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EKG Basics

• In 1790, the usually sedate audience of scientists gasped in disbelief as Luigi Galvani, in a flare of showmanship, made a dead frog’s leg dance by electrical stimulation.

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EKG Basics

• Galvani knew that the electrical current would stimulate the frog’s legs to jump, and with repeated stimuli, he could make them dance.

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EKG Basics

• In the 1790’s, bringing a dead frog “back to life” was a shocking and ghastly “supernatural” feat.

• Galvani loved shocking people!

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EKG Basics

• While conducting research in 1855, Kollicker and Mueller found that when the motor nerve to a frog’s leg was laid over it’s isolated beating heart, the leg kicked with each heartbeat.

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EKG Basics

• “Eureka!” they thought, “the same electrical stimulus that causes a frog’s leg to kick must cause the heart to beat.”

• Therefore, the beating of the heart must be due to a rhythmic discharge of electrical stimuli.

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EKG Basics

• In the mid 1880’s, while using sensor electrodes placed on a man’s skin, Ludwig and Waller discovered that the heart’s rhythmic electrical activity could be monitored from a person’s skin.

• However, their apparatus was not sensitive enough for clinical use.

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EKG Basics

• Enter Willem Einthoven, a brilliant scientist who suspended a silvered wire between the poles of a magnet.

• Two skin sensors (electrodes) placed on a man were then connected across the silvered wire, which ran between the two poles of the magnet.

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EKG Basics

• The silvered wire (suspended in the magnetic field) twitched to the rhythm of the subject’s heartbeat.

• This was very interesting, but Einthoven wanted a timed record.

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EKG Basics• So Einthoven

projected a tiny light beam through holes in the magnet’s poles, across the twitching silvered wire.

• The wire’s rhythmic movements were recorded as waves (named P, QRS, and T) on a moving scroll of photographic paper.

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EKG Basics

• The rhythmic movements of the wire (representing the heartbeat) created a series of distinct waves in repeating cycles.

• The waves were named P, QRS, and T.

• The clever Einthoven reasoned that he could record a heart’s abnormal electrical activity and compare it to the normal.

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EKG Basics

• Thus, a great diagnostic tool, Einthoven’s Electrokardiogram was created in 1901.

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EKG Basics

• The electrocardiogram (EKG) records the electrical activity of the heart, providing a record of cardiac electrical activity, as well as valuable information about the heart’s function and structure.

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EKG Basics

• The EKG is often recorded on a ruled piece a paper that gives a written record of cardiac activity.

• Cardiac monitors and cardiac telemetry provides the same information on a display screen.

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EKG Basics

• The EKG records the electrical impulses that stimulate the heart muscle (“myocardium”) to contract.

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EKG Basics

• The heart’s dominant pacemaker, the SA Node, begins the impulse of depolarization which spreads outward in wave fashion, stimulating the atria to contract.

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EKG Basics

• The SA Node is the heart’s dominant pacemaker, and it’s pacing activity is known as Sinus Rhythm.

• The ability to generate pacemaking stimuli is known as automaticity.

• Other regions of the heart also have automaticity, at slower rates than the SA Node.

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The “P” Wave

• The electrical impulse, originating at the SA Node, spreads as a wave of depolarization through both atria, and this produces the “P Wave” on the EKG.

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The “P” Wave

• Thus, the P wave represents the electrical activity (depolarization) of both atria, and it also represents the simultaneous contraction of the atria.

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The AV Node

• The atrial depolarization stimulus reaches the AV Node, where depolarization slows, producing a brief pause, thus allowing the blood in the atria to enter the ventricles.

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The AV Node

• Remember, the AV Node is the only electrical conduction pathway between the atria and the ventricles.

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“HIS” Bundle and Left and Right Bundle Branches

• Depolarization passes through the AV Node slowly, but upon reaching the ventricular conduction system, depolarization conducts very rapidly through the HIS Bundle, and the Left and Right Bundle Branches.

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Purkinje Fibers

• The left and right Bundle Branches transmits the wave of electrical activity to the Purkinje Fibers.

• The Purkinje Fibers distribute the depolarization stimulus to the ventricular myocardial cells, producing a QRS complex on the EKG.

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Ventricular Conduction System

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The “Q” Wave

• The Q Wave is the first downward stroke of the QRS Complex, and it is followed by an upward R Wave.

• The Q Wave is often not present.

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QRS Complex

• The upward R Wave is followed by a downward S Wave. This total QRS Complex represents the electrical activity of ventricular depolarization.

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ST Segment

• Following the QRS complex, there is a segment of horizontal baseline known as the ST Segment, and then a broad T Wave appears.

• The ST Segment represents the initial phase of Ventricular Repolarization.

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ST Segment

• The ST Segment should be flat and level with the baseline.

• If the ST Segment is elevated or depressed beyond the baseline, it is a sign of serious problems.

ST Normal ST Elevation

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T Wave

• The T Wave represents the final “rapid” phase of ventricular repolarization.

• At this time, the ventricular myocardial cells recover their resting negative charge, so they will be ready to depolarize again.

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QT Interval

• The QT Interval represents the duration of ventricular systole (contraction of the ventricles) and is measured from the beginning of the QRS until the end of the T Wave.

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The Cardiac Cycle

• The Cardiac Cycle is represented by the P Wave, QRS Complex, the T Wave, and the baseline that follows until another P Wave appears. This cycle is repeated continuously.

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The Cardiac Cycle

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The Cardiac Cycle

The P Wave represents atrial depolarization (contraction).

The PR Segment represents the pause at the AV Node.

The QRS Complex represents ventricular depolarization (contraction).

The ST Segment represents the initial phase of ventricular repolarization.

The T Wave represents the final, rapid phase of ventricular repolarization.

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EKG Paper

• The EKG is recorded on ruled (graph paper).

• The smallest divisions are 1 millimeter (mm) squares.

• The large black square has sides that are 5 mm long.

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EKG Paper

• The horizontal axis represents time.

• Each small box represents .04 seconds.

• Each large black box represents .2 seconds.

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EKG Paper

• By measuring along the horizontal axis, we can determine the duration of any part of the cardiac cycle.

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EKG Leads

• The standard EKG is composed of 12 separate leads (or wires) that are attached to electrodes (sensors).

• There are 6 limb leads recorded by using arm and leg electrodes.

• There are 6 chest leads obtained by placing electrodes at different positions on the chest.

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EKG Leads

Limb Leads Chest Leads

I V1

II V2

III V3

AVR V4

AVL V5

AVF V6

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EKG Lead Location

Leads What they are looking at:

V1, V2 Right side of heart -Anterior Descending Artery

V3, V4 Septum between ventricles -Anterior Descending Artery

V5, V6, I, AVL Left (lateral) side of heart -Circumflex Artery

II, III, AVF Inferior part of heart -Right or Left Coronary Artery

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Heart Rate

• When examining an EKG, you should first consider the rate.

• The rate is read as cycles per minute.

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Heart Rate

• The SA Node is the heart’s dominant pacemaker, generating a sinus rhythm.

• The SA Node paces at a resting rate range of 60 to 100 per minute.

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Heart Rate

• When the SA Node paces the heart rate slower than 60 per minute, it is called Sinus Bradycardia.

• When the SA Node paces the heart rate faster than 100 per minute, it is called Sinus Tachycardia.

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Heart Rate• Other potential pacemakers, known as ectopic

foci have the ability to pace the heart (at a slower rate), if the normal SA Node pacemaking fails.

• These foci are located in the :

-Atrial Foci – rate of 60-80 per minute

-Junctional Foci – rate of 40-60 per minute

-Ventricular Foci – rate of 20-40 per minute

*Rapid pacemaking activity suppresses slower activity

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Determining the Heart Rate from an EKG

• Step 1:

-Find a specific R Wave that peaks on a heavy black line (this will be the start line)

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Determining the Heart Rate from an EKG

• Step 2:

-Count off “300, 150, 100” for every thick black line that follows the start line, naming each line as shown…

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Determining the Heart Rate from an EKG

• Step 3:

-Count off the next three lines after “300, 150, 100” as “75, 60, 50.”

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Determining the Heart Rate from an EKG

• Step 4:

-Where the next R Wave falls, determines the heart rate.

-It’s that simple!

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Determining the Heart Rate from an EKG

What is this patient’s Heart Rate?

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Determining the Heart Rate from an EKG

In the previous EKG, the heart rate was 60, and P Waves were absent.

Which ectopic foci acted as the pacemaker for this case of bradycardia?

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Determining the following Heart Rates

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Determining the rhythm on an EKG

The EKG provides the most accurate means of identifying cardiac arrhythmias (abnormal rhythms).

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Determining the rhythm on an EKG

On an EKG, there is a consistent distance (duration) between similar waves during a normal , regular cardiac rhythm.

This is due to the automaticity of the SA Node, which maintains a constant cycle of pacing impulses.

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Determining the rhythm on an EKG

An EKG is scanned for the repetitive continuity of a regular rhythm. Breaks in the continuity, such as a pause, presence of an early (premature) beat, or sudden rate change warn us of a rhythm disturbance.

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Irregular Rhythms

Wandering Pacemaker

An irregular rhythm produced by the pacemaker activity wandering from the SA Node to nearby atrial foci.

This produces cycle length variation as well as variation in the shape of the P Wave

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Wandering Pacemaker

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Multifocal Atrial Tachycardia

Multifocal Atrial Tachycardia (MAT) is a rhythm of patients with Chronic Obstructive Pulmonary Disease (COPD).

The heart rate is over 100 bpm with P waves of various shapes, since three or more atrial foci are involved.

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Multifocal Atrial Tachycardia

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Atrial Fibrillation

Atrial Fibrillation is caused by the continuous, rapid firing of multiple atrial foci. Since no single impulse depolarizes the atria completely, and only one occasional atrial depolarization gets through the AV Node to stimulate the ventricles, an irregular ventricular rhythm is produced.

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Atrial Fibrillation

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A

B

C

What is pacing the rhythm of EKG C?

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Premature Beats

Premature beats occur when an irritable foci fires a single stimulus

Premature Atrial Contraction (PAC)

Premature Ventricular Contraction (PVC)

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Premature Atrial Contraction

A Premature Atrial Contraction (PAC) originates suddenly in an irritable atrial foci, and it produces an abnormal P Wave earlier than expected.

The abnormal P Wave leads to a QRS Complex that occurs “out of its normal rhythm.”

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Premature Atrial Contraction

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Premature Ventricular Contraction

A Premature Ventricular Contraction (PVC) originates suddenly in an irritable ventricular foci.

It produces a giant ventricular complex (big and wide QRS)on the EKG.

There is no P Wave before the abnormal QRS Complex, because the atria have not depolarized (contracted).

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Premature Ventricular Contraction

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Tachyarrhythmias

A Tachyarrhythmia originates in a very irritable foci that paces rapidly. Sometimes more than one active foci is generating the pacing stimuli.

Paroxysmal Tachycardia: 150-250 bpm

Flutter: 250-350 bpm

Fibrillation: 350-450 bpm

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First Degree AV Heart Block

Normally, there is a pause at the AV Node, which allows blood to enter the ventricles.

In First Degree AV Block, there is a longer than normal pause before ventricular stimulation.

This is seen on an EKG as a PR Interval longer than one large square (.2 Seconds).

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Myocardial Infarction

Myocardial Infarction (MI) results from the complete occlusion of a coronary artery.

The area of the myocardium supplied by the occluded coronary artery becomes non-viable and neither depolarizes or contracts.

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Myocardial Infarction

The classic triad of myocardial infarction is:

Ischemia

Injury

Infarction

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Myocardial InfarctionIschemia: a decrease

in blood supply from the coronary arteries to the myocardium of the heart.

Characterized by inverted T Waves on the EKG

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Myocardial Infarction

Injury: indicates the acuteness of an infarct.

ST Elevation denotes myocardial injury.

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Myocardial Infarction

Infarction: permanent damage to the myocardium is called an infarction.

A Significant Q Wave is one that is at least 1 small square wide (.04 sec), or 1/3 the height (or greater) of the QRS amplitude (Height).

Significant Q Waves indicate permanent damage to the myocardium from a heart attack.

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Myocardial Infarction

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Myocardial Infarction

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Myocardial Infarction