14. Cardiac arrhythmias

What are cardiac arrhythmias?

Disruptions in the regular rate and rhythm of the heart caused by issues in the heart's electrical conduction system.

Causes of Arrhythmias:

Causes of Arrhythmias:

• Cardiogenic causes

• Non-cardiogenic causes

What are some cardiogenic causes of arrhythmias?

Ischemic heart disease, valve diseases, cardiomyopathies, congenital heart defects, effects of heart surgeries, and disorders related to ion channels like the long QT syndrome.

What are some non-cardiogenic causes of arrhythmias?

Increased sympathetic nervous system activity, disturbances in electrolytes like potassium and calcium, acid-base imbalances, thyroid dysfunction, reduced oxygen levels (hypoxemia), and the impact of certain medications including antiarrhythmics and beta-blockers.

Pathophysiological Mechanisms:

Pathophysiological Mechanisms:

1. Accelerated Automaticity:

2. Triggered Activity (After-depolarizations):

   • Early After-depolarizations:

   • Late After-depolarizations:

3. Re-entry:

What is Accelerated Automaticity caused by?

Accelerated Automaticity is caused by an increased rate of diastolic depolarization and changes in the threshold potential, often due to alterations in calcium and potassium levels.

What are some factors contributing to Accelerated Automaticity?

Factors contributing to Accelerated Automaticity include enhanced sympathetic tone, reduced parasympathetic activity, thyroid conditions, and medications like digoxin, which also impairs the sodium/potassium pump affecting the resting membrane potential.

What are Early After-depolarizations?

After-depolarizations that occur during the relative refractory period and can extend the repolarization phase.

What can trigger Early After-depolarizations?

Electrolyte imbalances, use of potassium channel blockers, and conditions like long QT syndrome.

What are Late After-depolarizations?

After-depolarizations that happen during the resting phase.

What can trigger Late After-depolarizations?

Overload of intracellular calcium from excessive catecholamines or digoxin.

What is re-entry in the context of the heart's electrical activity?

Re-entry is when an electrical impulse circulates around a structural obstacle within the heart, creating a loop of electrical activity.

How does re-entry in the heart occur?

Re-entry occurs when the loop of electrical activity divides into two pathways - one fast-conducting with a long refractory period and another slow-conducting with a shorter refractory period, leading to additional beats when these pathways reconverge.

What structural changes can predispose the heart to re-entry mechanisms?

Structural changes like scarring, tissue degeneration, or chamber dilation can predispose the heart to re-entry mechanisms.

Basic Types of Arrythmias

Basic Types of Arrythmias

1. Bradyarrhythmias:

2. Tachyarrhythmias:

3. Supraventricular arrhythmias:

4. Ventricular arrhythmias:

What are Bradyarrhythmias characterized by?

Issues with signal generation or conduction, resulting in a slower heart rate (under 60 beats per minute).

What symptoms may be associated with Bradyarrhythmias?

Exertional dyspnea (shortness of breath during physical activity) and syncope (fainting).

What are tachyarrhythmias?

Tachyarrhythmias are abnormal heart rhythms characterized by a fast heart rate above 100 beats per minute. They can lead to symptoms like palpitations, dizziness, and shortness of breath.

What are some symptoms of tachyarrhythmias?

• Palpitations

• Dizziness

• Shortness of breath

• Chest pain

• Fainting

• Fatigue

• Rapid heartbeat

What is the origin of supraventricular arrhythmias?

Supraventricular arrhythmias originate in the atria (upper chambers of the heart).

Why do supraventricular arrhythmias typically show a narrow QRS complex on an ECG?

Supraventricular arrhythmias show a narrow QRS complex because the signal travels quickly through the normal conduction pathway.

What is the origin of ventricular arrhythmias?

Ventricular arrhythmias originate in the ventricles, which are the lower chambers of the heart.

Why is the QRS complex wider on an ECG in ventricular arrhythmias?

The QRS complex is wider in ventricular arrhythmias because the signal travels more slowly through the ventricular muscle rather than the normal conduction pathway.

Types of Atrial Origin Bradyarrythmias

Types of Atrial Origin Bradyarrythmias

• Respiratory sinus arrhythmia:

• Sinus bradycardia:

• Sinus arrest:

• Tachycardia-bradycardia syndrome:

What is respiratory sinus arrhythmia?

A physiological variation where the heart rate increases with inhalation and decreases with exhalation, often more pronounced in younger individuals.

What is sinus bradycardia?

Common in athletes or those on certain heart medications such as beta-blockers or calcium channel blockers, characterized by a normal ECG but a heart rate less than 60 bpm.

What is respiratory sinus arrhythmia?

A physiological variation where the heart rate increases with inhalation and decreases with exhalation, often more pronounced in younger individuals.

What is sinus bradycardia?

Common in athletes or those on certain heart medications such as beta-blockers or calcium channel blockers, characterized by a normal ECG but a heart rate less than 60 bpm.

What is sinus arrest?

A condition where the sinoatrial node (SA node) fails to produce an impulse, visible on an ECG as an absence of the P-wave, sometimes followed by an escape rhythm if the pause is prolonged.

What is tachycardia-bradycardia syndrome?

Characterized by alternating fast and slow heart rates, often a manifestation of sick sinus syndrome, where the heart's natural pacemaker (SA node) malfunctions.

Sick Sinus Syndrome SSS

Sick Sinus Syndrome SSS

Causes:

• Primary cause:

• Medication-induced:

Common Presentations:

• Bradycardia symptoms:

• Tachycardia-bradycardia syndrome:

Diagnostics of sick sinus syndrome:

• Electrocardiogram (ECG):

• Exercise stress test:

Treatment of sick sinus syndrome:

• Medication review and adjustment:

• Pacemaker placement:

• Selective beta-blockers:

What is sick sinus syndrome (SSS)?

A condition where the sinoatrial (SA) node malfunctions.

What are some arrhythmias associated with sick sinus syndrome?

Sinus bradycardia, SA pause or block, arrest, and supraventricular tachycardia.

Causes

Causes:

• Primary cause:

• Medication-induced:

What is the primary cause of Sick Sinus Syndrome (SSS)?

Degeneration and fibrosis of the SA node and surrounding myocardium, most common in the elderly.

Which medications can exacerbate or precipitate the symptoms of Sick Sinus Syndrome (SSS)?

Beta-blockers, digoxin, and non-dihydropyridine calcium channel blockers.

Common Presentations:

Common Presentations:

• Bradycardia symptoms:

• Tachycardia-bradycardia syndrome:

What are some symptoms of bradycardia?

• Bradycardia is a condition characterized by a slow heart rate.

• Symptoms may include dizziness, fatigue, shortness of breath, chest pain, and fainting.

• Consult a healthcare provider for proper diagnosis and treatment.

What is an Adams-Stokes attack?

An Adams-Stokes attack, also known as Stokes-Adams syndrome, is a sudden loss of consciousness caused by a lack of blood flow to the brain due to a complete heart block. It can lead to seizures, fainting, and even death if not treated promptly.

What is tachycardia-bradycardia syndrome characterized by?

Tachycardia-bradycardia syndrome is characterized by alternating fast and slow heart rates, leading to symptoms like dizziness, fainting, and palpitations.

Diagnostics of sick sinus syndrome:

Diagnostics of sick sinus syndrome:

• Electrocardiogram (ECG):

• Exercise stress test:

What can an ECG show in the diagnostics of sick sinus syndrome?

Various arrhythmias indicative of SSS.

What may an exercise stress test reveal in the diagnostics of sick sinus syndrome?

An inadequate increase in heart rate in response to exercise.

Treatment of sick sinus syndrome:

Treatment of sick sinus syndrome:

• Medication review and adjustment:

• Pacemaker placement:

• Selective beta-blockers:

How can medication-induced symptoms of sick sinus syndrome be managed?

Adjusting dosages or discontinuing offending drugs may be necessary.

When is pacemaker placement considered for patients with sick sinus syndrome?

Pacemaker placement may be necessary for patients with significant symptoms, especially those involving bradyarrhythmias.

What type of beta-blockers might be used for cases of sick sinus syndrome involving tachyarrhythmias?

Low-dose, cardioselective beta-blockers like metoprolol or bisoprolol.

AV BLOCKS

First-Degree AV Block

Second-Degree AV Block

Third-Degree AV Block (Complete Heart Block)

What are AV blocks?

Types of heart block that affect the electrical conduction between the atria and ventricles of the heart.

What can cause AV blocks?

Factors such as increased vagal tone, fibrosis of the conduction system, ischemic heart disease, cardiomyopathies, infections like Lyme disease, medication effects, or following cardiac procedures.

First-Degree AV Block

First-Degree AV Block

• Description:

• Causes:

• Symptoms:

• ECG Findings:

• Management:

What is First-Degree AV Block?

Prolonged conduction time through the AV node, but all impulses eventually reach the ventricles.

What are some causes of First-Degree AV Block?

Increased vagal tone, use of beta-blockers or calcium channel blockers.

What are the symptoms of First-Degree AV Block?

Often asymptomatic and discovered incidentally on an ECG.

What ECG finding is associated with First-Degree AV Block?

PR interval exceeds 200 milliseconds.

How is First-Degree AV Block managed?

Generally requires no treatment unless symptomatic or part of broader cardiac issues.

Second-Degree AV Block

Second-Degree AV Block

• Type I (Wenckebach or Mobitz I) Second-Degree AV Block:

• Type II (Mobitz II) Second-Degree AV Block:

What is the mechanism of Type I (Wenckebach or Mobitz I) Second-Degree AV Block?

Progressive prolongation of AV conduction until an impulse fails to be conducted.

What are the causes of Type I (Wenckebach or Mobitz I) Second-Degree AV Block?

Increased vagal tone or degenerative changes in the AV node.

What are the symptoms associated with Type I (Wenckebach or Mobitz I) Second-Degree AV Block?

Often asymptomatic, possible episodes of syncope.

What ECG findings are characteristic of Type I (Wenckebach or Mobitz I) Second-Degree AV Block?

Increasing PR interval followed by a non-conducted P-wave.

How is Type I (Wenckebach or Mobitz I) Second-Degree AV Block usually managed?

Usually only observation unless symptoms develop.

What is the mechanism of Type II (Mobitz II) Second-Degree AV Block?

Sudden failure of AV conduction without preceding PR interval prolongation.

What are the causes of Type II (Mobitz II) Second-Degree AV Block?

More likely due to disease within the conduction system.

What are the symptoms associated with Type II (Mobitz II) Second-Degree AV Block?

Higher risk of progressing to complete heart block, symptoms of bradycardia such as fatigue, dyspnea, chest pain, and syncope.

How is Type II (Mobitz II) Second-Degree AV Block managed?

Pacemaker implantation is often required due to the risk of progression to third-degree block.

Third-Degree AV Block (Complete Heart Block)

Third-Degree AV Block (Complete Heart Block)

• Description:

• Causes:

• Symptoms:

• ECG Findings of third degree AV block:

  • Junctional rhythm:

  • Idioventricular rhythm:

• Management of third degree AV block:

What is Third-Degree AV Block (Complete Heart Block) characterized by?

No atrial impulses are conducted to the ventricles; atria and ventricles beat independently.

What are some symptoms of Third-Degree AV Block (Complete Heart Block)?

Symptoms can include syncope, heart failure symptoms, Adams-Stokes attacks, and potential cardiac arrest.

What are the ECG findings of third-degree AV block?

Complete dissociation between P waves and QRS complexes.

What is a junctional rhythm?

A rhythm that occurs if the escape rhythm originates above the bundle of His, typically presenting with a narrow QRS complex and a rate of 40-60 bpm.

What is an idioventricular rhythm?

A rhythm that occurs if the escape rhythm originates below the bundle of His, presenting with a broad QRS complex and a rate of 20-40 bpm.

What is the recommended management for third-degree AV block?

Immediate pacemaker placement due to the risk of life-threatening arrhythmias and sudden cardiac death.

Bundle branch blocks (BBB)

Right Bundle Branch Block (RBBB)

Left Bundle Branch Block (LBBB)

What are bundle branch blocks (BBB)?

Disruptions in the normal pattern of electrical conduction in the heart's ventricles.

How do bundle branch blocks (BBB) occur?

They occur when the pathway that transmits electrical impulses to the heart muscle is delayed or blocked.

What is the mechanism of Right Bundle Branch Block (RBBB)?

Delay in the conduction of electrical impulses to the right ventricle, causing the left ventricle to contract before the right ventricle.

What are some causes of Right Bundle Branch Block (RBBB)?

Right ventricular hypertrophy, myocardial infarction (MI) of the lateral wall, pulmonary embolism, chronic lung disease.

What is the typical axis deviation in Right Bundle Branch Block (RBBB)?

+90 to +180 degrees.

In which leads do we observe negative deflections in Right Bundle Branch Block (RBBB)?

Lead I.

What is the characteristic QRS duration in Right Bundle Branch Block (RBBB)?

Greater than 120 milliseconds.

Which leads show the RSR' pattern in Right Bundle Branch Block (RBBB), resembling a 'rabbit ear' appearance?

Leads V1-V2.

What is the typical appearance of T-wave inversions and ST-segment depression in Right Bundle Branch Block (RBBB)?

Leads V1-V3, indicating right ventricular repolarization disturbances.

What is Left Bundle Branch Block (LBBB)?

Left Bundle Branch Block (LBBB):LBBB is a heart condition where there is a delay or blockage in the electrical impulses that control the left side of the heart. This can affect the heart's ability to pump blood efficiently.

What are some causes of Left Bundle Branch Block (LBBB)?

• Coronary artery disease

• Hypertension

• Cardiomyopathy

• Myocardial infarction

• Aortic stenosis

What is the axis deviation range in Left Bundle Branch Block (LBBB)?

-30 to -90 degrees

What is the characteristic QRS duration in LBBB?

Greater than 120 milliseconds

Which leads show positive deflections in LBBB?

Lead I

What is the characteristic appearance of R-waves in leads V5-V6 in LBBB?

Broad monophasic R-waves resembling an 'M' shape

What is the appearance of S-waves in leads V1-V2 in LBBB?

Deep S-waves

What is the mechanism of Left Bundle Branch Block (LBBB)?

Delay in the conduction of impulses to the left ventricle, causing the right ventricle to contract slightly before the left.

What are some causes of Left Bundle Branch Block (LBBB)?

Aging, left ventricular hypertrophy, myocardial infarction of the inferior wall.

What is the mechanism of Left Anterior Hemiblock (LAH)?

Conduction block in the anterior fascicle of the left bundle branch, resulting in a delay of impulses to the upper front part of the left ventricle.

What are the ECG characteristics of Left Anterior Hemiblock (LAH)?

Left axis deviation (-30 to -90 degrees) and a narrow QRS complex.

What is Left Posterior Hemiblock (LPH)?

• Mechanism: Conduction block in the posterior fascicle of the left bundle branch, affecting the electrical activity directed to the lower back part of the left ventricle.

What are the ECG characteristics of Left Posterior Hemiblock (LPH)?

• ECG Characteristics:

  • Right axis deviation (+90 to +180 degrees).

  • Narrow QRS complex.

What is the normal range for the electrical axis of the heart?

-30 to 90 degrees

In which leads do we expect to see upright QRS complexes in a normal axis?

Lead I, Lead II, Lead III

What does a normal axis orientation indicate about heart electrical activity?

It indicates normal heart electrical activity.

What is the characteristic of the QRS complex in Lead I for Physiologic Left Axis?

Upright QRS complex