Before understanding the dynamics of 12 Lead EKG interpretation, it is important to clearly understand the basic anatomy and physiology of the heart. This includes understanding why different rhythms occur and the consequences of those rhythms. So, let’s start by looking at basic A&P of the heart.
Right arm Lead I, Left arm Lead aVF. If right drops, RAD; if left drops, LAD. If both drop, combined L&RAD.
That all Atrial fibrillation patients MUST be anticoagulated! Clots form in the atria as it is fibrillating (quivering) and eventually get pumped out by the ventricles to vital organs! These patients need Coumadin, monitoring for INR and possibly evaluation for a filter in the Aorta to prevent the ejection of clots.
A PVC is an beat that comes earlier than expected and originates from somewhere in the ventricles, rather than the atria. These are ectopic beats that are non-perfusing. Why? Because they occur before there has been adequate filling time in the ventricle.
Why is this important as a primary provider? Because a PVC is a red flag that something is wrong. Electrolyte status and medication levels are the most common causes.
There are three leads which are usually designated as I, II and III.
They are all bipolar (i.e., they detect a change in electric potential between two points) and detect an electrical potential change in the frontal plane.
Lead I is b/w the right arm and left arm, the left arm being positive.
Lead II is b/w the right arm and left leg, the left leg being positive.
Lead III is b/w the left arm and left leg, the left leg being positive.
Augmented Leads- aVR, aVL, aVF
The same three leads that form the standard leads also form the three unipolar leads known as the augmented leads. These three leads are referred to as aVR (right arm), aVL (left arm) and aVF (left leg) and also record a change in electric potential in the frontal plane.
Next you are going to look for Axis, Hypertrophy and Infarct. This is very simple if you follow some basic rules.
Let’s start with an overview. All of the leads should be positive except aVR, aVL, V1 & V2. Look at how that is represented…think of the 8 outside leads as the cup holding the contents and the four inside leads as if they were poured into the cup.
So, lets go back and look at our normal 12 lead again.
Is Lead I and aVF mostly upright? Yes, then they are both positive which means the flow of electricity is following the same vector! You can also look at Lead II to help confirm, is it positive? Yes! So, this 12 lead has a Normal Axis.
The QRS is downward or negatively deflected in I and positive in aVF or Lead II.
The heart is lying in an angle lower the 30 degrees in the chest. Can be normal in young adults or "thin people." May be abnormal in people who have a block in the posterior division of the left bundle. Can imply delayed activation of the right ventricle ( as seen in RBBB ) or Right Ventricular enlargement. Pathology: Right Ventricular enlargement and hypertrophy. C.O.P.D. Pulmonary Embolism, Congenital heart Disease, Inferior wall MI.
The QRS is upright or positively deflection in I and negative in aVF or Lead II.
The heart is lying in an angle greater than 90 degrees in the chest. Can be normal in the presence of acites, abdominal tumors, pregnancy or obesity. Abnormalities are due to Left Ventricular enlargement or a Left anterior hemiblock. Pathology: Left ventricular enlargement, and hypertrophy, Hypertension, Aortic Stenosis. Ischemic Heart Disease. Inferior wall MI.
Echocardiogram is the Gold Standard for determining chamber size. EKG is not reliable. However, it can provide some insight or prompt you to order an echo. So, look at these basic Simplified Criteria for Diagnosing .
In Bundle Branch Block, the firing of the Ventricles does not occur simultaneously as it should. Conduction reaches a block in one of the branches (in the cardiac septum) and refers it to the opposing branch to be conducted completely. It is then when conduction jumps the Intra-Ventricular Septum to ultimately conduct to the remaining blocked Bundle Branch. It is because of this that you see two different distinctly separate QRS complexes over-lapping one another. Hence, the "Rabbit Ear“
The last 0.04 seconds of deflection on the QRS complex is used to determine the direction of the block.
ST segment elevation with an upward concavity (i.e., " smiley " configuration) is usually benign, especially when seen in an otherwise healthy, asymptomatic individual. This is known as early repolarization .
In contrast, ST segment elevation with coving or a downward convexity (" frowny " configuration) is much more likely to be due to acute injury (from acute infarction).
Remember, it isn’t as important to know every rhythm and every possible complication. What is important, is to know what is life threatening, what needs intervention in the primary care setting and what patient education can make a difference. Obviously, lifestyle modifications is very important in preventing or reversing many of these complications.