ECG Rhythm Strip

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Lopes

What are the five steps of calculating a heart rhythm?

-Step 1: Calculate rate.
-Step 2: Determine regularity.
-Step 3: Assess the P waves.
-Step 4: Determine PR interval.
-Step 5: Determine QRS duration.

Schematic representation of a normal ECG.

What is the first option for calculating heart rate?

Count the number of R waves in a 6 second rhythm strip, then multiply by 10.

What is the second option for calculating heart rate?

-Find a R wave that lands on or next to a bold line.
-Count the number of large boxes to the next R wave. If the second R wave is 1 large box away the rate is 300, 2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc.

What is the sequence of heart rates to memorize?

300 - 150 - 100 - 75 - 60 - 50

How do you determine regularity of an ECG?

Look at the R-R distances. If they are equidistant, the ECG is regular.

What is a P wave?

During normal atrial depolarization, the main electrical vector is directed from the SA node towards the AV node, and spreads from the right atrium to the left atrium. This turns into the P wave on the ECG.

What questions do you ask to assess the P waves (4)?

-Are there P waves?
-Do the P waves all look alike?
-Do the P waves occur at a regular rate?
-Is there one P wave before each QRS?

What is the normal P-R interval?

0.12 - 0.20 seconds
(3 - 5 boxes)

What is the normal QRS interval?

0.04 - 0.12 seconds
(1 - 3 boxes)

What are the normal rhythm parameters of a normal sinus rhythm?

-Rate 60 - 100 bpm
-Regularity regular
-P waves normal
-PR interval 0.12 - 0.20 s
-QRS duration 0.04 - 0.12 s

Any deviation from normal sinus rhythm can be what (3)?

-Sinus tachycardia
-Sinus bradycardia
-Arrhythmia

Arrhythmias arise from problems in what (4)?

-Sinus node
-Atrial cells
-AV junction
-Ventricular cells

What is the sequence of normal impulse conduction (5)?

-Sinoatrial node
-AV node
-Bundle of His
-Bundle branches
-Purkinje fibers

List the SA node problems (2)

The SA node can:
-Fire too fast: sinus tachycardia
-Fire too slow: sinus bradycardia

When is sinus tachycardia appropriate or physiologic?

Sinus Tachycardia is considered an appropriate (physiologic) response to stress, whether physical or emotional.

When is sinus bradycardia appropriate or physiologic?

Sinus bradycardia may be physiologic when it occurs at rest or during sleep.

List the atrial cell problems (4).

Atrial cells can:
-Fire occasionally from a focus: premature atrial contractions (PACs)
-Fire continuously due to a looping re-entrant circuit: atrial flutter
-Fire continuously from multiple foci: atrial fibrillation
-Fire continuously due to multiple micro re-entrant "wavelets": atrial flutter

What is a re-entrant pathway?

A re-entrant pathway (e.g., atrial flutter) occurs when an impulse loops and results in self-perpetuating impulse formation.

What are multiple micro re-entrant wavelets?

Multiple micro re-entrant "wavelets" refers to wandering small areas of activation which generate fine chaotic impulses. Colliding wavelets can, in turn, generate new foci of activation, as with atrial fibrillation.

List the AV junctional problems (2).

The AV junction can:
-Fire continuously due to a looping re-entrant circuit: paroxysmal supraventricular tachycardia
-Block impulses coming from the SA node: AV nodal blocks

List the ventricular cell problems (3).

Ventricular cells can:
-Fire occasionally from one or more foci: premature ventricular contractions (PVCs)
-Fire continuously from multiple foci: ventricular fibrillation
-Fire continuously due to a looping re-entrant circuit: ventricular tachycardia

List the different types of arrhythmias (5).

-Sinus rhythms
-Premature beats
-Supraventricular arrhythmias
-Ventricular arrhythmias
-AV nodal blocks

What are the different sinus rhythms that are categorized as arrhythmias (2)?

-Sinus bradycardia
-Sinus tachycardia

What is sinus bradycardia?

It is a heart rhythm that originates from the sinus node and has a rate of under 60 beats per minute.

Sinus bradycardia image.

What is the etiology of sinus bradycardia?

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

How does sinus bradycardia deviate from NSR (1)?

Rate, less than 60bpm.

What is sinus tachycardia?

It is a heart rhythm with elevated rate of impulses originating from the sinoatrial node, defined as a rate greater than 100 beats/min (bpm) in an average adult.

Sinus tachycardia image.

What is the etiology of sinus tachycardia?

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

What is important to note about sinus tachycardia as an arrhythmia?

It is a response to physical or psychological stress, not a primary arrhythmia.

How does sinus tachycardia deviate from NSR (1)

Rate, greater than 100bpm.

What are premature atrial contractions?

They are a common cardiac arrhythmia characterized by premature heartbeats originating in the atria. While the sinoatrial node typically regulates the heartbeat during normal sinus rhythm, PACs occur when another region of the atria depolarizes before the sinoatrial node and thus triggers a premature heartbeat.

Premature atrial contraction image.

What is the etiology of premature atrial contractions?

Excitation of an atrial cell forms an impulse that is then conducted normally through the AV node and ventricles.

What is important to note about conduction in the atria?

When an impulse originates anywhere in the atria (SA node, atrial cells, AV node, Bundle of His) and then is conducted normally through the ventricles, the QRS will be narrow (0.04 - 0.12 s).

How do premature atrial contractions deviate from NSR (3)?

-Regularity, normal with occasional irregularity
-P waves, irregularities have different contour
-PR interval, irregularities have different interval

What are premature ventricular contractions?

They are a relatively common event where the heartbeat is initiated by Purkinje fibres in the ventricles rather than by the sinoatrial node, the normal heartbeat initiator. A PVC may be perceived as a "skipped beat" or felt as palpitations in the chest.

PVC image.

What is the etiology of PVCs?

One or more ventricular cells are depolarizing and the impulses are abnormally conducting through the ventricles.

What is important to note about impulses originating in the ventricles?

When an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.

How do PVCs deviate from the NSR (3)?

-Regularity, occasional irregularity
-P wave, none before the irregular QRS
-QRS duration, irregular QRS is wide

What is important to note about the irregular QRSs?

When there are more than 1 premature beats and they look alike, they are called "unifocal". When they look different, they are called "multifocal".

Multifocal PVC image.

What is normal ventricular conduction?

Signal moves rapidly through the ventricles.

What is abnormal ventricular conduction?

Signal moves slowly through the ventricles.

What are the different kinds of supraventricular arrhythmias (3)?

-Atrial fibrillation
-Atrial flutter
-Paroxysmal supraventricular tachycardia

What is atrial fibrillation?

It is the most common cardiac arrhythmia (irregular heart beat). It may cause no symptoms, but it is often associated with palpitations, fainting, chest pain, or congestive heart failure. In AF, the normal regular electrical impulses generated by the sinoatrial node are overwhelmed by disorganized electrical impulses usually originating in the roots of the pulmonary veins, leading to irregular conduction of impulses to the ventricles which generate the heartbeat.

Atrial fibrillation image.

What is the etiology of atrial fibrillation?

Recent theories suggest that it is due to multiple re-entrant wavelets conducted between the R & L atria. Either way, impulses are formed in a totally unpredictable fashion. The AV node allows some of the impulses to pass through at variable intervals (so rhythm is irregularly irregular).

What are the causes of atrial fibrillation?

It is due to atrial enlargement, from chronic hypertension, heart failure, coronary artery disease and pulmonary disease. Mitral valve disease, thyroid disease and chronic excessive alcohol use are also related.

Why is atrial fibrillation life threatening (2)?

-Very fast rates can prevent the ventricles from emptying, thereby decreasing cardiac output
-Disorganized atrial contraction is associated with the risk of forming thrombi, or blood clots, which can cause strokes. Treatment with warfarin, a blood thinner, helps prevent thrombus formation

How does atrial fibrillation deviate from the NSR (3)?

-Regularity, irregularly irregular
-P waves, none
-PR interval, none

What is atrial flutter?

It is an abnormal heart rhythm that occurs in the atria of the heart. When it first occurs, it is usually associated with a fast heart rate or tachycardia (beats over 100 per minute), and falls into the category of supra-ventricular tachycardias. While this rhythm occurs most often in individuals with cardiovascular disease (e.g. hypertension, coronary artery disease, and cardiomyopathy) and diabetes, it may occur spontaneously in people with otherwise normal hearts.

Atrial flutter image.

What is the etiology of atrial flutter?

Re-entrant pathway in the right atrium with every 2nd or 4th impulse generating a QRS (others are blocked in the AV node as the node repolarizes).

How does atrial flutter deviate from the NSR (3)?

-P waves, flutter waves (sawtooth pattern) formed at an atrial rate of 180 - 350 bpm
-PR interval, none
-Ventricular rate is 1/4 or 1/2 of the atrial rate

What is paroxysmal supraventricular tachycardia?

It is an irregular, rapid heart rhythm originating at or above the atrioventricular node.

Paroxysmal supraventricular tachycardia image.

What is the etiology of PSVT (2)?

-There are several types of PSVT but all originate above the ventricles (therefore the QRS is narrow)
-Most common form: re-entry involving the AV node, atrium, or an accessory pathway between an atrium & ventricle

How does PSVT deviate from the NSR (3)?

-Rate, suddenly speeds up, sometimes with an initiating PAC
-P waves, normal then disappears
-PR interval, normal then nonexistent

What are the different types of ventricular arrhythmias (2)?

-Ventricular tachycardia
-Ventricular fibrillation

What is ventricular tachycardia?

It is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart.

Ventricular tachycardia image.

What is the etiology of ventricular tachycardia (2)?

-There is a re-entrant pathway looping in a ventricle (most common cause)
-Ventricular tachycardia can sometimes generate enough cardiac output to produce a pulse; at other times no pulse can be felt

How does ventricular tachycardia deviate from the NSR (4)?

-Rate, greater than 100bpm
-P waves, none
-PR interval, none
-QRS duration, greater than 0.12s (wide)

What is ventricular fibrillation?

It is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is the most commonly identified arrhythmia in cardiac arrest patients.

Ventricular fibrillation image.

What is the etiology of ventricular fibrillation (2)?

-The ventricular cells are excitable and depolarizing randomly, in a chaotic manner
-Rapid drop in cardiac output and death occurs if not quickly reversed (defibrillation)

How does ventricular fibrillation deviate from the NSR (5)?

-Rate, none
-Regularity, intermediate and chaotic
-P waves, none
-PR interval, none
-QRS duration, none

What is an AV nodal block?

It involves the impairment of the conduction between the atria and ventricles of the heart. Under normal conditions, SA node in the atria sets the pace for the heart, and these impulses travel down to the ventricles. In an AV block, this message does not reach the ventricles or is impaired along the way.

What are the four different kinds of AV nodal blocks?

-1st Degree AV Block
-2nd Degree AV Block, Type I
-2nd Degree AV Block, Type II
-3rd Degree AV Block

Where can a delay in AV conduction occur (3)?

-AV node
-His bundle
-His bundle branches

What are high grade AV nodal blocks?

Those that occur at the His bundle and beyond.

What is a 1st degree AV block?

PR interval greater than 0.20sec.

1st degree AV block image.

What is the etiology of a 1st degree AV block?

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

How does a 1st degree AV block deviate from the NSR (1)?

PR interval, greater than 0.20sec.

What is a 2nd degree AV block, type 1?

Progressive prolongation of PR interval with dropped beats (the PR interval gets longer and longer; finally one beat drops)

2nd degree AV block, type 1 image.

What is the etiology of a 2nd degree AV block, type 1 (2)?

-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
-Often benign and found in children, trained athletes, people with high vagal tone; can also develop secondary to structural damage

How does a 2nd degree AV block, type 1 deviate from the NSR (4)?

-Rate, less than 60bpm
-Regularity, regularly irregular
-P waves, no QRS after 4th P wave
-PR interval, lengthens then drops

What is a 2nd degree AV block, type 2?

PR interval remains unchanged prior to the P wave which suddenly fails to conduct to the ventricles.

2nd degree AV block, type 2 image.

What is the etiology of a 2nd degree AV block, type 2?

Conduction is all or nothing (no prolongation of PR interval); typically block occurs in the Bundle of His or more distally in the Purkinje system.

How does a 2nd degree AV block, type 2 deviate from the NSR (2)?

-Rate, less than 60bpm
-P waves, present but only every third one has a QRS

What is a 3rd degree AV block?

No association between P waves and QRS complexes.

3rd degree AV block image.

What is the etiology of a 3rd degree AV block?

There is complete block of conduction in the AV junction, so the atria and ventricles form impulses independently of each other. Without impulses from the atria, the ventricles own intrinsic pacemaker kicks in at around 30 - 45 beats/minute.

What is important to note about impulse conduction in the ventricles?

When an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.

How does a 3rd degree AV block deviate from the NSR (4)?

-Rate, less than 60bpm
-P waves, no relation to the QRS
-PR interval, none
-QRS duration, wide

What is a wandering pacemaker (2)?

-An irregularly irregular rhythm generated by multiple ectopic atrial foci, usually at a rate < 100 bpm
-When the rate is 100-200 bpm, then it's usually called Multifocal Atrial Tachycardia (MAT)

Wandering pacemaker image.

What is a junctional escape (2)?

-There are junctional pacemakers near the AV node that can rescue an inadequate sinus node by providing just 1 or a continual series of escape beats.
-A junctional rhythm is distinguished by a rate of 40-60 bpm and retrograde P waves occurring before, after or during the QRS

Junctional escape image.

What is junctional rhythm?

It describes an abnormal heart rhythm resulting from impulses coming from a locus of tissue in the area of the atrioventricular node, the "junction" between atria and ventricles.

Junctional rhythm image.

Describe accelerated junctional rhythm.

An accelerated junctional pacemaker rhythm is caused by events that accelerate the automaticity of pacemaker cells (e.g., ischemia, drugs, and electrolyte abnormalities). The rate is 60-100 bpm.

Accelerated junctional rhythm image.

What is ventricular bigeminy?

It is a descriptor for a heart arrhythmia in which abnormal heart beats occur every other concurrent beat.

Ventricular bigeminy image.

What is an idioventricular rhythm (2)?

-A rhythm sometimes seen during an acute MI or following reperfusion of a coronary artery. It probably represents a ventricular escape focus that has accelerated sufficiently to drive the heart
-The rate is usually < 50 bpm. When it is 50-100 bpm, it is usually called an accelerated idioventricular rhythm

Idioventricular rhythm image.

What is torsades de pointes?

-A unique form of ventricular tachycardia
-Develops from a prolonged QT interval

What are the causes of torsades de pointes (3)?

-Inherited form
-Electrolyte disorders: hypocalcemia, hypomagnesemia, hypokalemia
-Drugs: antiarrhythmics, tricyclics, phenothiazines, others

Torsades de pointes image.

What are preexcitation syndromes?

They are characterized by accessory pathways which bypass the AV node, allowing the electrical impulse to arrive more quickly at the ventricles.

What is Wolf-Parkinson-White syndrome (3)?

-The PRI is very short, < 0.12 seconds
-A small region of the myocardium depolarizes early, causing a characteristic slurred initial upstroke called a delta wave

What is the bypass called in WPW?

The bundle of Kent.

WPW is rare, why is it important to know?

50-70% of people with WPW will have at least one event of PSVT or A-fib.

WPW slurred upstroke image.

What is an electrophysiology study (EPS) used for?

It uses cardiac catheterization to precisely map the heart's electrical activity. This can localize the presence and activity of an accessory pathway in order to determine whether tissue ablation is indicated.

What is ablation?

It is removal of material from the surface of an object by vaporization, chipping, or other erosive processes.

How is ablation done?

Via catheterization using radiofrequency to disrupt the accessory pathway.

What is agonal rhythm?

A slow, irregular rhythm with wide ventricular complexes of varying morphology, which is often seen during the latter stages of unsuccessful resuscitation attempts as the heart dies.

Agonal rhythm image.

What is asystole?

Flat line, signifies the absence of cardiac activity.

Asystole image.

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