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Category: Reading an EKG

  • A Step-by-Step Guide to reading an EKG

    Interpreting EKGs (Electrocardiograms) is an essential skill for healthcare professionals. As with any complex ability, mastering it necessitates the cultivation of robust habits and consistent practice.

    I fear not the man who has practiced 10,000 kicks once, but I fear the man who has practiced one kick 10,000 times.

    – Bruce Lee

    Bruce Lee’s wisdom extends to the interpretation of EKGs: the most proficient interpreters cultivate a systematic approach that they consistently apply until they attain mastery. Although the repetitive process may seem tedious and sluggish at first, with diligent practice, mastery is simply a matter of time.

    This guide aims to simplify EKG interpretation by outlining a systematic approach that covers all the essential aspects. By establishing the right habits and recognizing normal patterns, identifying abnormalities becomes straightforward. Let’s delve into the steps to enhance your EKG reading skills.

    Verifying the EKG

    Before interpreting an EKG, always verify:

    • Correct Patient Information: Ensure the EKG belongs to the right patient.
    • Quality of the EKG: Check for artifacts and confirm that the EKG was performed correctly.
    • Calibration: Confirm that the EKG is appropriately calibrated.
    • Clinical Context: Understand the patient’s clinical history and current presentation.
    • Comparison with Previous EKGs: If available, compare the current EKG with prior ones to identify new changes.

    Four Steps to Reading Every EKG

    Adopt these four essential steps when interpreting every EKG:

    Step 1: Calculate the Rate

    Determine the heart rate:

    • Normal Rate: 60–100 beats per minute (bpm)
    • Tachycardia: Heart rate > 100 bpm
    • Bradycardia: Heart rate < 60 bpm

    Step 2: Determine the Rhythm

    Assess the heart rhythm by examining:

    Regularity

    Is the rhythm regular, regularly irregular, or irregularly irregular?

    P-waves

    • Are normal P waves present?
    • Is the P wave morphology normal?

    P:QRS Ratio

    Is there a 1:1 ratio of P waves to QRS complexes?

    QRS Complexes

    • Are the QRS complexes narrow (< 100 ms) or wide (> 100 ms)?
    • A narrow QRS suggests a supraventricular origin.

    Step 3: Check the Axes

    Determine the electrical axis of the heart:

    P-wave axis

    • Normal: 0° and +75°.

    QRS axis

    • Normal Axis: Between -30° and +90°
    • Right Axis Deviation: Axis > +90°
    • Left Axis Deviation: Axis < -30°
    • Extreme Right Axis Deviation: -90° and +180°

    Step 4: Examine Intervals and Morphology

    Evaluate the intervals and waveform morphology:

    • P-wave morphology
    • PR Interval:
      • Normal: 120–200 ms (3–5 small squares)
      • Short PR Interval: May indicate pre-excitation syndromes.
      • Prolonged PR Interval: Suggests first-degree AV block.
    • PR Segment:
      • Elevated?
      • Depressed?
    • QRS Complex Morphology:
      • Check for normal morphology.
      • Assess for bundle branch blocks:
        • Right Bundle Branch Block (RBBB)
        • Left Bundle Branch Block (LBBB)
        • Left Anterior Fascicular Block (LAFB)
        • Left Posterior Fascicular Block (LPFB)
        • Non-Specific Intraventricular Conduction delay
    • ST Segment:
      • Elevated?
      • Depressed?
    • QT Interval: Use QTc and recognize that it’s use is limited if the heart rate is too high or too low or if there is a conduction defect.
      • Prolonged QTc: > 440 ms in men, > 460 ms in women.
      • Short QTc: < 350 ms.
      • Rule of Thumb: A normal QT interval is less than half the preceding RR interval.
    • T-wave abnormalities
      • Too tall?
      • Inverted?
    • U-waves
      • Are they prominent?

    Applying Occam’s Razor in EKG Interpretation

    When interpreting EKG findings, apply Occam’s Razor: choose the simplest diagnosis that accounts for all findings within the clinical context. If multiple abnormalities are present, consider whether they could be due to a single underlying cause rather than multiple unrelated issues.

  • Recognizing Normal Variations and Artifacts on an EKG

    While identifying pathological findings is essential, recognizing normal variations and artifacts is equally important to prevent misdiagnosis. This article explores several common normal variations and artifacts encountered during EKG interpretation, providing detailed insights to help clinicians distinguish between benign patterns and true abnormalities.

    Normal Variations in EKGs

    Early Repolarization

    Overview

    Early repolarization is usually a benign EKG pattern commonly seen in healthy young adults, especially athletes. The changes are typically seen in the precordial leads. However, in some individuals, it may be associated with an increased risk of sudden cardiac death, making accurate recognition vital.

    Characteristics

    • J-Point Elevation: A subtle elevation of the J-point, which is the junction between the end of the QRS complex and the start of the ST segment.
    • Upwardly Concave ST-Segment Elevation: The ST segment shows a concave upward elevation.
    • Concordant T-Waves: Upright T-waves that are in the same direction as the QRS complex.
    • J-Point Notching: A small notch at the J-point may be present.

    Differentiation from Pericarditis

    Early repolarization can mimic pericarditis but can be distinguished by:

    • Absence of PR Segment Changes: Unlike pericarditis, early repolarization does not exhibit PR depression in most leads or PR elevation in aVR and V1.
    • Stable Pattern Over Time: Early repolarization patterns are usually consistent and do not evolve, whereas pericarditis shows dynamic changes.
    • Lack of Clinical Symptoms: Patients are typically asymptomatic, whereas pericarditis presents with chest pain.

    Non-Specific ST-T Changes

    Overview

    Non-specific ST-T changes are subtle alterations in the ST segment and T-waves that do not meet criteria for specific cardiac disorders.

    Characteristics

    • ST-Segment Deviations: Slight elevations or depressions that are not indicative of a particular condition.
    • T-Wave Changes: Relatively flat or minimally inverted T-waves.
    • Distribution: These changes can occur in one or multiple leads.

    Clinical Significance

    • Common Causes: Can result from electrolyte imbalances, medications, or be a normal variant.
    • Interpretation: Should be considered in the context of the patient’s clinical history and symptoms.

    Juvenile T-Waves

    Overview

    Juvenile T-waves refer to negative T-waves in the right precordial leads (V1-V3) seen in children and adolescents, sometimes persisting into young adulthood.

    Characteristics

    • Inverted T-Waves: Negative T-waves in leads V1 to V3.
    • Symmetry: Typically symmetrical and shallow.

    Differentiation from Pathological T-Wave Inversions

    • Age Consideration: Normal in younger individuals; persistence into adulthood is a benign variant.
    • Clinical Correlation: Absence of symptoms or risk factors for heart disease supports a benign interpretation.

    S1S2S3 Pattern

    Overview

    The S1S2S3 pattern is characterized by S waves in leads I, II, and III and is often a normal finding.

    Characteristics

    • Presence of S Waves: Prominent S waves in all three limb leads.
    • Normal Variant: Common in young, healthy adults.

    Clinical Significance

    • Differential Diagnosis: Must be distinguished from conditions like right ventricular hypertrophy or pulmonary embolism, which may present similarly but are associated with clinical symptoms.

    Changes Due to Hyperventilation

    • Effects on EKG: Can cause ST-segment depression and T-wave inversions.
    • Mechanism: Alterations in autonomic tone and electrolyte shifts during rapid breathing.
    • Clinical Relevance: temporary changes that may mimic more serious conditions.

    Changes Due to Hyperventilation or Large Carbohydrate Meals

    • Effects on EKG: May lead to transient ST-T changes.
    • Mechanism: Postprandial metabolic changes affecting cardiac repolarization.
    • Clinical Relevance: temporary changes that may mimic more serious conditions.

    Artifacts in EKG Interpretation

    Artifacts are extraneous markings on the EKG tracing that are not generated by the heart’s electrical activity. Recognizing artifacts is crucial to avoid misdiagnosis.

    Tremor Artifacts

    Causes

    • Muscle Tremors: Conditions like Parkinson’s disease can cause rhythmic muscle activity.
    • Shivering: Due to cold or fever.

    Appearance on EKG

    • Erratic Baseline: Wavy or fuzzy baseline mimicking arrhythmias like atrial flutter.
    • Identification: Normal P-waves and QRS complexes may be visible amidst the artifact.

    Differentiation

    • Consistency: True arrhythmias will have consistent patterns, whereas artifacts are irregular.
    • Patient Observation: Noting tremors or shivering during EKG recording.

    Artifacts from Patient Movement

    Causes

    • Physical Activity: Combing hair, brushing teeth, or other movements during EKG recording.

    Appearance on EKG

    • False Tachyarrhythmias: Rapid, irregular waves that may mimic ventricular tachycardia.
    • Identification: Presence of normal complexes within the artifact; correlation with patient activity.

    Skeletal Muscle Interference

    Causes

    • Voluntary Muscle Contractions: Tensing muscles can introduce noise.
    • Involuntary Movements: Such as spasms or twitches as in shivering.

    Appearance on EKG

    • Baseline Distortions: Irregular, high-frequency noise superimposed on the tracing.
    • Identification: Artifact is often localized to specific leads corresponding to the area of muscle activity.

    Equipment Issues

    Causes

    • Poor Electrode Contact: Due to dried gel, oily skin, or hair.
    • Faulty Leads: Damaged cables or connectors.
    • Machine Malfunction: Calibration errors or defective hardware.

    Appearance on EKG

    • Unstable Baseline: Wandering or drifting baseline making interpretation difficult.
    • Sudden Changes: Abrupt shifts or loss of signal in one or more leads.

    Resolution

    • Equipment Check: Ensuring all leads are properly connected and the machine is functioning.
    • Skin Preparation: Cleaning the skin and reapplying electrodes as needed.

    An interesting question: If you see a flat line, how do you know if it is because of sinus arrest or a third degree block or a disconnected lead?

    A flatline could be seen in one of the three conditions:

    • When a lead is connected to the chest, there is usually a “noise” even when it appears that the recording is a flat line- we would see some degree of activity because of reasons such as interference from other muscles, poor electrode contact from skin oil/ hair, etc. A perfectly flat line should prompt the consideration of a disconnected lead.
    • A flat line with small deflections may suggest a third degree heart block with asystole (the deflections being the p-waves) while a flat line would suggest sinus arrest.

    Unstable Baseline (Baseline Wander)

    Causes

    • Respiration: Deep breathing can cause the baseline to move up and down.
    • Movement: Shifting position or talking during the recording.

    Appearance on EKG

    • Slow Oscillations: The entire tracing appears to undulate over several seconds.
    • Identification: Baseline wander is typically synchronized with respiratory cycles.

    Management

    • Breath Holding: Asking the patient to hold their breath briefly can stabilize the baseline.
    • Comfortable Positioning: Ensuring the patient is relaxed and still.

    Understanding and recognizing normal variations and artifacts in EKGs are essential components of accurate interpretation. By being aware of these common patterns and their characteristics, clinicians can differentiate between benign findings and true abnormalities, thereby improving diagnostic accuracy and patient care.

  • Normal EKG Rhythm, Axis, Intervals, and Waves

    Normal Sinus Rhythm

    Normal sinus rhythm is the typical rhythm of a healthy heart, distinguished by the following characteristics:

    1:1 Ratio of P-Waves to QRS Complexes: Each P-wave is succeeded by a QRS complex, demonstrating that every atrial depolarization triggers a corresponding ventricular depolarization.

    Regular Rhythm: The intervals between heartbeats are consistent, indicating a steady and uniform heart rate.

    Consistent P-Wave Morphology: P-waves exhibit uniform morphology, typically appearing upright (positive) in lead II and inverted (negative) in lead aVR.

    Intervals and Waves

    Grasping the different intervals and waves on an EKG is essential for accurate interpretation of cardiac function. Here is an overview of each component.

    P-Wave

    Represents Atrial Depolarization: The process of electrical activation in the atria.

    Components:

    • The first part reflects the right atrium.
    • The middle part reflects both atria.
    • The terminal part reflects the left atrium

    Depolarization Pathway:

    • Begins at the sinus node in the right atrium.
    • Spreads from right to left and slightly downward (angle of 0–75 degrees).

    Lead Deflections:

    • Leads facing the depolarization wave (I, II, aVL, aVF, V5, V6) show a positive deflection.
    • Leads facing away (e.g., aVR) show a negative deflection.
    • Lead V1, being perpendicular, records a biphasic P-wave (positive then negative).

    Normal P-Wave Characteristics:

    • Axis: 0–75 degrees.
    • Duration: Less than 0.12 seconds.
    • Amplitude:
      • Less than 2.5 mm in lead II (usually the tallest P-wave).
      • In V1:
        • Positive portion less than 1.5 mm.
        • Negative portion less than 1 mm in amplitude and duration.

    Note: The P-wave is smaller in amplitude compared to the QRS complex because the atria are smaller and less muscular than the ventricles.

    An interesting Exercise: What does a normal P wave look like in lead III, assuming the normal P wave vector is 0 to 75 degrees?

    If the P wave axis falls between 0 and 30 degrees, lead III records a primarily negative deflection. If it’s 30 degrees, it’s biphasic. If it’s between 30 and 75 degrees, it records a primarily positive deflection.

    PR Interval

    • Definition: The time from the start of atrial depolarization (beginning of the P-wave) to the start of ventricular depolarization (beginning of the QRS complex).
    • Reflects: primarily the delay in conduction at the AV node.
    • Duration: Typically 0.12 to 0.20 seconds (three to five small boxes on the EKG).

    PR Segment

    Straight line from the end of p-wave to the beginning of QRS- Should be isoelectric (at baseline). Elevations or depressions may indicate underlying pathology.

    QRS Complex

    • Represents Ventricular Depolarization.
    • Duration: Normally less than 0.10 seconds.
    • Depolarization Pathway:
      • After the AV node, the impulse travels through the bundle of His.
      • Depolarization starts in the inter-ventricular septum, usually from left to right, handled by the left bundle branch’s septal fascicle..

    Q-Wave: Normal vs. Abnormal.

    • Small Q-waves may be seen in leads I, aVL, V5, and V6 due to septal depolarization as it travels from left to right, away from these leads.
    • Concerning Q-Waves:
      • Any Q-wave in leads V2 to V3 ≥ 20 ms or a QS complex in these leads.
      • Q-wave ≥ 30 ms and ≥ 0.1 mV deep in two contiguous leads where a positive deflection is expected.
      • QS complex in leads I, II, aVL, aVF, V4 to V6 (leads where we expect a net positive deflection)
    • Note: Q-waves in aVR are not significant; can be normal in lead III.

    QRS axis

    The QRS complex amplitude is significantly greater than the P wave amplitude due to the ventricles’ much higher muscular mass compared to the atria. Furthermore, the left ventricle dominates what we see on the EKG due to its larger mass.

    Determining the Axis

    A good way to determine the axis is by looking at the net vector of the wave being analyzed in 3 leads:

    • I: since it is aligned at 0°, any vector between – 90° and +90° will be registered as a net positive deflection. Otherwise, it will be negative.
    • II: since it is aligned at 60°, any vector between – 30° and +120° will be registered as a net positive deflection. Otherwise, it will be negative.
    • aVF: since it is aligned at 90°, any vector between 0° and 180° will be registered as a net positive deflection. Otherwise, it will be negative.

    By looking at the wave in each of these leads and looking for an overlap, we can determine the axis of a wave.

    IIIaVFOverlapQRS Axis
    +++0° to 90°Normal
    ++0° to -30°Normal
    ++N/ANot possible
    +-30° to -90°Left axis deviation
    ++90° to 150°Right Axis Deviation
    +N/ANot possible
    +150° to 180°Right Axis Deviation
    180° to -90°Extreme Right Axis Deviation

    Normal, early, and poor R-wave progression

    • R Wave Progression in Precordial Leads:
      • V1 and V2: Show deep S-waves due to right ventricle overlay.
      • V5 and V6: Show tall R-waves due to left ventricle overlay.
      • Transition Zone: R-wave becomes taller than the S-wave, usually in V3 or V4.
    • Early R-Wave Progression: Transition occurs in V1 or V2.
    • Late R-Wave Progression: Transition occurs in V5 or V6.

    Normal vs. Low voltage

    • Normal Voltage: R-wave height plus S-wave depth should be at least 5 mm in limb leads. Also, it needs to be at least 10 mm in precordial leads to avoid low voltage designation.

    J-Point

    • Definition: The point where the QRS complex transitions into the ST segment. The QRS complex represents the depolarization of the ventricles. The ST segment, on the other hand, represents the period when the ventricles are depolarized, but have not yet begun to repolarize.
    • Significance:
      • Used as a reference for assessing the ST segment.
      • Correct identification is crucial for detecting ST segment elevations or depressions, which can indicate myocardial infarction or ischemia.

    ST Segment

    • Definition: Extends from the end of the QRS complex to the beginning of the T-wave.
    • Represents: The period when the ventricles are depolarized but have not yet started repolarizing.
    • Normal Characteristics:
      • Usually horizontal or gently upsloping.
      • At the same level as the TP segment (isoelectric line).
    • Abnormal Elevations (Measured at the J-point):
      • Must be ≥ 0.1 mV in most leads.
      • In leads V2 to V3:
        • ≥ 0.15 mV in women.
        • ≥ 0.2 mV in men ≥ 40 years.
        • ≥ 0.25 mV in men < 40 years.
    • Abnormal Depressions: Horizontal or downsloping ST-segment depression ≥ 0.5 mm below baseline measured 0.08 seconds (2 small boxes) after the J-point in two contiguous leads.

    T-wave

    • Represents Ventricular Repolarization.
    • Normal Characteristics:
      • Positive in leads with a positive QRS complex.
      • Negative in leads with a negative QRS complex.
    • Amplitude: Usually 1/3 to 2/3 the height of the corresponding R-wave.
    • Shape: Typically asymmetric with a slow upstroke and rapid downstroke.
    • Abnormalities:
      • Peaked T-Waves: T-waves taller than 5 mm in limb leads or 10 mm in precordial leads may be concerning.
      • Inverted T-Waves: Symmetric inversion of more than 1 mm may indicate pathology.

    QT Interval

    • Definition: The time from the start of ventricular depolarization (beginning of QRS complex) to the end of ventricular repolarization (end of T-wave).
    • Measurement:
      • From the beginning of the QRS complex to where the T-wave returns to baseline.
      • Use a tangent line on the downslope of the T-wave if the end is not clear.
    • Duration:
      • Varies with heart rate; usually about 40% of the cardiac cycle.
      • Corrected QT (QTc): What is normal is dependent on the rate and QT is not very predictive of an adverse outcome at extremes of heart rate or in bundle branch blocks.
        • Adjusted for heart rate using the formula: QTc = QT / √RR.
        • Normal QTc Range: 0.35 to 0.46 seconds.
        • Quick Assessment: The QT interval should be less than half the preceding RR interval.

    U-Waves

    • Definition: A small wave that may follow the T-wave.
    • Origin: Not fully understood.
    • Characteristics: Typically a small upward deflection. Smaller than the T-wave and may be difficult to see.
    • Clinical Significance: Prominent U-waves (> 2 mm) may be seen in conditions like hypokalemia and bradycardia.

    TP Segment

    • Definition: The segment from the end of the T-wave to the beginning of the next P-wave.
    • Significance: Considered the true isoelectric line and used as a reference point to compare elevations or depressions in the PR and ST segments.

  • Estimating the Heart Rate on an Electrocardiogram

    This post will guide you through estimating the heart rate using the small and large squares on EKG paper, especially when the heart rhythm is regular.

    As we previously discussed, a standard EKG has several large squares measuring 5mm x 5mm that are divided into smaller squares measuring 1mm x 1mm. The standard EKG records at a rate of 25 mm/ second. Since each large square is 5mm wide, there are a total of 5 large squares per second. So one large square reflects 1sec/5 squares= 0.2 seconds. Since we have 5 small squares per large square, each small square is 0.2/5=0.04 seconds.

    Total Squares in One Minute

    Large Squares: 60 seconds / 0.20 seconds per large square = 300 large squares per minute.

    Small Squares: 60 seconds / 0.04 seconds per small square = 1500 small squares per minute.

    Calculating Heart Rate Using Large Squares

    Since we know that each large square is 0.2 seconds, if we had a QRS every large square, the rate would be 60 second

    Method: Divide 300 by the number of large squares between two consecutive heartbeats.

    • Formula: Heart Rate = 300 / Number of Large Squares between R-R intervals
    • Examples:
      • 1 Large Square: 300 / 1 = 300 bpm
      • 2 Large Squares: 300 / 2 = 150 bpm
      • 3 Large Squares: 300 / 3 = 100 bpm
      • 4 Large Squares: 300 / 4 = 75 bpm
      • 5 Large Squares: 300 / 5 = 60 bpm
      • 6 Large Squares: 300 / 6 = 50 bpm

    Calculating Heart Rate Using Small Squares

    Method: Divide 1500 by the number of small squares between two consecutive heartbeats (R-R intervals).

    • Formula: Heart Rate = 1500 / Number of Small Squares between R-R intervals
    • Example: If there are 25 small squares between beats, Heart Rate = 1500 / 25 = 60 beats per minute

    Estimating Heart Rate in Irregular Rhythms

    When the heart rhythm is irregular, the usual methods using small or large squares may not be accurate. Instead, use the 10-second rule.

    10-Second Rule Method

    • Step 1: Count the number of QRS complexes (heartbeats) in a 10-second EKG strip.
    • Step 2: Multiply that number by 6 to estimate the beats per minute.

    Why It Works

    • A standard EKG strip is 10 seconds long.
    • Multiplying by 6 extrapolates the 10-second count to a full minute (10 seconds x 6 = 60 seconds).

    Example

    • If there are 12 QRS complexes in a 10-second strip:
      • Heart Rate = 12 x 6 = 72 beats per minute

    Understanding Normal Heart Rates

    • Normal Range: 60 to 100 beats per minute for adults.
    • Below Normal (Bradycardia): Less than 60 beats per minute.
    • Above Normal (Tachycardia): More than 100 beats per minute.