Question 20

Mode

Advantages

Disadvantages

AAI

a) Requires a single lead, 
b) AV synchronicity maintained,
c) Able to assess ST
changes,

a) Unable to use in AF,
b) Ventricular bradycardia may occur in the presence of a high grade AV block, 
c) Instability of a single atrial lead,
d) Higher risk of perforation of thin atrial wall

VVI

a) Requires a single lead,
b) Useful in the presence of AF and high grade AV block,

a) AV synchronicity is lost 
b) Unable to assess ST changes 
c) Loss of atrial kick .

d) Risk of pacemaker syndrome

DDD

a) AV synchronicity maintained
b) Useful in the presence of AF and high grade AV block
c) Heart rate responsiveness

a) Pacemaker mediated endless-loop tachycardia
b) Pacemaker syndrome if incorrectly setup
c) May not be able to assess ST changes

• Only one lead required
• Preserves AV synchrony in the presence of an intact AV node
• Protects against interference by diathermy

• contraindicated in the presence of intrinsic cardiac rhythms. 
• If the rate is not high enough, you will have an underlying rhythm competing with the pacemaker.
• Useless if the AV node is dysfunctional
• Useless in the presence of AF
• Increased risk of perforating the thin atrial wall

• Only one lead required
• Preserves AV synchrony in the presence of an intact AV node
• Only paces on demand; allows intrinsic rhythm while the rate is high enough

• Useless if the AV node is dysfunctional
• Useless in the presence of AF
• Increased risk of perforating the thin atrial wall

• Only one lead required
• Preserves AV synchrony in the presence of an intact AV node
• Useful for testing atrial sensing (using the pacing spike)

• Useless if the AV node is dysfunctional
• Useless in the presence of AF
• Unproductive in general (paces in response to normal atrial contraction, while the atrium is in a refractory period); thus, not a useful permanent mode
• Increased risk of perforating the thin atrial wall

• Only one lead required
• Protects against interference by diathermy

• Asynchronous AV contraction
• May result in the R - on - T phenomenon
• Difficult to assess ST changes (LBBB-like QRS morphology)

• Only one lead required
• Only paces on demand; allows intrinsic rhythm while the rate is high enough

• Asynchronous AV contraction
• Difficult to assess ST changes (LBBB-like QRS morphology)

• Useful for testing ventricular sensing (using the pacing spike)

• Asynchronous AV contraction
• Unproductive in general (paces in response to normal ventricular contraction, while the ventricle is in a refractory period); thus, not a useful permanent mode
• Difficult to assess ST changes (LBBB-like QRS morphology)
• Possibility of "endless loop" tachycardia

• AV synchrony is preserved
• "Pacemaker syndrome" is thus avoided
• Advantageous in patients with normal atrial activity and a dysfunctional AV node

• Two leads required
• Bundle of His is bypassed
• Difficult to assess ST changes (LBBB-like QRS morphology)
• Increased risk of perforating the thin atrial wall

• AV synchrony is preserved
• "Pacemaker syndrome" is thus avoided
• Advantageous in patients with normal atrial activity and a dysfunctional AV node
• Versatile mode, with hemodynamic advantage 

• Two leads required
• Bundle of His is bypassed
• Possibility of "endless loop" tachycardia
• Increased risk of perforating the thin atrial wall