Question 20

List the advantages and disadvantages of the following pacemaker modes:
AAI, VVI, DDD.(You may tabulate your answer).

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College Answer

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

Discussion

Little can be added to the college answer. Advantages and disadvantages of various pacing modes enjoy a more thorough discussion elsewhere. And... there are fair few modes.

A Comparison of Single and Dual Chamber Pacing Modes
Pacing Mode	Description	Advantages	Disadvantages
AOO	asynchronous atrial pacing.	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
AAI	atrial demand pacing	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
AAT	atrial pacing	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
VOO	asynchronous ventricular pacing	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)
VVI	ventricular demand pacing	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)
VVT	ventricular pacing	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
VAT	atrial sensing, ventricular pacing	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
DDD	dual chamber demand pacing	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

References

Gillis, Anne M., et al. "HRS/ACCF expert consensus statement on pacemaker device and mode selection." Journal of the American College of Cardiology 60.7 (2012): 682-703.

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