electrocardiography lesson 2: performing an electrocardiogram

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Pearson's Comprehensive Medical Assisting: Administrative and Clinical Competencies, 2/e

Beaman • Fleming-McPhillips • Routh • Gohsman • Reagan

Pearson's ComprehensiveMedical AssistingAdministrative and Clinical Competencies

Second Edition

CHAPTERCHAPTER CHAPTERCHAPTER CHAPTERCHAPTER 4949

ElectrocardiographyLesson 2:Performing an Electrocardiogram





Lesson Objectives

Upon completion of this lesson, students should be able to …

• Define and spell the terms for this chapter.• Explain the significance of each ECG

wave.• Maintain and operate electrocardiogram

equipment.• Identify by name and function the controls

on an electrocardiograph machine.





Lesson Objectives

• Name the standard 12 leads and the locations of their sensors.

• State the cause and correction of artifacts.





Critical Thinking Question

1. What is the medical assistant’s role in ECGs?





The Electrocardiogram (ECG)

• Electrical charges created by the conduction system can be sensed throughout the body

• These charges can be picked up by placing sensors in specific areas of the skin

• Sensors transmit the electrical charge to a computer for amplification of the signal





The Electrocardiogram (ECG)

• Amplified signal is recorded on graph paper – A flat line means that no electrical signal is

sensed – A deflection above or below the flat line means

that there is an electrical signal of some kind– A positive (up) or negative (down) deflection is

called a wave– The height of the wave reflects strength of the

electrical signal





The ECG

• A normal cardiac cycle is one series of PQRST waves.– P – initial atrial depolarization (change in

electrical activity)– QRS complex – ventrical depolarization– T – repolarization (return to the resting

electrical state)

• Then it all starts over again





ECG Tracing





Time and the Cardiac Cycle

• The P wave represents the impulse that originated in the SA node and spread through the atria (called atrial depolarization)

• A normal looking P wave reflects a normally-functioning SA node

• The P-R interval is the time from the beginning of P to the beginning of QRS






• This time is between 0.12 and 0.20 seconds (2-5 small boxes on the EKG graph paper)

• A deviation could represent an abnormality in the electrical system or structure of the heart






• A P-R Interval that is too short means that the impulse has reached the ventricles through a shorter than normal pathway

• A P-R Interval that is too long means that there is a conduction delay in the AV node possibly






1. In the previous two examples, how many small boxes are between the P and R?






• The QRS complex represents the time necessary for the impulse to travel through the bundle of His, the bundle branches, and the Purkinje fibers to complete ventricular contraction

• This is ventricular depolarization• This usually takes less than 0.12

second (3 small ECG boxes)






1. In this example, how many small boxes are between the Q and S?






• The ST segment and the T wave represent repolarization of the ventricles

• The ST segment is normally flat (on the baseline) or only slightly elevated

• The T wave represents a part of recovery of the ventricles after contraction

• The QRS complex and T wave typically point in the same direction

• Anything else may indicate a problem in the heart or its electrical system






1. Is this a normal ST segment? Why?





ECG Machines

• All ECG machines are calibrated to align with the international standard

• The paper moves at a speed of 25 mm/second

• Given the same amount of electrical energy, the recording stylus also moves the same distance

• 1 mV of electricity input will cause the stylus to deflect 10 mm

• This allows uniform recordings worldwide





ECG Machines

• Older models are manual; newer models complete many of the procedures automatically via a computer

• During patient preparation, all ten sensors are placed on the patient

• The computer then switches from lead to lead in rapid succession





ECG Machines

• Patient data is entered into the machine (name, date of birth, diagnoses, height, weight, age, bp, medications, and other information)

• You can override the automatic controls, if desired






1. What can you do to help the patient relax during the preparation and testing? Why is relaxing important?





ECG Machines

• Each lead is recorded in a separate channel or pathway for the signal

• Many machines record more than one channel (typically 3) at once

• Some machines will print out a statement about the status of the heart

• Some even can fax the report to a physician’s office

• Computerized ECGs should still be carefully examined to make sure that a clear ECG is made before disconnecting the sensors





The ECG Control Panel

• Main power switch: Allows for a warm-up as specified by the manufacturer before using

• Record switch: This switch moves the paper at the “run 25” speed






• Lead selector: This determines from which sensors (electrodes) the machine will record:– Standard (limb) leads: Record from two

electrodes placed on all extremities– Augmented leads: Record from the midpoint

between two limb electrodes to a third limb sensor

– Chest leads: Record from various positions on the thorax






• Sensitivity control: Allows the operator to increase or decrease the recording size to enlarge or shrink the deflections to fit on the paper






• 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

• Stylus heat control: Increases or decreases heat and adjusts for the sharpest tracing

• Marker: Indicates, by a code, which lead is being recorded





The ECG Paper

• Paper is pressure sensitive and must be handled carefully

• If this paper is exposed to light for long periods, the markings will fade with time

• Many newer models use an ink cartridge to supply the stylus and provide a longer-lasting printout

• Paper records both time (horizontally) and voltage (vertically)





Time Markers on ECG Paper

• Time markers (3-second markers) are printed on the ECG paper– Located at the top of single-channel paper and

between channels in multi-channel paper– Small squares with a light line and larger squares

of a darker line– Small squares: 1 mm by 1 mm square = 0.1 mV

in height and .04 second time in the width– Large squares: 5 mm by 5mm square = 0.5 mV of

voltage in the height and 0.20 second time in the width





Heart Rate

• You can estimate the heart rate from an ECG

6-second Method– Begin at one 3-second marker and go to the

right for two additional markers, for a total of 6 seconds

– Count the number of QRS complexes between the first and third markers, and add a zero

– This is estimated ventricular rate per minute





Heart Rate

• You can estimate the heart rate from an ECGCount-off Method

– Locate a QRS complex close to a 5-mm line– Move to the next deflection at the right or the

left– Count how many 5-mm lines intersect the

tracing before the next QRS complex– Count off at each 5-mm line saying “zero,

300, 150, 100, 75, 60, 50”– Stop counting when you reach the next QRS

complex





Heart Rate

• You can estimate the heart rate from an ECG

Exact Calculation– Paper moves at a standard speed of 25

mm/second = 1500 mm/minute– Count the millimeter boxes between two QRS

complexes– Divide the number into 1500

Example: if there are 20 mm between two QRS complexes, 1500 divided by 20 = 75 beats per minute





Rhythm

• The regularity of the occurrence of heartbeats• Ventricular rhythm is determined by

measuring the distance between QRS complexes– There should be a consistent space between

complexes• Atrial rhythm is determined by measuring

the distance between P waves– There should be a consistent space between

waves





Sensor Placement

• The ECG machine records the cardiac cycle through sensors placed on the patient’s bare skin

• Sensors are placed:– Over the fleshy part of the inner aspect of

both lower legs (RL and LL)– Over both upper arms or both forearms,

avoiding the bony prominences (RA and LA)– Chest sensors (V) are placed in 6 locations

(V1 – V6)





ECG Leads

• Each lead will record from a specific combination of sensors

• By recording from different combinations of sensors, the electrical activity of the heart is seen from different angles





Einthoven’s Triangle





Patient Preparation for an ECG

• Explain to the patient the equipment and procedure as well as what you will expect the patient to do

• The surroundings should be pleasant and the table wide enough for adequate support

• Patients will need to be bare to the waist so privacy should be provided for disrobing





Patient Preparation for an ECG

• Position patient in the supine or semi-Fowler’s position

• Jewelry, particularly metal jewelry, must be removed so that it does not interfere with the electrical current of the ECG

• Prepare the skin where the sensors will be applied





Preparation of Equipment for an ECG

• ECG machine that has been calibrated and is in good working order

• Good supply of paper• Supply of electrolyte or conduction cream,

gel, or pads





The ECG Recording

• Normally, the ECG recording is made in sensitivity 1 = 10mm deflection per 1 mV of electricity

• If size is doubled, it is sensitivity 2• If size is cut in half, it is sensitivity 1/2





Satisfactory Tracings

• Accurate• Readable• Clear• Travels down the center of the page• Has a consistently horizontal baseline





Artifacts

• Electrical activity from a source other than the heart that the sensors detect

• Can impair accurate interpretation of the tracings

• Causes include:– Somatic tremors– Wandering baseline and baseline shifts– 60 cycle or AC interference– Erratic stylus





Mounting an ECG

• Select the best part of the recording for that lead

• Cut and trim it• Place it in the appropriate area of the

folder• Double-check to ensure you have read the

lead’s international code correctly• Repeat the process until all 12 leads have

been properly mounted





Normal Sinus Rhythm

• Has three distinct waves– P wave– T wave– QRS complex between the P and T waves where

the Q is a downward deflection, the R is an upward deflection, and the S is a downward deflection following an R

• The beats come at regular intervals• Within the lead being recorded, each cardiac

cycle appears the same as previous ones





Abnormalities Caused by Cardiac Pathology

• Atrial fibrillation• Atrial flutter• AV heart block• Myocardial infarction (MI)• Paroxysmal atrial tachycardia (PAT)• Premature atrial contractions (PACs)• Premature ventricular contractions (PVCs)• Sinus arrhythmia





Abnormalities Caused by Cardiac Pathology

• Sinus bradycardia• Sinus tachycardia• Ventricular fibrillation• Ventricular tachycardia





Questions?

electrocardiography lesson 2: performing an electrocardiogram

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