Chapter 17 Disorders of cardiac

Question 1

1. Define the normal properties of heart cells, and how they relate to the action potential

Answer 1

Automaticity
To spontaneously initiate an action potential 
SA node: 60-100/min
AV node: 40-60/min
Purkinjes: 20-40/min

Excitability
To respond to an impulse and then generate it’s own action potential

Conductivity
To conduct impulses

Phase 0
-sodium channel opens, sodium enters

Phase 1

• decrease in sodium permeability
• Potassium, chloride leaves cell

Phase 2

• plateau
• calcium enters
• potassium out

Phase 3

• potassium out
• channels close and the influx of calcium and sodium ceases

phase 4 is resting potential

Question 2

2. Define the following terms as they relate to the cardiac conduction system, and describe typical manifestations: bradycardia, tachycardia, atrial fibrillation, atrioventricular blocks, premature ventricular contraction, ventricular tachycardia, ventricular fibrillation, and asystole.

Answer 2

Bradycardia

• decreased perfusion
• 100

Atrial Fibrillation

• chaotic depolarization with only occasional contraction
• irregularly irregular
• quivering muscle
• poor emptying of atria
• poor filling of ventricle = decreased CO

SS

• irregular HR
• pulses will be irregular with varying strength
• low BP

Atrioventricular blocks
Blocks - AV nodes/Bundle of His issues

1ST degree

• consistent long PR interval, followed by a QRS
• SA to AV nodes but pauses there

2ND degree
Mobitz Type 1/Wenckebach
Increasing PR until QRS dropped

Mobitz Type 2
Occasional dropped QRS
PR stable

3RD AV block
-no electrical communications between atria and ventricles

Premature Ventricular Contractions

• due to irritability
• Abnormal EKG
• Irregular heart beat
• Shortness of breath
• Dizziness
• Feeling your heart beat (palpitations)
• Feeling of occasional, forceful beats
• Increased awareness of your heart beat

Ventricular Tachycardia
-palpitation, lightheadedness, and syncope from diminished cerebral perfusion. Chest pain may result from ischemia or from the rhythm itself

Ventricular Fibrillation
- sudden collapse of the individual with no preceding signs of distress

Asystole
-also known as flat line with no cardiac electrical activity

Question 3

3. Explain the impact of atrial fibrillation on cardiac output

Answer 3

-because the heart muscles are quivering instead of contracting, results in the poor emptying of atria which leads to poor filling of the ventricles ultimately decreased in cardiac output

Question 4

4. Discuss the treatment methods available for cardiac conduction disorders

Answer 4

Pharmacology
Electrical

Cardioversion

• Pharmacological (digoxin)
• Physiologic (hit from the car)
• Electrical (zap)

Defibrillation
pacemaker

Surgical