bradycardia - oxford

Question 1

what is bradycardia ?

Answer 1

defined as a heart rate <60bpm.

Question 2

what is the etiology of bradycardia?

Answer 2

trained athletes

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Cardiac:
• Degenerative changes causing fibrosis of conduction pathways (risk in elderly
patients; may have previous ECGs showing bundle branch block or 1st- or 2nddegree
heart block).

• Post-MI—particularly after an inferior MI (the right coronary artery supplies the
sinoatrial node and atrioventricular node in most people).

• Sick sinus syndrome
• Iatrogenic—ablation, surgery.
• Aortic valve disease, eg infective endocarditis
• Myocarditis, endocarditis cardiomyopathy, amyloidosis, sarcoidosis, SLE.

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Non-cardiac origin:
• increased Vasovagal— MOST COMMON
Can be physiological (particularly in athletes)
Obstructive sleep apnea
Neurocardiogenic (i.e., vasovagal response) 
Pain
Carotid sinus hypersensitivity

• Endocrine—hypothyroidism, adrenal insufficiency.
• Metabolic—hyperkalaemia, hypoxia.

• Other—hypothermia,
high ICP (Cushing’s triad: bradycardia, hypertension, and irregular
breathing

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• Drug-induced:
b-blockers,
 amiodarone, 
verapamil, diltiazem, digoxin.

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Poisoning/overdose
Carbon monoxide (see CO intoxication)
Cyanide (see cyanide intoxication)
Mercury

Question 3

what are the symptoms of bradycatrdia ?

Answer 3

may be normal and asymptomatic
in very fit, young individuals whose high stroke volumes will maintain adequate
cardiac output at low heart rates
Heart rates as low as 40bpm at rest and 30bpm in sleep can be accepted
in asymptomatic trained athletes

Often asymptomatic. Fatigue, 
nausea, 
dizziness. 
The presence of syncope,
chest pain, or breathlessness is concerning and suggests the presence of adverse
signs; sudden cardiac death can occur

Question 4

what is the management of bradycardia?

Answer 4

A-E

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The immediate management tends to relate more to cause and adverse
signs than to the underlying rhythm, which may be •sinus bradycardia •heart block
•AF with a slow ventricular response •atrial fl utter with a high-degree
block •junctional bradycardia

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Think ahead. If you may need an anaesthetist to sedate the patient for transcutaneous
pacing, or a cardiologist for transvenous pacing, call them now.

• Perform a 12-lead ECG,
• Connect patient to cardiac monitor/telemetry

check electrolytes (including K+, Ca2+, Mg2+),

do digoxin levels.

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if Adverse signs such as 
• Shock
• Syncope
• Heart failure
• Myocardial ischaemia

Give atropine 500mcg IV
repeat ever 5 min if adverse signs persist

• If atropine is insufficient and adverse signs persist, transcutaneous pacing should be considered . If this cannot be initiated immediately (eg waiting for an
anaesthetist), consider other medications such as isoprenaline infusion.
or
Adrenaline 2–10mcg/min IVI

• risk of asystole?
 give atropine (not to be given if patient has a transplanted heart).

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. Address causes: correct metabolic defects; give antidotes to medicines likely to have caused the bradycardia
(eg glucagon if b-blocker overdose).

• Remember electrical ‘capture’ with transcutaneous pacing does not guarantee mechanical
‘capture’. Once pacing is established, check the patient’s pulse!!

Question 5

what are the risk of asystole ?

Answer 5

Recent asystole
• Mobitz II AV block (p98)
• Complete heart block with
broad QRS
• Ventricular pause >3s

Question 6

we should treat bradycardia according to ther clinical state , can you describe how ?

Answer 6

It is possible to have two patients sat next to each other with identical bradycardic
ECG tracings, one of whom is peri-arrest, the other is sat comfortably and cannot
understand your concern. The clinical state is more important than the numbers
on the screen.

= unstable bradycardia with a pulse 
= IV atropine 
prepare for energency transvenous pacing whilst considering epinephrine 
dopamine 
isoproterenol 
transcutanous pacing 

= symptomatic stable bradycardia
atropine
then go to transvenous pacing preparation if no improvement

=asymptomatic stable bradycardia
Usually, no treatment is required.
Second-degree AV block, Mobitz II, or third-degree AV block: Consider transcutaneous or transvenous pacing therapy regardless of symptoms.
Consider TTE.

Question 7

WHAT are the signs of unstable bradycardia?

Answer 7

Signs of hypoperfusion -
poor capillary refill, cool/dry skin, pallor, poor saturation

Respiratory distress
Chest pain
Pulmonary edema
Shock
Altered mental status

Question 8

what is the sick sinus syndrome ?

Answer 8

known as sinus node dysfunction, occurs when sinoatrial node (SAN) dysfunction causes bradyarrhythmias or tachyarrhythmias.

Question 9

what are the risk factors for sick sinus syndrome ?

Answer 9

Intrinsic causes include:

Idiopathic fibrosis: age-related degeneration of the SAN is the most common cause of sinus node dysfunction
Ischaemic heart disease (e.g. myocardial infarction, ischaemia)
Myocarditis
Pericarditis
Rheumatic heart disease
Infiltrative diseases (e.g. sarcoidosis, amyloidosis, haemochromatosis)

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Extrinsic causes include:

Drugs: digoxin, beta-blockers, calcium channel blockers, anti-arrhythmics
‘Hypos’: hypothermia, hypothyroidism, hypoxia
‘Hypers’: hyperkalaemia, hyperthyroidism