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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). The cardiac conductive system stimulates the ventricles to depolarize in the proper direction.
*If the depolarization impulse originated in the atria and spread passively to the ventricles, then the ventricles would depolarize from superior to inferior and would be ineffective.
-The cardiac conduction system, therefore, must initiate an impulse, spread it through the atria, transmit it quickly to the apex of the heart, and thence stimulate the ventricles to depolarize form inferior to superior.
1. Excitability: the cells can respond to an electrical stimulus, like all other myo0cradial cells.
-If the cells next to them go off, they will go off too. They are easily excited.
2. Conductivity: The cell can propagate the electrical impulse from one cell to another.
-They pass the electric energy across from cell to cell. Once a couple go off it will just spread out from there.
3. Automaticity: The individual cells of the conductive system can depolarize without any impulse form an outside source.
-They can initiate an impulse by themselves. If the pacemaker of the heart fails, then these cells are starved for oxygen and they irritated then they take over for the pacemaker of the heart.
4. Contractility: Since the cells of the cardiac conductive system are specialized cardiac muscles cells, they retain the ability to contract.
-They squeeze when they get this stimuli. It's the whole reason this system works. *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." 1. Bipolar (limb leads)= They have one positive electrode and one negative electrode. Leads 1, 2, and 3 are commonly called limb leads. They only show 3 views of the heart.
^Limb leads are Bipolar leads.
-You use two separate attached leads to come up with one reading.
-The 3 leads create Einthoven's triangle.
-Lead 1- top of the triangle, lead 2- the right side, lead 3- left side.
2. Unipolar (Augmented)= All they have is a positive lead
- This leads evaluate different axes than the bipolar leads but they utilize the same electrodes. They do this by electronically combining the negative electrodes of two of the bipolar leads to obtain an axis.
~These leads are aVR, aVL, and aVF. The letter a means that the lead is augmented. The letter V identifies that it is unipolar. The R, L, and F identify the extremity where it is place. (right arm, left arm, and left foot)
3. Precordial Leads= These measure the electrical cardiac activity on a horizontal axis. These leads help view the left ventricle and septum. These are V1 through V6. The letter V identifying them as unipolar leads. 