Cardiac Arrhythmias

Questions and Answers

What is the primary role of the atrioventricular (AV) node in the cardiac conduction system?

Initiate the cardiac contraction cycle

Generate action potentials independently

Propagate impulses to the Purkinje fibers

Delay impulse propagation for ventricular filling (correct)

Which ions dominate the interior of myocardial fibers at rest?

Calcium

Chloride

Sodium

Potassium (correct)

What initiates the action potential in cardiac muscle fibers?

Spontaneous leakage of potassium ions

Calcium influx through voltage-gated channels

Depolarization from the AV node

Opening of voltage-gated sodium channels (correct)

Which component of the conduction system is responsible for rapid electrical signal transmission to the ventricles?

Bundle of His Signup and view all the answers

What describes the resting potential of contractile myocardial fibers?

Stable at approximately -90 mv Signup and view all the answers

What is the main consequence of the spontaneous depolarization in pacemaker cells?

Independence from central nervous system signals Signup and view all the answers

Which part of the conduction system first generates the electrical impulse that triggers heart contraction?

Sinoatrial (SA) node Signup and view all the answers

What is the role of Purkinje fibers in the cardiac conduction system?

Conduct impulses quickly to the ventricles Signup and view all the answers

What defines enhanced normal automaticity in the heart?

The SA node fires at a rate higher than normal. Signup and view all the answers

Which mechanism is primarily responsible for clinically important arrhythmias?

Enhanced automaticity Signup and view all the answers

What is a fundamental requirement for the re-entry mechanism to occur?

Unidirectional block Signup and view all the answers

Which statement correctly describes triggered activity in relation to abnormal impulse initiation?

It is characterized by impulses not initiated by the heart's natural pacemaker. Signup and view all the answers

What occurs during enhanced abnormal automaticity in the heart?

A different site fires faster than the SA node. Signup and view all the answers

What characterizes the conduction block mechanism in arrhythmias?

Impulses are blocked in one direction. Signup and view all the answers

In the context of cardiac action potentials, what phase requires a stimulus for depolarization?

Phase 4 Signup and view all the answers

What is the result of enhanced automaticity at the SA node?

It can cause sinus tachycardia. Signup and view all the answers

What is the mainstay of treatment for sinus tachycardia?

Reassurance and treatment of the underlying cause Signup and view all the answers

Which of the following statements about supraventricular tachycardia (SVT) is true?

Patients with SVT may experience attacks of rapid regular palpitations of sudden onset. Signup and view all the answers

Which method is first-line treatment for stable patients with SVT?

Vagal maneuvers and IV adenosine Signup and view all the answers

What is the common rate range for atrioventricular nodal reentrant tachycardia (AVNRT)?

160-220 bpm Signup and view all the answers

What characteristic is typically seen on the ECG of patients with AVNRT?

Narrow-complex tachycardia with hidden P waves Signup and view all the answers

What is the primary mechanism involved in AVNRT?

Reentry within the AV node Signup and view all the answers

In which situation is synchronized cardioversion recommended as the initial management for SVT?

Then the patient is hemodynamically unstable Signup and view all the answers

What is a likely symptom of patients experiencing episodes of SVT?

Symptoms of low cardiac output Signup and view all the answers

What pathway is utilized for impulse conduction during a premature beat when the fast pathway is refractory?

Slow pathway Signup and view all the answers

Which arrhythmia is characterized by abnormal depolarizations triggered by an action potential?

Torsades de pointes Signup and view all the answers

What condition describes a slower rate of depolarization by the SA node?

Sinus bradycardia Signup and view all the answers

Which symptom is commonly reported by patients experiencing tachyarrhythmias?

Palpitations Signup and view all the answers

What is a potential clinical manifestation of cardiac arrhythmias associated with low cardiac output?

Dizziness Signup and view all the answers

What type of conduction block can occur at the AV node?

Heart block Signup and view all the answers

Which of the following is NOT a symptom of low cardiac output during arrhythmias?

Severe abdominal pain Signup and view all the answers

What describes the condition where the fast pathway recovers retrogradely after a slow pathway impulse?

Reentrant tachycardia Signup and view all the answers

Which of the following is the most common cause of atrial fibrillation?

Systemic hypertension Signup and view all the answers

Which of the following conditions is most likely to contribute to thrombus formation in patients with atrial fibrillation?

Atrial dilatation Signup and view all the answers

What is a notable hemodynamic consequence of atrial fibrillation?

Loss of atrial contraction contributing to cardiac output reduction Signup and view all the answers

Which diagnostic finding in an ECG is characteristic of atrial fibrillation?

Irregular heartbeats without P waves Signup and view all the answers

Patients with which condition are particularly susceptible to the hemodynamic effects of atrial fibrillation?

Mitral stenosis and diastolic dysfunction Signup and view all the answers

Which of the following factors does NOT contribute to the etiology of atrial fibrillation?

Acute myocardial infarction Signup and view all the answers

What role does aging play in the development of atrial fibrillation?

Increases the risk due to structural changes in the heart Signup and view all the answers

During a clinical examination of a patient with atrial fibrillation, which finding would most likely be observed?

Irregularly irregular pulse with pulsus deficit Signup and view all the answers

Study Notes

Anatomy and Physiology of Cardiac Conduction System

Comprised of specialized myocytes that generate action potentials for synchronized muscle contraction.
Electrical impulses originate in the sinoatrial (SA) node in the right atrium.
Impulses stimulate atrial contraction, then propagate to the atrioventricular (AV) node, which delays conduction for ventricular filling.
Rapid conduction follows down the bundle of His, branching into left and right bundle branches, then to Purkinje fibers.

Cardiac Muscle Action Potential

Resting potential of contractile myocardial fibers is approximately -90 mV, influenced by sodium, calcium, and potassium ion concentrations.
Action potential initiation occurs when voltage-gated sodium channels open, causing depolarization.
Pacemaker cells have automaticity, resulting from spontaneous sodium ion leakage leading to depolarization.

Mechanisms of Cardiac Arrhythmias

Arrhythmias arise from abnormal impulse initiation or conduction.
Enhanced automaticity, re-entry, and triggered activity cause tachyarrhythmias.
Bradyarrhythmias result from suppressed automaticity and conduction blocks.

Types of Abnormal Impulse Initiation

Enhanced Automaticity: SA node or other foci firing at higher rates (e.g., sinus tachycardia, atrial/ventricular premature beats).
Suppressed Automaticity: Reduced rate (sinus bradycardia) or cessation (sinus arrest) of SA node firing.

Re-entry Mechanism

Most common mechanism for significant arrhythmias; entails circular propagation of excitatory waves.
Requires slow conduction pathways, unidirectional block, and a trigger (e.g., premature beat).

Triggered Activity

Uncommon mechanism; abnormal depolarizations occur due to membrane voltage instability (after depolarization).
Associated with arrhythmias like Torsades de pointes.

Clinical Manifestations of Cardiac Arrhythmias

Can be asymptomatic or manifest as palpitations, symptoms of low cardiac output (dizziness, dyspnea, fatigue).
Symptoms may arise both at rest and with exertion and can be chronic or paroxysmal.

Supraventricular Tachycardias (SVT)

Includes atrioventricular nodal reciprocating tachycardia (AVNRT) and atrioventricular reciprocating tachycardia (AVRT).
Typically presents with rapid, regular palpitations of sudden onset, lasting minutes to hours.

Management of SVTs

Immediate termination for hemodynamic instability via synchronized cardioversion.
For stable cases, initial treatments include vagal maneuvers or IV adenosine, followed by beta blockers or calcium channel blockers if needed.
Long-term management often involves catheter ablation.

Atrial Fibrillation (AF) Etiology

Multifactorial causes; structural heart disease is a common contributor.
Primary causes: systemic hypertension, mitral valve disease, coronary artery disease, thyroid disorders, atrial septal defects, constrictive pericarditis, and idiopathic cases.

Consequences of Atrial Fibrillation

Structural: atrial dilation, fibrosis, and necrosis leading to increased AF progression.
Hemodynamic: loss of atrial contraction reduces cardiac output by 15-20%.
Thrombosis risk due to blood stagnation in the left atrial appendage, increasing stroke risk.

Diagnosis and Workup of Atrial Fibrillation

Symptoms may be absent or include palpitations, fatigue, dyspnea, and chest tightness.
Clinical findings include an irregularly irregular pulse and pulsus deficit.
ECG analysis reveals irregular heartbeats and absent P waves.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers the anatomy and physiology of the heart's conduction system, as well as the basic mechanisms and types of cardiac arrhythmias. Students will also learn about the management and classification of atrial fibrillation, helping them understand clinical presentations and treatments. Test your knowledge and enhance your understanding of cardiac arrhythmias!