Module 9: Assessing and treating bradycardia

Question 1

Bradycardia

Answer 1

Heart rate <60 min-1.

May be:
- a physiological state in very fit people or during sleep
- an expected result of treatment (e.g. with a ß-blocker).
- Pathological (malfunction of the SAN or from partial/complete failure of atrioventricular conduction.

Question 2

Bradycardia

Answer 2

Heart rate < 60 beats min-1

• Physiological
• Pathological

Question 3

6 stage approach

Answer 3

6-stage approach
Stage 1 - Is there any electrical activity?

Stage 2 - What is the ventricular (QRS) rate?

Stage 3 - Is the QRS rhythm regular or irregular?

Stage 4 - Is the QRS width normal (narrow) or broad?

Stage 5 - Is atrial activity present? (If so, what is it: Typical sinus P waves? Atrial fibrillation? Atrial flutter? Abnormal P waves?).

Stage 6 - How is atrial activity related to ventricular activity? (e.g. 1:1 conduction, 2:1 conduction etc. or no relationship).

Question 4

Bradycardia algorithm

Answer 4

1. ABCDE assessment
2. Obtain 12-lead ECG & monitoring
3. ATROPINE 500 mcg IV if life-threatening features or risk of asystole
   - repeat up to max total 3 mg IV.
   - consider transcutaneous pacing.
4. No adverse features: monitor

Question 5

Extreme bradycardia

Answer 5

HR so low that CO reduces so low to cause cardiac arrest.

Question 6

Cardiac pacing

Answer 6

In some cardiac arrest or peri-arrest settings, use of cardiac pacing can be life-saving.

Non-invasive pacing may be used to maintain cardiac output temporarily while expert help to deliver longer-term treatment is obtained.

Non-invasive pacing can be established rapidly by ALS providers

Question 7

First degree AV block

Answer 7

• PR >0.20 s
• Common finding
• Delay in conduction through the AV junction (the AV node and immediately adjacent myocardium).
• Rarely causes Sx
• Rarely requires Tx

Question 8

Heart block: Third-degree AV block

Answer 8

• no relationship between P waves and QRS complexes
• atrial & ventricular depolarisation arise independently from separate ‘pacemakers’ - site of PM stimulating the ventricles will determine the ventricular rate and QRS width.

Pacemaker in AVN or proximal bundle of His:
- intrinsic rate ≥40-50 min-1
- narrow QRS complex unless additional BBB is present.

Pacemaker site in the distal His-Purkinje fibres or ventricles:
- broad QRS complexes
- rate of ≤30-40 min-1
- higher risk abruptly stopping causing asystole

Question 9

Agonal rhythms

Answer 9

Dying patients.

Slow, irregular, wide ventricular complexes, varying morphology.

Unlikely to produce a pulse.

Question 10

Escape rhythm

Answer 10

If normal cardiac pacemaker (SAN) fails or is abnormally slow, cardiac depolarisation may be initiated from a ‘subsidiary’ pacemaker in atrial myocardium, AV node, conducting fibres or ventricular myocardium.

Question 11

Bradycardia algorithm

Answer 11

1. Assess using the ABCDE approach
2. Life-threatening signs?
   - ATROPINE 500 mcg IV
   - repeated up to a maximum total doses of 3 mg IV

No life threatening features but risk of asystole? (recent asystole, mobitz 2, complete heart block, ventricular pause >3s)
- ATROPINE 500 mcg IV

5. No risk of asystole: observe

Question 12

As described in the ‘bradycardia algorithm’, the emergency treatment of most bradycardia is with ?

Answer 12

atropine and/or cardiac pacing.

atropine 500 mcg IV
- repeated up to a maximum total doses of 3 mg IV

if atropine fails:
- Consider Transcut pacing

Question 14

Second degree block

Answer 14

Some P waves are not conducted to ventricles

Type I: progressive prolongation of PR, until eventual drop
—> Tx depends on symptoms

Type II: constant PR in conducted beats, but some beats are not conducted. May be a consistent pattern (e.g. 2:1 block) or may be random.

Question 15

Cardiac pacemakers

Answer 15

Pacemakers may be
- Implanted for the treatment of bradycardia
(single or dual-chamber)
- Biventricular pacemakers (implanted for left ventricular failure)
- ICDs (which have pacing capability).

Question 16

Percussion pacing

Answer 16

When bradycardia is so profound that it causes clinical cardiac arrest, percussion pacing may be used in preference to CPR because it may produce an adequate cardiac output with less trauma to the patient.

To perform percussion pacing:
With the side of a closed fist deliver repeated firm thumps to the praecordium just lateral to the lower left sternal edge.
Raise the hand about 20 cm above the chest for each thump.
If initial thumps do not produce a QRS complex try using slightly harder thumps and try moving the point of contact around the praecordium until a site is found that produces repeated ventricular stimulation.
If attempted percussion pacing does not achieve a cardiac output within a few seconds, start CPR.

Question 17

Transcutaneous pacing

Answer 17

• Transcutaneous pacing and drugs used in extreme bradycardia should be a bridge to definitive treatment (transvenous pacing and/or correction of the cause of the extreme bradycardia).
• It causes painful contraction of muscles in the chest wall, so patients are likely to need sedation.
• Know your machine type – some require the operator to increase the current delivered until electrical capture is achieved whilst others deliver a constant current with longer duration v