PBL 1 - Heart Block Flashcards

1
Q

In electrocardiography, what is the PR interval, and what is its normal range?

A

The PR interval is the period in milliseconds from the beginning of the P wave (1/2 mark) until the beginning of the QRS complex (1/2 mark) it is normally between 120 and 200ms in duration (1 mark)

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2
Q

Explain carefully the difference between first and second degree heart block (2 marks)

A

In first degree AV block the conduction from AV node to ventricles is slower than normal (1/2 mark) but occurs with a normal regularity (1/2 mark).
In second degree AV block the conduction from AV node to ventricles is irregular so that PR interval is irregular ( 1 mark)

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3
Q

List four common causes of heart block (2 marks)

A

Plasma electrolyte imbalance
2. Myocardial damage following myocardial infarction;
3. Coronary artery disease
4. Myocarditis or other forms of cardiomyopathy
5. Heart enlargement related to heart failure
(any four ½ mark each)

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4
Q

An implanted pacemaker is not normally indicated for someone with second degree heart block. However, some patients do require a pacemaker. List two signs that indicate that a pacemaker is needed (2 marks)

A

Block associated with persistent bradycardia (1 mark), heart failure (1 mark), asystole greater than or equal to 3 seconds (1 mark) or associated with neuromuscular diseases (1mark) (any two marks)

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5
Q

Explain why a diet including leafy green vegetables helps reduce blood pressure (2 marks)

A

Leafy green vegetables contain nitrate (1/2 mark) which is converted in stomach to nitric oxide (1/2 mark). This nitric oxide then enters the bloodstream where it relaxes vascular smooth muscle (1 mark)

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6
Q

Describe the electrical conductivity in the heart (3)

A

Electrical impulse (SA node- r atrium) –> atrium contracts –> pushes blood into ventricles –> AV node (delay to allow atrium to finish contracting) –> bundle of His –> Purkinje fibres –> apex (papillary muscles)

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7
Q

What is the effect of Beta blockers? Name 2 beta blockers. (3)

A
Propanolol
Bisoprolol
Atenolol 
Bind to b-adrenoreceptors
Block the binding of norepinephrine and epinephrine 
inhibits sympathetic effects
Decreases contractility and heart rate
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8
Q

Why was Jennifer taken of Beta blockers? (2)

A

Related to heart block

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9
Q

What is Jennifer’s diagnosis (1)

A

Second degree heart block

Mobitz type 1 (wenckenback)

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10
Q

What is the difference between SA node block and AV node block? (1)

A

SA block - AV takes over from SA, not a cause for concern

AV block - Delay of atrial impulse conduction in AV node/from AV –> ventricles

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11
Q

3 signs and symptoms of second degree AV block? (3)

A
May be no symptoms 	
Palpitations (means regularly irregular) 
o	Bradycardia
o	Dizziness/syncope 
o	Chest pain.
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12
Q

Cause of Mobitz Type II

A

More severe
Structural damage in the conduction system (infarction, fibrosis, necrosis)
Usually fitted with pacemaker

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13
Q

What is third degree heart block

A
Complete heart block 
AV --> ventricles conduction fail completely
Severe bradycardia
PR is irregulat
can cause ventricular arrhythmia
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14
Q

How do you manage heart block? (3)

A
No therapy unless symptomatic
Discontinue BB - give ACE inhibitors
Moderate exercise 
Healthy lifestyle
Green veg
Severe - pacemaker
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15
Q

How can exercise improve BP

A

NO production –> vasodilation –> reduces total peripheral resistance –> reduces BP

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16
Q

What is heart block

A

condition where there is faulty or intermittent conduction in the conducting system of the heart. This may occur in the link between SA node and AV node or between AV node and ventricle.

17
Q

Describe 1st, 2nd and 3rd degree AV heart block (3)

A

In first degree AVblockthe conduction from AV node to ventricles is slower than normal but occurs with a normal regularity. Type is diagnosed by a PR interval > 200ms.
In second degree AV blockthere is an irregularity in the conduction from AV node to ventricles.
In third degree AV block conduction between AV node and ventricles fails completely (patient needs a pacemake

18
Q

Characteristics of wenckenback heart block

A

1.Gradually progressive PR interval prolongation occurs before the blocked P wave
2.The greatest PR increment typically occurs between the first and second beats of a cycle, gradually decreasing in subsequent beats
3.Shortening of the PR interval occurs after the blocked P wave.PR-interval shortening between last unblocked and first post
blocked QRS wave is a key to the diagnosis of Wenckenbach block