: Flecainide; effective for supraventricular arrhythmias, riskier for pro-arrhythmias.
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Class II: Beta-blockers that reduce heart rate and prevent re-entry arrhythmias, useful in emotional or exercise-induced atrial arrhythmias.
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Class III: Prolong action potential duration (e.g., Amiodarone); effective across multiple arrhythmia types with significant side effects.
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Class IV: Calcium channel blockers; primarily affect SA and AV nodes, used in atrial arrhythmias but not effective for ventricular types.
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Description
This quiz covers the cardiac conduction system, starting with the sinoatrial (S.A.) node and including its connection to the autonomic nervous system. It explores the roles of beta-1 and muscarinic receptors, inter-nodal pathways, and the atrioventricular (A.V.) node. Test your knowledge on how electrical impulses control heart function.
