what is avn conduction and what is the speed of it
excitation wave that spread rapidly thru atria converging on AVN thru interatrial pathways
-slowest conduction velocity
Ventricular myocardium conduction- speed
Conduction thru left wall is slower than right wall due to thickness of the wall
Atrial and ventricular activation (+ delays)
atrial activation occurs in .09 s
then .16 sec delay
ventricular activation occurs in .23 sec
What 3 drugs reduce conduction rate
Beta blockers
Calcium channel blockers
Digitalis
What is positive dromotrophic and negative dromotrophic effect
pos- increases conduction velocity in av node via b receptors
neg- decreases conduction velocity in av node
What is sinus tachycardia caused by
- increased sympathetic stim in stress/ex
- increased body temp
- low blood pressure
- hyperthyroidism
What is sunus bradycardia caused by
- increased vagal tone
- hypothyroidism
What is extrasystole and what is it due to
A beat that occurs before expected next normal beat
-heavy stress/ caffeine use
What is atrial flutter
atrial rates bw 250-350 bpm
What is the cause of atrial fibrillation
atrial activity bw 350-500bpm
What is the most dangerous fibrillation
ventricular fibrillation
-cant effectively pump blood/ no contraction
What occurs in a bundle branch block
Blockage of one side will result in one ventricle contracting a fraction of a second later than the other
What occurs in wolff parkinson white syndrome
Extra electrical pathway in the heart which allows early activation of a portion of one ventricla (can lead to periods of tachycardia)
What is the P wave and PR segment
P- depolarization of R+L atria
PR- AV nodal delay (conduction of atria to ventricles)
What is the QRS segment
Ventricualr depolarization
What is the St segment
Plateu phase of heart
What is the t wave
Ventricular repolarization
What occurs during ventricular filling and what is the amount of blood in the ventricles called at this point
Atrial systole
- Semilunar valves closed
- End diastolic volume
What is the 2 stages of the ventricular systole stage and what is the amount of blood left called
isovolumetric stage-ventricles begin to contract while semilunar valves still closed
Ejection phase- pressure rises and semilunar valves open
_ called end systolic volume
What occurs in early diastole
atria and ventricles in diastole
- semilunar valves close
- antri ventricular valves open allowing some blood to leave the atria (passive ventricular fillinG)
How long does the heart spend in diastole and systole
2/3 time in diastole
1/3 in systole
What is stroke volume
EDV-ESV=SV
What is the frank starling law
esentially prelode
- when there is more blood in ventricles the cardiac mm is streched leading to increased tension development
What is preload and what does it result in
The degree of strecth of cardiac mm cells before they contract (increased preload ejects more blood so ESV is lower)
