CH2 - Waves and Measurements

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29 Terms

1
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What are Electrodes?

  • Electrodes are sensors placed on the skin to detect electrical activity

  • 12-lead EKG uses 10 electrodes: 4 limb + 6 chest (precordial) leads

  • Placement accuracy is key for reliable readings

<ul><li><p>Electrodes are sensors placed on the skin to detect electrical activity</p></li><li><p><span style="color: green;"><strong>12-lead EKG uses 10 electrodes: 4 limb + 6 chest (precordial) leads</strong></span></p></li><li><p>Placement accuracy is key for reliable readings</p></li></ul><p></p>
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Rule of Electrical Flow

  • Electricity flows TOWARDS a positive electrode → positive (upright) deflection

  • Flows AWAY from positive electrode → negative deflection

  • Perpendicular flow → biphasic (equally up/down) waveform

<ul><li><p>Electricity flows <strong>TOWARDS</strong> a positive electrode →<span style="color: green;"><strong> positive (upright) deflection</strong></span></p></li><li><p>Flows <strong>AWAY</strong> from positive electrode → <span style="color: red;"><strong>negative deflection</strong></span> </p></li><li><p>Perpendicular flow → <strong>biphasic</strong> (equally up/down) waveform </p></li></ul><p></p>
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Which are the most common Monitoring Leads? Difference?

  1. Lead II → best for rhythm

  2. V1 → best for wide/narrow QRS

Each lead gives a different angle/view of the heart’s activity

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Know the Electrode Placement for Monitoring Lead II

  1. V1 → RIGHT Sternum

  2. V2 → LEFT Sternum

  3. V4 → LEFT under Nipple

  4. V3 → BETWEEN V2 & V4

  5. V6 → LEFT under Axillary

  6. V5 → BETWEEN V4 &.V6

<ol><li><p>V1 → RIGHT Sternum </p></li><li><p>V2 → LEFT Sternum</p></li><li><p>V4 → LEFT under Nipple </p></li><li><p>V3 → BETWEEN V2 &amp; V4</p></li><li><p>V6 → LEFT under Axillary </p></li><li><p>V5 → BETWEEN V4 &amp;.V6</p></li><li><p></p></li></ol><p></p>
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When a P wave originates in the SA node, it is expected to be smooth, rounded, and _____ in Lead II

Upright

<p>Upright</p>
6
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What explains why the QRS complex is typically upright in Lead II?

The mean electrical axis of ventricular depolarization is directed toward the left leg

<p>The mean electrical axis of ventricular depolarization is directed toward the left leg</p>
7
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Define Myocyte

  • Make up Myocardium

  • Contractile cells → pumps blood

8
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On a standard 12-lead EKG, what does one small box on the horizontal axis represent?

0.04 seconds

9
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Know Graph Paper Basics

  • Small square = 0.04 sec (horizontally)/ 1mm (vertically)

  • Large square = 0.20 sec (5 small squares) / 5mm

<ul><li><p><strong>Small square</strong> = 0.04 sec (horizontally)/ 1mm (vertically) </p></li><li><p><strong>Large square</strong> = 0.20 sec (5 small squares) / 5mm </p></li></ul><p></p>
10
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What is the Speed EGK usually runs?

25 mm/sec

11
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Vertical axis and Horizontal axis measure what on the EKG paper?

  • Vertical axis (Y) = voltage (amplitude), measured in mm or mV

  • Horizontal axis (X) = time, in seconds

12
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If the R-R intervals across the strip are consitent, then the rhythm is considered _____

Regular

13
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How to ACCURATELY measure Heart Rate?

  • 6 second method: Count the number of R waves in a 6 second strip x 10

    • Used for regular or irregular rhythms

  • Small box method: HR = 1500/ # Small boxe

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One Heartbeat =

  • P wave → QRS → T wave

  • Represents depolarization → contraction → repolarization → rest

<ul><li><p>P wave → QRS → T wave</p></li><li><p>Represents depolarization → contraction → repolarization → rest</p></li></ul><p></p>
15
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What describes the elements of a single cardiac cycle?

  1. P Wave

  2. PR Segment

  3. PRI

  4. QRS Complex

  5. T Wave

<ol><li><p>P Wave </p></li><li><p>PR Segment </p></li><li><p>PRI </p></li><li><p>QRS Complex </p></li><li><p>T Wave</p></li></ol><p></p>
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What happens during the PR interval on an EKG?

  • Atrial depolarization and conduction through the AV node

  • Normal: 0.12-0.20 sec

<ul><li><p><span style="color: red;"><strong>Atrial depolarization</strong></span> and conduction through the AV node</p></li><li><p><strong>Normal: 0.12-0.20 sec</strong></p></li></ul><p></p>
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What is the Role of the AV Node?

  • Acts as a gatekeeper between atria and ventricles

  • Slow conduction allow time for:

    1. Atrial contraction (atrial kick)

    2. Ventricular filling

  • Can act as a backup pacemaker if SA node fails

<ul><li><p>Acts as a <strong>gatekeeper</strong> between atria and ventricles</p></li><li><p>Slow conduction allow time for:</p><ol><li><p>Atrial contraction (atrial kick)</p></li><li><p>Ventricular filling</p></li></ol></li><li><p>Can act as a <strong>backup pacemaker</strong> if SA node fails</p></li></ul><p></p>
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What happens during the QRS Complex on an EKG?

  • Start to end of ventricular depolarization

  • Normal: <0.11 sec

<ul><li><p>Start to end of <span style="color: red;"><strong>ventricular depolarization</strong></span></p></li><li><p><strong>Normal: &lt;0.11 sec</strong></p></li></ul><p></p>
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The T wave on an EKG represents which electrical event?

Ventricular repolarization

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The P wave, QRS Complex and T wave on an EKG represents which electrical event?

  • P wave

    → Atrial Depolarization

    • Contraction

  • QRS complex

    → Ventricular Depolarization

    • Contraction

  • T wave

    → Ventricular Repolarization

    • Going towards resetting

  • U wave

    → Sometimes seen with hypokalemia

<ul><li><p><strong>P wave</strong></p><p><span style="color: red;"><strong>→ Atrial Depolarization</strong></span></p><ul><li><p>Contraction</p></li></ul></li><li><p><strong>QRS complex</strong></p><p><span style="color: red;"><strong>→ Ventricular Depolarization</strong></span></p><ul><li><p>Contraction</p></li></ul></li><li><p><strong>T wave</strong></p><p><span style="color: blue;"><strong>→ Ventricular Repolarization</strong></span></p><ul><li><p>Going towards resetting</p></li></ul></li><li><p><strong>U wave</strong></p><p>→ Sometimes seen with hypokalemia</p></li></ul><p></p>
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Describe ST segment

  • End of QRS to start of T wave

  • Look for elevation/depression

<ul><li><p>End of QRS to start of T wave</p></li><li><p>Look for elevation/depression</p></li></ul><p></p>
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The QT interval represents what event in the cardiac cycle

  • Ventricular depolarization and repolarization

    • Beginning of QRS to end of T wave

  • Varies with HR

  • Normal: MEN - <0.45sec; WOMEN: <0.46

<ul><li><p><strong>Ventricular </strong><span style="color: blue;"><strong>depolarization</strong></span><strong> and </strong><span style="color: red;"><strong>repolarization</strong></span></p><ul><li><p>Beginning of QRS to end of T wave</p></li></ul></li><li><p>Varies with HR</p></li><li><p><strong>Normal: MEN - &lt;0.45sec; WOMEN: &lt;0.46</strong></p></li></ul><p></p>
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Key Measurements

  • P wave

    • <0.12 sec, <2.5 mm tall

  • PRI

    • 0.12-0.20 sec

  • QRS

    • <0.12 sec

  • QT Interval

    • MEN <0.45sec

    • WOMEN: <0.46

    • Should be less than half the R-R interval

<ul><li><p><strong>P wave</strong></p><ul><li><p>&lt;0.12 sec, &lt;2.5 mm tall</p></li></ul></li><li><p><strong>PRI</strong></p><ul><li><p>0.12-0.20 sec</p></li></ul></li><li><p><strong>QRS</strong></p><ul><li><p>&lt;0.12 sec</p></li></ul></li><li><p><strong>QT Interval</strong></p><ul><li><p>MEN &lt;0.45sec</p></li><li><p>WOMEN: &lt;0.46</p></li><li><p>Should be less than half the R-R interval</p></li></ul></li></ul><p></p>
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What can cause artifact on an EKG tracing?

  • Caused by patient movement, loose electrodes, and electrical interference

  • Can mimic arrhythmias - ALWAYS CHECK THE PATIENT

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What example of Artifact/Interference is this?

Artifact: Muscle Tremors

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What example of Artifact/Interference is this?

Artifact: Patient movement

27
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What example of Artifact/Interference is this?

Artifact: Loose Electrode

28
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What example of Artifact/Interference is this?

Artifact: 60-Cycle Interference

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Explain Refractory Periods

  1. Absolute

    • No stimulus can cause a new depolarization

    • QRS → peak of T

  2. Relative

    • A strong enough impulse can trigger another beat (downward slope of T wave)

    • Dangerous time

    • R-on-T phenomenon

<ol><li><p><strong>Absolute </strong></p><ul><li><p>No stimulus can cause a new depolarization </p></li><li><p>QRS → peak of T </p></li></ul></li><li><p><strong>Relative </strong></p><ul><li><p>A strong enough impulse can trigger another beat (downward slope of T wave) </p></li><li><p>Dangerous time </p></li><li><p>R-on-T phenomenon </p></li></ul></li></ol><p></p>