Basic OverviewECG Rhythm Interpretation

Objectives

To recognize the normal rhythm of the heart - “Normal Sinus Rhythm.”

To recognize the most common rhythm disturbances.

To identify emergency interventions for life threatening arrhythmias

I. Impulse Conduction & the ECG

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

1. The “PQRST”-Reminder-the EKG only reflects the Reminder-the EKG only reflects the heart’s electrical activity-heart’s electrical activity-not its not its contractioncontraction P wave - Atrial

depolarization

• T wave - Ventricular repolarization

• QRS - Ventricular depolarization

2. The PR Interval

Atrial depolarization +

delay in AV junction

(AV node/Bundle of His)

(delay allows time for the atria to contract before the ventricles contract) normal time 0.12 to 0.20 sec.

3. Pacemakers of the Heart

SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.

AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.

Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 40 beats/minute.

4. The ECG Paper Horizontally

One small box - 0.04 sOne large box - 0.20 s

VerticallyOne large box - 0.5 mV

4. The ECG Paper (cont)

Every 3 seconds (15 large boxes) is marked by a vertical line (hash mark).

This helps when calculating the heart rate. You need a 6 second strip to calculate

heart rate (30 large boxes)

3 sec 3 sec

4. The ECG Paper (cont)

Count the number of P waves in a 6 second strip (30 large boxes) and multiply by 10 to determine atrial rate (9 x 10 = 90) Atrial rate = 90 beats/min

Count the number of QRS complexes in a 6 second strip (30 large boxes) and multiply by 10 to determine ventricular rate (9 x 10 =90) Ventricular rate + 90 beats/min

3 sec 3 sec

II. Normal Sinus Rhythm (NSR)Normal Rhythm of Heart--etiology

Etiology: the electrical impulse is formed in the SA node and conducted normally.

This is the normal rhythm of the heart; other rhythms that do not conduct via the typical pathway are called arrhythmias.

II. Normal Sinus Rhythm (NSR)Characteristics

Rate – 60 to 100 Regularity – rhythm is regular P waves – one P wave preceding each QRS PR interval – normal between 0.12 and 0.20 seconds and

constant in length QRS – all look the same QRS duration – equal to or less than 0.12 seconds and

constant in width QT interval – equal to or less than 0.44 seconds and constant in

length

III. SA Node Problemsdefined

The SA Node can: fire too slow fire too fast

Sinus Bradycardia

Sinus Tachycardia

A. Sinus BradycardiaRate less than 60 beats per minute--etiology

Etiology: SA node is depolarizing slower than normal, impulse is conducted normally (i.e. normal PR and QRS interval).

Significance: Lower rate may cause decrease in cardiac output

A. Sinus Bradycardia--

Characteristics

Rate: less than 60 beats per minute Regularity: rhythm is regular P wave: normal; one precedes each QRS PR interval: normal between 0.12 and 0.20

seconds QRS: normal, equal to or less than 0.12 seconds QT: normal or may be prolonged

A. Sinus BradycardiaSigns and Symptoms due to Sinus Bradycardia

May have no symptoms at all May have signs of decreased cardiac output - hypotension, cool clammy skin, - shortness of breath, chest pain or pressure - light headed, dizziness or blurred vision - syncope

A. Sinus BradycardiaTreatment for Sinus Bradycardia

Treat only if symptomatic - IV atropine

- IV dopamine

- Transcutaneous pacemaker

B. Sinus Tachycardia--etiologyRate greater than 100 beats per minute but less than 150 beats per minute

Etiology: SA node is depolarizing faster than normal, impulse is conducted normally.

Significance: increased workload of the heart Remember: sinus tachycardia is a response to

physical or psychological stress, (hypoxia, pain, hypovolemia).

B. Sinus Tachycardia-characteristicsRate greater than 100 beats per minute but less than 150 beats per minute

Rate: 100 beats per minute but less than 150 beats per minute.

Regularity: rhythm is regular P wave: normal, one precedes each QRS PR interval: normal between 0.12 and 0.20

seconds QRS: normal, equal to or less than 0.12 seconds QT: normal

B. Sinus TachycardiaSigns and Symptoms

May have no symptoms at all May have signs of decreased cardiac output

- hypotension, syncope and blurred vision

- chest pain and/or palpitations

- may report a sense of nervousness or anxiety

B. Sinus TachycardiaTreatment

Look for the cause (ie. pain, anxiety, fever, hemorrhage) and treat the cause.

If tachycardia leads to cardiac ischemia treatment may include medications to slow the heart rate Beta blockers or Calcium channel blockers

III. Atrial Arrhythmias

Single or Multiple irritable areas can depolarize and “take over” from the SA node.

Atrial tissue

A. Atrial Fibrillation etiology

Etiology: Atrial impulses are formed in a totally unpredictable fashion-there are no p waves.

Significance: The atria do not contract in a coordinated way

therefore, the cardiac output is decreased. The atria do not empty fully, so there is a risk of

atrial clots The AV node allows some of the impulses to pass

through at variable intervals (so rhythm is irregularly irregular). Rates can get dangerously high

A. Atrial Fibrillation characteristics

Rate:

Atrial rate: not measurable exceeds 400 beats per minute.

Ventricular rate: 30 to 220 beats per minute

Regularity: grossly irregular

P waves: absent; erratic baseline

PR interval: not measurable

QRS: normal QT: not measurable

A. Atrial Fibrillation Signs and symptoms

Patients with chronic atrial fibrillation may be asymptomatic

New onset atrial fibrillation patients may have symptoms related to decreased cardiac output (loss of atrial contraction and fast ventricular rate)

•hypotension, cool clammy skin,

•shortness of breath, chest pressure or pain,

•dizziness, blurred vision or syncope

A. Atrial Fibrillation treatment

If treatment is required:

Beta Blocker, Calcium Channel blockers will decrease rate

IV Amiodarone may decrease rate and convert rhythm (NOT IV bolus!)

Synchronized Cardioversion will convert the rhythm

B. Atrial Flutter

Deviation from NSRNo P waves. Instead flutter waves (note

“sawtooth” pattern) are formed at a rate of 250 - 350 per minute

Only some impulses conduct through the AV node

Significance & treatment -as in Atrial Fibrillation

C. Supra Ventricular Tachycardia (SVT)Atrial Tachycardia

Deviation from NSR Heart rate: speeds up to greater than 150 beats per

minute Rhythm: regular, with normal QRS complexes.

Significance: Greatly increased myocardial oxygen demand Could become life threatening

C. SVT – Signs and symptoms

Patient may be asymptomatic

May have signs of decreased cardiac output:

•Hypotension, cool clammy skin,

•shortness of breath, chest pain or pressure,

•dizziness, blurred vision or syncope

C. SVT Treatment

Treatment:

1. Adenosine followed by Beta Blocker or Calcium Channel Blocker

2. Synchronized Cardioversion in emergency

IV. Ventricular Cell ProblemsVentricular cells can: fire occasionally from

1 or more irritable area

fire continuously from multiple irritable areas

fire continuously from a single irritable area

Premature Ventricular Contractions (PVCs)

Ventricular Fibrillation

Ventricular Tachycardia

(VT)

IV. Ventricular beatsWhen an impulse originates in a ventricle:

conduction through the ventricles will be abnormal

QRS will be wide (greater than 0.12 seconds) and bizarre.

Multi-focal PVCs

IV. Ventricular Conduction

NormalSignal moves rapidly through the ventricles

AbnormalSignal moves slowly through the ventricles result is a wide QRS

A. PVCs--characteristics

Deviation from NSREarly beats originate in the ventricles

resulting in wide (greater than 0.12 sec.) and bizarre QRS complexes.

When there is more than one premature beat, and the beats look alike, they are called “unifocal”.

When there is more than one premature beat, and the beats look different, they are called “multifocal”.

A. PVCs etiology

Etiology: Ventricular irritability can be caused by hypoxia, electrolyte imbalances.

Significance: Early beats from the ventricle do not deliver full cardiac output; if untreated may lead to VT/VF.

B. Ventricular Tachycardia

Deviation from NSR:Impulse is originating in the ventricles (no P

waves, wide QRS, rate greater than 100).

Significance: greatly reduced cardiac output--Life threatening

arrhythmia!! Treatment:

IV Lidocaine or IV Amiodarone (NOT IV bolus)

C. Ventricular Fibrillation

Etiology: Hundreds of ventricular cells are excitable and depolarizing randomly

Significance: no cardiac output; no pulse Death producing arrhythmiaDeath producing arrhythmia

Treatment: CODE BLUE1. Defibrillation2. IV Epinephrine3. IV Amiodarone

V. Heart Blocks(Bradycardia)

Etiology: weakness, fatigue or damage to the AV node

Significance: Bradycardia may result in decreased cardiac output

Treatment (same as for bradycardia): IV Atropine IV Dopamine Transcutaneous Pacing

A. 1st Degree AV Block

Etiology: Prolonged conduction delay in the AV node or Bundle of His.

PR interval: greater than 0.20 seconds and is constant

B. 2nd Degree AV Block, Type I

Etiology: Each successive atrial impulse encounters a longer and longer delay in the AV node until one impulse (usually the 3rd or 4th) fails to make it through the AV node.

P waves: More than QRSs P-R interval: gets progressively longer

C. 2nd Degree AV Block, Type II

Etiology: Conduction is all or nothing (no prolongation of PR interval); typically block occurs in the Bundle of His.

More P waves than QRSs PR interval does not vary in length

D. 3rd Degree AV Block

Etiology: There is complete block of conduction in the AV node; atria and ventricles form impulses independently of each other.

More P: waves than QRSs QRS to QRS (ventricular rate) is regular P to P (atrial rate) is regular—faster than

ventricular rate

3rd Degree AV BlockCharacteristics

40 bpm• Rate?• Regularity? regular

no relation to QRS

wide (greater than 0.12 s)

• P waves?

• PR interval? none• QRS duration?

SummaryRhythm Rate (beats per

minute)Regularity Comments Treatment

Sinus 60-100 Regular Normal rhythm of heart None

Sinus Bradycardia Less than 60 Regular Slow rhythm-can cause symptoms of decreased cardiac output

If symptomatic: atropine 0.5 mg IV push

Sinus Tachycardia 100 – 150 Regular Fast rhythm-caused by fever, pain, dehydration

Treat the cause

Suprventricular Tachycardia (SVT)

Greater than 150 Regular Fast-can cause symptoms of decreased cardiac output

Adenosine, -blockers, Diltiazem (Cardizem), Cardioversion if unstable

Atrial Fibrillation 350-400 Irregular No p-waves, PR not measurable -blockers, Diltiazem (Cardizem)

Atrial Flutter 250-350 Regular or Irregular

No p-waves, flutter waves—sawtooth pattern

-blockers, Diltiazem (Cardizem)

Premature Ventricular Contractions

Varies—can be normal

Irregular Early beats, wide, bizarre Amiodarone

Ventricular Tachycardia

100-250 Regular Wide, regular, fast; no p-waves Amiodarone—if pulseDefibrillation—if pulseless

Ventricular Fibrillation

Rapid, Chaotic No pattern; Can lead to death Defibrillation!

End of Reading

Summary—Heart BlocksName of Block # p-waves

compared to # QRS complexes

PR interval QRS complexes

Treatment

First degree # p-waves = # QRS complexes

PR interval longer than 0.20; constant

All present Atropine, if slow

Second degree type I

More p-waves than QRS complexes

PR interval gets longer and longer

QRS dropped periodically

Atropine, if slow

Second degree type II

More p-waves than QRS complexes

PR interval is constant

QRS dropped periodically

Transcutaneous pacing

Third degree Complete block

More p-waves than QRS complexes

No PR interval; P to P constant

QRS to QRS constant

Transcutaneous pacing