Basic Pacing Modes

More detailed information regarding these modes will be provided as part of other study guides, further down the category list. As such, this covers the basics.

AAI Mode


AAI pacing allows the ventricles to do their own thing, and only concerns itself with the atrial activity. It is reserved for patients presenting with Sick Sinus Syndrome with no atrioventricular node conduction abnormalities.

In the absence of any AV nodal block, AAI mode will in essence, generate something pretty close to a natural heartbeat, as the ventricles will contract on their own.

Threshold levels need to be set lower in AAI pacing, compared to VVI, due to P waves being of a lower amplitude.

Note: This mode can be programmed on pacemakers other than single chamber, so in the event of an AVN decay, the ventricular lead can be programmed to pace as needed.

VVI Mode

temporary_1471260400111.pngGiven the nomenclature, VVI essentially functions as the antithesis to AAI; it only concerns itself with the BPM of the bottom chamber of the organ. This mode is a common way to treat patients presenting an AF with slow ventricular response; the atria don’t have a real beat in AF, so the best course is to ensure the ventricles, which do have a beat, can be stimulated in an appropriate manner.

Single lead VVI pacing is not suitable for patients with AV node dysfunction, as there is no lead to sense activity in the atria.

Note: As with AAI, this mode can be programmed on pacemakers other than single chamber.

DDD Mode


This mode treats the heart in the same way as AAI and VVI, but both of them at once, due to its employing (at least) two leads. At its simplest, DDD will give four possible outcomes;

  • ASVS
    • A sense V sense
    • Normal sinus rhythm
    • The device senses both chambers
  • APVS
    • A pace V sense
    • Atrial rhythm abnormality
    • The device paces the atrium, but senses the ventricle
  • ASVP
    • A sense V pace
    • AV nodal dysfunction
    • The device senses atrial activity, and paces the ventricle
  • APVP
    • A pace V pace
    •  Atrial and ventricular asynchrony. E.g. 3rd° AVB, or HB in which treatment has failed
    • The device paces both chambers

BiVent Mode

In cases of heart failure, the ejection fraction blood from the ventricles is reduced, due to what is essentially a decrease in efficiency. HF can begin to develop as a result of desynchronised function, also.


Filling your cheeks with air, and the slapping one side at a time expels a smaller quantity of air than that when slapping both at once. This is the same when thinking about the ventricles. BiVent mode is applied after echocardiography, and ensures that ventricular contractions remain in sync.