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CVS > Arrhythmias - Pathophysiology, presentation and investigation > Flashcards

Arrhythmias - Pathophysiology, presentation and investigation Flashcards

1
Q

Skip

Learning Outcomes for arrhythmias

A
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2
Q

What is meant by normal sinus rhythm?

A

Normal heart rhythm with electrical activation beginning in the SA node

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3
Q

Which lead is the best to assess rhythm?

A

Whichever lead that shows the P wave most clearly, usually limb lead 2 or V1

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4
Q

What is the PR interval?

A

Time taken for wave of depolarisation to travel from SA node to ventricular muscle

(usually no longer than 220 ms (6 boxes))

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5
Q

What is meant by first degree heart block?

A

Delay in conduction pathway from SA node to ventricles

Characteristic prolonged PR interval

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6
Q

What are the casues of first degree heart block?

A
  • Coronary artery disease
  • acute rheumatic carditis
  • digoxin toxicity
  • electrolyte disturbances
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7
Q

What is meant by second degree heart block?

A

On intermittent occasion, excitation completely fails to pass through AV node or bundle of His

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8
Q

What are the three different types of second degree heart block?

A

Mobitz type 1

Mobitz type 2

2:1 / 3:1 / 4:1 conduction

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9
Q

What is mobitz type 1 heart block?

A

Progressive lengthening of PR interval, then failure of conduction of an atrial beat

Followed by conducted beat with shorter PR interval then repetition of this cycle

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10
Q

What is mobitz type 2 heart block?

A

Most beats are conducted with a constant PR interval, occasional atrial depolarisation without subsequent ventricular depolarisation

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11
Q

What is meant by 2:1 / 3:1 / 4:1 conduction?

A

Alternate conducted and non-conducted atrial beats (or one conducted atrial beat and then two or three nonconducted beats)

Gives twice (three/four times) as many P waves as QRS complexes

‘2:1’ (‘two to one’), ‘3:1’ (‘three to one’) or ‘4:1’ (‘four to one’) conduction

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12
Q

What is meant by third degree heart block?

A

Complete heart block

Normal atrial contraction but no beats conducted to ventricles

When this occurs ventricles are excited by slow ‘escape mechanism’ from a depolarising focus within ventricular muscle

No relationship between P waves and QRS complexes

Abnormally shaped QRS complexes,

because of abnormal spread of depolarization from a ventricular focus

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13
Q

What is the effect on QRS complexes in third degree heart block

A

No relationship between P waves and QRS complexes

Abnormally shaped QRS complexes,

Due to abnormal spread of depolarization from a ventricular focus

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14
Q

What causes third degree heart block?

A

Acute - Patients with MI (when it is usually transient)

Chronic - due to fibrosis around bundle of His

Caused by block of both bundle branches

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15
Q

What are the common causes of heart block?

A
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16
Q

Where does mobitz 1 and mobitz 2 take place?

A

Mobitz 1 - AV node, healthy people, no symptoms, rarely needs treatment

Mobitz 2 - below AV node in other conduction tissue

  • aging
  • Significant heart disease
  • Large heart attack
  • Lightheadedness, fainting
  • May progress to 3rd degree
  • Requires pacemaker
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17
Q

What causes third degree heart block?

A
  • Aging
  • medicines
  • heart attacks
  • infiltrative heart diseases (amyloidosis, sarcoidosis)
  • infectious diseases (endocarditis, Chagas disease)
  • May occur after heart surgery
  • Can be present from birth (congenital)
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18
Q

What are the presentations of third degree heart block?

A

Fainting, light headedness

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19
Q

When is heart rhythm said to be arrhythmia?

A

Depolarisation sequence begins somewhere out with SA node

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20
Q

What can control the rhythm of contraction in the ventricles?

A

Most parts of the heart can depolarize spontaneously and rhythmically

Rate of ventricle contraction controlled by part of heart depolarizing most frequently

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21
Q

What makes up suprventricular rhythm?

A

Sinus rhythm, atrial rhythm and junctional rhythm

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22
Q

Which rhythms have narrow/wide QRS complexes?

A
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23
Q

What is the rate of contraction in supraventricular / ventricular rhythm?

A

Atrial muscle or the area around the AV node (the junctional region) have spontaneous depolarization frequencies of 50/min

If these fail, or if conduction through His bundle is blocked, ventricular focus will take over ventricular rate will be 30/min.

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24
Q

Why are escape rhythms called escape rhythms?

A

Occur when secondary sites for initiating depolarization escape from their normal inhibition by the more active SA node

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25
Q

What does atrial flutter look like on an ECG?

A

Atrial rate is greater than 250/min, no flat baseline between P waves, ‘atrial flutter’ is present

26
Q

What is meant by fibrillation?

A

Individual muscle fibres contract independently

27
Q

Explain why there are irregular QRS complexes present in atrial fibrillation

A

Depolarization spreads at irregular intervals down the His bundle

AV node conduction, ‘all or nothing’, depolarization waves passing into His bundle have constant intensity

Waves are irregular, and ventricles contract irregularly

28
Q

What is meant by supraventricular tachycardia?

A

Involves, atrial tachycardia, atrial flutter and nodal tachycardia

29
Q

Why are some of the P waves not followed by a QRS complex in atrial tachycardia?

A

Atria depolarise faster than 150/min

AV node cannot conduct atrial rates of discharge greater than 200/min

If atrial rate is faster than this, ‘atrioventricular block’ occurs, with some P waves not followed by QRS complexes

30
Q

Explain the relationship between the P wave and the QRS complex in nodal tachycardia?

A

If area around AV node depolarises frequently, P waves may be seen very close to QRS complexes, or may not be seen at all

QRS complex has normal shape due to other supraventricular arrhythmias, ventricles are activated by His bundle in normal way

31
Q

What is the diffrence between atrial tachycardia and heart block?

A

AV node working properly vs AV node and possible HIS bundle not working properly

32
Q

What is meant by the Wolff–Parkinson–White syndrome?

A

‘accessory’ conducting bundle, forms direct connection between atrium and ventricle

Left side of the heart

No AV node to delay conduction. Depolarization wave reaches ventricle early, and ‘pre-excitation’ occurs

PR interval is short, QRS complex shows early slurred upstroke called a ‘delta wave’

Second part of QRS complex is normal, conduction through His bundle catches up with pre-excitation

33
Q

What is meant by ventricular tachycardia?

A

If focus in ventricular muscle depolarises with high frequency

34
Q

What is seen on an ECG of ventricular tachycardia?

A

Excitation has to spread by abnormal path through ventricular muscle, QRS complex is wide and abnormal

Wide and abnormal complexes are seen in all 12 leads of standard ECG

35
Q

What is meant by sinus tachycardia?

A

Asinus rhythm with elevated rate of impulses

Rate greater than 100 beats/min (bpm) in average adult.

Three or less large squares between QRS complexes represents tachycardia on ECG sheet

36
Q

How do you calculate heart rate in a patient with irregular qrs complexes?

A

Count number of QRS complexes over 30 large squares (corresponds to 6s) then multiply by 10 to give number of beats per min

37
Q

Define sinus bradycardia

A

Sinus rhythm with rate lower than normal

Rate under 60 beats per min

QRS complex present every 5 boxes or more

38
Q

Define sinus arrest

A

Sinoatrial node of heart transiently stops generating electrical impulses.

Lasts 2s to several minutes

Since heart has multiple pacemakers, interruption only lasts a few seconds before another part of heart begins pacing and restores heart action

39
Q

What is meant by extrasytole or ectopic beat?

A

Premature contraction of heart independent of normal rhythm

Arises in response to impulse in some part of heart other than normal impulse from SA

Extrasystole followed by pause, as heart electrical system “resets”

Contraction following pause is more forceful than normal, frequently perceived as palpitations

40
Q

What is an atrial extrasystole seen as?

A

Looks similar to atrial escape beat where abnormal P wave is seen because excitation of atrium has begun somewhere other than SA node

Extrasystole comes early and escape beat comes late

41
Q

What do junctional extrasystoles look like?

A

No P wave or P wave appears immediately before or after QRS complex

42
Q

Describe ventricular extrasystole

A

Abnormal QRS complexes, typically wide and almost any shape

Common, usually of no importance

If they occur early in T wave of preceding beat they can induce ventricular fibrillation, potentially dangerous

43
Q

Discuss the prevalence of af in england

A

1.36 million have AF. 2.4% of population

AF prevalence higher in men than women, 2.8% v 2.0%

AF prevalence increases with age

2.9% of total estimated AF in population likely to occur in people aged under 45, 16.6% aged 45-65 and 80.5% over 65

44
Q

What are the signs and symptoms of AF?

A

AF causes ventricles to contract faster than normal

Ventricles can’t completely fill with blood

May not be able to pump enough blood to lungs and body, can lead to signs and symptoms, such as:

Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)

Shortness of breath

Weakness or problems exercising

Chest pain

Dizziness or fainting

Fatigue (tiredness)

Confusion

45
Q

What is thetreatment for atrial fibrilaltion?

A

Rule out over active thyroid, medication to treat overactive thyroid may stop af

Medicines - control af (sub divided into medication that can either restore heart rhythm or control the rate at which the heart beats)

Anticoagulation - prevent risk of stroke (warfarin or a newer type of anticoagulant, such as dabigatran, rivaroxaban, apixaban or edoxaban)

Cardioversion (It involves giving the heart a controlled electric shock to try to restore a normal rhythm.)

Pacemaker

Catheter ablation (a procedure that very carefully destroys the diseased area of your heart and interrupts abnormal electrical circuits.)

(Catheters (thin, soft wires) are guided through one of your veins into your heart, where they record electrical activity. When the source of the abnormality is found, an energy source, such as high-frequency radiowaves that generate heat, is transmitted through one of the catheters to destroy the tissue.)

46
Q

What medications are able to restore normal rhythm?

A

Flecainide

beta-blockers, particularly sotalol

amiodarone

dronedarone (only for certain people)

47
Q

What drugs are used to control the rate of heart beat?

A

Beta blocker (bisoprolol or atenolol)

Calcium channel blocker (verapamil, diltiazem)

Digoxin may be added to help control HR further. In some cases, amiodarone may be tried.

48
Q

What can cardioversion be used to treat?

A

Ventricular tachycardia

Supraventricular tachycardia due to re-entry

Atrial fibrillation

Atrial flutter

Atrial tachycardia

Monomorphic VT with pulses

49
Q

If you’ve had atrial fibrillation for more than two days, cardioversion can increase the risk of a clot forming, how is clot formation avoided?

A

Anticoagulant for three to four weeks before cardioversion, for at least four weeks afterwards

50
Q

What are the indications for ICD therapy (implantable cardioverter-defibrillator)?

A

Cardiac arrest due to VF/VT

Not due to transient or reversible cause eg early phase of acute MI

Sustained VT causing syncope or significant compromise

Sustained VT with poor LV function

51
Q

What are the indications for temporary pacing?

A
  • Intermittent or sustained symptomatic bradycardia, particularly syncope
  • Prophylactic when patient at high risk for development of severe bradycardia eg 2nd or 3rd degree AV block, post anterior MI, even when asymptomatic

(basically if there is bradycardia or risk of bradycardia)

52
Q

What are the indications for permanent pacing?

A
  • Symptomatic or profound 2nd/3rd degree AV block, particularly when cause unlikely to disappear
  • Probably Mobitz type II 2nd/3rd degree AV block even if asymptomatic
  • AV block associated with neuromuscular diseases after (or in preparation for) AV-node ablation
  • Alternating RBBB/LBBB
  • Syncope when bifascicular/trifascicular block and no other explanation
  • Sinus node disease associated with symptoms
  • Carotid sinus hypersensitivity/malignant vasovagal syncope
53
Q

What is meant by bifasicular block?

A

conduction disturbances below AV node

Right bundle branch and one of two fascicles (anterior or posterior) of left bundle branch are involved

54
Q

Define trifasicular block

A

Prolongation of PR interval (first degree AV block)

Right bundle branch block

Either left anterior fascicular block or left posterior fascicular block.

55
Q

What is a bundle branch block?

A

Abnormal conduction through either right or left bundle branches

Delay in depolarization of part of ventricular muscle

Extra time taken for depolarization of the whole of the ventricular muscle causes widening of QRS complex.

Normal heart, time taken for depolarization wave to spread from interventricular septum to furthest part of the ventricles less than 120 ms, three small squares of ECG paper

If QRS complex duration is greater than 120 ms, then conduction within ventricles must have occurred by an abnormal and slower pathway

56
Q

What is the approach to assess ECG?

A

ARIBAR

A - Any electrical activity

R - Rate

I - Irregular or regular

B - QRS complexes Broad or Narrow

A - Atrial activity

R - Relationship between atrial acivity and ventricular activity

57
Q

What are the four main types of supraventricular tachycardia?

A
  • atrial fibrillation
  • paroxysmal supraventricular tachycardia (PSVT)
  • atrial flutter
  • Wolff-Parkinson-White syndrome
58
Q

What is the disease mechanism behind paroxysmal supraventricular tachycardia?

A

Underlying mechanism typically involves accessory pathway that results in re-entry

59
Q

How is diagnosis of paroxysmal supraventricular tachycardia achieved?

A

Diagnosis typically by electrocardiogram (ECG) Shows narrow QRS complexes and fast heart rhythm typically between 150 and 240 beats per minute

60
Q

What is the initial treatment of paroxysmal supraventricular tachycardia?

A

Vasalva manouvre

CVS (26 decks)

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