Bradycardia + cardiac devices Flashcards
Define bradycardia
heart rate <60 bpm
Physiological causes of bradycardia
sleep
high level athletic conditioning
Pathological causes of bradycardia
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)
Bradycardia symptoms
dizziness
fatigue
difficulty concentrating
exercise intolerance
falls
syncope
breathlessness
What type of MI can cause bradycardia?
RCA supplies SA and AV nodes, therefore MI affecting RCA can cause bradycardia
How can bradycardia be caused by ageing?
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
What can go wrong with the SA node?
can fail to:
- generate an impulse (sinus bradycardia, sinus arrest)
- conduct an impulse to the atrium (sinoatrial block)
What is sinus bradycardia?
fewer impulses are generated than usual
What is sinus arrest?
no impulse is generated
What are escape rhythms? Describe 2 types
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
What is sinoatrial block?
impulse is generated but not conducted out of the SA node to the atrium
pause in ECG = twice the P-P interval
What is tachycardia-bradycardia syndrome?
sinus arrest, sinus bradycardia or sinoatrial block + atrial tachyarrhythmias
treat slow HR = pacemakers
treat fast HR = drugs + anticoags
Describe AV block
problem somewhere between AV node and ventricles
3 types of AV block
Describe first degree AV block
PR interval prolonged but all impulses are conducted to the ventricles
can be normal (eg. overnight)
Describe second degree AV block
some (but not all) impulses are conducted to the ventricles
Describe third degree AV block
no impulses are conducted to the ventricles
life-threatening
First degree heart block ECG
PR interval prolonged
there is a relationship between every P wave and QRS complex
Third degree heart block ECG
there is a relationship between QRS complexes
there isa relationship between P waves
but there is no relationship between P waves and QRS
Name 4 types of second degree heart block
Wenckebach
Mobitz 2
2:1 AV block
Advanced AV block
Describe type 1 second degree heart block (Wenckebach)
Pr interval gets progressively longer until there is a P wave not followed by a QRS
occurs in AV node itself
usually benign
Describe type 2 second degree heart block (Mobitz 2)
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
Describe 2:1 AV block
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
How does atropine work?
blocks effects of vagus nerve on heart
blocks effect on parasympathetic nerves
(not likely to work if bradycardia cause is below AV node)
How does isoprenaline work?
stimulate sympathetic nervous system (B1 agonist) = will generally increase heart rate irrespective of site of block
