Electrical system, ST elevation, and lead placement

When we look at an EKG, the electrical system of the heart is what we are seeing.  Please note how the electrical system functions.  The way the EKG leads are placed on the body is how the electrical system is read.  The following diagram shows the limb lead and precordial lead positions and what is seen on the EKG. 

 Leads II, III, and AVF are the inferior leads and look at the inferior surface which is the right side of the heart. When there is ST elevation in these leads then there is an  inferior injury or myocardial infarction (MI) to the heart.  It is considered an ST elevation MI or STEMI.  Leads I, AVL, V5, and V6 are lateral leads.  When you look at the EKG and see ST elevation in these leads it is a left lateral wall MI as the EKG view is looking at the left lateral side of the heart.  Leads V1, V2, V3, and V4 view the anterior portion of the heart and when there is ST elevation in these leads it is considered an anterior MI as the EKG looks at the left ventricle which is the front of the heart. V1 and V2 also lies over the right ventricle and septum of the heart and are considered to be the leads for the septal portion of the heart.  Therefore, an injury or MI showing injury to V1, V2, V3, and V4 is considered an anterioseptal MI.  

When there is an understanding of the EKG lead placement and the electrical system of the heart and where each lead is looking at the heart it makes understanding the connection of what part of the heart the EKG is viewing easier.  When there is ST elevation in certain leads, there is a greater understanding of what part of the heart is having the injury take place. 

Continue to practice reviewing EKGs and look for EKGs that have ST elevation and look at those particular leads to see if you can tell what area of the heart is being affected.                     

Now that we understand what a PQRST is, the anatomy function that occurs to produce each letter, and some actual rhythms, let's try to understand an EKG and what leads affect what part of the heart.  On a 12-lead EKG, there are 6 limb leads which include 3 standard leads and 3 augmented leads. The 3 standard leads are: Lead I, Lead II, and Lead III by placing 2 electrodes, one on each arm and 2 electrodes, one on each leg.  The 3 augmented leads are somewhat different.  Any of the three leads can be positive and the other two negative with their average serving as the negative electrode or common ground.  Lead AVL, Lead AVR, and Lead AVF.  Lead AVL is created with left arm positive and the other limb leads negative, lead AVR is created with right arm positive and the other limb leads negative, and AVF is created with the legs being positive and the other limb leads negative.   There are also 6 precordial or chest leads arranged across the chest in a horizontal plane.  They are: V1, V2, V3, V4, V5, and V6 and are placed in specific areas on the chest.  V1is placed 4th intercostal space (ICS) to the right of the sternum, V2 placed 4ICS to the left of the sternum, V3 between V2 and V4, V4 placed 5ICS at midclavicular line, V5 placed between V4 and V6, and V6 placed 5ICS at the midaxillary line.  I understand this is a lot of information but please watch the video and you will understand better.  When the video is finished, please try on your own to mark the areas where the leads should be placed.  We will continue the 12-lead EKG in the next session.  If you have any questions please feel free to ask Marna!

Can you tell me the differences?

This is what sinus arrythmia sounds like.  Can you hear the difference between sinus arrthymia and normal sinus rhythm?  Please listen to both videos and explain the difference between the sounds and rthythms. What do you think can cause a sinus arrhythmia? 

                      

Rhythms and rationale? Anyone?

Sinus Arrythmia

 Can anyone identify why this is a sinus arrythmia?  How do you count the ways?

Normal Sinus Rhythm

Sinus bradycardia

How is this normal sinus rhythm different from sinus brady and sinus arrythmia?





What makes this rhythm sinus bradycardia?

Can anyone identify the rate of each rhythm? 
How do we determine the rhythm?
How do we count?

For those of you who can answer these questions, please feel free to leave your answers on the blog and we can discuss them next time. 

Review and What's Ahead

Now that we have the basics out of the way, let's take a moment and review.
EKGs can tell us a lot about a patient.  An EKG should be done on every patient that complains of chest.  Knowing how to interpret them may save someone's life.  For every P wave there should be a QRS followed by a T wave.  Knowing what the PR interval, ST segment and QT interval are can tell us whether the rhythm is normal, there is injury or ischemia, or if there may be  medication affecting the rhythm. 

Tomorrow we will begin to look at normal sinus rhythms, sinus brady, and what asystole and look at some atrial  arrhythmias.  Please feel free to review the videos to stay up on what we have just learned.  Any questions, feel free to ask Marna.

How do they measure?

Ekg rhythm's have a certain measurement for every  PR interval, QRS width, ST segment and the QT interval on Ekg paper. The PR interval typically measures 0.12 to 0.2 seconds, QRS typically measures 0.06 to 0.1 seconds,  ST segment if elevated 1mm or greater is ST elevation and means there is active injury taking place. If there is ST depression there is ischemia that has occurred.  QT interval measures the time it takes for the ventricles to depolarize an repolarize to the ventricular repolarization. For more information on this topic please see: http://geekymedics.com/body-systems/cardiology/understanding-an-ecg/. 
This Ekg grip can show the rhythm strip paper and what each box measures.  One small box measures 0.04 seconds.  There are 5 small boxes measuring 0.04 in one large box.  0.04 x 5= 0.2 seconds.  When looking at rhythms and measuring them these boxes are an important component of measurements and rhythm rate.  Please review this grid and see the example rhythm strips below.  Can you identify the PR interval, QRS width, ST segment and is it ST elevation or ST depression and the QT interval? If you have any questions feel free to ask Marna.

Putting it all together

Can you identify the PQRST, PR, QT, and ST parts of this EKG?  What do the lines on the paper help determine?  Does anybody have any experience in reading EKGs?  If you do, what is this rhythm?  How do you know? What identifying features does this rhythm have?  We will discuss the large and small blocks on the paper and what they represent the next time we meet.