Week 1/2 - A(2) - Yr 4 ECG Module (Section 3) - Rhythms - Supraventricular/ventricular, Aberrancy, Heart block, Cardiac arrest

Question 1

What is the stepwise approach to analysing a an ECG?

Answer 1

* Rate * Rhythm * Axis * P-waves * PR interval * QRS complex * ST segment * QT interval * Twave

Question 2

What are the 6 questions to ask yourself to help determine the rhythm?

Answer 2

Rhythm Is there electrical activity? Are there p-waves presents? What is the QRS rate? Are the QRS complexes irregular/regular? Are the QRS complexes broad/narrow? What is the relationship between p waves and QRS complexes?

Question 3

SUPRAVENTRICULAR RHYTHMS Supraventricular rhythms are any rhythm which originates above the AV node, whether it is conducted through it or not Give examples of these rhythms? What happens to the QRS complex in supraventricular rhythms?

Answer 3

Supraventricular rhythms usually have a narrow QRS complex Causes eg * Sinus rhythm * Sinus arryhtmia * Atrial fibrillation * Atrial flutter * Supraventricular tachycardia * AV nodal re-entry tachycardiaa * AV re-entry (reciprocating) tachycardia * Wandering atrial pacemaker

Question 4

In normal sinus rhythm, what is the relationship between P waves and QRS complexes?

Answer 4

Every P wave is followed by a QRS complex Every QRS complex is preceded by a P wave (1:1 relationship_

Question 5

What happens in sinus rhythm ie Where is atrial contraction initiated? What is the potential propogated through? What is the delay?

Answer 5

In normal sinus rhythm atrial contraction is initiated by SA node depolarisation which is propogated through the AV node to the ventricle after a delay <200ms (PR interval 0.12 to 0.2 seconds) This delay ensures that the atria have ejected their blood into the ventricles first before the ventricles contract

Question 6

Is sinus arrhythmia considered to be a normal variant (physiological variant) or a pathological variant? Describe the rhythm?

Answer 6

Sinus arrhythmia is considered to be a physiological variant of sinus rhythm It occurs when the ECG meets all the criteria of a normal sinus rhythm but the rhythm itself is irregular * Every P-wave followed by a QRS complex * Every QRS complex preceded by a P-wave * PR interval

Question 7

Why cause the RR interval irregularity in sinus arrhythmia?

Answer 7

The RR interval is irregular due to physiological changes in the cardiac timing caused by changes in vagal tone during respiration

Question 8

What happens in atrial fibrillation to the electrical activity that is meant to go from SA node through the atrial mycoardium and to the AV node?

Answer 8

Atrial fibrillation occurs due to disorganised electrical activity in the atria * The impulses no longer travel from the SA node through the atrial myocardium and to the AV node * The AV node receives continuing electrical impulses and conducts some of these to the ventricle

Question 9

What is atrial fibrillation characterised by on the ECG?

Answer 9

Atrial fibrillation is characterised by * No P waves * Ragged/wavy baseline * Irregularly irregular QRS complexes

Question 10

What is atrial flutter caused by? What is the rate in atrial flutter?

Answer 10

Atrial flutter is a regular, usually narrow complex tachycardia It is caused by a re-entry circuit within the atria The re-entry circuit within the atria results in an atrial rate of 300bpm. The AV node filters this in a ventiruclar rate so that the rate of patients heart rate is a divisible of 300 (150, 100, 75 bpm).

Question 11

Describe they rhythm in atrial flutter?

Answer 11

Regular rhythm Regular QRS complexes - rate is usually divisble into 300 Saw tooth baseline

Question 12

What is a junctional rhythm? Where does the rhythm originate and how does it spread?

Answer 12

Junctional rhythm- the electrical impulse starts in the AV node (the “junction” between atria and ventricles.) instead of the SA node (automaticity of the AV node) Therefore this results in the electrical impulse travelling simultaneously to the atria and ventricles

Question 13

How does a junctional rhythm appear on the ECG?

Answer 13

Due to the electrical impulse travelling simultaneously to the atria and ventricles, this often results in an inverted pwave (potential travel away from recording electrode) which is seen just after the QRS complex. Regular rhythm P wave may be seen in QRS or retrograde

Question 14

A supraventricular tachycardia is a tachycardia that originates above or involves the AV node Although the term technically covers sinus tachycardia, atrial fibrillation and atrial flutter, these are normally excluded Generally what is the term supraventricular tachycardia used to describe?

Answer 14

SVT is used to describe - Involvement of the AV node itself AVNRT (AV nodal re-entrant tacychycardia (IMAGE A) An accessory pathway - AVRT (AV re-entrant tachycardia) ie WPW syndrome (IMAGE B) (less commonly can originate in the atria (IMAGE C) or SA node)

Question 15

How does the ECG appear in supraventricular tachycardias?

Answer 15

The ECG shows a regular, narrow complex tachycardia with often no clear p-waves preceding the QRS for each beat May sometimes have a retrograde p-wave (in AVNRT)

Question 16

How is a supraventricular ecoptic characterised on ECG?

Answer 16

Supraventricular ectopic occurs due to an ectopic beat occurring above the ventricles in atria or AVN ECG In normal sinus rhythym (Pwave for every QRS, every QRS preceded by pwave, PR interval <200ms) P, QRS an T waves present BUT P wave morphology changes due to ectopic beat (atrial ectopic in image)

Question 17

What causes a supraventricular atrial ectopic beat?

Answer 17

A supraventricular atrial ectopic beat is usually due to a group of atrial cells outpacing the SAN - causes a change in p-wave morphology as seen on previous card

Question 18

VENTRICULAR RHYTHMS Ventricular rhythms originate in the ventricle Supraventricular rhythms can be physiological (such as sinus arrhythmia (caused by increased vagal tone during respiration causing an increase in RR in terval)) but are usually pathological * Which ventricular rhythms are physiological? * What happens to the QRS complexes * What must ventricular rhythms be differentiated from?

Answer 18

Ventricular rhythms are always PATHOLOGICAL and always cause a broad QRS complex (QRS >0.12 seconds) Ventricular rhythms need to be differentiated from thos conducted with abberancy (will explain in later cards) (eg supraventricular rhythm with a bundle branch block)

Question 19

What is a ventricular premature complex? What is it also known as?

Answer 19

Ventricular premature complex (VPC) (aka ventricular premature beat (VPB) or premature ventricular contraction (PVC)) are single ventricular impulses usually arising due to ectopic automaticity of the ventricular cells or re-entry signalling within the ventricle

Question 20

What is the difference between ventricular bigeminy and ventricular trigeminy?

Answer 20

In ventricular bigeminy, the heart beats with one sinus beat and one abnormal premature ventricular complex In ventricular trigeminy, the heart beats with one sinus beat and two abnormal premature ventricular complexes

Question 21

How would you describe a ventricular tachycardia? What is the difference between appearance monomorphic and polymporhic ventricular tachycardia?

Answer 21

Ventricular tachycardia is regular a broad complex (QRS>0.12seconds) tachycardia Monomrphic VT has identical appearing QRS complexes Polymorphic VT has irregular varying QRS complexes

Question 22

What is a polymporhic VT also known as and what is it said to look like? What is it often associated with?

Answer 22

A polymorphic VT is also known as Torsade de pointes (twisting around the point) - it has the appearance of the Forth Rail Bridge It may be difficult to discern from ventricular fibrillation Polymporphic VT is often associated with long QT syndrome

Question 23

What is the phenomonen seen in cases of polymorphic ventricular tachycarda? - usually precedes the tachycardia

Answer 23

The “R-on-T phenomenon” is the superimposition of an ectopic ventricular beat on the T wave of a preceding beat - this is likely to initiate sustained ventricular tachyarrythmias

Question 24

What may ventricular tachycardia frequently deteriorate to if not treated? How does this appear on ECG? Does patient pass out or not?

Answer 24

Ventricular tachycardia may deteriorate to ventricular fibrillation Irregular random baselines, no clear discernable waveforms. ALWAYS ASSOCIATED WITH LOSS OF CONSCIOUSNESS

Question 25

What is useful to help differentiate between a ventricular tachycardia and a SVT with abberancy? If in doubt treat as VT

Answer 25

The presence of capture and fusion beats signifies that this is a ventricular tacycardia instead of SVT with abberancy

Question 26

What is a capture beat and what is a fusion beat?

Answer 26

A capture beat is the presence of a normal QRS amongst runs of VT - would not be expected if the QRS breadth was down to BBB or metabolic causes A fusion beat is when a normal beat fuses with a VT complex creating an unsual complex

Question 27

The hallmark of a rhythm that originates in the ventricle is that the QRS complex is broad. However this can also occur with supraventricular rhythms. How can this occur in a SVT and what is it known as?

Answer 27

When a supraventricular tachycardia occurs there is usually a narrow QRS complex. If it is broad it is called a SVT with abberancy It occurs when there is a superventricular tachycardia that occurs with a left or right bundle branch block which causes the QRS complex to become wide

Question 28

SVT with aberrancy vs Ventricular tachycardia What is a good predictor of SVT with aberrancy? What is a good predictor of it being VT? What are fusion and capture beats diagnostic off?

Answer 28

A good predictor of SVT with aberrancy is the pre-existence of LBBB / RBBB A good predictor of VT is pre-existing coronary disease Capture an fusion beats are almost always diagnostic of Vt

Question 29

What is heart block? What should it not be confused with? What part of the heart conduction is it due to?

Answer 29

Heart block is the term given to a block in conduction between the atria and ventricles due to AV nodal dysfunction (it is also known as AV block) DO NOT CONFUSE WITH BUNDLE BRANCH BLOCK

Question 30

Name some causes of heart block?

Answer 30

Heart block is caused by different causes * Age related * Ischaemic heart disease * Drugs

Question 31

Types * 1st degree * 2nd degree * Mobitz Type 1 * Mobitz Type 2 3rd degree Describe how 1st degree heart block appears on the ECG?

Answer 31

1st degree heart block Regular rhythm with prolonged PR interval (PR>0.2s) with no progressive lengthening

Question 32

What are the types of 2nd degree heart block? Which is considered more benign?

Answer 32

Mobitz type 1 heart block is considered a more benign entity than Mobitz type 2 heart block

Question 33

State the differences between Mobitz 1 and 2 on an ECG?

Answer 33

Mobitz 1 - characterised by an progressive PR elongation until there is eventually a missed beat - eventually a pwave occurs without a QRS complex following Mobitz 2 - characterised by constant PR interval and then a missed beat - pwave not followed by a QRS complex

Question 34

What is the difference in the treatment of Mobitz type 1 and 2 AV block?

Answer 34

Mobitz type 1 may be normal and does not usually require treatment Mobit type 2 needs intervention as it can progress to complete heart block / asystole

Question 35

Describe how 3rd degree heart block looks on ECG? How is rhyhtm maintained?

Answer 35

Complete hear block aka 3rd degree heart block there is no relationship between pwaves and QRS complex - completely irregular PR interval - this is because there is no communication between atria and ventricle Broad QRS complexes appear due to ventricular escape rhythms

Question 36

Normally heart rate is controlled by the SA node. All cells within the heart are capable of automaticity ie if electrically isolated they will continue to depolarise at a given rate. The SA node has the highest rate, followed by the AV node, the his bundle and subsequently the ventricular myocardium Why does the ventricular escape rhythm arise? What does it cause?

Answer 36

The ventricular escape rhythm arises due to an ectopic automaticity in the ventricles which causes the ventricles to contract - occurs at around 30-40bpm and is broad, regular and dissociated from atrial activity The broad QRS complexes in image are due to ventricular escape rhythms

Question 37

We refer to the fascicles (bundle of nerve or muscle fibres) in the heart as * AV node * The right bundle branch (RBB) * Left bundle branch (LBB) contains two * The left anterior fascicle (LAHB) * The left posterior fascicle (LPHB) What is the blockage of any of these known as? What is the blockage known as when each individual fasiccle is blocked?

Answer 37

Blockage of any of the fascicles is known as ……. FASCICULAR BLOCK AV node block - heart block Right bundle branch being blocked –> right bundle branch block Left anterior fascicle being blocked - left anterior hemiblock Left posterior fascicle being blocked - left posterior hemiblock

Question 38

Fascicular block can be bifascicular or trifascicular What are the criteria for bifascicular block?

Answer 38

Bi-fasicicular block = 2 out of the three following PR > 200ms ( due to AV block) Left axis deviation (due to left anterior fasicular block aka left anterior hemiblock) Right bundle branch block Image shows PR>200ms, left axis deviation and RBBB (just to show what all three look like)

Question 39

What are the two different criteria for trifascicular block?

Answer 39

Trifascicular block - All three of (TOP IMAGE) * PR>200ms * Left axis deviation * RBBB or (BOTTOM IMAGE) * Alternating LBBB and RBBB

Question 40

Cardiac arrest is a sudden loss of blood flow resulting from the failure of the heart to pump effectively. It is important for early identification of cardiac arrest rhythms Try and name the rhythms which can cause cardiac arrest? What are the shockable rhythms and which are non shockable?

Answer 40

Shockable rhythms causing cardiac arrest include pulseless ventricular tachycardia and ventricular fibrillation Non shockable rhythms include pulseless electrical activity and asystole (terminal rhythm sequence)

Question 41

Describe both ventricular tachycardia and ventricular fibrillation? When is ventricular tachycardia thought to cause cardiac arrest?

Answer 41

Ventricular tachycardia - regular broad complex tachycardia - if pulseless in carotids then assume cardiac arrest Ventricular fibrillation - ireegular random baseline with no clear waveforms, always associated with LOC and pulseless

Question 42

What is the initial treatment of shockable cardiac arrest? When are drugs considered?

Answer 42

COntinous CPR - stop when giving shck INITIAL treatment once rhythm is identified is to DC cardiovert If rhythm persists after 3 shocks, give drugs - adrenaline and amiodorane

Question 43

Describe both pulseless electrical activity and asystole?

Answer 43

Pulseless elcetrical activiy - cardiac arrest occurring with any rhythm which would usually be associated with a pulse Asystole (terminal rhythm sequence)- cardiac flatline - total cessation of electrical acitvity from the heart

Question 44

What is the treatment of non-shockable cardiac arrest?

Answer 44

Continuous CPR (30 chest compression : 2 breaths) Give adrenaline to the patient every 3-5 mins once the rhythm has been identified (adrenaline increases arterial blood pressure and cornoary perfusion during CPR via alpha-1-adrenoreceptor agonist effect)

Question 45

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Answer 45

Atrial fibrillation - due to disorganised electricala ctivity within the atria No P waves Ragged/wavy baseline Irregularly irregular QRS complexes

Question 46

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Answer 46

Ventricular tachycardia - the QRS complexes would be broad

Question 47

What is the most likely rhythm in this ECG? * VF * AF with aberrant conduction * VT * Sinus tachycardia with aberrant conduction * Atrial flutter with aberrant conduction

Answer 47

QRS complexes are broad so must be ventricular in origin or supraventricular with aberrancy - all options remain Won’t be sinus tachy or atrial flutter due to irregular QRS complexes No p-waves are clear Potential LBBB in lead II Correct answer = AF with aberrant conudction - can almost make out an irregular irregualr QRS complex and LBBB