12-Lead Electrocardiogram Notes

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• Sharing, reproduction, or use of the material is prohibited outside of educational purposes at Anderson College.

• ©2022, MLA/T Program, Anderson College

Readings

• Hampton, J.R., The ECG Made Easy (Current Ed.). Elsevier Health Sciences.

  • Chapter 9

• Christianson, J., An EKG Interpretation Primer. Retrieved from a Google Drive link.

  • Chapter 2

Learning Objectives

• Describe the 12-lead electrocardiogram and its clinical significance.

• Explain patient identification and preparation for a 12-lead ECG, emphasizing psychological preparation.

• Explain the preparation and maintenance of ECG equipment, including calibration.

• Demonstrate the 10 electrode placements for a 12-lead ECG, ensuring precise anatomical positioning.

• Identify what the leads are measuring in terms of electrical activity.

• Identify what the waves on an electrocardiograph represent in terms of cardiac events.

• Explain how to adjust the electrocardiogram paper speed and amplitude to accommodate for pulse rate and waveform clarity.

• Discuss lead placement errors, artifacts, and corrective actions to ensure accurate readings.

• Describe how to label a completed ECG with patient demographics and technical details.

• Discuss various ECG analyzers and Holter monitors and their applications.

Electrocardiogram (ECG/EKG)

• An electrocardiogram may be used to detect:

  • Abnormal heart rhythm (arrhythmias) or palpitation: irregular heartbeats and their patterns

  • Blocked or narrowed arteries (coronary artery disease) causing chest pain or heart attack: ischemia and infarction

  • Effectiveness of heart disease treatments like pacemakers: monitoring device functionality

ECG Indications

• An ECG may be needed for the following signs and symptoms:

  • Chest pain: angina pectoris, myocardial infarction

  • Dizziness, lightheadedness, or confusion: potential cardiac causes such as arrhythmia

  • Heart palpitations: awareness of heartbeats, regular or irregular

  • Rapid pulse: tachycardia

  • Shortness of breath: dyspnea potentially related to heart failure

  • Weakness, fatigue, or decline in ability to exercise: reduced cardiac output

Electrical Basis of the ECG

• Electrical activity is sensed by electrodes placed on the skin surface to detect cardiac potentials.

• This activity is recorded as an electrocardiogram, showing voltage changes over time.

• Cardiac monitors depict electrical impulses on a screen or oscilloscope, providing real-time visualization.

Electrocardiogram Apparatus and Function

• An electrocardiograph is used to generate electrocardiograms, converting electrical signals into visual representations.

• ECG is a graphic tracing of electrical, not mechanical, activity of the heart, reflecting depolarization and repolarization.

• Electrical impulses from the heart are picked up by electrodes that detect voltage differences.

• Electrodes are good conductors of electricity, facilitating signal transmission.

• The heart's electrical impulses are small (around 0.002 volts), requiring amplification to be visible.

• These impulses are amplified by an amplifier within the electrocardiograph to produce a readable ECG.

• Amplified voltages are converted to mechanical motion by a Galvanometer, moving a stylus.

• This motion is recorded on ECG paper by a terminal print head, creating a graphical output.

ECG Machine Types

• In-hospital 12-lead ECG machine: stationary units for comprehensive cardiac assessments.

• Pre-hospital 12-lead unit: portable devices for emergency and field use, enabling rapid diagnosis.

Electrical Basis and Recording

• Electrical impulses on the skin surface are low voltage and amplified for accurate measurement.

• The printed record of electrical activity is a rhythm strip or ECG strip, used for analysis.

• The recording is printed at a set speed (25 mm/sec) to show the heart's electrical conductivity, timing of events.

• The recording plots voltage on the vertical axis against time on the horizontal axis, displaying wave morphology.

• Electrodes connect to a galvanometer, which records a potential difference, translating electrical signals into deflections.

ECG Graph Paper

• Electrocardiographic paper is divided into small squares that are 1 millimeter (mm) in width for precise measurements.

• Each small square represents a time interval of 0.04 seconds, facilitating rate and interval calculations.

• Darker lines divide the paper every fifth square both vertically and horizontally, aiding quick recognition of larger intervals.

• Large squares measure 5 millimeters in height and width, providing reference points.

• Each large square represents a time interval of 0.20 seconds and contains five small squares for detailed analysis.

• Paper leaves the machine at a constant speed of 25 millimeters per second (mm/sec), the standard for accurate timing.

• Amplitude or voltage is measured on the vertical axis (y-axis) in millimeters or millivolts.

• Time is measured on the horizontal axis (x-axis) in seconds, crucial for interval assessment.

Adjusting ECG Speed

• Increasing the speed to 50 mm/second can reveal subtle ECG findings by spreading out waveforms.

• The waveform becomes wider, enhancing detail.

• Useful for patients with tachycardia (>100 BPM) and particular atrial flutter waves, improving wave recognition.

• The speed needs to be indicated on the tracing to avoid misinterpretation.

ECG Leads Explained

• Electrode: An adhesive pad with conductive gel that attaches to the patient's skin to record electrical impulses from the heart, facilitating electrical contact.

• Leads: How electrodes are connected to the cardiac monitor, forming circuits to measure voltage differences.

• Three leads:

  • Positive: electrode that detects positive deflections

  • Negative: electrode that detects negative deflections

  • Ground: reduces electrical interference

Bipolar and Limb Leads

• Bipolar leads: Leads with one positive and one negative electrode, measuring potential differences.

• Limb leads: I, II, and III, placed on the extremities to view the heart's electrical activity in the frontal plane.

• Lead II is the most common because it best visualizes the P wave, aiding in rhythm analysis.

• Lead configurations:

  • Lead I = right arm (-) to left arm (+): measures the lateral aspect of the heart

  • Lead II = right arm (-) to left leg (+): measures the inferior aspect of the heart

  • Lead III = left arm (-) to left leg (+): measures the inferior-lateral aspect of the heart

Einthoven's Triangle and Law

• Einthoven's Triangle: Imaginary inverted triangle around the heart formed by proper placement of bipolar leads, visualizing electrical forces.

• The top of the triangle is Lead I, the right side Lead II, and the left side Lead III, each providing a different perspective.

• Each lead offers a different view of the heart, essential for comprehensive assessment.

• Einthoven's Law: Lead I + Lead III = Lead II, verifying proper lead placement and signal integrity.

Frontal and Horizontal Planes

• The 12-lead ECG views the heart in two planes:

  1. Frontal plane: viewed by limb leads, observing the heart's electrical activity from the limbs

  2. Horizontal plane: viewed by vector (V) leads, assessing the heart's electrical activity from the chest

Standard and Augmented Limb Leads

• Standard Limb Leads: I, II, III

  • Specific placement on the limbs to capture different angles of the heart's electrical activity.

  • Two-arm leads should be placed between the shoulder and wrist, avoiding bony prominences.

  • Two-leg leads should be placed between the hips and ankles, avoiding bony prominences.

• Augmented Limb Leads: aVR, aVL, aVF

  • Utilizes the four limb leads, amplifying the signals for better readings.

  • The heart is the focal point, with leads measuring potentials relative to a central point.

  • Current flows from the heart outward to the extremities, detected by these leads.

  • The ECG machine boosts amplification due to lead positions, enhancing waveform visibility.

Chest Leads Placement

• Chest Leads (Precordial or Vector (V) Leads):

  • Look at the horizontal or transverse plane, providing anterior and lateral views of the heart.

  • Proper placement is crucial for accurate interpretation, aligning with anatomical landmarks.

  • Should be measured each time electrodes are placed to ensure consistency and accuracy.

Electrode Placement Diagram

• Diagram showing the placement of electrodes on the body. Includes:

  • RA (Right Arm), LA (Left Arm), RL (Right Leg), LL (Left Leg): Limb lead positions

  • V1, V2, V3, V4, V5, V6: Chest lead positions

Standard 12-Lead ECG

• Brief mention of standard 12-lead ECG setup, combining limb and chest leads for a comprehensive view of the heart's electrical activity.

Standardization of the Electrocardiograph

• The electrocardiograph must be standardized for accurate QRS complex amplitude recording, ensuring reliable measurements.

• An application of 1 millivolt (mV) of electricity should cause the stylus to move 10 millimeters high (10 small squares), a standard calibration.

• A three-channel electrograph automatically records standardization marks on the tracing, indicating calibration status.

Standardization Mark

• Voltage vs. Time representation on the ECG paper, confirming proper calibration.

• ECG machines automatically place a standardization mark at the beginning of the tracing, essential for validation.

• Ensuring the mark is present at the beginning of each patient’s tracing is essential, confirming accurate settings.

• Examples of standardization:

  • 10mm/1mV (standard)

  • 5mm/\frac{1}{2}mV (half-standard)

  • 20mm/2mV (double standard)

Electrocardiograph Paper

• The paper has a black or blue base with a white plastic coating to facilitate thermal recording.

• A heated stylus moves over the paper, melting the coating to record the ECG, creating visible lines.

• The paper is pressure-sensitive and must be handled carefully to avoid accidental marks.

ECG Waveforms: Overview

• Baseline/Isoelectric Line: the flat segment representing zero electrical activity.

  • Wave or waveform refers to movement away from the baseline or isoelectric line (beginning and ending of all waves), indicating electrical changes.

  • Positive deflection: above the isoelectric line, representing positive electrical activity.

  • Negative deflection: below the isoelectric line, representing negative electrical activity.

Components of ECG Waveforms

• Electrical impulses leaving the SA node produce waveforms on graph paper, creating the ECG.

• One complete cardiac cycle includes the P wave, QRS complex, and T wave, representing atrial and ventricular activity.

P Wave Details

• First wave, produced by the electrical impulse from the SA node, initiating atrial depolarization.

• Smooth, rounded upward deflection, typical morphology.

• Represents depolarization of the left and right atria, causing atrial contraction.

• 0.10 seconds in length, a typical duration.

PR Interval Explained

• Time the impulse travels from SA node through internodal pathways in atria toward the ventricles, measuring conduction.

• Time interval from the start of the P wave to the start of the QRS complex, reflecting AV node delay.

• 0.12 to 0.20 seconds in length, the normal range.

QRS Complex Components

• Consists of Q, R, and S waves, representing ventricular depolarization.

• Represents the conduction of the impulse from the bundle of His through the ventricular muscle, initiating ventricular contraction.

• Ventricular depolarization, the main event.

Detailed Description of QRS Waves

• Q wave = first downward deflection, often small.

• R wave = first upward deflection (largest in Leads I and II), representing initial ventricular depolarization.

• S wave = downward deflection after the R wave, completing ventricular depolarization.

• Measures less than 0.12 seconds (three small boxes), the normal duration.

J Point Identification

• Point where the QRS complex meets the ST segment, indicating the end of ventricular depolarization.

• Analysis of ST-segment elevation or depression starts with the J point, crucial for detecting ischemia.

ST Segment Details

• Time interval during which ventricles are depolarized, and repolarization begins, a relatively quiet period.

• Isoelectric or consistent with the baseline, indicating no significant electrical activity.

T Wave Representation

• Follows the ST segment, representing ventricular repolarization.

• Represents ventricular repolarization, restoring the resting state.

• Slightly rounded, positive deflection, typical morphology.

• Resting phase of the cardiac cycle, preparing for the next depolarization.

QT Interval Definition

• From the beginning of the QRS complex to the end of the T wave, measuring total ventricular activity.

• Represents all ventricular activity (depolarization and repolarization), reflecting the duration of the ventricular cycle.

• Normal range: 0.28 - 0.44 seconds, dependent on heart rate.

U Wave Characteristics

• Usually absent, often not visible.

• If present, height should be < 1/3 of the T wave, a small deflection.

• Tall U wave indicates electrolyte imbalance, often low potassium (hypokalemia), or other cardiac abnormalities.

12 Leads Overview

• Leads I, II, III: QRS complex is a positive deflection, indicating normal electrical flow.

• aVR: QRS complex is a negative deflection, due to the lead's position relative to the heart.

• aVL: QRS complex is biphasic, showing both positive and negative deflections.

• aVF: QRS complex is a positive deflection, similar to Leads I, II, and III.

V Leads Progression

• V1: QRS complex is a negative deflection, reflecting initial ventricular depolarization.

• QRS progresses through until V6, changing morphology.

• V6: QRS complex is a positive deflection, reflecting complete ventricular depolarization.

• Referred to as normal R wave progression, indicating proper lead placement and cardiac health.

12-Lead Check

• Illustrative check of leads:

  • I, II, III, aVR, aVL, aVF, V1, V2, V3, V4, V5, V6, ensuring proper lead connections and signal acquisition

Einthoven's Triangle and Law Recap

• Einthoven's Law: In the ECG tracing, Lead II = Lead I + Lead III, verifying proper lead placement.

• Review and count positive deflections on leads I, II, and III to verify the law, confirming signal integrity.

Summary of ECG Waveforms

• P wave = atrial depolarization, initiating atrial contraction.

• QRS complex = ventricular depolarization, atrial repolarization, initiating ventricular contraction.

• T wave = ventricular repolarization, restoring the resting state.

Artifacts Defined

• Artificial or abnormal recordings not caused by the heart's electrical activity, distorting the true ECG signal.

• Indicate a technical problem with either the patient setup or the ECG instrument, requiring troubleshooting.

Muscle (Somatic) Tremor Artifact

• Discussion of artifacts caused by muscle tremor, affecting ECG quality.

Muscle Artifact Details

• Erratic spikes interrupting waveforms or the baseline, usually in affected leads, obscuring the ECG signal.

• Causes:

  • Patient movement: voluntary or involuntary

  • Muscle tension or rigidity: due to discomfort or anxiety

  • Chills: shivering causes muscle activity

  • Nervous system disorders (e.g., Parkinson's disease): causing involuntary movements

Muscle Artifact Troubleshooting

• Ensure the patient is relaxed and comfortable, reducing muscle tension.

• Support all body parts on the bed, minimizing movement.

• Ask patients to place hands under their buttocks to reduce shaking, stabilizing arm muscles.

• Check limb sensor position and move if tremulous or move limb sensor to torso if tremors cannot be controlled, repositioning electrodes.

Wandering Baseline Artifact

• Discussion of wandering baseline artifacts, affecting baseline stability.

Wandering Baseline Causes and Solutions

• Complexes are present, but the baseline waves up and down rhythmically, distorting the ECG signal.

• Causes:

  • Dry electrodes: loss of conductivity

  • Dangling lead wires: movement causing interference

  • Loose electrodes: poor contact with skin

  • Broken lead wires: signal disruption

• Troubleshooting: Use new electrodes and/or change the wires, ensuring good contact and signal transmission.

AC Artifacts Explained

• Alternative name: 60 Hz interference, common electrical artifact.

• Appears as uniform small spikes, making the baseline look thick, obscuring the ECG signal.

• Causes:

  • Electrical currents from nearby equipment: interference from power sources

  • Poorly grounded ECG machine: inadequate grounding

  • Loose or broken ground connector or power cord: disrupting grounding

Alternating Current (AC) Artifact Illustration

• Visual example of AC interference on an ECG tracing, demonstrating the typical appearance of this artifact.

AC Artifact Causes and Solutions

• Causes (continued):

  • Improperly connected or unconnected right leg electrode: disrupting the grounding circuit

  • Patient's bed not grounded; patient touching metal frame: creating an electrical pathway

  • Corroded or dirty electrodes/cable tips: impairing electrical contact

• Solution: Use a three-pronged grounded outlet, do not cross lead wires, unplug other appliances, move the table away from the wall, and turn off fluorescent lights, optimizing grounding and reducing interference.

Filter Functionality

• Filters remove high-frequency muscle artifact and external interference, improving signal clarity.

• May cause slight adjustments to ST segments, potentially affecting diagnostic accuracy.

• Most ECGs are done with the filter “on”, balancing artifact reduction and signal fidelity.

Discussion of artifact filters.

Electrical Contact Interruption

• Spikes obliterating the tracing, appearing in one or more leads, disrupting the ECG signal.

• Causes:

  • Broken wire: signal discontinuity

  • Poor sensor contact: inadequate electrical connection

  • Electrode tip slipped out of the holder: signal loss

• Broken wires and cables cannot be repaired; they must be replaced, ensuring signal integrity.

Pacemaker Artifacts

• Pacemaker rhythm is recognizable on the ECG, showing device functionality.

• Shows pacemaker spikes: vertical signals representing the electrical activity of the pacemaker, indicating pacing activity.

• Spikes are more visible in unipolar than in bipolar pacing, due to different electrode configurations.

ECG Patient Preparation Steps

• Introduce yourself and ensure you have the right patient, verifying identity.

• Explain the procedure and obtain consent, ensuring patient understanding and agreement.

• Ask the patient to adjust or remove clothing from the waist up, exposing the chest area.

• Wash hands (PPE is not required), maintaining hygiene.

• Position the patient reclining on a bed with a pillow, arms not dangling, promoting comfort and reducing muscle tension.

• Cover the patient to maintain dignity after electrode placement, ensuring privacy.

• Shave excess chest hair if needed (with consent), improving electrode contact.

• Clean skin with alcohol wipe or soap and water if greasy or dirty, enhancing conductivity.

Quality ECG Recording Checklist

• Correct patient information: accurate demographics

• Smooth tracing baseline: minimal artifact interference

• Standardization mark present: confirms proper calibration

• Einthoven's Law is met (II = I + III): verifies lead placement

• aVR lead is a negative deflection: confirms proper lead orientation

• R wave progression in chest leads: indicates normal electrical activity

• Lead II is a positive deflection: confirms proper lead placement

ECG Quality Check Example

ECG Equipment

• Disposable Electrodes, ECG Cable.

• Three Channel ECG machine.

• Reusable Electrodes with Electrode Cream.

Test Your Knowledge: Electricity

• Why minimize external sources of electricity before an ECG?

  • Answer: External electrical currents can interfere with the ECG tracing, causing artifact.

Test Your Knowledge: Patient Refusal

• What if a patient refuses the ECG procedure?

  • Answer: Determine the reason, try to fix the problem, report to your supervisor, and document the refusal, following protocol.

Test Your Knowledge: Anatomy

• Which anatomical landmark starts in the middle of the axilla and runs down the side of the chest?

  • Answer: Midaxillary line.

Test Your Knowledge: V1 Placement

• Where should the V1 electrode be placed?

  • Answer: The 4th intercostal space on the right sternal border.

Test Your Knowledge: Alternate Electrode Placement

• Acceptable alternate site for electrode placement on the upper extremity?

  • Answer: Deltoid (shoulder).

Test Your Knowledge: Standard Precautions

• True or False: Standard precautions should be practiced on every patient when performing an ECG.

  • Answer: True.

Test Your Knowledge: Artifacts

• What are the 4 most common artifacts?

  • Answer: Muscles, AC, Wandering, and Interrupted baseline.

Test Your Knowledge: Artifact Identification

• Can you identify the following artifact?

  • Answer: AC artifact

Test Your Knowledge: ECG Use

• What is an electrocardiogram used for?

  • Answer: To check heart rhythm and electrical activity.