Chapter 25 Electrocardiograms (EKGs) and Related Tests

EKG

shows electrical activity of the heart. The hearts electrical activity causes the muscle contractions that pump blood. This activity occurs in patterns, they are shown in the EKG.

Cardiac Conduction

Movement of electrical signals in the heart. It starts in the upper part of the heart. It's continuous, changes in pattern may be a sign of a heart problem.

Depolarization

a change in electrical charge from negative to positive. Each heartbeat begins with one small area of the heart muscle depolarizing.

Repolarization

A change in electrical charge from positive back to negative. This causes the muscle to relax.

Cardiac Cycle

Each cardiac cycle has a depolarization and repolarization phase. The cycle causes the atria and the ventricles to contract and relax at opposite times. As this happens, the chambers fill and then pump blood.

Sinoatrial node

A.k.a SA node or sinus node, is in the upper part of the right atrium. It's the main, pacemaker of the heart. It sets the timing of the hearts contractions. From the SA node, the electrical impulse moves to the atrioventricular node, also called the AV node.

AV node (atrioventricular node)

located at the bottom right atrium, behind the tricuspid valve. As the impulse from the SA node enters the Av node it's slowed down a tiny bit, just a fraction of a second. W/o this delay the atria and ventricles would contract at the same time. Then the electrical impulse then moves through an area known as AV junction to the bundle of HIS, or AV bundle.

AV bundle

Located in the upper part of the wall between the left and right ventricles. The bundle of His divides into the right and left bundle branches. These branches carry the electrical impulse to the walls of the ventricles. The bundle branches divide into smaller and smaller branches and then from the purkinje fibers.

Electrodes

EKG machines are connected to Pt. using these. These are pads that conduct electricity. They are attacked to lead wires. The lead wires transmit the hearts electrical signals to the EKG machine. Which measures the heart. It takes info from different electrodes to created different "Views" of the heart. Which the views are called leads

Leads

Different views of the heart, gives info about the heart. The info is based on the electrical activity between 2 or more electrodes.

What aren't electrodes?

Leads

The hearts mechanical activity

The muscle contractions of the heart. EKGS don't give direct info about the hearts mechanical activity. they only record the electrical activity. The hearts electrical activity prompts, or causes, the hearts contractions. Because of this relationship, EKGs provide info about heart health. If the heart's electrical activity is normal so is the mechanical activity.

other types of tests to find mechanical acitivity in the heart

Echocardiograms, CT scans, and MRIs

What does an EKG record?

The voltage, or difference in electrical charge, created by depolarization and repolarization. The tracings are sometimes called EKG strips.

You can't read an EKG tracing as an

MA, it's beyond the scope of practice.

The isoelectric line

A.k.a the baseline, is the straight line between the upward and downward movements. Those upward and downward movements are called waves.

Waves

A deflection or movement upward from the baseline is a positive wave. A deflection downward is a negative wave.

Segment

The area between two waves, where the EKG goes back to the baseline.

interval

A wave and a segment taken together.

Complex

Several waves together

normal sinus rhythm (NSR)

When the heart is functioning normally. NSR on an EKG looks diff from person to person. It also looks diff in diff leads on the same person.

When the heart is working properly

there's a correlation between the electrical and mechanical actions of the heart. Each electrical change matches up with a mechanical action.

P wave

first positive deflection, or upward movement, in the complex. It represents atrial depolarization. The mechanical activity related to the P wave is contraction of the atria.

The QRS complex is made up of 3 waves..

The Q wave is the first negative deflections, or downward movement, after the P wave. The R wave is the next positive deflection. The S wave is the next negative deflection. The QRS complex represents ventricular depolarization.

The T wave

Comes after the QRS complex. It shows ventricular repolarization, When this happens, the ventricles relax.

The typs of EKG-based tests

A provider orders a specific type of EKG based on the info she needs. If the Pt. EKG must be monitored for an extended time, either 3 or 5 leads will be used. This type of monitoring is often done in emergency care settings. It allows the provider to continuously check the Pt. rate and rhythm.

telemetry monitoring

used in large facilities to monitor a patient's EKG on an ongoing basis. The Pt. wears a small device w/ 5 lead wires. The device transmits info to a central monitoring station.

Ambulatory monitoring

Used when a Pt. is not hospitalized and the doctor needs info about the heart over a longer period of time. Holter monitors are one common type of ambulatory monitoring. An ambulatory monitor usually stays with the Pt. They are usually placed on the Pt. in a medical office and then removed after 24-48 hours.

Telemetry pack

stays w/ the Pt. it allows the Pt. to be monitored remotely

Holter monitor

allows the Pt. to continue everyday life while being monitored.

Event monitors

a type of ambulatory monitor. They only record the heart's electrical activity when the patient presses a button. Pressing the button indicates that the Pt. is having symptoms

mobile cardiac telemetry

a type of ambulatory monitoring that automatically alerts a healthcare professional if irregularities in the heart rate or rhythm are detected.

12-lead EKG

the most common EKG test for screening and diagnosis. Used during stress tests.

Stress test

Checks how the heart responds to physical activity on a treadmill or stationary bicycle. Test used to increase heart rate.

Limb leads

Leads 1, 2, and 3. These leads are called bipolar leads. They measure differences in voltage between an electrically positive point and an electrically negative point.

Poles

Points with opposite electrical charges.

Lead 1

measures the voltage between the left arm electrode (the positive pole) and right arm electrode (the negative pole).

Lead 2

records the voltage between the left leg electrode (positive) and the right arm electrode (negative)

lead 3

records the voltage between the left leg electrode (positive) and the left arm electrode (negative)

Augmented limb leads

Leads aVR, aVL, and aVF. They use the same electrodes as leads 1,2, and 3 but are unipolar leads. Each one focuses on the electrical activity of one positive pole. It measures the flow of electrical current in one direction only. they measure voltage at a positive pole in comparison to neutral reference point. Positive input is recorded at the right arm for aVR, the left arm for aVL, and the left leg for aVF.

Neutral

w/o pos or neg electrical charge

Percordial leads

A.k.a chest leads, Leads V1-6. They are also unipolar.

Each lead on the EKG gives info about a specific area of theart

Leads 2,3, and aVF give info about the inferior wall of the heart, this is part of the left ventricle. Leads V1-4 give info about the anteroseptal wall of the heart. Leads 1, aVL, and V5-6 give info about the left lateral wall of the heart

Anteroseptal wall of the heart

the front part of the wall that divides the right and left side of the heart

EKG recordin

Incorrect electrode placement creates errors in EKG tracings. Most EKG tests use either 3,5, or 12 leads with 3,5, or 10 electrodes. Some leads in a 12-lead EKG share the same electrodes so only 10 electrodes are needed for the test.

3-lead testing

the electrodes are usually placed on the chest and lower torso. The electrodes are called the right arm, left arm, and left leg electrodes but these electrodes are often placed on the torso The allows the Pt. to move freely.

RA, LA, LL

RA -right arm electrode, right upper torso

LA -left arm electrode, left upper torso

LL -left leg electrode, left lower torso

One of the most common mistakes in electrocardiography is

the reversal of limb leads

5-lead testing

The right and left arm, and left leg electrodes are placed as in 3-lead testing. the V1 electrode is placed to the right of the sternum at the 4th intercostal space. the right leg electrode (RL) is placed on the right lower torso. A.k.a ground electrode.

Where are the 12-lead EKG placed?

in four limb locations and six chest locations

12 lead EKG placement

RA -right upper torso

LA -left upper torso

V1 -in the 4th intercostal space (between ribs 4 and 5) just to the right of the sternum

V2 -in the 4th intercostal space, just to the left of the sternum

V3 -between electrodes for V2 and V4

V4 -in the 5th intercostal space (between ribs 5 and 6) in the left midclavicular line

V5 -horizontally even with V4 in the left anterior axillary line

V6 -horizantally even with V4 and V5 in the left midaxillary line

RL -right lower torso

LL -left lower torso

Location of 3 and 5-leads

the limb electrodes are placed on the torso. This leaves the Pt. free to move more normally

For most resting EKGs

the Pt. is in the supine position with standard electrode placement.

Dextocardia

Dextocardia is a rare heart condition. It causes the heart to point to the right side of the chest rather than the left side. The chest electrodes must be placed over the heart on the right side of the chest, otherwise the EKG won't be accurate. right side placement is a mirror of left sided placement.

Limb amputation/injury

The electrodes may be placed on the torso, as close as possible to the amputated limb. It can be placed on the limb itself, but closer to the torso. The electrodes should not be placed over the scar tissue. The unaffected side should mirror the affected side.

Scar tissue or injury on the chest wall

Electrodes shouldn't be placed on scar tissue from a mastectomy or other chest wall surgery. Scar tissue can be fragile and may be injured when the electrode is removed. electrodes should be placed as close as possible to standard locations.

Medical implants

Electrodes shouldn't be placed over implanted medical equipment like a pacemaker, or over breast implants. The MA should place the electrodes to the side of the implant. They should be as close as possible to the standard positions.

Large breasts

the breast tissue should be moved away from the electrode site as much as possible. This allows placement of the electrodes on the chest wall. The Pt. can lift her own breast tissue or the MA can move the breast using the back of her hand. Don't place electrodes on top of breast tissue.

Pediatric Pt.

Electrode placement is diff for some pediatric Pt. The electrodes used may be smaller or have a gentler adhesive. Children under 2 require a right-sided EKG same for dextocardia. For children 2-12, the standard 12-lead electrode placement is used for all electrodes except V4. The V4 electrode is moved to the right side of the chest at the 5th intercostal space at the midclavicular line. This placement is called V4R. This is needed cause the right ventricle extends past the right side of the sternum in small children.

Posterior EKG

This can help diagnose a type of heart attack called an inferior wall MI. The MA will use the lead wires commonly used for V4-6 and place the electrodes on the patient's back. These locations are called V7-9. The Pt. is seated upright while the electrodes are placed on their back. The Pt. then put into a supine position

In a posterior EKG

V7 takes the place of V4, V8 takes the place of V5, and V9 takes the place of V6

Alternate patient positions

A Pt. who's over 6 months prenant shouldn't be placed in the supine position for an EKG cause it can cause the fetus to compress the Pt. vena cava. the Pt. can become weak and possibly faint. They should lie down and be tilted to the left.

If a patient has orthopnea

They should be placed in a semi-Fowlers positions (45 degree angle) for an EKG, this will help them breathe during the test.

If an EKG machine isn't set up properly

on the tracing it will be accurate and it won't show interference or distortion, known as artifact.

Where should the EKG be placed?

on the left side of the patient. Electrodes for the precordial leads are placed on the left side of the chest.

Attaching the lead wires to the electrodes before applying them to the Pt. reduces

pressure on the patients skin

The defauly standard paper speed is

25mm per second. The ekg machine prints the paper speed on each electrocardiogram. paper speed can be increased to 50mm/s if the provider requests it. The faster speed spreads out the tracing making it easier to see. this can be helpful for fast rhythms.

Gain

a measurement of how high or low the stylus (the part of the machine that makes the marks on paper) moves. Gain is measured in mm per millivolt. (mm/mV)

Millivolts

are a measurement of how many mm the stylus will move to record each mV of electricity

Gain control and standard gain

Gain control on an ekg machine can be used to change the sensitivity of the machine. the standard gain, is 10mm/mV, this means 1-milivolt signal makes a mark on the ekg tracing that measures 10mm. Increasing gain makes easier to see EKG tracings. Higher gain creates a taller tracing. lower creates shorter.

calibration marker

the vertical rectangle with the bottom line missing. The standard gain mark should be 5mm wide by 10mm tall when the machine is used at default speed.

Pediatric patients

children may be scared of Doctors, it's important to tell them it won't hurt and will only take a few minutes, the MA should describe the tests in words children would understand like electrodes=stickers. And let children ask questions.

Obtaining a lead Ekg

for a male Pt. chest hair may need to be removed, pt. needs to undress waist up, a female can leave her bra on or take it off its her choice, the Pt. needs to remove socks or stockings, remove jewelry, prepare the Pt. skin, dry or remove lotion.

patients who have had heart surgery usually have a

stress test once a year to monitor heart function.

Pharmalogic stress test

when the stress is created with medications

Nuclear stress test

A type of cardiac stress test. A harmless radioactive substance called a tracer is injected into the Pt. bloodstream. Before the stress test is done, the patient is placed in a supine position with her arms over her head. A special camera records the motion of the tracer through the heart. This test gives the provider more detailed info about possible blockages in coronary arteries.

Pt education for stress tests

avoid caffeine for 24 hours before the exam. some meds need to be stopped temporarily, don't eat or drink anything except water for 3 hours before the test. wear comfortable loose clothing and athletic shoes. bring all meds on test day. the procedure last 2-4 hours.

A 12-lead Ekg is conducted before

the Pt statyes exercising, and then during the test. The ekg is repeated at 5,10 and 15 mins after the exercise is completed. vital signs are measured every 2.5 mins.

age-predicted maximal heart rate

the Pt. heart must reach a particular hear rate for the stress test to be considered valid. Calculate it by subtracting the patients age from 220 which equals the age-predicted maximal heart rate and then multiply than by 0.85 to get the target heart rate for the stress test ex. 220-54 = 166. 166 x 0.85 = 141 bpm = target heart rate. The Pt must reach a heart rate of 141 bpm for the test to be valid.

A stress test should only be done by

people who are trained in Cpr. and should be stopped if the Pt. has dizziness, chest pain, shortness of breath, a sudden increase or decrease in systolic or diastolic bp, leg cramps, etc. If Pt. wants to stop then stop, if heart rate doesn't rise above 120bpm then stop test aswell.

Most ambulatory monitors

use 5 electrodes. MAs should ensure that the monitor batteries are fresh before attaching the electrodes to the Pt. Some facilities provide extra batteries to Pt.

because patients using an ambulatory monitor continue their everyday activities

electrodes and wires may be tugged or strained, this can disrupt the EKG recording or make it harder to read.

Stress loop

some electrodes for ambulatory monitoring have a built-in clip or slot. This allows the Ma to create a loop with the lead wire. It can reduce tension placed on the electrodes by the patients movements. A stress loop can also be created by looping the lead wire and then placing tape over the loop.

When attaching electrodes in correct positions avoid

bony areas, broken skin, scar tissue, and skin over implanted devices

The muscle action involved in any patient movement will show up on an ekg tracing this can crated 2 types of

artifact: somatic tremor and wandering baseline

Somatic tremor artifact

makes a fine, choppy distortion on the EKG tracing. This makes the ekg difficult or impossible to read. This interference is usually caused by tremors or shivering. may occur if Pt. is cold.

wandering baseline artifact

the normally flat baseline goes up and down across the tracing. it makes it hard to see the features of the EKG tracing. Sometimes the tracing runs off the paper. The movement of the muscles used for breathing can cause wandering baseline artifact. The MA should remind Pt. to breathe as normally as possible and stay quiet and still during the test. placing electrodes on wrists and ankles reduces wandering baseline irregularities.

Loose electrodes or poor electrode contact

are common causes of wandering baseline. Sweaty or wet skin, oily, or soiled skin, dry skin, and body hair ruins electrode contact. Abrading tape can improve skin electrode contact.

Other factors that cause wandering baseline

electrodes that are expired or dried out, they may prevent the ekg machine from picking up any signals at all. electrodes should be stored in an airtight container. Tension on the lead wires or wires that aren't secured well can also cause wandering baseline artifact

Artifacts

called electrical interference and broken recording can be caused by factors in the care environment. Electrical interference is also called alternating current (AC) interference or 60-cycle interference. it can be caused by other appliances or equipment in use in the area near the ekg machine.

Some ways to eliminate electrical interference

-turning off other electrical appliances, changing the outlet being used to power the ekg machine, not plugging the ekg machine into an extension cord, etc. EKGs usually have a built in filter to reduce electrical interference.

Broken recording

also called interrupted baseline, occurs when the ekg machine cannot find a signal. the sylus goes from side to side as the machine searches for a signal. The most common cause is frayed or broken lead wires.

regularity of heart rhythm

a normal rhythm has a clear, repeating pattern. A normal rhythm has clear P wave, a wide spread-out QRS complex may be a sign of a problem.

If rhythms start in an area of the heart other than the SA node then

a dysrhythmia has occured and the rhythm may be too fast or too slow.

Atrial rhythms

have abnormal P waves. The P wave may also be hard to see

junctional rhythms

may have P waves that go down, rather than up, from the baseline. P waves may also be hidden

Ventricular rhythms

have QRS complexes that are wider than normal. Ventricular rhythms can be dangerous

Heart block rhythms

usually have long spaces between the P wave and the R wave. This is called a long PR interval.

Artificial pacemakers

are put in when a patients normal cardiac pacemakers no longer work. They can change how EKG tracings look. Dysrhythmias (especially very slow rhythms), heart blocks, cardiomyopathy, and heart failure are conditions that may be treated with a pacemaker.

Pacemaker impulses

make a spike-like wave on ekg tracings. MAs may see these spikes when doing an EKG on a patient with a pacemaker.