Skip to Main Content

++

Introduction

++

Electrocardiography (ECG) is a standard intensive care unit monitoring modality both in the continuous and twelve lead formats. It is used both for the detection of cardiac ischemia and arrhythmias.

++

Definitions and Terms

+

  • ▪  ECG waves (Figure 33-1)
    • —P wave—initial electrocardiographic deflection from the baseline in a cardiac contraction—corresponds to the electrical activation of the atria following sinoatrial node depolarization
    • —PR interval—corresponds to the period of atrial conduction through the atrioventricular node
    • —QRS complex—corresponds to electrical activation of the ventricles
    • —ST segment—segment connecting the QRS complex to the T wave, and may indicate coronary ischemia (if depressed below baseline) or myocardial infarction (if elevated above baseline)
    • —T wave—corresponds to repolarization of the ventricles
  • ▪  ECG lead—used to mean both the electrical wire connecting the patient to the ECG machine, and one of the axes of cardiac electrical conduction commonly evaluated by ECG.
    • —Limb leads show conduction between any two of the three limbs comprising Einthoven’s triangle (right arm, left arm, left leg) as shown in Figure 33-2. Green is traditionally used as a ground lead.
    • —Lead vector—shows the direction of conduction between the negative and positive terminals of a given lead as shown in 12-lead ECG in Figure 33-3
      • • Limb leads
  • ▪  Lead I shows the axis of conduction from the right arm (white lead) to the left arm (black lead), with an upward deflection indicating conduction from right to left.
  • ▪  Lead II shows the axis of conduction from the right arm toward the left leg (red lead).
  • ▪  Lead III shows the axis of conduction from the left shoulder toward the left leg.
    • —Augmented limb leads show the axis of conduction from an imaginary central location (comprised of the center point between the three reference limbs) toward those limbs.
  • ▪  aVR shows electrical conduction from the central lead toward the right arm.
  • ▪  aVL shows conduction from the central lead to the left arm.
  • ▪  aVF shows conduction from the central lead to the left leg (or foot).
    • • Precordial leads show conduction from the imaginary central point toward various locations on the chest wall (Figure 33-4).
  • ▪  V1 is placed in the fourth intercostals space on the right side of the sternum.
  • ▪  V2 is placed in the fourth intercostals space to the left of the sternum.
  • ▪  V3 is placed midway between leads V2 and V4.
  • ▪  V4 is placed in the fifth intercostals space in the midclavicular line.
  • ▪  V5 is placed next to V4 but in the anterior axillary line.
  • ▪  V6 is placed next to V5 but in the midaxillary line.
    • • Modified chest leads closely approximate true precordial leads, so MCL1 (modified chest lead 1) approximates V1 etc.
  • ▪  Ground lead—the green lead often placed by convention of the right leg, but can be anywhere on the body and used ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessAnesthesiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.