My goof is your gain
In lecture on Tuesday, I spent some time talking about premature ventricular contractions and how they affect the heart. Unfortunately, I didn't have a PVC EKG in front of me, and I miss-remembered the effect of PVC's on the EKG.
You can make up for my failings by posting a (new) link to a description of PVCs that includes an image of a PVC EKG. Be sure to describe what you've learned in your comment.
24 comments:
Here is an EKG of Premature Ventricular Contraction
http://pediatriccardiology.uchicago.edu/pp/Images/0pac.jpg
if you want to see the whole site, the link is here:
http://pediatriccardiology.uchicago.edu/pp/ecg%20for%20parents%20body.htm
in the image specifically, you can see the fourth QRS complex occurring earlier than the other ones, almost randomly. The fourth heartbeat didn't follow the normal beat exactly. The atria didn't seem to contract fully because the p wave seems kind of low and out of sync, but the ventricles managed to contract fully. However, in the recovery the atria tried to compensate and the ventricles didn't contract because they were still trying to recover.
This is an image of a PVC's EKG as well as an animation with information:
http://www.medmovie.com/mmdatabase/MediaPlayer.aspx?ClientID=66&TopicID=776
(Note: to get the image of the EKG, once its done loading, select forward (below the image of the heart), then normal sinus rhythm, and the PVC; the image of the EKG PVC and a normal EKG should come up along with the animation)
By looking at the PVC's EKG and the animation along with it, I was able to better understand how the heart weakly contracts a second time before getting the signal from the AV node to do so. This difference is better shown with the image of a normal EKG next to the abnormal one, stressing the difference between the two.
http://www.gwc.maricopa.edu/class/bio202/cyberheart/ekgqzr0.htm
This is picture of the EKG of PVC and also a picture of a normal EKG below it for comparison.
This only shows that with a PVC the QRS complex is wider and comes more often then it should normally. The P waves and the T waves do not seem to be affected by PVC.
The widen QRS complex seems to come as a result of both ventricles contracting at the same time and also at inappropriate times.
http://www.learnwell.org/EKG500.htm
This page, if you scroll down, shows that PVCs are really inconsistent, meaning that they can occur once or multiple times and then this causes different things to happen to the heart. But mainly means the ventricles are contracting more often than usual which will contract not much blood because of the unnecesary contractions so the atria does not have time to recover (repolarize) in time to contract itself and have blood flow into the ventricles.
I found a website that no only has the EKG of PVC, but also EKG's of Arrhythmia, Atrial fibullation and others.
http://www.bannerhealth.com/Services/Heart+Care/Heart+Information/arrhythmia.htm
The image shows a PVC QRS, two regular heart beats follwed by another PVC. This occurs when the ventricles are the one's starting the heartbeat instead of the S node. The article states that PVC's are common in both healthy people and people with heart disease. Factors such as stress, axiety, and caffine can cause PVC's to occur in both young and old people. Two common symptoms are an accelerated heart rate and light-headed or dizziness.
http://library.med.utah.edu/kw/ecg/mml/ecg_402.html
In this EKG, you can see clearly the that in this image a PVC exists in that the distance of the QRS complex is shorter than the distances of the other QRS complexes. The PVC makes it so that the QRS complex occurs faster and spontaneously than in a consistent heart beat, where all the QRS complexes occur at the same rate.
http://www.frca.co.uk/article.aspx?articleid=100688
Along side other heart failings, this site shows the EKG of premature ventricular contraction. I learned that after the wide, slurred, bizarre QRS complex, a T wave occurs, but in the opposite direction of the QRS. The images on the website compares the difference between a normal QRS, the premature contraction, and then the recovery contraction.
A narrative video of the cardiac conduction system including premature ventricular contractions and atrial tachycardia can be found at the following link:
http://198.172.140.119/myheartdr/common/artprn_rev.cfm?filename=&ARTID=422
There are two different videos available to watch.
http://davidge2.umaryland.edu/~emig/ekgtu04.html
This site shows examples of many different common EKGs. The PVC image is about two-thirds down the page. I find this image to be very accurate. In a PVC, the ventricles contract on their own because of a premature action potential. This makes the first QRS complex small. As a result, the second QRS complex is huge because the heart had to beat harder to get the blood out. The end result is basically that the heart takes another heartbeat that in the end is unneeded.
From the article, I learned that three or more PVCs in a row is known as a Ventricular Tachycardia. If the PVCs lasts for more than 30 seconds than it is known as a sustained VT.
I learned that PVC's are also known as ventricular premature beat (VPB) or extrasystole. It is an irregular heartbeat in which a skipped beat is formed. I learned that the depolarization is taking place in the ventricle first instead of the Av node. PVC's also lead to heart rate turbulence, and they are the most common form of arrhythmia. In the image, the two arrows show the PVC's.
http://en.wikipedia.org/wiki/Premature_ventricular_contraction
http://www.mededsys-nurse.com/courses_online/203/203.html
Figure 5-1 on this website shows an irregular QRS pattern. The premature QRS complex shown is measured at .14 seconds in width which is over the normal .12 seconds, therefore categorizing it as a premature ventricular contraction. Typical early QRS complexes are wide than those of normal QRS complexes. PVC's cause a pause between normal QRS complexes. These pauses are often double the length between normal QRS complexes. By comparing figure 5-1 and 5-2 to figure 1-7, it is evident that a normal EKG shows equal distances between QRS complexes as opposed to an EKG showing a PVC. Also PVC's can occur every other beat or every third beat.
This is an example of a Premature Ventricular Contraction:
http://www.rnceus.com/ekg/ekgpvc.html
It has an EKG diagram of the PVC and also has descriptions of the different phases of it and how the PVC affects it. The ventricle contracts too early and has to refract before it can contract again. Therefore the ventricle fills twice as much with blood and must have a large contraction in order to push all of the blood through. This results in a missed beat and then a very large beat that can be felt by the patient.
In lecture, you drew out the PVC EKG with a normal heartbeat (P, QRS Complex, Q wave), then a 'skipped' QRS followed by a huge surge in QRS.
In this picture below (a premature ventricular contraction)http://starklab.slu.edu/PhysioLab/skips.jpg,
one can notice the skipped P-Wave, followed by a delay. As discussed in lecture, one can see the huge QRS complex to compensate for the skipped beat (at 2:34).
http://www.seattleavir.com/pvc.jpg
This image is not too clear, but it is still visible that there is an irregular beat amongst regular beats. The first six heartbeats are regular, then the seventh one is irregular. As we have learned in class, PVC, or premature ventricular contraction, occurs when the ventricle contracts prematurely. Depolarization does not start in the SA node, or the pacemaker, but it starts in the ventricle before the SA node has time to recover to make another heartbeat.
http://www.medceu.com/index/index.php?courseID=1152&nocheck=&page=get_course
This site provides an image of a Premature Ventricular Contraction EKG along with many other defect EKGs. The site describes a PVC as being a "depolarization that can arise in either ventricle before the next expected beat, i.e. prematurely". I also learned that with a PVC, both ventricles dont depolarize simultaneously, they depolarize sequentially. I also found out that with PVCs, P waves can either precede, coincide with, or follow a QRS, which surprised me because I didnt think it was possible for them to coincide.
http://butler.cc.tut.fi/~malmivuo/bem/bembook/19/19.htm
This site is old but it shows many different EKGs for heart problems and gives brief explanations for each. I learned that the EKG for PVC shows an early QRS complex right after the T wave. The baseline is stable unlike the ones for atrial fibrillation or atrial flutter, which shows multiple depolarizations. The QRS complex for PVC is longer than normal. I assumed this is because an action potential would originate on one side of the ventricle and then spread to the other ventricle causing it to contract slightly later. The image shows that the time interval between two R peaks including the PVC QRS complex is twice as long as a normal R-R interval.
http://yourtotalhealth.ivillage.com/premature-ventricular-contractions.html
In this image, you can see pretty much everything dealing with PVC's. It talks about the electrical impulse being started in teh SA Node, and the process of how it goes through the heart. Also it shows several images in a short slideshow showing how there are several QRS Complexes randomly distributed.
This is an EKG of a Premature Ventricular Contraction:
http://www.bannerhealth.com/NR/rdonlyres/5CFF4A7B-01B5-4B7A-BF9B-02737DF18C02/24237/premature_ventricular_contr.jpg
In a premature ventricular contration you can see that there are normal QRS's followed by much wider QRS's. The QRS for a PVC is abnormal because the ventricles are trying to contract blood isn't in the ventricles. The ventricular contraction is premature because the signal from the SA node isn't being properly transmitted by the AV node to the ventricles.
This is a web site that shows the EKC for several different ventricular disorders: http://library.med.utah.edu/kw/ecg/ecg_outline/Lesson5/ventricular.html
This site includes the EKG of the PVC disorder. According to this site, PVC can be unifocal, multifocal, or multiformed. Multifocal PVCs have different sites of origin, meaning their coupling intervals that are measured from the previous QRS wave, are different. Unlike the multifocal PVC, a multiformed PVC, the intervals are the same but the conduction through the ventricles differ.
This website describes all the various forms of PVC, showing images of their EKGs as well.
The EKG of a premature ventricular contraction
http://www.scribd.com/doc/2155828/EKG-Examples
From the EKG of the premature ventricular contraction, it can be seen that between each of the QRS complex, the rate seems to be faster compared to the normal rate.
After a PVC has occurred, it takes a longer time for the next QRS complex to happen. Also, there is no P wave associated with PVC.
http://butler.cc.tut.fi/~malmivuo/bem/bembook/19/19.htm
This website explores the importance of the EKG in diagnosis of heart arrhythmias. The EKG and explanation for PVC is located around halfway down the page.
A diagram shows the PVC originating from a random location in the ventricle, called the ventricular pacemaker. The QRS waves caused by the PVC are not linked to the QRS waves that originate in the AV node, and the EKG reveals this. The normal R waves occur at multiples of a regular interval. The PVC squeezes in oddly between a multiple of two regular intervals. The QRS triggers earlier and has a distorted, elongated shape, resulting in a weaker contraction with less blood. The time period from the PVC to the next normal QRS wave is also longer than a normal R-interval. This extra time is often described as a "skipped beat".
http://davidge2.umaryland.edu/~emig/ekgtu04.html
This site has the EKGs for many arrhythmias including atrial fibrillation, First to Third Degree AV Block, and, of course, PVC. Along with the image of the EKG for each respective arrhythmia, it also has a description of the disorder and how it effects the EKG.
We know that because of PVC, there are irregular QRS complexes--namely that they occur out of cycle (not following a P wave) and that they are wider than normal. The QRS is wider because since there is an electrical signal starting in the ventricle, completely apart from the SA node, the ventricles are contracting not only on their own accord, but sequentially rather than simultaneously as well. Moreover, because the ventricles contract on their own, they can occur more than once out of cycle--a regular EKG completed, followed by 1+ abnormal QRS's. By looking at this EKG, you can see how much the EKG is thrown off by the presence of PVC; rather than keeping a regular rhythm, it is slower in some places because of the wider than normal QRS's.
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