Bradycardia + cardiac devices

Question 1

Define bradycardia

Answer 1

heart rate <60 bpm

Question 2

Physiological causes of bradycardia

Answer 2

sleep
high level athletic conditioning

Question 3

Pathological causes of bradycardia

Answer 3

congenital

acquired:
- degenerative
- ischaemic heart disease
- drugs
- electrolyte/metabolic (eg. hypothyroidism)
- infection (eg. endocarditis, lyme disease)
- Iatrogenic (eg. ablation)
- Infiltrative diseases (eg. sarcoid, amyloid)
- neuromuscular diseases (eg. myotonic dystrophy)

Question 4

Bradycardia symptoms

Answer 4

dizziness
fatigue
difficulty concentrating
exercise intolerance
falls
syncope
breathlessness

Question 5

What type of MI can cause bradycardia?

Answer 5

RCA supplies SA and AV nodes, therefore MI affecting RCA can cause bradycardia

Question 6

How can bradycardia be caused by ageing?

Answer 6

SA nodal cells set in dense fibrous tissue
as we get older the amount of fibrous tissue increases
fibrosis can also affect pacemaker cells
leads to sinus node dysfunction

Question 7

What can go wrong with the SA node?

Answer 7

can fail to:
- generate an impulse (sinus bradycardia, sinus arrest)
- conduct an impulse to the atrium (sinoatrial block)

Question 8

What is sinus bradycardia?

Answer 8

fewer impulses are generated than usual

Question 9

What is sinus arrest?

Answer 9

no impulse is generated

Question 10

What are escape rhythms? Describe 2 types

Answer 10

when the AV node or lower takes over as the pacemaker

Junctional = AV node takes over:
- no p waves
- slower than sinus rhythm
- QRS narrow

Ventricular = below AV node:
- 20-40bpm (much slower)
- broad QRS

Question 11

What is sinoatrial block?

Answer 11

impulse is generated but not conducted out of the SA node to the atrium

pause in ECG = twice the P-P interval

Question 12

What is tachycardia-bradycardia syndrome?

Answer 12

sinus arrest, sinus bradycardia or sinoatrial block + atrial tachyarrhythmias

treat slow HR = pacemakers
treat fast HR = drugs + anticoags

Question 13

Describe AV block

Answer 13

problem somewhere between AV node and ventricles
3 types of AV block

Question 14

Describe first degree AV block

Answer 14

PR interval prolonged but all impulses are conducted to the ventricles
can be normal (eg. overnight)

Question 15

Describe second degree AV block

Answer 15

some (but not all) impulses are conducted to the ventricles

Question 16

Describe third degree AV block

Answer 16

no impulses are conducted to the ventricles
life-threatening

Question 17

First degree heart block ECG

Answer 17

PR interval prolonged
there is a relationship between every P wave and QRS complex

Question 18

Third degree heart block ECG

Answer 18

there is a relationship between QRS complexes
there isa relationship between P waves
but there is no relationship between P waves and QRS

Question 19

Name 4 types of second degree heart block

Answer 19

Wenckebach
Mobitz 2
2:1 AV block
Advanced AV block

Question 20

Describe type 1 second degree heart block (Wenckebach)

Answer 20

Pr interval gets progressively longer until there is a P wave not followed by a QRS
occurs in AV node itself
usually benign

Question 21

Describe type 2 second degree heart block (Mobitz 2)

Answer 21

PR interval constant then there is a P wave not followed by a QRS
site of block below AV noe
not benign
complete heart block can occur at any time

Question 22

Describe 2:1 AV block

Answer 22

every other P wave is not conducted through the AV node to get to the ventricles, and thus every other P wave is not followed by a QRS complex

Question 23

How does atropine work?

Answer 23

blocks effects of vagus nerve on heart
blocks effect on parasympathetic nerves
(not likely to work if bradycardia cause is below AV node)

Question 24

How does isoprenaline work?

Answer 24

stimulate sympathetic nervous system (B1 agonist) = will generally increase heart rate irrespective of site of block

Question 25

Parasympathetic/sympathetic nerve supply to heart

Answer 25

sympathetic = whole cardiac conduction system

SA + AV nodes also supplied by the parasympathetic nerves

Question 26

What is an ILR and what is it used for?

Answer 26

implantable loop recorder
used for diagnosis
records if heart goes above or below certain rates
useful if symptoms rarer

Question 27

What is CRT and what is it used for?

Answer 27

cardiac resynchronisation therapy
heart failure (severe systolic heart failure and a broad QRS) who remain symptomatic despite medical therapy

Question 28

What is an ICD and what is it used for?

Answer 28

implantable cardioverter defibrillator
for ventricular arrhythmias

Question 29

How is a pacemaker inserted?

Answer 29

local anaesthetic + sedation
feed wires through vein under clavicle into the heart, insert into right atrium and right ventricle walls

Question 30

What are the 2 roles of a pacemaker?

Answer 30

sense = detect a patient’s own intrinsic impulses
capture = depolarise the heart if there aren’t any impulses

Question 31

Who are ICDs given to as primary prevention?

Answer 31

severe LV impairment
inherited cardiac conditions

Question 32

Who are ICDs given to as secondary prevention?

Answer 32

survivors of VF/VT
cardiac arrest
sustained VT with haemodynamic compromise
sustained VT and severe LV impairment

Question 33

How do ICDs recognise ventricular arrhythmias?

Answer 33

looks at heart rate
>220bpm = ICD will deliver a shock
>180bpm = will look at other parameters:
- how did arrhythmia start? (gradual/sudden)
- is it regular or irregular?
- is QRS narrow or broad?

Question 34

What can ICDs do?

Answer 34

atrium + ventricle = bradycardia pacing
ventricle = anti-tachycardia pacing, cardioversion, defibrillation

Question 35

How are ICDs deactivated?

Answer 35

done by pacing physiologist who can turn them off
emergency = doughnut magnet strapped over ICD

Question 36

Who needs a pacemaker?

Answer 36

symptomatic bradycardia
high risk (but asymptomatic) bradycardia