EKG Ch 5

Introduction to EKG Technology and Applications

1. Electrical Activity of the Heart

  • An electrocardiogram (EKG) illustrates the electrical activity of the heart, corresponding to muscle contractions that facilitate blood pumping.

  • Cardiac Conduction: This refers to the movement of electrical signals throughout the heart, initiating from the upper parts and following a predetermined pathway. The conduction must remain consistent; deviations may indicate cardiac issues.

  • The electrical activity documented by the EKG is essentially driven by chemical shifts within the heart's cellular structures.

Key Definitions

  • Depolarization: This is characterized by a shift in electrical charge from negative to positive. It begins in a small area of heart muscle before propagating to adjacent cells, resulting in heart muscle contraction.

  • Repolarization: This is the process where the electrical charge reverts from positive back to negative, leading to heart muscle relaxation. It is crucial for the rhythmic functioning of the heart where atria and ventricles undergo depolarization and repolarization at alternating times to properly fill and pump blood.

EKG Machine Connection

  • EKG machines are connected to patients via electrodes, which are pads that conduct electrical signals and are linked to lead wires or EKG cables. The machine processes the electrical signals to produce various leads, each providing distinct insights into the heart's activity.

  • EKG Tracing: The machine creates recordings on graph paper that advances at a consistent rate, resulting in the visual representation known as an EKG tracing.

Clarification on Terminology

  • While many mistakenly refer to electrodes as leads, in cardiology, leads specifically denote measurements of electrical activity from multiple electrodes. Electrode refers to the pads applied to the skin.

  • EKGs do not directly assess the heart's mechanical activity; they focus strictly on electrical activity, which informs about the heart's location, rate, and rhythm. If mechanical activities need evaluation, an echocardiogram is ordered, leveraging ultrasound technology for visual representation.

2. Portable EKG Machines

  • Functionality: Portable EKG machines measure subtle voltage differences between electrodes on a patient's body, producing a record of the cardiac electrical activity.

  • Components: Generally includes a screen, keyboard, and printer, often mounted on a wheeled cart; they feature a lengthy cable dividing into ten lead wires, which attach to electrodes on the patient.

  • Electrodes connect to the lead wires typically via snaps or clips and should be appropriately placed on the chest and limbs.

  • Different types of electrodes include:

    • Resting Electrodes: Flat and used for routine EKG screenings.

    • Monitoring Electrodes: Circular pads for continuous monitoring, beneficial when resting electrodes might not adhere properly (e.g., due to diaphoresis).

3. Types of EKG Tests

  • EKG technicians administer various tests necessitating different electrodes and lead combinations, dictated by the healthcare provider’s information requirements.

Test Types Overview

EKG Test Type

Purpose

Continuous (3- or 5-lead)

Monitors heart rate/rhythm using a bedside monitor; extended measurements enable identification of arrhythmias.

Telemetry Monitoring

Remote heart rate monitoring through a small wearable device; identifies rhythm problems, though data may be less comprehensive compared to ambulatory monitors.

Holter Monitoring

Uses a portable device worn by the patient for 24-48 hours to check for signs of heart problems, often used outside hospital settings.

12-lead EKG

Common for assessment during stress tests (exercise or cardiac drugs) evaluating heart response under exertion.

Stress Test

Assess cardiac function under stress conditions; typically performed on a treadmill or with drug-induced heart rate acceleration.

Personal EKG Devices

  • Home-use EKG devices are increasingly prevalent, found in smartwatches and handheld gadgets capable of single-lead readings, syncing with smartphones for data sharing with healthcare providers.

4. EKG Leads and Lead Groups

  • The standard 12-lead EKG is significant, showcasing a 2.5-second trace from each lead, organized into a grid. A rhythm strip displaying a 12-second trace for lead II is included, which is preferred for monitoring heart rate and rhythm.

Lead Designation

  • All used leads and their respective groups are:

    • Limb Leads (Bipolar): Leads I, II, III—measure voltage differences between positive and negative electrical points, forming Einthoven's triangle.

    • Lead I: Between left arm (positive) and right arm (negative).

    • Lead II: Between left leg (positive) and right arm (negative).

    • Lead III: Between left leg (positive) and left arm (negative).

    • Augmented Limb Leads (Unipolar): Leads aVR, aVL, aVF—focus on one positive pole compared to a neutral reference, deriving from the same limb electrodes.

    • Precordial (Chest) Leads (Unipolar): Leads V1, V2, V3, V4, V5, and V6, capturing electrical activity against Wilson's Central Terminal, acting as a neutral reference point.

Cardiovascular Insights by Lead

  • Each lead traces specify regions of the heart:

    • Leads II, III, aVF: Inferior wall (left ventricle).

    • Leads V1, V2, V3, V4: Anteroseptal wall (divisional wall).

    • Leads I, aVL, V5, V6: Left lateral wall (left ventricle).

5. Electrode Placement and Utilization


  • Depending on testing type, EKGs require varied lead numbers, as summarized below:

    Number of Leads

    Application


    3

    Continuous heart rhythm monitoring.


    5

    Continuous rhythm monitoring and telemetry.


    12

    Resting 12-lead EKG and stress tests.

    General Placement Guidelines

    • 3-lead Placement: Consists typically of electrodes placed on the chest or torso, facilitating patient mobility.

    • 5-lead Testing: Involves placement similar to 3-lead, with an additional V1 electrode and a ground electrode (right leg).

    • 12-lead Testing: Utilizes a total of 10 electrodes positioned on limbs and chest, specific placements illustrated in accompanying figures.

    • Error Prevention: It's crucial to ensure correct lead placement, as incorrect electrode positioning leads to inaccurate EKG results.

    6. EKG Machine Setup

    • Ensuring proper setup of the EKG machine is critical for obtaining accurate tracings without artifacts.

    • Machines undergo an automatic self-test on startup, displaying alerts for any operational failures.

    • Technicians must ensure the machine is positioned close to the patient, minimizing stress on lead wires.

    • Regular checks of battery status are vital for uninterrupted functionality during tests.

    • Paper Settings: The default speed for EKG paper is 25 mm/s, adjustable as required. Gain controls enhance tracing clarity, with standard configurations at 10 mm/mV.

    Conclusion

    • EKG machines and thorough understanding of their operation are vital for assessing cardiac health, requiring meticulous execution of procedures by EKG technicians to ensure accurate recordings and effective patient care decisions.