EKG

EKG Basics

Definition of Key Components

  • Voltage: Measurement of electrical potential.
  • Time: Refers to the duration of the heartbeat cycle as displayed in EKG readings.

Key EKG Waveforms and Intervals

  • P Wave: Ablation of atrial depolarization.
  • PR Interval: Time between the start of atrial depolarization and the start of ventricular depolarization.
  • QRS Complex: Represents ventricular depolarization.
  • ST Segment: Time between ventricular depolarization and repolarization.
  • T Wave: Represents ventricular repolarization.
  • U Wave: Not consistently seen, may be related to repolarization changes.

EKG Wave Representation

  - Each component reflects different electrical activity phases in the cardiac cycle.

Review - Pathway of Blood Flow Through the Heart

Major Components of Heart Circulation

  • Pulmonary Arteries: Carry deoxygenated blood from the heart to the lungs.
  • Pulmonary Veins: Bring oxygenated blood back to the heart.
  • Superior Vena Cava and Inferior Vena Cava: Major veins returning deoxygenated blood to the right atrium.
  • Aorta: Supplies oxygenated blood to the body.

Flow of Blood in the Heart

  1. Right Atrium: Receives deoxygenated blood from the body via vena cavae.
  2. Tricuspid Valve (AV Valve): Blood flows from right atrium to right ventricle.
  3. Right Ventricle: Pumps blood through the pulmonary semilunar valve into pulmonary arteries.
  4. Lungs: Blood is oxygenated.
  5. Pulmonary Veins: Oxygenated blood flows to the left atrium.
  6. Left Atrium: Blood passes through the bicuspid (mitral) valve into the left ventricle.
  7. Left Ventricle: Pumps oxygen-rich blood through the aortic semilunar valve into the aorta.
  8. Body Tissues: Blood travels throughout the body delivering oxygen and nutrients.

Summary of Valves

  • Atrioventricular Valve (Tricuspid and Bicuspid): Prevent backflow during ventricular contraction.
  • Semilunar Valves (Aortic and Pulmonary): Prevent backflow after the blood is ejected from the ventricles.

The Cardiac Cycle: Systole and Diastole

Phases of the Cardiac Cycle

Systole (Heart Pumping)
  • Function: The ventricles contract, increasing pressure inside the heart; the contraction forces blood out into the arteries, creating the pulse.
Diastole (Heart Filling)
  • Function: The ventricles relax which allows blood to flow from the veins into the heart, enabling the heart to refill.

The Heart: Cellular Structure

Types of Cells

Electrical Cells
  • Function: Specialized cells responsible for conducting electrical impulses that initiate and transmit the heart's electrical activity.
  • Key Term: Pacemaker cells which exhibit automaticity by continually generating action potentials.
Mechanical Cells (Myocytes)
  • Function: These cells form the bulk of the heart muscle and contract in response to the electrical stimulation from the electrical cells.

Electrophysiology

  • Action Potentials: The electrical events initiated by the electrical cells leading to heart contraction.

Sequence of Electrical Conduction in the Heart

  • Starts at the SA Node: Functions as the heart's primary pacemaker located in the right atrium.
  • To AV Node: When SA node fires, it spreads impulses to the atrioventricular node.
  • Bundle of His: Conducts impulses from the AV node down through the ventricles.
  • Purkinje Fibers: Spread throughout the ventricles to coordinate contraction.

Key Definitions

  • Depolarization: Electrical event that triggers heart contraction, represented by the P wave (atria) and QRS complex (ventricles).
  • Repolarization: Allows the heart to relax and fill, represented by the T wave.
  • Systole: Contraction of heart muscles.
  • Diastole: Relaxation of heart muscles.

Electrical Conduction through the Heart

  • SA Node Rate: Fires at 60-100 beats per minute, causing atrial depolarization and contraction.
  • AV Node Rate: Slows impulses from the SA node, firing at 40-60 bpm leading to ventricular depolarization and contraction.
  • Ventricular Firing Rate: If SA and AV nodes fail, ventricles may fire at 20-60 bpm.

Phases of the Cardiac Cycle

  1. Atrial Systole: Atria contract, forcing blood into ventricles.
  2. First Phase of Ventricular Systole: Ventricles contract, AV valves close.
  3. Second Phase of Ventricular Systole: Semilunar valves open, ejecting blood.
  4. Early Ventricular Diastole: Semilunar valves close, blood enters atria.
  5. Late Ventricular Diastole: Chambers relax, ventricles fill with blood.
EKG Wave Contributions to Cardiac Phases
  • P Wave: Atrial depolarization.
  • QRS Complex: Ventricular depolarization.
  • T Wave: Ventricular repolarization.

Echocardiogram (EKG) Measurement

Key Functions

  • Records Electrical Activity: Monitors depolarization and repolarization of cardiac cells, not mechanical function.
  • Conditions Detected: Can identify ischemia, chamber enlargement, and dysrhythmias.
  • Diagnostic Tool: More informative than telemetry.

EKG Interpretation Steps

  • Step 1: Determine the Heart Rate
      - Normal: 60-100 bpm.
      - Method: Count a 6-second strip and multiply by 10.

  • Step 2: Determine the Rhythm
      - Analyze R-R interval for regularity.

  • Step 3: Evaluate the P Wave
      - Confirm the presence and regularity of P waves in relation to QRS complexes.

  • Step 4: Evaluate the PR Interval
      - Normal range: 0.10-0.20 seconds (less than 5 small squares).

  • Step 5: Analyze the QRS Complex
      - Should be present for every P wave and lasts less than 0.12 seconds.

Normal EKG Characteristics

  • Heart Rate: 60 to 100 bpm.
  • Rhythm: Regular and consistent.
  • P Wave: Present before each QRS complex.
  • QRS Complex: Narrow (less than 0.12 seconds).
  • PR Interval: 0.12 to 0.20 seconds.
  • T Wave: Normal.