Chapter 26: Principles of Electrocardiography

Arrhythmia

An abnormal heart rate or rhythm.

Artifact

A signal distortion or unwanted, erratic movement of the stylus that is caused by outside interference during an ECG procedure.

Bipolar

Having two poles or electrical charges.

Caliper

A pocket-sized tool used for measuring the height and width of the ECG waves and intervals.

Dextrocardia

The condition in which the heart is located on the right side of the chest, and the apex is pointing to the right.

Echocardiography (ECHO)

The use of ultrasonic waves directed through the heart to study the structure and motion of the heart. The visual record produced is called an echocardiogram.

Electrocardiogram (ECG, EKG)

A record or recording of electrical impulses of the heart as produced by an electrocardiograph.

Electrodes

Adhesive patches that conduct electricity from the body to the ECG machine wires.

Ions

An electrically charged atom, or the smallest component of an element.

Unipolar

Having one pole or electrical charge.

Heart Chambers

There are four chambers: two atrial chambers (receive blood from the body) and two ventricle (pump blood out to the body) chambers.

Heart Septum

Divides the right and left sides of the heart.

ECHO

Evaluates the mechanical action of the heart and valves.

Heart Wall Layers

Epicardium, myocardium, endocardium.

Conduction System of the Heart

Made up of electrical cells within the myocardium.

Structures of the Conduction System

SA node, AV node, Bundle of His, Purkinje fibers.

Sinoatrial (SA) Node

Located in the posterior superior wall of the right atrium. Called the pacemaker of the heart.

Atrioventricular (AV) Node

Located at the base of the interatrial septum.

Bundle of His (AV Bundle)

Located in the upper interventricular septum.

Right and Left Bundle Branches

Located in the lower interventricular septum.

Purkinje Fibers

Splits off of the bundle branches.

Polarized State

The resting state before the impulse hits the cardiac cell.

Depolarized State

Action potential occurs due to the movement of sodium and potassium ions within the cell, allowing the impulse to move through the cell.

Repolarized State

The recovery state where the sodium and potassium ions move back to their original location after the impulse has passed over the cell.

Isoelectric Line

A straight line that is also called the baseline; Represents a period of time with no electrical activity.

Deflection

Any movement away from the baseline in the tracing that reflects the heart's electrical flow.

Wave

A deflection from the baseline on an ECG.

Complex

A form made up of many waves on an ECG (e.g., QRS complex).

Segment

A part of a line between two points on an ECG (e.g., ST segment).

Interval

A period of time between two points or events on an ECG. During an interval, many waves can occur.

P Wave

Small "hill" (positive deflection); Atrial depolarization.

PR Segment

Appears as an isoelectric line.

QRS Complex

Made up of Q-S waves; Ventricular chambers contract.

Q Wave

Negative deflection; Interventricular septal depolarization.

R Wave

Positive triangular deflection; Ventricular depolarization.

S Wave

Any downward deflection following the R wave; Ventricular depolarization.

ST Segment

Isoelectric line; Ventricles finish contracting.

T Wave

Positive deflection; Ventricular repolarization.

U Wave

Usually not seen; Repolariztion of Purkinje fibers.

I Point

The point where the QRS complex ends and the ST segment starts.

PR Interval

Starts at the beginning of the P wave and ends at the start of the Q wave; Atrial depolarization.

QT Interval

Starts at the beginning of the Q wave and ends at the end of the T wave; Atrial chambers move to polarized state; Ventricular chambers move to repolarized state.

Amount of Electrodes Used With a 12-Lead ECG

10 electrodes.

Lead

Images generated when performing an ECG.

Right Leg Electrode

Ground electrode; Required for a clear ECG tracing.

Bipolar (Standard) Leads

Leads I, II, and III; Uses both arms and left leg electrode to create pictures of the frontal plane of the heart.

Lead I

Right arm (RA) to left arm (LA).

Lead II

Right arm (RA) to left leg (LL).

Lead III

Left leg (LL) to left arm (LA).

Einthoven Triangle

A triangle formed by the joining the positive poles of leads I, II, and III.

Augmented Vector (aV) Leads

Unipolar leads that provide information on the frontal plane of the heart; Uses the right arm, left arm, and left leg electrodes.

Chest (Precordial) Leads

Unipolar leads that provide information on the horizontal plane of the heart; V1-V6.

Caliper

Used to measure the height and width of the waveforms on an ECG tracing.

Voltage

Amplitude; Measured by the vertical lines of the waveforms on an ECG tracing.

Horizontal Lines on an ECG Tracing

Measures the time.

Electrodes

Single-use disposable adhesive tablets that are placed on the skin.

Alligator Clip (Patient End Adaptor)

The snap/clip attached to the lead wires that is attached to the electrode during an ECG.

Types of ECG Devices Used

Box model; Computer model.

Right Arm Electrode

White; Above wrist or upper arm.

Left Arm Electrode

Black; Above wrist or upper arm.

Right Leg Electrode

Green; Inner lower leg above ankle.

Left Leg Electrode

Red; Inner lower leg above ankle.

Chest V1

Red; Fourth intercostal space at the right sternal edge.

Chest V2

Yellow; Fourth ICS at the left sternal edge.

Chest V3

Green; Midway between V2 and V4.

Chest V4

Blue; Fifth ICS on the midclavicular line.

Chest V5

Orange; The midpoint between V4 and V6.

Chest V6

Purple; Same horizontal plane as V4 and the midaxillary line.

Dextrocardia Electrode Placement

Chest electrodes should go on the right side of the chest and the limb lead wires should be swapped.

Wandering Baseline Artifact

An upward and downward movement of the waveform. This is caused by poor skin preparation, poor electrode placement/condition, and movement.

Somatic Tremor (Muscle) Artifact

Appears as jagged peaks with irregular heights and spacing. This is caused by voluntary/involuntary movement.

Alternating Current (AC) Interference Artifact

60-cycle interference artifact; Appears as a series of small spikes that create a thick-looking tracing. Caused by electrical interference.

Interrupted Baseline Artifact

Intermittent signal artifact; Appears as a normal at first then becomes distorted when the electrical connection is interrupted.

Premature Atrial Contractions (PAC)

Occurs when the atria contract sooner than they should. The P wave appears abnormal or there is an additional P wave.

Atrial Flutter

Occurs when the atria contract faster than the ventricles. Extra P waves can be seen.

First-Degree Heart Block

The impulse slows as it moves from the atria to the ventricle, creating a longer PR segment.

Second-Degree Heart Block

The impulse is blocked/slowed as it moves into the ventricles. Blocked: Ventricles do not contract and there is no QRS complex after the P wave. Slowed: The PR segment is longer.

Third-Degree Heart Block

The impulse does not reach the ventricles. The P wave is faster than normal and the QRS complex does not coordinate with the P wave.

Premature Ventricular Contractions (PVC)

Occurs when the ventricles contract sooner than they should. The P wave may be absent or appear after the QRS complex, the T wave may be abnormally shaped, and the QRS complex may be widened.

Ventricular Tachycardia

Occurs when the ventricles beat at a rapid rate (up to 250 BPM. Can turn into V-fib if not treated.

Ventricular Fibrillation

Occurs when the ventricles quiver uncontrollably, making them ineffective at pumping any blood.

Asystole

Results in the absence of a heartbeat and appears as a flatline on the tracing.

Holter Monitor

Monitors the heart over a 24- to 48-hour period while patients go about their normal activities.

Cardiac Event Recorder

Portable, battery powered ECG device that is activated by the patient when symptoms occur, and it is worn for 30 days.

Implantable Loop Recorder

A small recorder that is surgically implanted in the upper left chest, that continuously records the ECG for 2 to 3 years.

Transtelephonic Monitor (TTM)

Small device that records a patient's ECG when the patient pushes the activation button. Data is sent via phone.

TTM With Internal Memory

The ECG is recorded and stored when a button is pressed. The data can be sent to the provider via phone.

TTM With No Internal Memory

When activated, the phone receiver is placed over the TTM and immediately sends the live ECG to the provider over the phone.