Lecture 8 Cardiac Disorders

Question 1

What is a Cardiac Dysrhythmia?

Answer 1

An abnormality of formation or conduction of an electrical impulse, leading to alteration in heart rate or regularity. Also called arrhythmia (“without rhythm”).

Question 2

Why are Dysrhythmias Significant?

Answer 2

They may indicate an underlying pathophysiological disorder. They may impair normal cardiac output (CO), which can reduce perfusion of organs like the brain, heart, and kidneys.

Question 3

What are two functions of Autorhythmic Fibers in the heart?

Answer 3

1. Spontaneously depolarize to generate action potentials that trigger cardiac contraction. 2. Form the conduction system to propagate action potentials through the heart muscle.

Question 4

What is the main role of the Sinoatrial (SA) node?

Answer 4

Acts as the pacemaker to initiate regular contractions. Baseline rate is 100 APs/min (can be modified). APs stimulate synchronous contractions of both atria.

Question 5

What is the role of the Atrioventricular (AV) node?

Answer 5

Delays signals before transmission to the AV bundle.

Question 6

What are the main parts of the heart’s conduction system after the AV node?

Answer 6

AV bundle (bundle of His) and bundle branches (transmit signals toward apex). Subendocardial conducting network (Purkinje fibers) (stimulate synchronous contractions of both ventricles).

Question 7

What are general causes (etiologies) of Dysrhythmias?

Answer 7

Structural abnormalities (congenital or acquired), Injury to the heart (e.g., ischemia), Genetics (e.g., channelopathies), Drugs and toxins, Electrolyte imbalances, Autonomic imbalances.

Question 8

What are three possible mechanisms for Dysrhythmias?

Answer 8

1. Abnormal automaticity. 2. Triggered activity. 3. Re-entry circuits.

Question 9

What is Abnormal Automaticity?

Answer 9

Altered rate or site of impulse generation. Examples: ischemia, electrolyte imbalances, channelopathies.

Question 10

What is Triggered Activity?

Answer 10

Extra impulse(s) generated during or after repolarization. Examples: genetic abnormalities or drugs altering Ca2+ homeostasis.

Question 11

What are Re-entry Circuits?

Answer 11

Altered conduction speed or pathway allows the cardiac impulse to continually depolarize the heart after the main impulse finished. Examples: cardiac scarring, mutations of gap junction genes.

Question 12

How are Dysrhythmias analyzed?

Answer 12

Using ECG recordings. Electrodes on the chest and back monitor electrical signals.

Question 13

What do ECG waveforms represent?

Answer 13

Action potentials spreading through the conduction system and recovery of myocardial cells after depolarization.

Question 14

Identify the main ECG waveforms.

Answer 14

P wave: SA node / atrial depolarization. QRS complex: ventricular depolarization. T wave: ventricular repolarization.

Question 15

What is Normal Sinus Rhythm?

Answer 15

Starts in the SA node. Follows the normal conduction pathway. Impulse rate is between 60 – 100 beats/min. Regular rhythm. P wave precedes every QRS complex. Normal PR, QRS, QT intervals.

Question 16

What is Sinus Tachycardia?

Answer 16

Abnormally fast heart rate > 100 bpm. Often a compensatory response (increased CO demand, reduced SV). Causes: sympathetic activation, hyperthyroidism, hypoxia.

Question 17

What is Sinus Bradycardia?

Answer 17

Heart rate < 60 bpm. May be normal in fit individuals. Causes: parasympathetic activation, pain.

Question 18

What does it mean for a cardiac impulse to start at an “Ectopic Site”?

Answer 18

The impulse is initiated at a site other than the SA node. Can be due to Escape rhythm (SA node failure) or Enhanced excitability/triggered activity/reentry overriding the SA node.

Question 19

What is Atrial Flutter on ECG?

Answer 19

Rapid atrial rate (240 – 350 bpm) characterized by a sawtooth pattern of atrial depolarizations. Most often caused by reentrant rhythm in atria. AV node limits conduction (usually 2:1 to 5:1 ratio).

Question 20

What is Atrial Fibrillation?

Answer 20

The most common serious dysrhythmia. Irregular atrial rhythm with irregular ventricular rhythm. Caused by rapid depolarizations from numerous ectopic foci.

Question 21

What is Ventricular Tachycardia (V-tach)?

Answer 21

3 or more consecutive ventricular complexes at a rate > 100 bpm. Impulse from an automaticity focus in the ventricle. Causes widening of the QRS complex. Often associated with myocardial ischemia/infarction, ↓ K+, sympathetic stimulation.

Question 22

What is Ventricular Fibrillation (V-fib)?

Answer 22

The most serious dysrhythmia and most common cause of sudden death. Often the terminal rhythm in cardiac disease. Multiple foci fire chaotically. Produces a quivering myocardium. No pumping occurs.

Question 23

What are Atrioventricular (AV) Blocks?

Answer 23

Problems between the sinus impulse and the ventricular response. Can be slowed or completely blocked. Due to a defect in the AV node, AV bundle, or bundle branches.

Question 24

Describe First-degree AV Block.

Answer 24

Prolonged PR interval (> 0.20 s). Regular rhythm. Usually asymptomatic, no treatment needed.

Question 25

Describe Second-degree AV Block.

Answer 25

Intermittent atrial conduction to ventricles. Type I (Wenckebach): PR intervals progressively lengthen until a QRS complex is dropped. Type II: A number of atrial depolarizations are dropped before one conducts. May need pacing.

Question 26

Describe Third-degree AV Block.

Answer 26

Complete block of atrial conduction to ventricles. Atria and ventricles paced independently. Slow ventricular rate leads to decreased CO. Almost always requires a pacemaker.

Question 27

When is Treatment for Dysrhythmias necessary?

Answer 27

When they produce significant symptoms or are expected to progress.

Question 28

What are some General Treatment Approaches for Dysrhythmias?

Answer 28

Vagal maneuvers (stimulate parasympathetic NS). Ablation procedures (destroy abnormal tissue). Electrical interventions (pacemakers, cardioversion, defibrillation). Anti-arrhythmic drugs (suppress abnormal rhythms).

Question 29

Differentiate Cardioversion and Defibrillation.

Answer 29

Cardioversion: Restore normal rhythm via impulses synchronized to QRS. Patient has a pulse. Defibrillation: Reset irregular rhythm with a shock applied randomly. Patient does NOT have a pulse (e.g., V-fib).