L6 Cardiac Conduction

Question 0

structure-function relationship of diff cardiac cell types

Answer 0

SA/AV node:
small, few gap junctions, slow/weak conduction, few myofibrils, PACEMAKER

Atrial/ventricular muscle:
medium size, LOTS of gap junctions, strong contraction and rapid conduction.

His bundle/Purkinje system:
Large, LOTS of gap junctions, VERY RAPID CONDUCTION, weak contraction

Question 1

Intercalated disc & Gap junctions

Answer 1

Intercalated disc - specialized region where sarcomeres attach. Connection between cardiac cells.
Junctions:
Fascia adherens - connects actin to cell wall
Macula adherens - connects cells together (like tight junction)
Gap Junctions - allow current to pass thru at low internal resistance

Question 2

Space Constant and AP upstroke can determine electrical conduction…

Answer 2

by making it faster if SConstant is long and AP upstroke is rapid.

???

Question 3

RMP and Na channel availability

Answer 3

When the RMP becomes more positive, there are fewer Na channels available. This is crucial because when the RMP changes, so does the ability to make APs

See the Na+ inactivation curve

Question 4

PR & QRS interval determine conduction by…

Answer 4

PR interval should be 120-200 msec. If it’s longer, it means the conduction is slowed in the AV node.

QRS should be 70-100 msec. If it’s longer, it means the rapid conduction through the his/purkinje system is blocked/messed up and not all cells are contracting in synchrony

Question 5

Ach and Parasympathetic nerve activity

Answer 5

-Ach- acts via muscarinic receptors (metabotropic) and increases K permeability so hyperpolarizes the cell.
It also inhibits adenylyl cyclase therefore no cAMP and no slow inward Ca current.
It also directly inhibits atrial muscle, SA and AV node
SLOWS HR

Question 6

NE and Sympathetic nerve activity

Answer 6

NE acts on all areas of the heart using B1 adrenergic receptors.
Increases cAMP, therefore increases inward Ca current
Increases atrial and vent muscle contraction and SA/AV node rate
INCREASES HR

Question 7

ANS induced changes in the AV conduction and how they manifest on EKG

Answer 7

These changes affect the AV itself, which would decrease or increase the P-R interval. This means that the time in between atrial and ventricular pumping is shortened

Question 8

1st degree heart block

Answer 8

A block where the PR interval is lengthened (>200 msec)

Means the general AV node conduction is affected because the atria to ventricle connection is off

Question 9

2nd degree heart block

Answer 9

P wave doesn’t always produce QRS wave.

Atrial beat does not always produce a ventricular beat

Question 10

3rd degree heart block

Answer 10

P waves and QRS waves do not correlate at all
Complete AV node block. The AV node doesn’t confer beats to the Ventricle.
A latent pacemaker come makes the ventricles beat!

Question 11

Supraventricular tachycardia (SVT)

Answer 11

Something above the ventricles is causing the heart to beat very fast. Looks like sinus tachycardia (fast HR when exercising) but is caused by a pathological thing, like abnormal SA node ???????????

Wall motion and CO are normal; filling time is shorter

what is an example of the cause of SVT?

Question 12

Ventricular tachycardia

Answer 12

Impulse from AV node is not conducting through the His-Purkinje system but is going around in a circle.

Less filling time, less CO. Can lead to V-fib!

Question 13

Atrial fibrillation

Answer 13

DUE TO RE-ENTRY OF EXCITATION
pumping action becomes asynchronous and doesn’t work as well.

CO IS NORMAL - this is why a-fib is compatible with life (Atria don’t contribute much to CO

Question 14

Atrial flutter

Answer 14

Example of a Supraventricular Tachycardia
generally beats are in a regular pattern
could be due to re-entry

Different than A-fib

Question 15

Ventricular fibrillation

Answer 15

DUE TO RE-ENTRY OF EXCITATION
Ventricles have stopped beating synchronously and pumping ceases.

CO DRASTICALLY DECREASED, RAPIDLY FATAL bc blood and oxygen isn’t getting sent to body