Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

- Y6 Cardiovascular > Heart block (1st, 2nd and 3rd degree) and LBBB/RBBB > Flashcards

Heart block (1st, 2nd and 3rd degree) and LBBB/RBBB Flashcards

1
Q

Give 5 causes of sinus bradycardia.

A

Sinus bradycardia can be

  • normal in athletes

caused by

  • hypothermia,
  • hypothyroidism,
  • vagal stimulation,
  • drugs (e.g. beta blockers),
  • raised intracranial pressure
  • myocardial infarction.

Sinus bradycardia can also be a feature of certain infections including Legionnaire’s disease, typhoid fever and Lyme disease.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the normal PR interval and what does it show?

A

Time taken for spread of depolarisation from the SA node to the ventricular muscle

Normally <200ms - 5 small squares.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the heart block poem?

A

If the R is far from P, then you have 1st degree

Longer, longer, longer… drop, then you have a Weckenbach

If some Ps don’t get through then you have Mobitz II

If Ps and Qs don’t agree then you have a 3rd degree

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe the cause of first degree heart block and give examples.

A

Delay of wave of depolarisation from SA node to ventricles, causing a prolonged PR interval - 1st degree HB

May be caused by:

  1. CAD
  2. acute rheumatic carditis
  3. digoxin toxicity
  4. electrolyte disurbances
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe the cause of second degree heart block. What are the three typs?

A

Sometimes excitation completely fails to pass through AV node or bundle of His. There are three variations:

  1. Wenckebach/Mobitz I - progressive lengthening of PR interval then failure of conduction of atrial beat, and shorter PR interval. Then cycle repeats.
  2. Mobitz II - most beats are conducted with constant PR interval but ocassionally there is atrial depolarisation without ventricular depolarisation.
  3. 2:1, 3:1, 4:1 conduction - alternate conducted and non-conducted atrial beats e.g. one conducted atrial beat then a non conducted beat giving twice as many P waves as QRS complexes therefore 2:1 block .
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the underlying causes of second degree HB?

A

Same as those of first degree HB:

  1. CAD
  2. acute rheumatic carditis
  3. digoxin toxicity
  4. electrolyte disturbances
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the prognosis with second degree HB?

A

Weckenbach is usually benign

But Mobitz type 2 and 2:1, 3:1, 4:1 block may herald “complete/third degree” heart block

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What type of heart block is shown?

A

2nd degree HB, Mobitz type 2

  • PR interval of the conducted beats is constant
  • One P wave is not followed by a QRS complex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What type of heart block is shown?

A

Second degree HB, Mobitz type 1/Weckenbach

  • Progressive lengthening of the PR interval
  • One nonconducted P wave
  • Next conducted beat has a shorter PR interval than the preceding conducted beat
  • As with any other rhythm, a P wave may only show itself as a distortion of a T wav
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What type of heart block is shown?

A

Second degree HB, 2:1 ype

  • Two P waves per QRs complex
  • Normal and constant PR interval in the conducted beats

NB: P wave may only show itself as a distrotion of the T wave sometimes, as below. P wave in the T wave can be identified because of its regularity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the cause of third degree heart block? What are some underlying causes?

A

Occurs when atrial contraction is normal but no beats are conduced to the ventricles. When this occurs the ventricles are excited by a slow “escape mechanism” from a depolarising focus within the ventricular muscle.

3rd degree HB may occur in :

  1. acute MI (usually transient)
  2. fibrosis around the bundle of His (chronic)
  3. block of both bundle branches
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What type of heart block is shown?

A

Third degree HB

  • P wave rate is 90bpm
  • No relationship between P waves and QRS complexes
  • QRS complex rate 36bpm
  • Abnormally shaped QRS complex, because of abnormal spread of depolarisation from a ventricular focus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is shown on this ECG?

A

Complete heart block

  • Sinus rhythm but no P waves conducted
  • Right axis deviation
  • Broad QRS complexes (160ms)

Probably from fibrosis of bundle of His

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

List some general causes of AV block/heart block.

A
  • Fibrosis/calcification of the conduction system, can be age related.
  • Usually male aged 50-60yrs
  • CAD
  • AV-node blocking drugs e.g. beta-blockers, CCBs, digitalis, adenosine
  • Anti-arrhythmics e.g. Na-channel blockers, class III agents like sotalol and amiodarone
  • High vagal tone
  • Cardiomyopathy
  • Calcification from valvular calcification
  • Post-catheter ablation of arrhythmias
  • Post-surgical
  • Blunt cardiac injury
  • Indigenous medicines
  • Metabolic -electrolyte disturbance, acidosis, hypoxaemia
  • Neuromuscular disorders - myotonic dystrophy, Erb dystrophy,
  • Myocarditis, IE, Lyme disease
  • Congenital
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the signs/symptoms of heart block?

A
  • Syncope
  • Fatigue
  • Dyspnoea
  • Chest pain
  • Palpitations
  • N&V
  • Slow HR (if <40 admit for pacemaker implantation)
  • High BP with wide pulse pressure, low BP in emergency
  • Cannon A waves in irreversible/complete heart block
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What investigations would you do for heart block?

A

ECG

Serum troponin

Serum electrolytes - calcium, potassium

Serum pH

Toxicology screen - serum digitalis levels may be high and cause reversible AV block.

24hr ambulatory monitoring - measured if AV block is suspected

CXR - may show hilar lymphadenopathy (sarcoid), cardiomegaly, coronary or valvular calcification, signs of pulmonary congestion

Echo - ventricular dysfunction or hypertrophy, valvular disease, wall-motion abnormalities

EP study - may show significant infranodal condustion disease which needs pacemaker

Serological test for Lyme disease

Tilt-table testing, implantable loop recording, cardiac stress testing, coronary angiography, serum CK-MB

17
Q

What is significant infranodal conduction disease?

A

Defined by a His-bundle-to-ventricle (HV) interval >100 ms.

18
Q

How do you manage heart block?

A

1st degree or Mobitz I

  • If asymptomatic - monitoring as low risk of progression
  • If symptomatic - discontinuation of AV nodal blocking medications, infrequent PPM or cardiac resynchronisation therapy +/- ICD placement
    • PPM = permanent pacemaker implantation if symptoms are severe. Usually a dual-chamber pacemaker.

2nd degree or 3rd degree

  • Asymptomatic/mid-mod symptoms -
    • Treat underlying cause/discontinue drugs
    • Digitalis toxicity - digoxin immune Fab
    • Beta blcoker toxicity - glucagon
    • CCB toxicity - calcium chloride
    • PPM or cardiac resynchronisation +/- ICD
  • Severely symptomatic -
    • Condition specific management, discontinue drugs, temporary pacing
    • PPM or cardiac resynchronisation therapy +/- ICD placement
19
Q

What is the prognosis with heart block?

A

1st degree has x2 increase risk AF and increase in all cause mortality

2nd degree, if irreversible has a high risk of progression to 3rd degree or ventricular asystole.

Symptomatic AV block treated with PPM has an excellent prognosis with low rate of complications.

20
Q

What is a bifascicular block?

A

e.g. RBBB + LAD*

*left anterior or posterior hemiblock

21
Q

What is a trifascicular block?

A

RBBB + LAD + 1st degree HB (long PR)

22
Q

What is shown below?

A

Trifascicular block - RBBB + left anterior hemiblock + 1st-degree heart block

23
Q

What is shown below?

A

Bifascicular block

  • Sinus rhythm, rate 70 bpm
  • Left axis deviation (S wave greater than R wave in leads II and III)
  • Right bundle branch block – wide QRS complexes (135 ms); RSR 1 pattern in lead V 1 ; and a wide slurred S wave in lead V 6

- Y6 Cardiovascular (47 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions