1.2 Complete Heart Block

Question 1

History An 80-year-old male patient presents to pre-assessment clinic for
SCC removal on his forehead. He complains of dizzy spells. The pre-assessment
nurse wants to know what to do. See Figure 1.3.

What does the ecG show?

Answer 1

• Regular P waves and QRS complexes are seen
  but are unrelated to each other
• No QRS widening
• Voltage criteria for LVH
• No obvious features of coronary ischaemia

The ECG shows third-degree AV block, with a ventricular rate of 34/min.

Question 2

What are the causes of complete heart block?

Answer 2

Congenital
* With maternal antibodies to SS-A (Ro) and SS-B (La)

Acquired
* Drugs:
quinidine, procainamide, disopyramide, amiodarone, β blockers

• Infection:
  Lyme disease, rheumatic fever, Chagas disease
• Connective tissue disease:
  ankylosing spondylitis, rheumatoid arthritis, scleroderma
• Infiltrative disease:
  amyloidosis, sarcoidosis
• Neuromuscular disorders:
  muscular dystrophy
• Ischaemia:
  e.g. AV block associated with inferior wall MI

Iatrogenic
* AV block may be associated with aortic valve surgery, PCI

Question 3

Would you anaesthetise him now?

Answer 3

No.

Patient is at high risk of severe peri-operative bradycardia
leading to cardiac decompensation,
or even cardiac arrest.

• He requires referral to a cardiologist,
  and probably electrical pacing,
  ideally with a permanent pacemaker.
• Further cardiac investigations to determine the cause
  (e.g. angiogram)

and to establish his baseline cardiac function
(e.g. echocardiogram) would also be helpful.

• If the surgery is deemed too urgent to wait for further
  investigation and PPM implantation,
  other options include a temporary pacing wire, or
  pharmacological chronotropy via an isoprenaline infusion.

Question 4

How would you manage this if it occurred intraoperatively?

Answer 4

Ask surgeons to stop,
check correct attachment of monitoring,
and feel for a pulse.

If there is no pulse palpable,
start CPR and then
treat the underlying problem.

Pharmacological options

1. • Trial of antimuscarinic drugs (e.g. atropine or glycopyrollate)
2. • Carefully titrated adrenaline boluses (10–100 mcg)
3. • Isoprenaline infusion (β-agonist): 0.02–0.2 mcg/kg/min

Electrical/mechanical options

1. • Percussion pacing using a clenched fist
     (rarely achieves electrical capture)
2. • Transcutaneous external pacing via defibrillator pads; increase current
     until electrical capture achieved. Set rate at 70–80 bpm
3. • If pharmacological measures fail to restore an adequate heart rate,

a temporary pacing wire (inserted via a central line)
will probably be necessary,
but this takes time to organise
(and should be done under aseptic conditions by an
appropriately trained cardiologist under X-ray guidance)

4. • Transoesophageal pacing is also possible but similarly requires specialist
     equipment and expertise to set up

As for all emergencies, management would also require simultaneous rapid
assessment/management of airway and breathing/ventilation
- Is airway patent? Give 100% o2, check ETT/LMA position
- Is oxygenation/ventilation intact? Manually ventilate patient, check for
bilateral chest rise, air entry on auscultation, EtCo2, misting of ETT, and
saturation
- Remember to maintain anaesthesia while you sort out the new-onset
complete heart block!

Question 5

What are the indications for
insertion of a permanent
pacemaker?

Answer 5

• Any symptomatic bradycardia (i.e. causing collapse/syncope/presyncope)
• Complete heart block
• Mobitz type II block
• Sick sinus syndrome
• Hypersensitive carotid sinus syndrome
• Symptomatic bradycardia in transplanted heart
• Severe heart failure (cardiac resynchronisation therapy)
• Some patients with dilated or hypertrophic cardiomyopathy

Question 6

What are the indications for insertion of temporary pacing?

Answer 6

All of the above indications for permanent pacemaker insertion are also
indications for temporary pacing in an emergency situation (or if a permanent
pacemaker is unavailable/contraindicated (e.g. systemic sepsis).

1. • Acute myocardial infarction causing asystole/bradyarrhythmia
     that entails haemodynamic compromise
2. • Drug overdose (e.g. β-blockers, calcium channel blockers, digoxin)
3. • Surgery/general anaesthesia for patients with
     stable heart block not causing haemodynamic compromise
     but potentially at risk of worsening bradycardia/asystole
4. • Following cardiac surgery
     (usually involves placement of epicardial pacing wires,
     rather than transvenous pacing wire,
     at end of surgery by surgeons)

Question 7

What features are associated
with a high risk of asystole?

Answer 7

1. • Pauses of >3 seconds
2. • Previous asystolic episodes
3. • Complete heart block with wide QRS complexes

Question 8

What do you want to know before anaesthetising a patient with a PPM?

Questions

Answer 8

Preoperative assessment should be aimed at
finding answers to the following questions:

1. • Indication of pacemaker insertion
2. • Check date (Does it need checking again before theatre?)

3 * Is the patient pacing dependent?

4. • Type of PPM
     (unipolar/bipolar, number of leads, biventricular/
     univentricular, etc)
5. • Programmed mode

Question 9

What do you want to know before anaesthetising a patient with a PPM?

Investigations / Preparation

Answer 9

Investigations/preparation

1. • All patients should have CXR
     (to show PPM position and number of leads)
2. • ECG: look for pacing spikes before each QRS
     to determine whether pacing-dependent
3. • Correction of any electrolyte abnormalities
     (which may cause loss of capture)
4. • Switched to fixed rate mode if necessary
5. • PPM check if any doubts re:
     function/battery life/failure of capture, etc.
6. • May need to arrange cardiac-monitored bed post-op
     (plus another PPM check)

Question 10

What hazards arise in theatre in patients with a PPM?

Answer 10

1. Electromagnetic interference
   (mainly from monopolar diathermy)
   may reprogram the PPM
   (usually into a fixed rate back-up mode)
   or inhibit pacing inappropriately.

To reduce the risk of PPM malfunction, use bipolar diathermy.

If monopolar diathermy is unavoidable,
the pad should be placed as far as possible from PPM;
diathermy current should flow perpendicular to PPM current.

2. • Sensing
     Patient shivering, fasciculations following suxamethonium, and sources
     of vibration may cause inappropriate ‘sensing,’ which will inhibit pacing or
     rate modulation (if not previously switched to fixed rate mode).
3. Dislodged
   PPM may be dislodged during patient positioning or CVP line insertion.
4. Microshock
   Theoretical risk of microshock via PPM lead, which may induce
   arrhythmia.
5. pacing dependency
   All PPM-dependent patients are at risk of asystole or bradyarrhythmias if
   the PPM fails for any reason.
   Emergency drugs and pacing facilities (as
   discussed above) should therefore be readily available.

Question 11

other potential questions for
this case:

Answer 11

Physiology of cardiac conduction
Hazards associated with diathermy
ICD and anaesthesia—NPSA guideline