ECG Basics Module 2( Arrhythmias level 1)

Dr. Jeffrey Elliot Field, HBSc. DDS, Fellow, American Dental Society of AnesthesiaDiploma, the National Dental Board of Anesthesia.

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OBJECTIVESTO LEARN TO INTERPRET BASIC

ARRYTHMIAS

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Lets Review What an ECG Is. An ECG is a recording of the electrical activity

within heart muscle.Heart muscle unlike other muscle can contract

without a an external nerve input or action potential.

The interesting thing about cardiac muscle is: it can depolarize as the result of adjacent cells depolarizing.

Like a wave in the crowd at a football game. Pacemaker cells can spontaneously depolarize as a result of

spontaneous intracellular mechanisms. All other muscle cells only depolarize as the result an external

mechanism ( motor neuron stimulation)This depolarization and repolarization cycle is

what we see on an ECG

Basic Cardiac PhysiologyThe pacemaker sites within the heart are the

SA node, AV node and Purkinge fibers in the heart.

As discussed earlier each pacemaker site within the heart has its own unique firing rate.

As a result the heart rate can often be a clue as to which pacemaker is in charge at that point in time. ( see diagram on next slide)

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HOW TO READ A THREE LEAD RYTHYM STRIP

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The 3 Steps In ECG Determination Are:

1) Establish whether are not there is there electrical activity.

2)Rate determination. 3) Rhythm identification.

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STEP 1IS THERE ANY ELECTRICAL ACTIVITY?IF NO ACTIVITY IS SEEN YOU MUST

FIRST CHECK THE LEADS ARE ADHERING TO THE SKIN AND ALL CONNECTIONS ARE INTACT.

IF THE CONNECTIONS ARE ALL OK, THEN CHECK THE PULSE. IF NO PULSE EXISTS AND IF EVERYTHING IS HOOKED UP PROPERLY AND THERE IS NO ELECTRICAL ACTIVITY ,THEN A DIAGNOSIS OF ASYSTOLE IS MADE.

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Note: In asystole the straight baseline wanders. If a true straight line exists this usually indicates that a lead has come loose.

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P wave AsystoleIn this case asystole exists even though

there is P wave electrical activity . Please note that there is NO ventricular activity and therefore NO blood Flow.

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AGONAL RYTHYMThis is another example of asystole in

which the heart displays the last moments of it’s electrical activity. This rhythm is also called dying heart.

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To REVIEW , THESE ARE THE THREE FORMS OF ASYSTOLE

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Next if there is electrical activity is there a rhythm ?

If there is no rhythm then think about ventricular fibrillation ( V-fib).

V-fib can be categorized as follows: Fine V-fib Coarse V-ifib Torsades De Pointes ( twisting pointes)

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Step 2 Basic Rhythm Determination

Fine V-Fib

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Coarse V-fib

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Torsades de pointes ( twisting points)

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This is often a sign of hypomagnesemia

( low magnesium)

What,s really happening in V-Fib ?

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Immediate action is required!!!

STEP 2 RATE DETERMINATION

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HOW TO EVALUATE TIME/RATE ON STANDARD ECG PAPER

04/19/23 21There are 15 large boxes in every 3 seconds

Since the ECG paper moves at 25 mm/second and therefore 25 of the 1.0 mm ( small)boxes or 5 of the big boxes pass in one second.Therefore 1 small box = 0.04 seconds and 5 small boxes or 1 big box =0.20 seconds( as discussed in module1).Now you have all the information you need to calculate rates

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There Are 3 Methods To Determine Rate1) Counting the R-waves per minute with respect to the large boxes on the ECG paper.

2)Quick rate determination) Counting R-waves per minute with respect to small boxes on the ECG paper.

QUICK METHOD FOR RATE DETERMINATION.It is possible to now calculate rate by

counting the number of R waves in one minute. However this is very tedious and time consuming.

The quick method involves memorizing the following chart which entails counting the number of large boxes ( i.e. 5 small boxes) between R waves.

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Quick Method of Rate Determination

Number of large boxes between R-waves 1 2 3 4 5 6 7 8 9 10

A final method is to count the number of small ( 1.0mm) boxes between 2 consecutive R waves and divide this into 1500.

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CAN YOU DETERMINE THIS RATE?

04/19/23 2775 bpm

RATE NOMENCLATURENormal heart rates are from 60-100 beats per minute.

Rates above 100 are termed tachycardia.

Rates below 60 are termed bradycardia.

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TachycardiasTachycardia's can be divided into two groups.

-Supraventricular are tachycardia's in which the pacemaker site is above the AV node. In this case the QRS width is normal (under 0.12 seconds or 3 small boxes)

Supraventricular tachycardia's are: Paroxysmal super ventricular tachycardia( an SVT

that comes and goes) Supraventricular tachycardia( a sustained SVT) Atrial flutter( a characteristic type of sustained SVT)

Ventricular Tachycardia's ( also called wide complex tachycardia's) are tachycardia’s in which the pacemaker lies below the AV node. In this case the QRS width is prolonged. (over 0.12 seconds or 3 small boxes)

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Superventricular Tachycardia

Atrial Flutter ( Note the characteristic sawtooth pattern)

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Classic Ventricular Tachycardia ( VTACH)

Ventricular Tachycardia with Capture Beats( see ). That is there are quasi normal beats interspersed between the wide complex beats.

Clinical Relevance of TachycardiasWith each heart beat blood is ejected from

the ventricles . 70% of the refill of the ventricles is passive.

That is after the ventricle squeezes the blood out it relaxes and blood is passively drawn in.

The final 30% of ventricular filling is the result of active pushing of blood from the atria ( also called the atrial kick) . With atrial flutter and atrial fibrillation you loose the atrial kick.

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also as the rate increases the time available for passive ventricular filling is decreased.

therefore less and less blood is moved which

leads to a decrease in the pulse or even loss of the pulse.

In this case the organs and tissue receive little or no blood and in turn little or no oxygen.

With atrial flutter and atrial fibrillation the loss of the atrial kick ends in poor tissue perfusion. This is also called a loss of perfusion pressure.

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Rhythm Determination

STEP 3 IS TO DETERMINE THE RYTHYMThis is done by looking at the following

factors.-Is the rhythm regular or irregular-Is the QRS complex width normal or

prolonged-Is atrial activity present and if present how

does the atrial activity relate to the ventricular activity

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IS THE RYTHYM REGULAR OR IRREGULARLook at the R-R intervals and see if they all

are the same. If so the rhythm is regular.If not, is the rhythm totally irregular ? {“

irregularly irregular”} or is there cyclical variation (i.e. the pattern

is irregular but repeats)

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Use calipers to mark out the R-R interval and see if it repeats. If it does, it’s a regular rhythm and if it doesn’t, it is irregular.

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Regular Rhythms

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Sinus Rhythm

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Diagnosis of Sinus Rhythm 1)P-waves are present, upright and precede each QRS complex2)The P-R interval is normal (0.12-2.0 seconds)3)QRS complexes are of normal (less than o.12 seconds) size and morphology( no pathologic Q waves-see later module)4)The Q-T interval is normal in duration ( around 10 small boxes based on rate-see later discusson on the QT interval)5)The T-wave is upright

Paced Rhythm

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Note the pacer spikes which generate a QRS complex

Irregular Rhythms

IRREGULARLY IRREGULAR RhythmThis is always atrial fibrillation. In this case the atrial cells are firing off in a non

coordinated pattern which causes the atria to quiver rather than contract. This of course moves NO BLOOD.

Blood still however moves between the atria and ventricles but only via passive filling such that you loose the 30% of ventricular filling given by the atrial kick.

Different pacemaker sites within the atria in random order cause ventricular depolarization, which leads to the irregularly irregular rhythm.

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Note there are no P-waves.

You can see QRS complexes but there is NO PATTERN to the R-R interval. That is each R-R interval is different. Hence the rhythm is irregularly irregular.

Atrial fibrillation

OTHER CAUSES OF IRREGULAR, BUT CYCLICALLY REPEATING RYTHYMS

Ectopic beats such as:-PVC’s ( Premature ventricular

contractions). -Junctional Escape rhythms PAC’s ( Premature atrial contactions) -

Escape beats where a pacemaker in the atria other than the SA node generates the beat.

Heart Blocks or AV nodal blocks

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PVC’s ClassificationPVC’s are a premature ventricular contraction.

That is the ventricle contracts on its own, without receiving a signal from the SA node.These are classified as follows:

1)UNIFOCAL( originating from the same site in the ventricle). Therefore all PVC’s look exactly alike.

2) MULTIFOCAL( originating from different sites in the ventricle). Such that the PVC’s have different morphologies.

3) PVC Nomenclature: BIGEMINY ( one normal beat alternating with a PVC) , TRIGEMINY two normal beats followed by a PVC) etc .

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Examples of Unifocal and Mutifocal PVC’s04/19/23 46

Unifocal PVC ( both PVC’s look alike)

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Multifocal PVC’s ↑ ( with run of unifocal PVC’s) (↑ run of unifocal PVC’s)

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↑ ↑↑↑ ↑

Why are PVC’S Important?

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The Answer is the R on T PhenomenonIn these cases if a PVC’s R-wave falls on the

previous QRS’s T-wave, this can generate a run of ventricular fibrillation.

This usually is not an issue with single unifocal PVC’s but becomes a worry in cases with multifocal PVC’s or runs of unifocal PVC’s. In these cases you should treat the PVC’s with either lidocaine or amiodarone.

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R on T Phenomenon triggering course V-fib.

04/19/23 51 ↑note the triggered run of V-fib

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Junctional Beats and Rhythms

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Note the lack of a P-wave ↑ in the junctional escape beat.

This signifies a lack of atrial depolarization associated with this beat. In other words this beat originated at or just above the AV node because the QRS width is normal but

there is no P-wave.

Junctional Beats

Junctional Rythms

Note the slow rate and lack of a P-wave. This rhythm is being generated in or just below the AV-node as evidenced by the widened QRS complex and lack of a P-wave.

Premature Atrial ContractionThis occurs when a pacemaker in the atria other than the SA node initiates an

impulse. This results in 2 possible phenomenon:

1)A QRS complex is produced by the PAC2)A QRS complex is not produced by the

PAC

In either case there is usually some pause in the rhythm following the PAC.

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Why Is There A Pause In The Cycle ?The ectopic P-wave generates a QRS complex such that when the normal p-wave occurs, the ventricle is in its refractory phase and cannot produce a QRS complex.

That is why there is a pause in the cycle.

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In this Case the PAC generates a QRS complex but there is a pause in the cycle following the PAC

PAC Pause

The Fates of PAC’s

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Heart Blocks

Heart Blocks. Know When To Be Concerned!!!There are 3 types of heart blocks, also called

AV blocks ( AV refers to the AV node):First degree heart block/AV block.Second degree heart block/AV block. Second

degree heart block has 2 subdivisions. Second degree block type one( also called Mobitz

One). Second degree block type two (Als0 called Mobitz

Two).Third degree heart block/AV block.

Know When To Be Concerned!!!First degree and second degree type 1 blocks are usually very stable and are not of much concern.

Alternatively second degree type 2 and third degree heart blocks are of great concern.

Know When To Be Concerned!!!Second degree type 2 blocks can deteriorate to third degree blocks.

Third degree blocks require immediate pacing in most instances as they only support rates of under 40-60 bpm and usually are more in the 40s.

How to Diagnose Heart Blocks

First DEGREE AV BLOCKIn First degree AV Block there is a constant

prolongation of the PR interval above 0.20 seconds or 5 small boxes. This is a fixed conduction block such that the P-R interval does not vary beat to beat.

Remember the PR interval is measured from the beginning of the P-wave to the beginning of the Q-wave.

First degree heart block is usually not of great concern clinically.

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Note the P-R interval is actually 9 small boxes which equals 0.36 sec not 0.35 as the author of the image notes.

First degree Heart Block

Second Degree AV block(Types 1 and 2)

2. Type 2 (Mobitz 2) heart block.

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1. Type 1 (Mobitz 1) heart block.

Type 1 “Mobitz 1” Block

Almost always a disease of the AV NodeWith 2nd degree type 1 heart block

there is progressive prolongation of the P-R interval beat to beat until a beat is dropped.

Once the beat is dropped the PR interval returns to normal or almost normal and the cycle repeats.

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Note the progressive lengthening of the PR intervals, before a beat is dropped.

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Second Degree Heart Block Type 1

Second degree heart block type 1 if stable is similarly not of great concern but no treatment should be provided without first consulting the patient’s physician.

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Second Degree Heart Block Type 2 “Mobitz 2” Block

Second degree heart block type 2 is almost always a disease of the distal conduction system (His-Purkinge System).

Second degree heart block type 2 is characterized by a fixed conduction block ( increased PR Interval that is stable ,beat to beat) with dropped beats.

Second degree heart block type 2 is also named or classified for the degree of blockade( i.e. the number of propagated beats).

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Mobitz Type 2 with a 2:1 heart block ( only every second beats is propogated)

Mobitz Type 2 with a 3:1 heart block ( every third beat is propogated)

Non propogatedP-waves

Second degree heart block type 2 is of great concern as these often deteriorate into Third degree heart block (Complete Heart Block)

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Third Degree Heart BlockThe impulse generated in the atria does not propagate to the ventricles.

So, there is a complete dissociation of the P-waves and the R-waves.

The P-waves occur at regular intervals and seem to “March through the R waves”.

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↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑

Note the p-waves (↑) are marching through at regular intervals even at times being buried(↑) in the QRS complexes. There is no association between the p-waves and the QRS complexes. (see red arrows)

With third degree heart block The ventricles are contracting at

their own inherent rate of 20-40 beats per minute

This often is a life threatening occurrence as this rate usually fails to maintain an adequate perfusion pressure( adequate perfusion is when blood flow maintains adequate tissue oxygenation)

These patients usually require immediate pacing.

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Where do heart blocks occur?

END OF PRESENTATIONThank you for your commitment to

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