“Interpretation Basic Dysrhythmias 5 Steps.pdf”

8/12/2019 Interpretation Basic Dysrhythmias 5 Steps.pdf

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EKG GRAPH PAPER

ECG graph paper is composed of groups of horizontal and vertical lines printedon graph paper that provides a graphical representation of the electrical activityof the heart. The paper is standardized to run at a speed of 25 millimeters persecond. Below you will find an example of ECG graph paper. Note the

horizontaland the vertical lines. Horizontallines measure voltage, which wewill not be studying in this class. We will pay particular attention to the verticallines, which measure time.Inside the bold lines you will find 5 small boxes. Each box measures 0.04seconds. There are 5 boxes in one large box (indicated by the bold lines).Therefore, one large box measures 0.20 seconds. 5 X 0.04 = 0.20 secs. Thesquares represent the time it takes for the electrical impulse to reach a specificpart of the heart. You will need to understand the parts of the box and theirmeasurements in order to interpret rhythm strips. Also, note at the top of therhythm strip, the three black lines. These black lines are referred to as ticmarks. The time from one tic mark to the next tic mark is 3 seconds. In order to

determine the heart rate on a strip using the rule of 10 method you will need asix second strip. When you look at the strip, ensure there are 3 tic marks at thetop of the strip. The tic marks also prove helpful in determining the length of timea patient was in a particular rhythm. Just look at the top of the ECG graph paperand count the number of tic marks you see. 3, 6, 9, 21 . 24 seconds ofventricular tachycardia.

3 seconds 3 seconds

1 second

10

1 large box (inside the bold lines) = 0.20 seconds

1 small square = 0.04 seconds


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ECG WAVEFORMS

A waveform is what is recorded each time an electrical impulse travels throughthe heart. After initiation of the electrical impulse, waveforms are graphicallyrepresented on the ECG paper. One cardiac cycle is represented on graph paperby the following waves: P wave, Q, R, and S waves, and the T wave. First view apicture of the waveforms and then we will discuss each one:

ISOELECTRIC LINE

The baseline voltage of the ECG is referred to as the isoelectric line. Isoelectricrefers to no electrical activity. The isoelectric line is usually measured from theend of the P wave to the beginning of the R wave. Most often the nurse can refer

to the PR segment for locating the isoelectric line. Observe the isoelectric line inthe following picture.

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Isoelectricline

Positivedeflection

Negativedeflection

So if you look at the picture you will see that in the normal heart the waves P, R,T and U have a positive deflection. The following waves are negatively deflected:Q and S. In the beginning, drawing the isoelectric line across the strip will assistyou in identifying waves and correctly measuring intervals.


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Determining the Isoelectric Line

On the following rhythm strip, practice drawing the isoelectric line.

While looking at this picture, go ahead and review where the PR segment, PRinterval and QT intervals are located.

P WAVE

As we discussed earlier, the heart has the ability to generate its own electricalimpulse. In the normal heart electrical impulses start in the SA node. As the SAnode fires, the electricity spreads into the right atrium and along the intraatrialpathway to the left atrium. The atria contract, producing a P wave.A P waveisnormally upright, rounded and uniform (meaning they look alike) defection butcan be negative or biphasic (half above the isoelectric line and half below the

isoelectric line). The P waverepresents atria depolarization. A P wave isgenerally < 2.5 mm tall and < 0.12 seconds or less than 2 to 3 small boxes on theECG graph paper.

This P measures three blocks or 0.12 seconds

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Measuring the PRI, QRS and QT Interval

PR INTERVAL (PRI)

The PRI measures the time it takes for the electrical impulse to travel from theSA node through the internodal pathway to the AV node and downward to theventricles. The PRI starts at the first sign of the P (atrial depolarization) andends at the beginning of the QRS (the beginning of ventricular depolarization).The normal PRImeasurement is 0.12- 0.20seconds or 3 to 5 small blocks on theECG graph paper.

This PRI measures 4 blocks or 0.16 seconds

PR SEGMENT

The PR segmentis the horizontal line located between the P and the QRS. Atrialrepolarization occurs during the PR segment. The PR segment provides the bestplace to locate the isoelectric line, particularly in fast rhythms. With that said,know that most sources will say to look for the TP segment. There are certaindisease states such as COPD and ventricular hypertrophy that may cause the

PR segment to be depressed and therefore not the best place to locate theisoelectric line.

QRS COMPLEX

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The QRSconsists of 3 waves, the Q, R and S waves. It measures the timeinterval it takes the impulse to go from the Bundle of His to the perkinje fibers andthroughout the ventricular muscles. The QRS represents ventriculardepolarization. The Q wave is the first negative deflection following the P waveor before the R wave. The R wave is the first positive deflection after the P wave.


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The S wave is the negative deflection after the R wave. A QS wave would be atotally negative wave. The normal QRSmeasurement is < 0.12seconds or lessthan 3 small squares on the ECG graph paper. Look at the following example.

This QRS measures 3 blocks or 0.12 seconds

Practice labeling the following QRS complexes. Please come to class preparedto discuss QRS waves. The answers are at the end of the packet.

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If the 6thQRS does not look familiar, you are right. There are times when thepatient has something we call a Bundle Branch Block (we will cover later). Theimpulse travels down the conduction system and encounters a blockage in eitherthe right or left bundle. The impulse has to get around the blockage and so ittravels another route to cause the ventricles to contract. So in QRS number sixthe first negative deflection is a Q, the first upright deflection is an R. The Rcrosses over the isoelectric line becoming and S wave. But you have another

positive deflection referred to as R1

or R prime.

T WAVE

The T waveis a slightly asymmetrical positive deflection following the QRS. Incertain disease states the T wave can be negatively deflected or peaked. The Twaverepresents ventricular repolarization(resting phase of the cardiac cycle).

This is what a normal T wave would look like.

QT INTERVAL (QT)

The QT interval is measured from the beginning of the Q (If you have one; if not,from the R) to the end of the T wave. The QT interval represents the time fromventricular depolarization to ventricular repolarization. The normal QT intervalmeasures: up to 0.45 in the male and 0.46 in the female. Why is the QTinterval measurement important? Delays in ventricular repolarization, somemedications; specifically antiarrhythmics and antibiotics and hypomagnesemia


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states predispose the patient to developing Torsades de Pointes, a form onventricular tachycardia that causes sudden death.

This QT interval measures 9 blocks or 0.36 seconds

U WAVE

The U waveis a small waveform following the T wave. Causes of U wavesinclude electrolyte imbalance and certain medication like amiodarone, digitalis,and procainamide.

REFRACTORY PERIODS

Cardiac cells need time to recover (relax) after discharging impulses before thecell can depolarize (discharge) another stimulus. Refractory periods are shorterfor the atria than the ventricles. During cardiac repolarization (resting) phase, theheart goes through two refractory periods. During the absolute refractoryperiodthe cardiac cell is not able to respond to another stimulus, or depolarize(discharge another impulse). No matter how strong the electrical impulse is thecell will not discharge a new impulse. However in the relative refractory period,if the stimulus is strong enough, the cardiac cell can generate a new impulse. Ifyou look at the ECG strip, the absolute refractory periodstarts at the beginningof the Q and ends at the upslope of the T wave. The relative refractory periodbegins at the down slope of the T wave until the end of the T wave. This

corresponds to the period when ventricular repolarization is almost completetherefore the cardiac cell is vulnerable to a strong stimulus.

ARTIFACT, INTERFERENCE

Even in the best of situations a hospitalized patient will move about in bed andequipment will wear out or need replacement. These in addition to other eventswill at times make it difficult at time to interpret rhythm strips. Practice inidentifying the P and QRS waves on the rhythm strip will enable you to becomesuccessful in rhythm interpretation even when artifact or interference are present.Some common examples of patients that are hard to monitor include those

patients with tremors, shivering and agitation. Also diaphoresis, loose electrodes,breaks in the ECG lead wires, a dead battery or other electrical equipment in theroom can affect the look of the rhythm strip.

INTERPRETING AN ECG STRIP

First and most important; it is valuable to mention that no matter what ishappening on your ECG strip look at what is happening with your patient! Ifthe patient is laughing and talking with their family there is no need to be alarmed

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if you see a straight line going across the monitor. In his/her laughter, the patientprobably just pulled a lead wire off his/her chest.

CALCULATING THE HEART RATE

There are two methods that you can use to interpret the heart rate of a rhythmstrip.

1. Rule of 10 Use the tic marks to locate a six second rhythm strip. Count thenumber of R waves within the six-second strip (stay inside the tic marks).Multiply the number of R waves counted (or whatever represents the R wave)times ten (10). Using the example located in the booklet on page 11. There areeight (8) R waves (remember the R waves are the first positive deflection afterthe P wave), so multiply that times 10 and you get a heart rate of 80 BPM.

2. R to R Method One large square of ECG graph paper is equivalent to 0.20seconds. There are five (5) large squares per second and 300 per minute.When the rhythm is regular and the speed is running a 25 mm/sec., the heartrate can be calculated using this method. Look for a QRS that falls on a bold

line on the graph paper. Next, count the number of large boxes between thefirst R wave and the next R wave. Divide 300 by that number. An example:There are 5 large boxes between two consecutive R waves. Divide 5 into 300.The heart rate will be 60 BPM. It is helpful if you are going to use this methodto memorize that 1 large square = 300 BPM, 2 large squares = 150 BPM, 3large squares = 100 BPM, 4 large squares = 75 BPM, 5 large squares = 60BPM, 6 large squares = 50 BPM. You can also count the number of smallsquares between two (2) consecutive R waves and divide by 1500. This is themost accurate method for interpreting the heart rate. An example: There are17 small squares between two consecutive R waves. Divide 1500 by 17. Theheart rate will be 88.

Most nurses will find the Rule of 10 method adequate for rhythm interpretationand it is the method we used in class instruction.

Using the RULE OF TEN to determine heart rate

Count the number of R waves and multiply X 10

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1 2 3 4 5 6 7 8


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FIVE STEP ARRROACH

When examining an ECG strip, we use a systematic approach to look for cluesand then we assess information found in the rules to determine the namedarrhythmia. It is very important in the beginning of learning ECG interpretationnot to skip steps. Answer each question in the five-step approach and apply allnormal parameters for each measurement. The following five steps are vital tointerpreting strips: regularity, rate, P waves, PR interval, and QRS complex.

Regularity - Are the P to P and R to R intervals regular or irregular? Are thereany patterns to the irregularity? Are there any premature (early) beats?

Rate Determine the heart rate using one of the two methods discussed? Howmany electrical impulses (PQRST) do you see in a 6 second strip?

P waves- Are P waves present? Are the P waves rounded and smooth? Do allthe P waves look alike? Is there one P wave for every QRS? Is a P wave infront of every QRS? Are there P waves behind the QRS? Are there more Pwaves than QRS complexes?

PR Interval Are all PRI measurements of normal duration (0.12 to .20)? Doesthe PRI measurement vary. Do you see any patterns?

QRS- Are all QRS complex measurements of normal duration (0.06 to 0.12secs)? What is the QRS measurement? Do all the QRS complexes look alike?Does every QRS have a P wave before it?

STEP SIX---DID I SAY FIVE?

With the invention of new medications and new procedures, it has become

necessary to add a sixth step to ECG interpretation. Certain medications likeamiodarone, sotolol, levofloxacin, procainamide, haloperidol and erthyromycincan lead to prolongation of the QT interval. This can result in a drug-inducedrhythm, Torsades des Pointes, which causes sudden death. Other causes ofprolonged QT syndrome include hypokalemia, hypomagnesemia andhypocalcemia, anorexia nervosa, hypothyroidism and myocardial infarction.

The QT intervalis measured from the beginning of the Q (or the R if there is noQ wave) to the end of the T wave. The measurements should be no more than0.45 seconds for the male and no more than 0.46 seconds for the female.Adecision to say that a patient has a prolonged QT interval should come after at

least three consecutive measurements of a prolonged QT.

Good luck on your pre-test!

R R R R R R1

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S Q S Q QS Q S

“Interpretation Basic Dysrhythmias 5 Steps.pdf”

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