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What is the basic information about an electrocardiogram (ECG)?
- Is the most important diagnostic tools used in medicine.
- The information obtained noninvasively fro the ECG tells the diagnostician about the electrical activity of the heart.
What are the Clinical Findings Suggestive of the Need for an ECG?
Understand the Conduction System of the Heart
The heart is a 4 chambered muscle that functions as a pump to pump blood through the circulatory system
What is depolarization and repolarization?
- Depolarization: When the cells are stimulated and contract, (exchanging potassium for sodium) becoming negatively charged on the outside of the cell
- Repolarization: After contraction (depolarization), (exchange sodium for potassium), becoming positive on the outside of the cell
Know where the positive and negative ions are located when the cell is in the following states: polarized resting cell, depolarizing cell, depolarized cell, repolarizing cell
- A. Polarized resting cell
- The heart muscle is in the resting, or polarized state; that is, the cell carries an electrical charge, with the inside negatively charged with sodium.
- B. Depolarizing cell
- When the muscle cell is stimulated, the cell begins to depolarize; that is, the positively changed ions (sodium) flow into the cell, and the negatively charged ions flow out of the cell.
- C. Depolarized cell
- During the period that the cell is depolarized, all the positively charged ions are on the inside of the cell, and all the negatively charged ions are on the outside of the cell.
- Depolarization causes the muscle cells to contract momentarily.
- D. Repolarizing cell
- After the muscle cell has depolarized, it begins to return to the resting state; that is, the negatively charged ions flow into the cell, and the positively charged ions flow out of the cell.
- Repolarization reestablishes the electrical imbalance across the cell membrane
What parts does the Cardiac Conduction System consist of?
- Sinoatrial node (SA node)
- Atrioventricular node (AV node)
- Bundle of His
- Right and Left bundle branches
- Purkinje fibers
Know about the SA node and that it functions as the heart�s pacemaker
- It ensures that the heart will beat rhythmically without any external sources of stimulation.
- It usually initiates about 75 impulses/min.
- The cardiac conduction cycle begins at the SA node.
What is the order of the cardiac conduction cycle?
- So, once the SA node sends an impulse, the conduction system depolarizes, sending the impulse through the conduction system to the heart muscle, which depolarizes and contracts.
- After contraction, repolarization occurs, which is the heart in a resting state, called diastole.
- The term used for the heart in contraction is systole
What are the parts of a normal ECG tracing?
what does the ECG tracing represent?
- The ECG tracing represents a two-dimensional view of the heart�s electrical activity.
- ECG tracings record the waves of depolarization and repolarization traveling across the myocardium
What are the waves, represented by letters, present in one cardiac cycle?
P, Q, R, S, and T (and sometimes U)
Know the details about each wave (5 total), the QRS complex, the PR interval, and the ST segment
- –P wave
- •Positive wave
- •Represents atrial depolarization (contraction)
- •Duration 0.06 to 0.10 sec
- –Q wave
- •Negative wave that follows the P wave
- •May be absent even in healthy people
- –R Wave
- •Positive wave that follows the Q wave
- –S Wave
- •Negative wave that follows the R wave
- –QRS Complex
- •Represents ventricular depolarization (contraction)
- -PR interval
- Measured from the beginning of the P wave to the beginning of the Q wave
- Represents the time it takes for the impulse to travel from the SA node through the AV node.
- Represents the total atrial electrical activity
- Duration: 0.12 to 0.20 sec
- May be prolonged in first- and second-degree heart block
- ST Segment
- Measured from the end of the S wave to the beginning of the T wave.
- Measures the time that is required for ventricular repolarization to begin.
- The ST segment may by elevated above the baseline or depressed below the baseline.
- This is an indication of cardiac ischemia.
- ST segment elevation or depression is a sign of coronary artery disease.
The 12 lead ECG consists of __ limb leads and __ chest leads
Each lead of a ECG system does what 3 things?
- Views the electrical activity of the heart from a different angle
- Has a positive and negative component
- Monitors specific portions of the heart from the point of view of the positive electrode in that lead
Know about the three standard limb leads
- Standard : I, II, III Augmented: aVR, aVL, aVF
- View heart on frontal plane used to determine axis
Where is each lead placed, including the ground lead?
- Lead I : the left arm is positive and the right arm is negative.
- Lead II : the right arm is negative and the left leg is positive.
- Lead III : the left arm is negative and the left leg is positive.
- A ground lead is placed on the right leg
why are Augemented lead termed augmented?
because the electrocardiograph machine must amplify or augment the weak signal more than the other leads to obtain a useful tracing
How are Augemented lead created?
by making a single limb positive and all other limbs negative
Where is each Augemented lead placed?
- Lead aVR : leads are connected to the right arm (+), left arm and left leg. The right arm is the positive electrode and records electrical activity from the direction of the right arm.
- Lead aVL : leads are connected to the left arm (+), right arm and left leg. The left arm is the positive electrode and views the electrical activity from the direction of the left arm.
- Lead aVF : leads are connected to the left leg (+), right arm and left arm. The left leg is the positive electrode and views the electrical activity from the direction of the bottom of the heart.
Where is each of the 6 precordial (chest) leads positioned?
- Lead 1 (V1) : positioned at the 4th intercostal space at the right border of the sternum
- Lead 2 (V2) : positioned at the 4th intercostal space at the left border of the sternum
- Lead 3 (V3) : positioned in a straight line between lead 2 and lead 4
- Lead 4 (V4) : positioned at the midclavicular line and the 5th intercostal space
- Lead 5 (V5) : positioned at the anterior axillary line, level with lead 4 horizontally
- Lead 6 (V6) : positioned at the midaxillary line, level with lead 4 and 5 horizontally
What does Einthoven�s Triangle state?
In the normal heart, the dominant electrical current in the heart flows from the base to the apex in a right to left direction.
How do you place the leads for long term ECG monitoring?
- The first electrode is placed on the upper right side of the chest (-).
- The second electrode is placed on the lower side of the chest (+)
- The third electrode is used as a ground and may be attached to any location that is convenient.
What does each square on an ECG paper represent?
- One small square is 0.04 seconds
- One large square is 0.20 seconds (1 large square = 5 small squares)
- To make counting time easier, there is a darkened line at every fifth small square; from one darkened line to the next is 0.20 sec (0.04 sec x 5 squares).
What does Length on the ECG represent?
Knowing the time interval between squares, the heart rate may be calculated by measuring between R waves
What does Height on the ECG represent?
- Height (vertical distance) on the graph paper is representative of voltage
- A one millivolt standard is used to determine the voltages of each wave.
- One small square is 0.1 mV vertically
How many boxes make up the 3 and 6 second markers?
There are 15 blocks in 3 seconds and 30 blocks in 6 seconds
What are the steps that should be taken for ECG Interpretation?
- 1. Identify the heart rate
- 2. Evaluate the rhythm
- 3. Note the presence of P waves
- 4. Measure the PR interval
- 5. Measure the width of the QRS complex
- 6. Inspect the ST segment in all leads
- 7. Identify the mean QRS axis
- 8. Assess the waveform morphology
- 9. Evaluate the Q wave
- 10. Look for signs of chamber enlargement
How do you identify the rhythm by calculating the heart rate using the box counting method?
Count the number of R waves in a 6 second period and multiply by 10 to obtain the number of beats per minute.
What are the different heart rates?
- Normal rate: 60 to 100 beats/min
- Bradycardia: less than 60 beats/min
- Tachycardia: more than 100 beats/min
what tool is used to determine the rhythm of the heart and how do you evaluate the rhythm (determine the regularity of the rhythm)?
- calipers, measure the distance between a pair of R waves. Leave the caliper at the distance and measure the next pair of R waves to see if the distance is the same.
- Continue measuring the distance between the successive R waves to see if it is constant. If the distances remain constant, the rhythm is regular
How should you observe P waves and PR interval?
- Make sure that there is a P wave before every QRS complex and that they are of the same shape.
- Using calipers, measure several P-R intervals to determine if they are consistent.
- As stated earlier, the normal PR interval is 0.12 to 0.20 sec.
- If the PR interval is longer than 0.20 sec, first-degree heart block is present.
How should you measure the QRS complex, what values are normal, and what problems can be indicated by QRS?
- Determine length of the QRS complex
- Remember, that the QRS complex represents the time it takes for ventricular depolarization to occur.
- With the normal QRS complex taking 0.06 to 0.12 secs, any longer duration would indicate heart block.
What should the waves look like for a normal Sinus Rhythm?
- P Wave: P waves are positive (upright) and uniform. A QRS complex follows every P wave.
- PR Interval: The duration of the PR interval is between 0.12 and 0.20 second and is constant from beat to beat.
- QRS Complex: The duration of the QRS complex is 0.06 to 0.12 seconds. A P wave precedes every QRS complex.
- Rate: Between 60 and 100 beats per minute.
- Rhythm: Regular
What is indicative of sinus bradycardia?
- Meets all criteria for Normal Sinus Rhythm but is too slow
What is indicative of sinus tachycardia?
- Meets all criteria for Normal Sinus Rhythm but is too fast
What is indicative of sinus arrhythmia?
- Similiar to Normal Sinus Rhythm, but:
- Rhythm: Irregular
- Wave form abnormalities: R to R cycles vary more than 0.16 sec
What is indicative of Premature Ventricular Contraction (PVC) and how should it be treated?
- Underlying rhythm is interrupted by wide QRS (>0.12 s) not preceded by a P wave, with an inverted T
- Rate: that of the underlying rhythm; 60 to 100 beats/min; less than 6 PVCs/min is considered minor and more than 6/min is considered major
- PR interval: not measurable
- QRS: wide (>0.12 second), premature, abnormal configuration, followed by compensatory pause and has no preceding P wave
- Treatment: lidocaine IV or other antiarrhythmia drug
What is indicative of atrial fibrillation and what is the Treatment for it?
- Characterized by chaotic baseline between QRS's
- Treatment: Cardioversion, propranolol, digitalis
What is indicative of atrial flutter and what is the Treatment for it?
- Distinct rapid sawtooth pattern between normal QRS
- Treatment: cardioversion, carotid artery massage, procainamide, digitalis, tranquilizers
What is indicative of ventricular tachycardia and what is the Treatment for it?
- This rhythm is lethal
- VT represents a serious arrhythmia that often progresses to V fib if untreated.
- Wide QRSs occurring rapidly without P waves
- Rate: 140 to 300 beats/min
- Rhythm: regular
- Treatment: lidocaine, defibrillation, CPR
What is indicative of ventricular fibrillation and what is the Treatment for it?
- This rhythm is lethal
- Represents the most life-threatening arrhythmia
- Defined as erratic quivering of the ventricular muscle mass
- Chaotic, characterized by wavy irregular pattern
- The ECG show grossly irregular fluctuations with a zigzag pattern.
- Rate: none; cannot be determined
- Rhythm: irregular, chaotic waves; cannot be determined
- P waves: none
- PR Interval: none
- QRS: none or sporadic low-amplitude waves
- Causes cardiac output to drop to zero
- Treatment: defibrillation, CPR, oxygen, and antiarrhythmic medications. If this arrhythmia is not reversed, death soon results
What is indicative of asystole and what is the Treatment for it?
- Characterized by a straight or almost flat line
- Complete absence of electrical and mechanical activity
- Rate: none
- Rhythm: none
- P waves: none
- PR Interval: none
- QRS: none
- Treatment: the morgue
What is ECG artifact?
- artificial electrical impulses or current that can ruin an otherwise good ECG tracing
What are the three most common types of artifact?
- 1. Patient motion
- - Occurs when the patient is restless or moves their limbs during the ECG
- 2. Wandering baseline
- - Is caused by poor electrical contact between the patient and the electrodes placed on the patient to record the ECG
- - The baseline will rise and fall
- 3. 60 Hz
- Occurs from electrical interference external to the patient.
- - It may be a faulty ground on the electrocardiograph or current leakage from adjacent equipment.
- - It is called 60 Hz artifact because in the United States and Canada, electricity is supplied as alternating current at 110 volts and 60 Hz
What is the equipment required for an ECG?
- Electrical wires (leads) : which are attached to the cable that provides the input to the electrocardiograph
- Suction cups and electrode jelly or disposable adhesive electrode patches
- Isopropyl alcohol and a clean towel or washcloth
- A second towel or washcloth : helpful to remove any electrode jelly left by the suction cups or electrode patches after the ECG is completed
How should the patient be positioned for the ECG?
What is the proper placement of the leads for the ECG?
- The limb leads are placed on the right and left arms and the right and left feet.
- The precordial leads are positioned at precise locations around the anterior chest
How do you find the 4th intercostal space by palpating the sternal angle?
By palpating two ribs inferiorly
What is the importance of arrhythmia recognition and artifact recognition?
- Arrhythmias: Life-threatening arrhythmias may occur during an electrocardiograph
- Artifact: Careful patient preparation (clean skin, good electrode contact, and sufficient electrode jelly) will eliminate wandering baselines.
- Patient motion is often difficult to control
- You instructions to the patient to lie still and your emphasis on how important it is may help.
- Pain, anxiety, and restlessness are difficult to control.
- Sometimes you must just do your best to obtain the best tracing.
- 60 Hz artifact may sometimes be eliminated by changing electrical outlets that the electrocardiograph is powered by or turning off unneeded electrical equipment near the patient
How do you operate the ECG machine?
- Pretty general and basic, just understand the gist of the following:
- Some are manual, single channel machines: requiring the operator to manually switch leads
- Some are multi-channel and automatic: recording all 12 leads automatically
- Some instruments have arrhythmia recognition and interpretation built into their electronics
- Manufacturers and experienced cardiologists will agree with a machine interpretation greater than 90% of the time.
- Make sure you learn about the machine that will be in use at your hospital facility.
- Read the owner�s manual on how to operate the machine.
- Observe a skilled RCP obtain an ECG on several patients.
- After observation, have that RCP observe you in the use of the equipment.
- Through practice you will become proficient
How do you properly handle the ECG tracing?
- it is important to record the patient�s name, hospital number, the date, and time of the ECG tracing
- in emergency setting, physician may want to see right away, other times you may return respiratory dept. and place in file for interpretation
An ECG provides a picture of what?
heart's electrical activity
ECG can identify the condition of the heart's what?
electrical conduction system
The ECG can also identify abnormal ____ that may be of little consequence or very serious and life threatening
Does the ECG measure pumping ability of the heart?
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