12-Lead EKG Fundamentals

Vocabulary flashcards covering essential terms, anatomy, and concepts related to 12-lead EKG interpretation and myocardial infarction detection.

12-Lead EKG

A diagnostic test that records electrical activity from 12 different perspectives to evaluate the left ventricle and detect acute cardiac events.

Limb Leads

The four electrodes placed on the arms and legs that provide leads I, II, III, aVR, aVL, and aVF.

Precordial Leads

The six chest electrodes (V1–V6) placed in specific positions to view horizontal planes of the heart.

SA Node

The heart’s primary pacemaker located in the right atrium; initiates impulses that set normal rhythm.

AV Node

Conduction tissue that receives impulses from the atria and relays them to the ventricles; backup pacemaker if the SA node fails.

Bundle Branches

Right and left pathways that carry impulses from the AV node down to the Purkinje fibers.

Purkinje Fibers

Network of fibers that distribute electrical impulses throughout ventricular muscle for coordinated contraction.

Automaticity

The ability of cardiac cells, especially in the conduction system, to initiate an impulse without external stimulus.

P Wave

The EKG deflection representing atrial depolarization.

QRS Complex

The combination of Q, R, and S waves representing ventricular depolarization.

T Wave

The EKG deflection representing ventricular repolarization.

Isoelectric Line

The baseline of an EKG tracing where no net electrical activity is detected.

ST Segment

The flat section between the S wave and the start of the T wave; evaluated for elevation or depression.

ST Elevation

Upward displacement of the ST segment above the isoelectric line indicating acute injury such as myocardial infarction.

Myocardial Infarction (MI)

Death of heart muscle cells due to prolonged ischemia, often identified by ST elevation on an EKG.

Ischemia

Insufficient blood flow and oxygen to tissue, producing EKG changes such as ST depression or T-wave inversion.

Inferior Wall Leads

Leads II, III, and aVF that monitor the inferior wall supplied mainly by the right coronary artery.

Septal Leads

Leads V1 and V2 that view the interventricular septum.

Anterior Leads

Leads V2–V5 (especially V3–V4) that examine the anterior wall supplied mainly by the left anterior descending artery.

Lateral Leads

Leads I, aVL, V5, and V6 that view the lateral wall supplied mainly by the circumflex artery.

Right Coronary Artery (RCA)

Coronary vessel most commonly supplying the inferior wall of the left ventricle.

Left Anterior Descending (LAD)

Coronary artery that primarily supplies the anterior wall and septum.

Circumflex Artery

Branch of the left coronary artery that mainly supplies the lateral wall.

Reciprocal Changes

ST depression or opposite deflections seen in leads opposite the area of injury, supporting MI diagnosis.

Premature Ventricular Contraction (PVC)

Early, wide, and abnormal QRS beat originating in the ventricles; must be ignored when assessing ST segments.

Bigeminy/Trigeminy

Patterns in which every second (bigeminy) or third (trigeminy) beat is a PVC.

Eye Analogy

Concept that each lead acts as an ‘eye’ viewing electrical flow through a specific heart region.

10 Electrodes, 12 Leads

Configuration in which 10 physical electrodes create 12 recorded leads.

EKG Snippets

Each lead on a printed 12-lead shows approximately 3-second samples, not continuous rhythm.

ST-Segment Criteria

Diagnostic rule that ST elevation must appear in at least two contiguous leads of the same wall to confirm an MI.