Thursday, October 14, 2010

Ch. 6 Interpretation of an EKG strip

Interpretation of an EKG Strip
General Rules
Few basic rules that will assist you in your quest to correctly identify  heart rhythms
1. First and most important, look at your patient!
A. What is the patient’s clinical picture, and how is it significant to the rhythm noted on the monitor?
2. Read EVERY strip from left to right, starting at the beginning of the strip.
3. Apply the five-step systematic approach that you will learn in this chapter.
 4. Avoid short cuts and assumptions. A quick glance at a strip will often lead to an incorrect assumption.
 5. Ask and answer each question in the five step approach in the order that it is presented here. This is important for consistency.
6. You must master the accepted limits or parameters for each dysrhythmia and then apply them to each of the five steps when analyzing the strip.
The Five-Step Approach
    Step 1: Heart Rate
Step 2: Heart Rhythm
Step 3: P wave
Step 4: PR interval
Step 5: QRS complex
Remember a quick glance can be deceiving!
Heart Rate
Heart Rate can be defined as the number of
electrical impulses conducted through the myocardium in 60 seconds.
When calculating heart rate, we are usually referring to the ventricular
heart rate. BUT is appropriate in certain strips to calculate both the
atrial heart rate and the ventricular heart rate.
Simply stated atrial heart rate can be determined by counting the
number of P waves noted; ventricular heart rate is determined by
counting the number of QRS complexes.
If the heart rate is less than 60 it is known as bradycardia
If the heart rate is more than 100bpm the correct term is tachycardia.

Heart Rate Continuation
Note: Keep in mind that your patient’s clinical picture is critical to proper assessment and management.
Ask yourself: How is the Rhythm significant to the patient’s clinical picture?
There are two methods commonly used to determine heart rate by visual examination of an EKG strip. The first and simplest is called the 6-second method.
To use this method properly you must first a 6-interval on the EKG strip.
Simply count number of QRS complexes that occur within the 6-secong interval and then multiply the number by 10.
If the strip does not have 3 to 6 second intervals count 30 squares.
The second method is the R-R method. This method is most accurate id the heart rhythm is regular. Otherwise it is just an estimation.
You should look for a QRS complex (specifically an R wave). That falls on a heavy line on the strip. Then you should count the number or large boxes between the first R wave and the next R wave.
After you have determined that number you must divide it into 300. Remember that it normal pulse is 60-100.
Heart Rhythm
Heart Rhythm can be defined as the sequential beating of the heart as a result of the generation of electrical impulses.
Calculating heart rhythm establishes pattern of QRS complex. Calculations of heart rhythms are classified as either regular or irregular.
Heart Rhythm
Determining if EKG is Regular or Irregular Rhythms
To determine whether the ventricular rhythm is regular or irregular you need to measure the R to R waves. 
To determine whether the atrial rhythm is regular or irregular you need to measure the P to P waves.
It rhythm is considered regular if the intervals vary by less than 0.06 seconds (or 1.5 small squares)
If rhythm is more than 0.06 seconds the rhythm is considered irregular.
 Calipers are helpful when you begin to analyze EKG rhythms.
 If you don’t have calipers you may use a piece of paper placed on the EKG strip just below the peak of the R wave. Look at the piece of paper and analyze if the markings are regular.
Heart Rhythm
If the markings are relatively even then we can say that the rhythm is regular
If the markings are uneven then we can say that the rhythm is irregular.
Rhythms are classified as:
A. Regularly Irregular-------irregular rhythms that occur in a pattern.
B. Occasionally irregular---intervals of only one or to R-Rs are uneven.
Irregularly Irregular----R-R intervals exhibit no similarity.
Practice EKG Strips
EKG Strip Practice
The P wave
P wave when R and L atria depolarize. The P wave is the first deviation seen.
It should always look rounded and upright (positive) in the EKG strip (chest Lead II).
P wave is not upright in Lead II you are not looking at a sinus rhythm (rhythm originating from the SA node).
The P wave
Ask yourself these five questions when evaluating the P wave.
 1. Are P waves present?
2. Are the P waves occurring regularly?
3. Is there one P wave present for each QRS complex present?
4. Are the P waves smooth, rounded, and upright in appearance or are they inverted?
5. Do all the P waves look similar?
 SA node (sinoatrial) is the primary pacemaker of the heart and is located in the right atrium. If the SA node is firing at regular intervals the P wave will also follow regular intervals.
This pattern is referred to as a normal sinus rhythm.
The PR interval
The PR interval measures the time intervals from the onset of atrial contraction to the onset of ventricular contraction or the time necessary for the electrical impulse to be conducted through the atria and the AV node.
 IT is called the PR interval BUT it includes the entire P wave.
You measure the PR interval from the onset of the P wave to the onset of the Q wave of the QRS complex.
 The normal length of the PR interval is 0.12-0.20 seconds (3-5 small squares).
 The PR interval should be constant across the EKG strip in order to be considered “within normal limits”
 A shortened PR interval may be indication
PR interval
that the usual progression of the impulse was outside of the normal route.
Prolonged PR intervals may indicate a delay in the electrical conduction pathway or AV node.
Three questions that should be asked when evaluating PR intervals:
1. Are the PR intervals greater than 0.20 seconds?
2. Are the PR intervals less than 0.12 seconds?
3. Are the PR intervals constant across the EKG strip? 
The QRS complex
The QRS complex represents the depolarization (contraction) of the ventricles. It is important to note whether all QRS complexes look alike
Q wave-The first negative or downward deflection of this large complex. Often Q waves are not seen.  
R wave- The first upward or positive deflection following the P wave. In chest Lead II, the R wave is the tallest waveform noted.
S wave- The sharp negative or downward deflection that follows the R wave.
The QRS complex
The overall appearance of the QRS as well as its width, can provide important information about the electrical conduction system.
When it functioning normally, the width of the QRS complex will be 0.12 seconds or less formed in the ventricles.
The normal or narrow QRS complex indicates that the impulse was not formed in the ventricles and is thus referred to as supraventricular “Above the ventricles”.
Wider QRS complex indicate that the pulse is either of ventricular origin or of supraventricular origin with conduction that deviates from the normal course of pattern.
QRS complex question to ask
1. Are the QRS intervals greater than 0.12 seconds (wide)? If so, the complex may be ventricular in origin
2. Are QRS intervals less than 0.12 seconds (narrow)? If so, the complex probably is supraventricular in origin.
3. Are the QRS complexes similar in appearancea across the EKG strip?
ST Segment
The ST segment begins with the end of the QRS complex and end with the onset of the T wave. The ST segment is usually consistent with the isometrical line of the EKG strip.
The point where the QRS meets the ST segment is referred to as the J point.
If the ST segment is elevated or depressed, myocardial ischemia may be indicated.
T wave
Is produced by ventricular repolarization or relaxation. T wave are commonly seen as the first upward or positive deflection following the QRS complex.
The U wave
Not usually visible
U wave may represent the purkinje Fibers repolarization
If U wave appears is much smaller than the T wave.
Is defined as EKG waveforms from sources outside of the heart.
1. Patient movement (wandering baseline)
2. Loose or Defective Electrodes “Fuzzy basline
3. Improper grounding—Artifact may occur when the patient is in touch with an outside source of electricity, such as a poorly grounded electrical bed.
4. Faulty EKG apparatus—Broken wires or cables may produce artifact.
Artifacts can mimic certain lethal dysrhythmias, it is important to assess patient at all times for signs.

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