Cardiac Conduction

Question 1

Properties of heart cells

Answer 1

1.  Automaticity
To spontaneously initiate an action potential
SA node: 60-100/min
AV node: 40-60/min
Purkinjes: 20-40/min
2. Excitability
To respond to an impulse and then generate it’s own action potential
3. Conductivity
To conduct impulses

Question 2

Depolarization and Repolarization

Answer 2

- Depolarization wave
From the SA node to the AV node & over to the LA = P wave
Thru the AV node, Bundle of His, L&R bundle branches, & perkinjes = PR interval
Thru the ventricular wall = QRS
- Repolarization
Of the atrial = hidden
Of the ventricles = T wave
Of the perkinjes? = U wave

Question 3

Sinus (SA) Node Arrhythmias

Answer 3

- Sinus bradycardia (100)
Normal with exertion/fever
Ischemia, hypoemia
Increases myocardial 
workload, decreases 
coronary artery perfusion

Question 4

Sinus arrest & Sick sinus syndrome

Answer 4

Sinus Arrest: Failure of SA node, usually intermittent
Sick Sinus Syndrome: d/t SA node injury,
unknown cause

Question 5

Premature atrial complexes (PAC)

Answer 5

Early depolarization originating in the atria (not SA node)
Common
(premature atrial contraction)

Question 6

Paroxysmal supraventricular tachycardia (PSVT)

Answer 6

• 140-240/min, sudden onset and cessation
• d/t ischemia, reentry
• wolff parkinson white syndrome

Question 7

Atrial flutter

Answer 7

• Ectopic atrial tachycardia 240-450/min

- d/t reentry

Question 8

Atrial fibrillation

Answer 8

• Chaotic depolarization with only occasional contraction
• Paroxysmal/chronic
• d/t MI, HF
  What is happening in the heart?
• Quivering muscle
• Poor emptying of atria
• Poor filling of ventricle = decreased CO
  How will your patient present?
• Heart rate will be irregular
• Pulses will be irregular with varying strength
• BP will be low
• All other systems will exhibit the S&S of decreased CO

Question 9

AV Conduction Arrhythmias (1st degree block)

Answer 9

Blocks (1st, 2nd, 3rd degree)
AV node/Bundle of His/bundle branch issue

1st degree Atrioventricular Block
Consistent long PR interval, followed by a QRS

Question 10

2nd degree block

Answer 10

Mobitz Type 1/Wenckebach
- Increasing PR until QRS dropped     
Mobitz type 2
- Occasional dropped QRS
- PR stable

Question 11

3rd degree block

Answer 11

• No electrical communication between atria and ventricles

Question 12

Ventricular Arrhythmias (PVC)

Answer 12

• Premature ventricular complexes (PVC)
• d/t irritability (ischemia/necrosis)
• common
• isolated (single)
• couplet (two-three in a row…not good)
• bigeminy (every 2nd beat)

Question 13

Ventricular fibrillation & Asystole

Answer 13

Ventricular fibrillation: ventricle is vibrating, no blood can be pumped.
Asystole: when the heart is not doing anything

Question 14

Cardiac Conduction Diagnostics

Answer 14

• Electrocardiography (ECG)
  12 lead
  16 lead
• Holter Monitor
  Exercise Stress Test
  Electrophysiologic Studies

Question 15

Treatments for Conduction Disorders

Answer 15

Cardioversion - the person is still conscious

• Pharmacological (digoxin)
• Physiologic (precardial thump, cough)
• Electrical (paddles)

Defibrillation - defibrilating the person
- Electrical

Pacemaker

Surgical
- Ablation/pacemaker/defibrillator