HST NHA ECG CV Student Test Review

What is an ECG?

An electrocardiogram (ECG or EKG) records the heart's electrical activity.

Electrodes

Adhesive sensors attached to the patient's skin

Detect electrical activity of the heart

Leads

Views or angles of the heart's electrical activity

A standard ECG uses 12 leads

ECG facts

A standard 12-lead ECG uses 10 electrodes

The Right Leg (RL) electrode serves as the ground electrode

ECGs record electrical activity, not mechanical contraction

V1

4th Intercostal Space (ICS)

Right sternal border

V2

4th ICS

Left sternal border

V3

Midway between V2 and V4

V4

5th ICS

Left midclavicular line

Midclavicular

V5

Left anterior axillary line

Level with V4

V6

Left midaxillary line

Level with V4

Systole

Ventricular contraction

Blood is pumped out of the heart

SQUEEZE

Diastole

Ventricular relaxation

Heart chambers fill with blood

FILL

Pathway of Electrical Conduction

SA Node → AV Node → Bundle of His → Right & Left Bundle Branches → Purkinje Fibers

SA node

Natural pacemaker of the heart

AV Node

Delays impulses before they enter the ventricles

Bundle of His

Carries impulses from the AV node to the bundle branches

Right Bundle Branch

Conducts impulses to the right ventricle

Left Bundle Branch

Conducts impulses to the left ventricle

Purkinje Fibers

Rapidly distribute electrical impulses throughout the ventricles

P Wave

Atrial depolarization: Electrical activation of the atria

QRS Complex

Ventricular depolarization

Components of QRS complex

Q wave, R wave, S wave

Q wave

Septal depolarization moving left to right

R wave

Main bulk of ventricular depolarization

S wave

Final depolarization of the upper ventricular walls

T wave

Ventricular repolarization

Inverted T Wave May Indicate:

Ischemia

Abnormal ventricular repolarization

U Wave may indicate:

Hypokalemia (low potassium)

PR Segment

Represents the delay through the AV node before ventricular activation.

PR interval

Represents the time from the beginning of atrial depolarization to the beginning of ventricular depolarization.

ST segment

Represents the period when the ventricles are fully depolarized.

QT interval

Represents the total time required for ventricular depolarization and repolarization

Depolarization

Electrical activation

ON

Repolarization

Electrical recovery

RESET

Right Atrium

Receives deoxygenated blood from the body

Right Ventricle

Pumps blood to the lungs

Left Atrium

Receives oxygenated blood from the lungs

Left Ventricle

Pumps oxygenated blood to the body

Tricuspid Valve

Prevents backflow into the right atrium

Mitral (Bicuspid) Valve

Prevents backflow into the left atrium

Pulmonary Valve

Prevents backflow into the right ventricle

Aortic Valve

Prevents backflow into the left ventricle

Capillaries are the site for:

Gas exchange

Nutrient exchange

Hormone exchange

Waste exchange

Pulmonary Circulation

Heart ↔ Lungs

Does gas exchange

Systemic Circulation

Heart ↔ Body

Delivers oxygen and nutrients to tissues

Coronary Circulation

Blood flow that supplies the heart muscle (myocardium)

The "Widow Maker" Left Anterior Descending (LAD) Artery

A severe blockage can cause a large anterior myocardial infarction.

Artifact

Any distortion or interference on the ECG tracing

Somatic Tremor

Muscle movement

Shivering