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Electrocardiography

ECG

Heart Structure & Function

1. Heart:
Located in the thoracic cavity between the lungs behind the sternum in an area called the mediastinum.
Hollow triangular organ about the size of a fist enclosed within a double-walled sac called the pericardium.
a. The middle layer or myocardium makes up most of the heart wall and is composed of cardiac muscle and fibrous tissue.
b. The endocardium lines the upper chambers, or atria, and lower chamber, or ventricles, of the heart.
2. The function of the cardiovascular system is to carry oxygen from the lungs to all the tissues of the body.
3. The deoxygenated blood then circulates through the body and discharges carbon dioxide, the waste product of cell metabolism, from the lungs.
4. Blood circulates throughout the body and returns from the general circulation by way of the superior and inferior vena cava, to the right atrium, moving in one direction through the heart.
a. When the right atrium is full, the atrium contracts and blood is pumped into the right ventricle through the tricuspid valve.
b. Upon filling, blood is pumped by contraction of the right ventricle through the semilunar valves into the pulmonary artery going to the lungs.
c. There, blood is oxygenated and returned to the left atrium through the four pulmonary veins.
d. When that chamber is full, it contracts and blood is squeezed into the left ventricle through the mitral (bicuspid) valve.
e. In the left ventricle, blood will enter the aortic semilunar valve and move into all parts of the body except the lungs.
f. Blood travels to all parts of the body via the aorta and then goes into all other arteries.
5. The heart muscle receives its supply of oxygen and nutrients through the coronary artery system on the outside of the heart.
a. The blood that flows through the heart to the body is not used for energy for the heart tissues.
b. As blood leaves the left ventricle rich with oxygen it enters immediately into aorta and the coronary arteries to supply the heart muscle.
c. Deoxygenated blood returns to the general circulation through the cardiac veins, which empty into the coronary sinus in the right atrium.
B. Discuss heart valves and their function.
1. Heart valves
a. Act as gates to prevent the backward flow of blood.
b. Open and shut in response to the changing pressure brought about by cardiac contraction and relaxation.
c. The contraction and relaxation of the chambers occurs in sequence because electrical impulses move smoothly along the electrical conduction system of the heart.
2. This conduction system involves the movement of charged particles or ions during different phases.
a. Minerals (sodium, potassium, and calcium) are responsible for smooth contractions and consistent rhythm.
b. At rest, the cells of the heart are polarized—that is, they are charged with energy (negative inside the cell and positive outside).
c. As the cells are stimulated to contract, the mineral particles move like a wave, and the charge within the cells changes to positive inside and negative outside.
d. The cells are depolarized and contraction occurs.
e. The cells then return to a resting state, called repolarization, as their electrical charge returns to the original negative inside and positive outside.
C. Identify and explain the conduction system.
1. The four major components of this conduction system are the
a. Sinoatrial (SA) node.
b. Atrioventricular (AV) node.
c. Bundle of His with the right and left bundle branches.
d. Purkinje fibers.
2. The heartbeat is controlled by rhythmic impulses that arise in the SA node and move through the conduction system.
a. The SA node, located in the right atrium, is made of modified myocardial cells and acts like a battery.
b. The SA node is known as the pacemaker of the heart because it establishes the pace.
c. It may accelerate or slow the heart rate or beats per minute, under the influence of the autonomic nervous system.
3. The conduction system carries the impulse from the SA node and spreads it through the atria. This process is called atria depolarization.
a. The impulses reach the AV node (also made of modified myocardial cells) where they are momentarily delayed.
b. During this delay, the atria rest and recover. This is known as atrial recovery, atrial rest, or atrial repolarization.
c. The impulse passes from the AV node down the bundle of His as it divides into two bundle branches, carrying the impulse along both sides of the interventricular septum.
d. The bundle branches spread to form a network, the Purkinje system, that distributes the impulse to all parts of the ventricular muscle, resulting in ventricular contraction and or ventricular depolarization.
e. Ventricular depolarization follows atrial repolarization, and is followed by a period of ventricular recovery known as ventricular repolarization or rest.
f. There is a brief pause, and the cycle begins again.
g. Atrial and ventricular depolarization plus atrial and ventricular repolarization comprise the cardiac cycle, one pulse and one heartbeat.
h. The term systole refers to the contraction phase of the heart and conversely diastole refers to the relaxation phase of the heart.
4. A unique property of cardiac muscle is that all conductive tissue has the potential to serve in the role of pacemaker—that is, any area can set the cardiac rate if the SA node fails.
a. Under abnormal circumstances, such as when damage has occurred, other areas may assume the role of the pacemaker.
b. Slower rhythms are generated by the AV node (40 to 60 beats per minute), by the bundle of His (less than 40 beats per minute), and by the Purkinje system.
c. Normally the SA node generates the controlling impulses at a resting rate of 60 to 80 beats per minute.
5. Heart sounds are important clues for the physician during an examination.
a. Two types of heart sounds, namely murmurs and gallops, and are associated with certain abnormal conditions.
b. Causes of murmurs
• damaged valves
• regurgitation or back flow of blood through a valve
• high flow rates
• all of the above cause a kind of turbulence
c. Gallops, or galloping rhythm, is an abnormal rhythm indicated by three distinct sounds in each heartbeat similar to the sounds of a galloping horse.
d. The physician documents normal heart sounds, along with any murmurs, gallops, or other abnormal heart sounds that are present.

Performing an ECG

of how electrical charges created by the cardiac conduction system are recorded.
1. The electrical charges created by the cardiac conduction system can be sensed throughout the body.
a. Electrodes placed in specific areas of the skin can detect those electrical charges and then transmit them to a computer for amplification of the signal to be recorded on paper for physician assessment.
b. If no energy is sensed, then the equipment records a flat line, or isoelectric line.
c. When the equipment senses an electrical charge, this is recorded as either an upward or a downward deflection on the readout.
d. Movement away from the baseline is called a deflection or wave.
e. The waves or deflections may go up (positive) or down (negative) from the baseline and represent amplitude or voltage.
f. The strength or voltage of the electrical impulse will determine the size of the deflection.
g. Large voltages will cause larger deflections, whereas small voltages create smaller deflections.
2. The deflections from the heart are labeled P, Q, R, S, and T.
a. Sometimes a small U wave follows the T wave. This is considered normal and may be due to a potassium deficiency.
b. A normal cardiac cycle is one series of PQRST waves.
• The P represents atrial depolarization (change in electrical activity).
• The QRS complex represents ventricular depolarization.
• The T is repolarization (a return to the resting electrical state).
c. On an ECG, the horizontal axis (line) represents time; a slower heart rate has more space between the PQRST complexes.
d. On a patient with a faster heart rate, the cardiac cycles are closer together.
e. When a heart skips a beat, there is a long flat line between PQRSTs.
f. The amount of space between the P wave and the QRS complex indicates the time required for the conduction system to carry the impulse from the SA node to the Purkinje fibers.
3. Recordings are made from a variety of perspectives or angles known as leads.
a. Each lead will record from a specific combination of sensors.
b. When completed, the 12-lead ECG produces a three-dimensional record of cardiac impulses.
c. The pattern of deflections will appear quite different on each lead.
d. The pattern of deflections recorded, voltage or amplitude and time, assist the physician in evaluating the status of the patient’s heart.
e. In some instances, it may be necessary to enlarge or shrink the recording.
f. Under ordinary circumstances, a recording is made in sensitivity 1, which represents a 10-mm deflection per 1 millivolt (mV) of electricity. The size is doubled in sensitivity (sensitivity 2) or halved in sensitivity (sensitivity ½)
B. Examine the cardiac cycle. Point out that while the medical assistant should not try to interpret the ECG, understanding what is normal in the cardiac cycle is helpful.
1. The P wave represents the impulse that originated in the SA node and spread through the atria, called atrial depolarization.
2. When the P wave is present in normal size and shape, then the stimulus causing the heart to beat originated in the SA node.
3. Normally, the P-R interval (time from the beginning of P to the beginning of QRS) is between 0.12 and 0.20 seconds (three to five small boxes on the ECG graph paper).
4. A deviation from these times could represent an abnormality in the electrical system of the heart or in the structure of the heart that impacts the electrical system.
a. This interval represents the time it takes for the impulse to cross the atria and the AV node and reach the ventricles.
b. A P-R interval that is too short means the impulse has reached the ventricles through a shorter than normal pathway.
c. If the interval is too long, a conduction delay in the AV node might be assumed.
5. The QRS complex represents the time necessary for the impulse to travel through:
a. the bundle of His
b. the bundle branches
c. and the Purkinje fibers
6. Once the impulses have traveled through each of these areas the ventricular activation or contraction is complete, known as ventricular depolarization.
a. This usually takes less than 0.06–0.12 second (three small ECG boxes).
7. The ST segment and the T wave represent repolarization of the ventricles.
a. The ST segment is normally flat (on the isoelectric line or baseline) or is only slightly elevated.
b. The T wave represents a part of recovery of the ventricles after contraction.
8. The QRS complex and the T wave typically point in the same direction.
a. T waves that are opposite in direction from the QRS may indicate a problem in the heart or its electrical system.
C. Describe the various types of ECG machines that are used. Note that all the machines should be calibrated to align with the international standard.
1. Calibration of ECG machines
a. This means that the paper in all machines moves at the same speed of 25 mm/second.
b. Given the same amount of electrical energy, the recording stylus will move the same distance (1 mV of electricity input will cause the stylus to deflect 10 mm), thus giving uniform recordings worldwide.
c. Standardization is a means of verifying that each machine deflects 10 mm in response to 1 mV of electricity in sensitivity.
2. Older models are manual, meaning that the machine must be told what to do.
a. You may record from arms and legs in fairly rapid succession.
b. You must move the chest sensor and record from each lead, then move the sensor again.
3. Newer models of electrocardiographs are computerized.
a. Computerized models have automatic features so you may only need to push a button.
b. All 10 sensors are placed on the patient at the beginning of the procedure and the computer switches from lead to lead in rapid succession.
c. Before operating the machine, the medical assistant will enter data into the computerized electrocardiograph.
d. Data usually includes the patient’s name, date of birth, diagnoses, height, weight, age, blood pressure, medications taken, and information pertinent to the ECG.
e. The medical assistant may ask the patient these questions while placing the data in the computer, which helps the patient to relax a bit before beginning the procedure.
4. The operator may override the automated machines if there is a need for manual controls.
a. For example, the physician may have just ordered one rhythm strip of lead II, rather than a complete 12-lead ECG.
5. Many computerized models can record from more than one lead at once, to save time.
a. Each is recorded in a separate channel or pathway for the signal and, typically, these machines record three channels at once.
6. Other machines have a built-in interpretive feature and will print out a statement as to the status of the heart.
7. Others can connect directly via fax with a regional office that will carry out the interpretation function and fax results to your office.
8. Although computerized electrocardiographs save considerable time in mounting ECGs, care should still be taken to ensure that a clear ECG is made before disconnecting the sensors.
D. Explain the importance of making sure that electrocardiographs are clear and accurate with no artifacts, or errors. Knowledge of the control panel helps in producing a tracing that is clear, accurate, and easy to read. The control panel consists of the following items.
1. Main power switch (off/on):
• Allow for a warm-up time as specified by the manufacturer before using.
2. Record switch:
• This switch moves the paper at the standard “run 25” speed (25 mm/sec).
• ECGs are usually recorded at this speed.
• Another option is “run 50” (50 mm/sec or twice as fast).
• This is used when the heart rate is so rapid that interpretation requires that it be stretched out.
• This is only used for detailed interpretations, because it tends to waste paper and can be more difficult to read.
3. Lead selector: this determines from which sensors the machine will record:
• Standard (limb) leads: record from two sensors placed on all extremities.
• Augmented leads: record from the midpoint between two limb sensors to a third limb sensor.
• Chest leads (also called precordial leads): record from various positions on the thorax.
4. Sensitivity control:
• Allows the operator to increase or decrease the recording size in order to enlarge or shrink the deflections to fit on the paper.
• When changing from the international standard of sensitivity 1 to sensitivity of 1/2 or 2, the operator needs to include a standard for the interpreter information.
5. Standard button:
• Allows verification of calibration to the international standard.
• Stylus control: Centers the recording in the middle of the page or the center of each channel by moving the stylus.
6. Stylus control
• Centers the recording in the middle of the page or the center of each channel by moving the stylus
7. Stylus heat control:
• Increases or decreases heat and adjusts for the sharpest tracing.
• New machines use an ink cartridge instead of heat stylus.
8. Marker:
• Indicates, by a code, which lead is being recorded.

Electrocardiogram paper
1. The paper is pressure sensitive and must be handled carefully.
a. If paper is exposed to light for long periods, the markings will fade with time.
b. Many newer machines use an ink cartridge to supply the stylus and provide a longer-lasting printout.
2. “Time” markers, referred to as 3-second markers, are printed on all ECG paper.
a. These are located at the top of single-channel paper and between channels in multichannel paper.
b. The time markers are small squares with a light line and larger squares with a darker line.
c. The small squares are 1 mm by 1 mm square and represent 0.1 mV of voltage in the height and .04 second time in the width.
d. The larger squares are 5 mm by 5 mm square and represent 0.5 mV of voltage in the height and 0.20 second time in the width.
b. The paper records both time (horizontally) and voltage (vertically).
E. Explore heart rate.
1. The same as beats per minute.
2. It is possible to estimate the heart rate from an ECG.
3. To estimate the cardiac rate (beats per minute) from the tracing use the 6-second method.
a. Begin at one 3-second marker and go to the right for two additional markers, for a total of 6 seconds.
b. Count the number of QRS complexes between the first and third markers and add a zero. This is the estimated ventricular rate per minute.
4. A similar atrial estimate can be made by counting the P waves between these markers.
a. This estimate is accurate even if the rhythm is irregular (arrhythmia).
5. The heart rate can be estimated by locating a QRS complex close to a 5-mm line, which is the darker line on the paper.
a. Move to the next deflection at the right or the left, counting how many 5-mm lines intersect the tracing before the next QRS complex.
b. Count off at each 5-mm line, beginning at the deflection near the 5-mm line and saying “zero, 300, 150, 100, 75, 60, 50.”
c. Stop counting when you reach the next QRS complex.
d. This count-off method is an estimate of the ventricular rate.
e. This estimate is accurate only for the complexes where it was done.
6. To obtain on exact calculation of the heart rate, recall that the paper moves at a standard speed of 25 mm/second, so it will move at 1500 mm/minute (25 mm  60 seconds = 1500).
a. An exact calculation of ventricular heart rate is achieved by counting the millimeter boxes between two QRS complexes and dividing that number into 1500.
• For instance, if there are 20 mm between two QRS complexes, 1500 divided by 20 equals 75 beats per minute.
b. An exact calculation of atrial heart rate is achieved by counting the millimeter boxes between two P waves and by dividing that number into 1500.
• These calculations are accurate only for the complexes where they were done.
7. Rhythm is the regularity of the occurrence of heartbeats.
a. Ventricular rhythm
• Determined by measuring the distance between QRS complexes.
• There should be a fairly consistent space between complexes.
b. Atrial rhythm
• Determined by measuring the distance between P waves.
• There should be a fairly consistent space between waves.
F. Discuss sensor placement.
1. The ECG machine records the cardiac cycle through sensors placed on the patient’s bare skin.
2. Sensors are placed:
a. Over the fleshy part of the inner aspect of both lower legs.
b. On either both upper arms or both forearms.
c. Avoid bony prominences.
3. Locations are abbreviated LA for left arm, RA for right arm, LL for left leg and RL for right leg.
a. The RL sensor serves as an electrical reference point and is not actually used in the recording.
b. If you have a patient on whom you cannot place one extremity sensor as planned, you must place the sensors on both extremities symmetrically.
• For example, a patient in a cast up to the knee requires that both sensors be placed above the knee.
• If a hand and forearm are amputated, both arm sensors are placed on the upper arm.
c. The chest sensor, abbreviated with V, is used in six locations, with a number following the V, as in V1, V2, and so forth.
d. Placement of chest sensors must be anatomically correct.
4. By recording from different combinations of sensors, the electrical activity of the heart is seen from different angles.
a. A lead selector switch or lead indicator selects the combination of sensors for that lead.
b. One sensor is used for chest (unipolar) leads.
c. A combination may be two sensors, as with standard limb (bipolar) leads, or three sensors, as with augmented limb leads.
5. With many sensors and many views possible, it is important to indicate on the tracing from which lead you are recording.
a. An international marking system has been devised using dashes and dots.
b. Some machines automatically mark the code just above the cardiac tracing.
c. Others require manual marking with the international code.
6. It is beneficial to memorize the sensors used in the limb and augmented leads.
a. Then, if difficulty getting a clear recording from one lead occurs, you do not have to look at all the sensors, only those involved.
b. Some find it easier to remember all the leads and the sensors being recorded or by picturing Einthoven’s triangle which is a pictorial guide to the leads.
Refer students to Table 49-1 in Chapter 49 of the textbook that lists limb, augmented, and chest leads indicating proper placement and marking codes.
G. Discuss patient preparation for an ECG.
1. Explain to the patient the equipment and procedure as well as what you will expect the patient to do.
2. The surroundings should be pleasant and the table wide enough for adequate support.
3. Patients will need to be bare to the waist so privacy should be provided for disrobing.
a. Offer female patients a gown, to be worn with the opening at the front.
b. Bare skin on the lower legs is also required.
• Patients have to remove socks or stockings.
• Roll long pant legs out of the way.
4. Position the patient comfortably supine with a pillow under the head, and another under the knees, if needed, to eliminate back strain.
5. If the patient cannot tolerate lying down, use the semi-Fowler’s position instead and note that the ECG was done in that position.
6. Jewelry, particularly metal jewelry, must be removed so that it does not interfere with the electrical current of the ECG.
7. Prepare the skin where the sensors will be applied.
a. Any area that has been treated with talcum powder or skin lotion must be rubbed with alcohol to remove the residue to facilitate the adherence of the leads.
b. Some shower gels leave sufficient moisturizer as a residue that can interfere with sensor contact. Such residue must be removed with alcohol before the electrolyte sensors may be applied.
H. Discuss the technical preparation that must occur prior to performing an ECG.
1. If you are to obtain a clear recording of the patient’s cardiac cycle, the machine must be calibrated and in good working order, with a good supply of paper.
2. To improve the contact between the skin and electrodes, a supply of electrolyte or conduction cream, gel, or pads should be present.
3. The sensors may be metal plates that attach with rubber straps or they may be small suction cups called Welch electrodes.
a. These will need to be cleaned between patients to prevent the accumulation of electrolyte.
b. Adhesive disposable sensors that contain electrolyte are widely used today.
I. Review the process of performing an ECG.
1. The placement of chest sensors must be precise.
a. It is possible to complete this task without unnecessary exposure for female patients.
b. The landmarks you need to palpate or view are the sternum, the fourth intercostal space, both clavicles, and the left axilla.
c. To locate V1 and V2:
• Stand on the left side of the patient and expose the sternum.
• Locate the right clavicle and the space immediately inferior to it.
• This is a supracostal space; that is, it is above the first rib and does not count as an intercostal space.
• Proceed toward the feet at the right edge of the sternum and, using the tips of your fingers, palpate the first rib and first intercostal space, second rib and intercostal space, and so forth until you feel the fourth intercostal space.
• This space at the right sternal margin is the location of V1.
• Lead V2 is placed at the same level on the left side of the sternum.
d. Next, locate V4:
• From the middle of the left clavicle, draw an imaginary line toward the feet, stopping one intercostal space below the level of V2.
• This is V4 (5th intercostal space, midclavicular left).
• Lift a female patient’s gown up from the hemline in respect of patient privacy.
• Lead V4 must be at the base of the breast and, in some patients, under the breast.
• In males, it should be at about nipple level.
e. Now you can locate V3 midway between V2 and V4. It is on a rib.
f. V5 is at a point where two imaginary lines intersect.
• Continue to work under the patient’s gown.
• Draw a line from the front of the left axillary fold toward the feet, parallel to the table on which the patient is lying.
• Draw another line toward the table from V4.
• Where these lines intersect is V5.
g. Lead V6 is placed at the midaxilla, in line with V4 and V5.
2. Arrange the patient cable to follow the body contours, avoiding the coils.
3. Connect the patient cable and begin to record by performing a standard.
a. For manual machines, select the STD lead, “run 25,” and push the standard button.
b. Stop the machine and count the boxes included in the deflection.
c. You should get a reading of 10 mm.
d. Use the lead selector knob and select the leads in sequence, running a 6-inch strip, marking the lead code, if necessary.
e. The length of the tracing needed depends on how your office mounts single-channel cardiograms. Have information about your mounting format before you begin to record.
f. Adjust the stylus to the center of the paper.
• For automatic machines, depress “auto-run” and adjust the stylus to the center of each channel.
g. Record the tracing, using problem-solving skills.
h. When the cardiogram is completed, remove the sensors and wipe the electrolyte from the patient’s skin.
i. Dismiss the patient.
j. Clean the machine.
k. Mount the ECG, if necessary, and transfer the patient information.
l. Sign or initial your work.

Steps for performing a 12-Lead electrocardiograph
1. Perform hand hygiene.
2. Assemble necessary supplies.
3. Attach and plug in the power cord.
4. Verify that the machine is operational and positioned properly.
5. Identify, interview, and instruct the patient on the procedure.
6. Offer female patients gowns to be worn with the opening down the front.
7. Position the patient flat on the table with a pillow under the head and one under the knees if needed.
8. Prepare the electrode sites and attach the electrodes.
9. Limb electrodes should be applied over the fleshy part of the inner aspects of the lower legs and on the upper part of the forearms.
10. Connect the patient cable.
11. Instruct the patient to relax, breathe normally, and refrain from speaking.
12. Standardize the machine.
13. Adjust the stylus to the center of the paper or the center of each channel.
14. Record.
15. For automatic machines, depress AUTO-RUN.
16. For manual machines, select the leads in sequence and use RUN 25.
17. Use your problem-solving skills if you encounter artifacts.
18. Mark the leads, if necessary.
19. Remove the sensors; wipe electrolyte from the patient’s skin, if used.
20. Politely dismiss the patient, aiding the patient in getting up and dressed, if necessary.
21. Perform hand hygiene.
22. Clean the machine, straps, and sensors according to manufacturer’s instructions.
23. Mount the ECG if necessary and transfer patient information.
24. Chart the procedure in the patient’s record.
25. Sign or initial your work.
J. Define a satisfactory tracing as one that is accurate, readable, and clear; travels down the center of the page; and has a baseline that is consistently horizontal. Knowledge of the leads and their sensor locations help the medical assistant to trace back to the source any irregular or erratic markings (artifact). If the tracing is not desirable, consider the following:
1. If the baseline begins to drift upward or downward, use the position control knob to return it to the center of the page.
2. Observe whether the tracing remains within the graph portion of the paper.
3. If the deflections are so large that they exceed the upper and lower limits of the graph, reduce the sensitivity from 1 to ½.
a. This will make the tracing half as large.
b. Be sure to include a standard to let the interpreter know what has been done.
c. One mV of electricity will cause a deflection of 5 mm in sensitivity ½.
4. If the tracing in sensitivity 1 is so tiny that it is not readable, increase the size by changing the sensitivity from 1 to 2.
a. Again, place a standard on the page to let the physician know that you have made a change.
b. Just 1 mV of electricity will cause a deflection of 20 mm in sensitivity 2.
5. Because the paper moves through the machine at the rate of 25 mm/second, an option available in recording is to move the paper twice as fast, or at 50 mm/second.
a. This would only be necessary if the cardiac cycles were compacted by a very rapid heart rate.
b. In this case, a better quality cardiogram would be produced if the cycles were stretched out.
c. If you have to change the speed or sensitivity, mark the tracing to indicate that you did so.
d. In machines that mark the lead with an international code, the code marks are stretched out. The dots appear as dashes, and the dashes are long ones.
6. Multichannel machines produce an ECG very quickly, on a single sheet of paper about 8 inches by 11 inches.
a. You will have to center three baselines.
b. A sensitivity or speed change affects all three channels.
K. Examine the types of artifacts that can occur on an electrocardiogram.
1. Occasionally, the sensors will detect electrical activity from a source other than the heart.
2. These deflections or artifacts impair accurate interpretation of the tracing.
3. The medical assistant must find the cause of the artifact and correct it.
4. The different causes of artifacts and how to correct them include the following:
a. Somatic tremor:
• A tense muscle or a muscle contraction, even one that cannot be seen.
• May result from patient discomfort, tension, chills, and talking or moving.
• Calm and reassure the patient.
• Suggest that the patient relax, breathe normally, and not talk.
• If necessary, place the patient’s hands palm-side down under the hips. This is especially helpful if the patient is not relaxed on the narrow table.
• The hands palm-side down under the hips position is also best for patients with a tremor disorder. They will display the smallest number of artifacts in this position.
b. Wandering baseline, baseline sway, and baseline shift:
• Caused by poor sensor contact with the skin, such as when sensors are dirty or applied too tightly or too loosely, when lotion or talcum prevents good contact with the skin, or when the patient cable slips toward the floor, pulling on the lead wires.
• Readjust, reapply, or clean the sensors, and place the patient cable securely on the table.
• It may be necessary to clean the skin with alcohol or cut chest hair.
c. 60 cycle or AC (alternating current) interference:
• Electrical current in wires and equipment may be picked up by the patient’s body and the recording machine.
• This appears in the recording as small regular spikes or static, and is due to improper grounding, nearby electrical equipment in use, or twisted and coiled lead wires.
• Ground the machine properly.
• Unplug other electrical equipment in the area.
• Move the machine to the patient’s feet and away from walls containing cables.
• You may have to wait until a procedure in an adjacent room, such as an X-ray, is completed.
d. Erratic stylus:
• Loose or broken lead wires cause the stylus to thrash erratically and go off the page, leading to broken recording.
• Repair the wires, replace them, or call for service on the equipment.
L. Discuss the mounting of an electrocardiogram recoding.
1. Machines that record one lead at a time produce a tracing that is 6 or 12 feet long.
2. To have a document that will fit into the patient record, use a mounting device.
a. Manufacturers make heavy paper folders with pockets or self-stick areas labeled for each of the leads.
b. Many different forms are available.
c. Knowing the form you will use for mounting helps avoid the waste in obtaining a longer tracing than needed.
d. Select the best part of the recording for that lead.
e. It must have a straight baseline and no artifacts.
f. Cut and trim it, and place it in the appropriate area of the folder.
g. Double-check your work to make certain you have read the international code for leads correctly.
h. Repeat the process until all 12 leads have been properly mounted.
i. Employer preference will determine where to place the standardization.
j. Machines that record from three leads at once do not require mounting.
M. Explain normal and abnormal sinus rhythms.
1. Normal sinus rhythm
a. Means that each heartbeat has three distinct waves:
• P wave
• T wave
• Between the P and T, a QRS complex, where the Q is a downward deflection, the R is an upward deflection, and the S is a downward deflection following an R.
b. The beats come at regular intervals, indicating the impulse originates in the SA node.
c. Within the lead being recorded, each cardiac cycle appears the same as previous cycles.
2. Cardiac conditions that create abnormal sinus rhythms:
a. Atrial fibrillation: there are as many 350 irregular P waves and 130–150 irregular QRS complexes per minute.
b. Atrial flutter: this rapid fluttering of the upper chambers looks on the ECG like the pattern of teeth on a saw.
• The atrial rate is 250–350/minute.
• Not all of the impulses are conducted through the AV node because they are coming too fast.
• There is some “blockage” at the AV node.
• This is one type of heart block.
c. AV heart block: the node is diseased and does not conduct the impulse well. There are three types:
• First-degree, where the PR interval is prolonged.
• Second-degree, where some waves do not pass through to the ventricles.
• Third-degree or complete AV block, where the atria and ventricles beat independently.
d. Myocardial infarction (MI): there are broad and deep Q waves.
• Old injury: the ST segment is usually depressed below the baseline.
• New injury: the ST segment is usually elevated above the baseline.
• Angina pectoris is the name for the syndrome of pain and oppression in the anterior chest due to heart tissue being deprived of oxygen.
• If this pain lasts 20–30 minutes, suspect a myocardial infarction in which the heart tissue is actually dying.
e. Paroxysmal atrial tachycardia (PAT): common arrhythmia, usually seen in young adults with normal hearts.
• There are no visible P waves because they are hidden by the T wave of the previous cycle.
• The atrial rate is between 140–250/minute.
• In many ways it looks on the ECG like repeated PACs.
f. Premature atrial contractions (PACs): a P wave occurs earlier than expected, usually from a source outside the sinus node. Therefore, P waves are distorted.
g. Premature ventricular contractions (PVCs): the wide QRS complexes occur without preceding P waves.
• May be caused by electrolyte imbalance, stress, smoking, alcohol, or toxic reactions to drugs and in a majority of patients who have had a heart attack.
h. Sinus arrhythmia: normally seen in children and young adults.
• All aspects of the ECG are normal except the irregularity.
• The space between QRS complexes is not equal.
• The heart rate increases on inspiration and decreases on expiration.
i. Sinus bradycardia: fewer than 60 beats per minute; cycles are normal.
j. Sinus tachycardia: more than 100 beats per minute; cycles are normal.
k. Ventricular fibrillation: the waves are irregular and rounded, the contractions uncoordinated. Death may occur in as little as 4 minutes.
l. Ventricular tachycardia: three or more consecutive PVCs.
• Usually originating below the SA node.
• The complexes are wide and bizarre in appearance.

Intro to ECG Interpretation

ECG Interpretation Part 2

Related Diagnostic Procedures

ECG-related diagnostic procedures may involve additional lengths of tracings. These include:
1. Rhythm strip:
a. Runs on lead II for 20 seconds at the physician’s request or if the medical assistant sees anything that appears abnormal on the tracing.
b. This is not cut and mounted, but carefully folded and given to the physician for interpretation.
2. An inspiration strip:
a. Runs on lead II for 10 seconds with the patient holding his or her breath.
b. This is of greatest value when, as the patient breathes, your tracing shows wandering baseline.
c. This will eliminate any respiratory impact on the tracing.
B. Review the purpose of an exercise tolerance test.
1. At times patients will have symptoms that are not obvious on a resting ECG.
2. Stress test or treadmill test:
a. Involves an evaluation of the heart’s response during moderate exercise while a 12-lead ECG is performed.
b. A diagnostic procedure performed to determine the likelihood of coronary artery disease (CAD), blockage of the arteries that supply the heart muscle.
c. The patient is asked to exercise on a bicycle or treadmill which stresses the heart and requires more oxygen for the heart muscle cells.
d. A faster heart rates make it easier to detect decreased blood flow.
e. The treadmill test is noninvasive and frequent blood pressure measurements are taken while exercise is in progress.
f. Goal of the test is to increase the heart rate to a maximal level and increase the myocardial demand for oxygen.
g. Test continues to a predetermined level or until the patient experiences fatigue or chest pain.
h. Test concludes when the patient’s symptoms of chest pain or fatigue or ECG changes indicate significant changes, especially to the ST segment.
i. After the conclusion of the test the patient rests while the monitoring of blood pressure and heart rate continue until both are within normal range.
j. Complications may occur and emergency carts appropriately stocked should be on hand.
3. Stress testing may be used:
a. To evaluate patients with a high risk for developing heart disease.
b. For patients known to have early heart disease.
c. For patients about to begin a strenuous exercise program.
d. For patients who have cardiac complaints such as shortness of breath when exercising and as an evaluation of their rehabilitation following cardiac surgery.
C. Review and explain patient preparation for a stress test
1. The patient should be given instructions before the scheduled test day to wear comfortable exercise or walking shoes and loose-fitting clothes.
a. Female patients should be instructed to wear a bra to minimize artifacts on the ECG.
b. Instruct all patients not to eat a large meal for at least four hours before the test to avoid nausea.
c. Patients should take their normal medications unless instructed otherwise by the physician.
2. The patient should know that a resting ECG is done as a baseline first along with baseline vital signs.
a. Vital signs are measured with the patient in supine position and standing.
b. Another ECG is taken with the patient standing and breathing rapidly or hyperventilating.
c. This is done because rapid breathing can produce some changes in the ST segment and the T wave.
d. Thus it is important to know this in advance so the interpretation of the stress test ECG is not compromised.
e. Also, a thorough history is taken, emphasizing any symptoms such as shortness of breath or chest pain.
f. Explain to the patient that an ECG will be recorded as he or she walks or bikes at a carefully prescribed pace in the presence of the physician.
g. Increases in rate or incline will be made, but the patient should not feel discomfort or shortness of breath.
3. The medical assistant prepares the patient, connects the patient to the recording devices (ECG, heart rate, BP), and frequently checks blood pressure during the test.
a. The sensors are all placed on the torso.
b. The precordial sensors (V1–V6) are placed as for the regular ECG, but the arm and leg sensors are put at the midclavicular line on the top of the torso and on the midclavicular line on the abdomen.
c. The electrodes should adhere securely to the skin and may need to be taped in place.
d. If a male patient has a very hairy chest, the hair may need to be shaved to improve attachment of electrodes.
e. At the conclusion of the test the physician evaluates the effect of exercise on the heart rate, blood pressure, and ECG.
f. The physician may order the test to be stopped if the patient has trouble breathing or complains of chest pain or there are significant ECG changes which contraindicate continuing the test.
D. Point out that there are a variety of exercise protocols used in treadmill testing involving the speed and incline of the treadmill and how quickly these changes are introduced during the test.
1. The stress test is continued until 85% of the maximum target heart rate is achieved or the patient becomes symptomatic.
2. The maximum target heart rate is calculated by using the following formula: 220 minus the patient’s age = the maximum target heart rate for that person.
3. For a sixty-year-old patient, 220 - 60 = 160 x .85 = 136 or the maximum target heart rate for this patient.
4. For patients who have had myocardial infarction (MI) or heart attack, the target heart rate is set lower at 70%.
5. This is known as a submaximal test

Thallium (a radioisotope used in nuclear medicine and emits gamma rays) is sometimes injected into the patient’s vein during a stress test for better understanding of perfusion or blood flow to the myocardium.
1. Thallium is injected during the last minute of exercise.
2. The patient lies on a special table and a gamma camera takes pictures.
3. If the heart muscle is ischemic, receiving less than normal amount of blood flow, there will be poor uptake of the thallium.
4. This is indicated as a “cold spot” on the pictures.
5. Normal perfusion of the myocardium is indicated by “hot spots” on the pictures.

Another type of test, known as the multiple gated acquisition (MUGA) scan, can be done to check blood flow in the myocardium.
1. This involves injection of an isotope.
2. This is followed by a nuclear scan performed to detect myocardial perfusion.

Pharmacologic stress testing involves no exercise.
1. In this case a medication is given to the patient that causes the heart rate to climb to the target heart rate.
2. Continuous ECGs and vital sign evaluation are performed.
3. This test procedure is useful on patients with physical limitations or the elderly who cannot perform enough exercise to elevate the heart rate.

The patient’s safety during a stress test is paramount.
1. Because there is always the risk of cardiac arrest, the medical assistant becomes responsible for maintaining emergency equipment that might be needed and having it in the room at the time of the test.
2. Oxygen equipment, a defibrillator, an airway, intravenous solutions, and medications should be periodically checked and replaced, if outdated or not functioning.
3. Always be sure a physician is available when a stress test is done.

Steps for preparing and monitoring the patient during a treadmill stress test
1. Assemble necessary supplies.
2. Plug in the power cord and turn on the machine.
3. Verify that the treadmill is operational.
4. Identify, interview, and instruct the patient.
5. Measure vital signs and record.
6. Attach the electrode patches securely using tape to hold in place if necessary. Attach limb leads on torso at midclavicular line and on the abdomen of torso at midclavicular line. Attach chest leads as usual.
7. Perform a baseline resting ECG (see Procedure 49-1). If facility protocol requires, perform a standing ECG as well.
8. Disconnect the patient cable from the ECG machine.
9. Attach a sphygmomanometer to the patient’s arm.
10. Permit the patient to walk about the room or on the slow-moving treadmill to see what it feels like.
11. Connect the patient to all recording devices.
12. Check with the physician to determine the pace and incline of the treadmill.
13. Record BP, ECG, and heart and respiratory rate periodically as you observe the patient’s face for redness, difficulty breathing, chest pain, and so forth.
14. Allow the patient to rest, and continue monitoring vital signs and ECG as required.
15. When the test is completed, clean the patient’s skin and assist with dressing as needed.
16. Organize the documentation into the patient record.
E. Identify and explain the Holter monitor.
1. The Holter monitor records cardiac activity while the patient is ambulatory for at least a 24-hour period.
a. Holter monitoring is performed when the ECG is not conclusive or the cardiac irregularity was not captured on the tracing.
b. A small tape recorder and a patient diary are used to detect heart irregularities that are infrequent and not detected on the standard 12-lead cardiogram.
c. It may be set to record continuously and/or to record when the patient presses an “event” button at the onset of symptoms.
d. The medical assistant may instruct the patient and apply the chest sensors.
2. Patient preparation should stress the importance of the diary.
a. Patients carry out all routine daily activities except showering or bathing.
b. They must avoid areas of high voltage, as the tape will be affected.
c. Patients use the diary to record their activities during the day.
d. They indicate in the diary or by depressing an “event button” when they experience any cardiac symptoms, such as chest pain, shortness of breath, or palpitations.
e. Patients should record in the diary such activities as stair climbing, sexual activity, having bowel movements, sleeping, eating, exercising, and so forth.
f. The physician will compare the tape with the activity log to determine which activities were stressing the patient.
3. The five special disposable chest sensors are attached more securely than in the 12-lead ECG because they must remain in place during all activity.
a. In addition to the usual skin preparation to remove oils, areas for attachment may have to be shaved and an abrasive skin cleaner used.
b. Peel off the cover on the adhesive backing on each sensor and attach one sensor to each of the following locations:
• third intercostal space: 2 or 3 inches to the right of the sternum
• third intercostal space: 2 or 3 inches to the left of the sternum
• fifth intercostal space: at the left sternum margin
• sixth intercostal space: at the right anterior axillary line
• sixth intercostal space: at the left anterior axillary line

Steps for applying a Holter monitor
1. Assemble necessary supplies.
2. Install new batteries and a blank tape.
3. Verify that the machine is operational.
4. Identify, interview, and instruct the patient.
5. Have the patient remove clothing to the waist (female patients may wear a gown opened down the front) and sit on an examination table.
6. Perform hand hygiene.
7. Prepare the electrode sites and attach the electrodes.
8. Attach the wires so that they point toward the feet and connect the patient cable.
9. Secure each sensor with adhesive tape.
10. Connect the patient cable.
11. Assist the patient with replacing his or her shirt. Extend the cable between the buttons or under the hem.
12. Place the recorder in the carrying case and either attach to the patient’s belt or to the shoulder strap. Check that there is no tension on the wires.
13. Plug the cable into the recorder.
14. Record the starting time in the diary.
15. Ensure that the patient understands what he or she is to do.
16. Confirm the time for the patient to return to the clinic for removal of the Holter monitor.
17. Chart the procedure in the patient’s record.
18. Sign or initial your work.
F. Explain telemetry.
1. Involves using radio waves to transmit the heart’s electrical activity to a central monitoring station.
2. Allows the patient to move around the room or other limited space while the heart is monitored.
3. Patient should be made aware of the range of movement permitted.
4. Used in inpatient facilities but may be encountered in ambulatory care settings as well.
G. Explore the use of pacemakers.
1. Pacemakers are electronic devices that help the heart maintain normal rhythm. Uses include:
a. Increase heart rate in patients with bradycardia (slow heart rate).
b. Override the heart beat in a patient with tachycardia (rapid heart rate).
c. Address other dysrhythmias.
2. Pacemakers may be temporary or permanently installed in the patient.
a. Temporary pacemakers are used in acute settings to stabilize and maintain the patient for shorter periods of time.
b. Patients with temporary pacemakers must be hospitalized and continuously monitored.
c. The pulse generator is located outside the body.
d. Leads are either threaded through specific veins (subclavian, femoral, brachial, or external jugular) to the right atrium or the right ventricle.
e. A temporary pacemaker may be attached during surgery to the outer surface of the heart.
f. The wires then exit the chest and are attached to an external pulse generator.
3. The type of permanent pacemaker implanted depends on the patient’s condition and the type of cardiac problem involved.
a. These are long-term devices and the pulse generator is implanted into the subcutaneous tissue of the upper chest.
b. The leads are inserted into a major vein into the heart in the region of the myocardium which is impaired.
c. The opposite ends of the leads are attached to the pulse generator.
4. If the patient has an implanted automatic pacemaker, spikes will appear on the ECG with each cardiac cycle.
a. These spikes should be rhythmically spaced on the ECG if the pacemaker is programmed for a certain rate.
b. Some pacemakers are fixed rate or continuous.
c. Some fire only when needed (on demand).
d. Some are rate responsive to physiological changes and respond to the body’s demands according to changes in the patient’s activities.
e. The atrial-paced pacemaker will show a spike with the P wave.
f. Pacemakers that spike with the QRS wave are ventricular paced.
g. Notify the physician if the implanted pacemaker is visible on the surface of the skin.
h. Defibrillators are used in emergencies to send a small amount of electricity to the heart.
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