Problem of exit block and hence failure to capture with reference to pulse amplitude and pulse duration

1. Failure to capture

a) Occurs when pacemaker spike is not followed by a P &/or QRS

b) Technical causes

i) loose connection

ii) lead dislodgment

iii) inadequate mA output

c) Increased pacing threshold

i) Inflammation & fibrosis around pacing electrode

ii) Myocardial ischaemia/infarction

iii) Acute electrolyte/acid-base disturbances

a) Elevated potassium

b) Elevated pCO2

c) hypoxia

d) hyperglycaemia

iv) Metabolic disturbance

a) Hypothermia

v) Drugs

a) Antiarrhythmics

b) Beta-blockade

2. Treatment

a) If due to increased pacing threshold

i) Increase output (mA)

ii) ?increase pulse duration (seldom a problem )

iii) Often pacing thresholds are different for both electrodes; use electrode with lowest threshold

b) Correct underlying physiological disturbance

c) Atrial capture is not achievable if develop AF or Af