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Terms in this set (64)

1. Preload: The pressure in the filled ventricle at the end of diastole is called preload, or end-diastolic volume.

*Preload influences the force and amount of the next contraction and is based on Starling's law of the heart.

-Starling's law of the heart= states that the more the myocardial muscle is stretched, the greater its force of contraction will be. In other words, the greater the volume of blood filling the chamber, the more forceful the cardiac contraction. Therefore, the greater the venous return, the greater the preload and the greater the stroke volume.
^Atrial kick at work...

2. Cardiac Contractility

3. Afterload: The resistance against which the ventricle must contract. An increase in peripheral vascular resistance will decrease stroke volume, and conversely a decrease in peripheral vascular resistance will allow stroke volume to increase.\


**Atrial Kick:
-The priming force contributed by ATRIAL systole (contraction) immediately before VENTRICULAR systole (end of diastole)
-that acts to increase the efficiency of ventricular ejection due to acutely increased preload. This accounts for 5-30% (avg. 20%) of cardiac output!
-Starling's Law at work...

*There is no force bringing blood back to the heart, so net pressure is essentially zero. So when the atria fires, it takes all the blood and over fills the ventricles. It stretches that muscle out giving us additional contractility then once it has squeezed all the blood form the atrium to ventricle to valve snaps shut from back pressure and then the ventricle pumps out with all the force.
-In order to have atrial kick, your atria has to fire correctly. ex. A-fib doesn't allow the atria to fire in the correct direction or order. It is just sitting there shaking. It's not moving any blood. They lose the atrial kick so they lose 20-30% of cardiac output. So if you go into A-fib your body loses 5-30% (average of 20 %) of your hearts ability to move blood to your entire body.
-Atria (plural of Atrium) contracts toward the apex, forcing blood into Ventricles, overfilling (stretching) them.
-Ventricles contract toward base ejecting blood from the heart into the great vessels (PA and Aorta).
*AV node

-Intrinsic rate of excitation (40-60)

-Conduction speed of 200 mm/sec
-"The atria fires off at 1000 mm/sec, but when it gets to the AV node it slows down to 200 mm/sec to allow the ventricles to have fill time. If it didn't slow down and went straight down to the ventricles, it wouldn't get the fill time and we would lose our atrial kick."

-Av node is the gateway to the ventricles. It slows the impulse to allow ventricles time to fill. Also called the " gate keeper".

"If the atria starts going nuts and the AV node gets hit 300 times, it wont allow all 300 to go through. It will only allow one, takes a period time to reset, then will let another one through.

" It is our back up pacemaker. So if our SA node fails to fire, the heart rate drops below 60, and we need more than 60 to meet our metabolic demands, the AV node will get irritated and start firing off somewhere between the 40-60.
The metabolic damned was thrown in because people who are athletic and all of us while we are asleep have no metabolic demand so the SA node will start firing below 60. The AV node wont take over because the AV node is happy,. Its metabolic demand has been met. We are not too acidic, were are not too hypoxic, so everything is happy so the AV node doesn't care that we are beating less than 60 in that case. BUT if we start beating less than 60 and becoming hypoxic, acidic, or hypercarbic, that effecting all the cells and the AV node doesn't like it so it takes over the pacemaker of the heart. The problem here is if you already have cardiac sickness enough it will start screwing up you SA node and the AV node may not be all that healthy."
*Refactory Period= The period of time when myocardial cells have not yet completely repolarized and cannot be stimulated again.

*Absolute Refactory Period= The period of the cardiac cycle when stimulation will not produce any depolarization whatsoever.
~This usually last from the beginning of the QRS complex to the apex of the T wave. (Half way through the T wave)
~Stimulation will not cause depolarization

*"Even if electrical stimulus is applied to the heart, the heart will not respond to it. The cells have not moved enough potassium or sodium around to be able to respond to it. The electric impulses will hit them and they will say "ok, well im just going to keep resetting."

*Relative Refactory Period= The period of the cardiac cycle when a sufficiently strong stimulus may produce depolarization.
-Rest of the T wave
~Strong stimulation may produce depolarization and potentially lethal arrhythmias.

* "When we say strong stimulation may produce it, we mean the ventricles firing off again. The ventricles got irritated and fired off prematurely. If that firing off happens to land within this period, that could cause them to go into a lethal arrhythmia and die. This is important for us to realize because if we see that extra ventricular beat getting closer and closer to our T wave (closer and closer to this period) there is a real danger to our patient."

-In defibrillation, we smack the whole heart really hard to try to smack all the cells into depolarizing so they reset normally and start a legitimate heart beat again.

-Synchronized Cardio version is different. When we have a really rapid heart rate where there is an extra pathway and we get into a reentry syndrome . One way to beat that is to smack it with a large amount of energy to stun that pathway and the heart will start firing off again in the right direction at the right rate. We don't use defibrillation because there is no fibrillation to knock out. We are just slowing the heart rate down by giving it a smack.

*If the cells are hit with energy during the relative refactory period, the reset cells will fire off and the ones that weren't reset will be reset momentarily then they are going to fire off. This cause a REALLY rapid arrhythmia. This will just continue. the next firing will be in the relative refactory period and they will go into a ventricular tachycardia or straight into a V-fib. This will kill our patient.