11 10 2014 Cardiac Arrythmias

Question 1

how does SA node establish itself as the main pacemaker?

Answer 1

SA node is much faster.

Overdrive suppression: suppresses other’s automaticity by continuously activating Na+/K+ ATPase!
- membrane potential becomes increasingly negative= hyperpolarized membrane potential but SA node’s If current is sufficiently large to overcome the hyperpolarization effects

Pacemaker : If

HCN ( I Na+): Hyperpolarization activated cyclic nucleotide-gated

• membrane potentials determine how many Na+ channels are in active form.

Question 2

Anatomical connections that limit pacers:

Answer 2

AV node is suppressed via connection with atrial myocytes

Purkinje cells are suppressed via nonautomatic ventricular cells

• SA node is LESS TIGHTLY coupled with atrial myocytes : Less subject to electronic interaction

Question 3

What would cause an escape rhythm?

Answer 3

Escape rhythms are late and they terminate a pause caused by a slowed sinus rhythm.

• SV nodal dysfunction ( medication/ disease)
• AV block ( 3rd degree especially)

Question 4

What would cause an ectopic rhythm?

Answer 4

When latent pacemakers have a faster depolarization than SA node

• catecholamines
• MI (AV node is affected)
• Digitalis toxicity
• Aortic/mitral valve surgery

Question 5

Explain how abnormal automaticity is caused and what are the things that cause it?

Answer 5

there is cardiac tissue injury and cells outside of conduction system acquire automaticity and spontaneous depolarization.

If rate of depolarization is greater than SA node THEN non- pacemaker cells take over.
- mostly happens when membrane potential drops ( goes to -60mV – no SA node na+ and Ca2+ channels don’t open)

• injury is usually due to MI, idiopathic ventricular tachycardia, ischemia ( VENTRICLE tachycardia or ventricle ectopic)

Atrial tachycardia

Question 6

Trigger activity – causes of monomorphic vs. polymorphic delayed afterdepolarization

Answer 6

monomorphic– idiopathic – RV outflow tract tachycardias / Repetitive monomorphic ventricular tachycardias

Polymorphic is caused by a mutation in receptor Ran..something – affects responds to catecolamines

Question 7

What are the causes of abnormal impulse conduction and block?

Answer 7

1. decremental conduction and block

2. reentry

Question 8

What causes decremental conduction and block ( abnormal impulse)

Answer 8

• Lev-Lenegre syndrome: complete heart block due to idiopathic fibrosis and calcification of conduction system.
• MI
• Hyperkalemia: relatively hyperpolarizes cell
• Gap junction abnormalities
• Prolonged refractoriness

Question 9

What are the EKG abnormalities with someone that has WPW?

Answer 9

• Delta wave
• widened QRS
• shortened PR interval

Question 10

What are the EKG abnormalities one would see with TYPE1 Second degree AV block?

Answer 10

PR interval increases at an interval
QRS is normal

This is usually due to a toxic effect of a medication or toxin on the AV node. So the AV node is blocked in this specific case.

Treat with medication

Question 11

What are the EKG abnormalities one would see with TYPE2 Second degree AV block?

Answer 11

sudden intermittent loss of AV conduction.

Two sequential P-waves

Caused by a block BEYOND the AV node! (BBB or Purkinje)
- extensive MI involving septum OR chronic degeneration of His- Purkinje System