Bradycardia

Bradycardia module: http://www.doctors.net.uk/ecme/wfrmNewIntro.aspx?moduleid=1575

Bradycardia
Bradycardia is defined as a heart rate of < 60 min-1. It may be:
- physiological (e.g., in athletes);
- cardiac in origin (e.g., atrioventricular block, sinus node disease, aortic stenosis);
- non-cardiac in origin (e.g., vasovagal, hypothermia, head injury, hypothyroidism, hyperkalaemia, muscular dystrophies);
- drug-induced (e.g., beta blockade, diltiazem, digoxin, amiodarone).

Adverse Signs
- Shock – hypotension (systolic blood pressure < 90 mmHg), pallor, sweating, cold, clammy extremities, confusion or impaired consciousness.
- Syncope – transient loss of consciousness due to global reduction in blood flow to the brain.
- Myocardial ischaemia – typical ischaemic chest pain and/or evidence of myocardial ischaemia on 12-lead ECG.
- Heart failure – pulmonary oedema and/or raised jugular venous pressure (with or without peripheral oedema and liver enlargement).

ECG Things

1st degree heart block: no worries
2nd degree (Mobitz I, Wenkenback): progressive PR prolongation. Normally a benign rhythm.
2nd degree block (Mobitz II): Regular P waves, but not all conducted.
Complete Heart Block: Maintained by junctional or escape rhythm. Might be caused by drugs or inferior MI.

J waves - sign of hypothermia. Resolve as patient warms up. Size is proportional to degree of bradycardia.
Carotid hypersensitivity - see later
Sick sinus syndrome
Junctional rhythm

Treatment Options
Treat any reversible causes.

1. Electrical (cardioversion for tachyarrhythmia or pacing for bradyarrhythmia)
2. Simple clinical intervention (e.g., vagal manoeuvres, fist pacing)
3. Pharmacological (drug treatment)
4. No treatment needed

Atropine
Give atropine 500 mcg intravenously if adverse signs present.
Repeat every 3-5 min to a total of 3 mg.

Doses of atropine of less than 500 mcg have been reported to cause paradoxical slowing of the heart rate.
Use atropine cautiously in the presence of acute coronary ischaemia or myocardial infarction.
Do NOT give atropine to patients with cardiac transplants. Their hearts are denervated and will not respond to vagal blockade by atropine, which may cause paradoxical sinus arrest or high-grade AV block.
The half life is 2-3hours. May not work on older SA nodes.

Second-line drugs
Seek expert help to select the most appropriate choice. In some clinical settings second-line drugs
may be appropriate before the use of cardiac pacing.
Intravenous glucagon -  beta-blocker or calcium channel blocker
Digibind -  in digoxin toxicity
Theophylline (100-200mg slow IV infusion) - for bradycardia complicating acute inferior wall myocardial infarction, spinal shock
Thyroxine - if myxoedemic crisis suspected

Pacing 
- First pacing can be used.
- Verify electrical capture on the monitor or ECG and check that it is producing a pulse.
- Use analgesia and sedation as necessary to control pain; sedation may compromise respiratory effort so continue to reassess the patient at frequent intervals.
- Consider if there is documented recent asystole (ventricular standstill of more than 3s), Mobitz type II AV
block; complete (third-degree) AV block (especially with broad QRS or initial heart rate <40 beats min-1).
- AP pads. Start at 70mA and increase until capture achieved.
- If no capture at 130mA, re-site pads and repeat.