Module 3 - Electrical system of heart

diastole

heart muscle is relaxed

heart fills with blood

systole

heart muscle contracts

pushes blood out of the heart and into the large blood vessels

LV ejection fraction

amount of blood pumped out of the LV / amount of blood in the LV

depolarization >

repolarization >

contraction

relaxation

automaticity cells

SA node, AV node, and purkinje network

electrical activity always precedes

mechanical activation

main idea for cardiac ablation

oxygenated blood comes into the LA through the 4 pulmonary veins (2 from each lung), where atrial fibrillation is commonly identified. scars are created at those vein openings inside the LA to block/jail the electrical signal from coming in

depolarization

electrically charged ions travel in and out of the cell causing contraction

repolarization

after depolarization it returns to its resting state

automaticity

ability for cells to contract or relax spontaneously without external influence

in pacemaker cells, what is all involved

SA node, AV node, bundle of His/Purkinje fibers

pacemaker cell action potential

phase 4: opening

phase 0: depolarization, slow calcium channels open

phase 3: repolarization, potassium outflow and calcium channels close

cardiac muscle cells involve

atrial and ventricular cardiac muscle cells

in cardiac muscle cell action potential, action potential steps

phase 0: rapid depolarization with influx of fast sodium ions

phase 1: early repolarization with onward movement of K+ ions

phase 2: plateau, continued influx of Na+ ions and slow influx of Ca2+ ions

phase 3: repolarization, outflow of K+

phase 4: resting phase

within cardiac myocytes, what is the significance of Ca2+ ions?

trigger for contraction

the synchronous contraction of pacemaker cells and cardiac cells are electrically coupled through the presence of

gap junctions

effective refractory period

phases 0-3, where depolarization can’t be initiated no matter how strong the impulse

prevents the heart from beating too fast

relative refractory period

cardiac cell; phases 3-4, where heart is stimulated to depolarize by only a stimulus or impulse that is stronger than what is normally required for depolarization

can potentially cause arrhythmias

benefit of automaticity and conduction

if the SA node fails, it falls on the AV node, then the purkinje fibers, getting slower each iteration

what is the escape rhtym

the rhythm recorded at the purkinje network at 20-40 bpm

which bundle branches has greater mass

left bundle splits into two fasicles because of the greater muscle mass of the LV

conduction system of the heart steps

1.  Impulse Formation at the SA Node

2. Depolarization of the Right and Left Atria

3. Delay at the AV Node

4. Conduction at the Bundle Branches

5. Conduction through the Purkinje Fibers

6. The Mechanical Contraction of the Ventricle, or Systole

   1. The Mechanical Relaxation of the Ventricle, or Diastole

parasympathetic activation characteristics

lowered rate SA node

lowered rate of conduction

lowered force of contraction

lowered irritability of atrial

sympathetic system activation

increased rate SA node

increased rate of conduction

increased force of contraction

increased irritability of atrial

parasympathetic; what receptors binding to what and secreted by what

cholinergic receptors binding to acetyl choline that are secreted by cholinergic neurons

sympathetic; what receptors binding to what and secreted by what

adrenergic receptors binding to norepinephrine secreted by adrenergic neurons

orthostatic hypotension; occurs how? symptoms? next steps?

sympathetic control is compromised

patient feels dizzy, lightheaded, generalized weakness

requires pacemakers to elevate HR

merciful syncope or vasovagal syncope; occurs how? next steps?

parasympathetic activation and sympathetic inhibition

requires pacemakers to control HR

vagal maneuvers; what does it do ?

helps terminate SVTs through parasympathetic activation

what do parasympathetic neurons help control in the heart?

resting heart rate

electrocardiogram

recording of the electrical activity of the heart, obtained by placing electrodes on the skin surface

lead 1

R arm (-) to L arm (+)

lead 2

right arm (-) to left leg (+)

lead 3

left arm (-) to left leg (+)

aVF

left leg (+) to center

aVL

left arm (+) to center

aVR

right arm (+) to center