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Day 10: Electronic Pacemakers

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  1. Pacemaker nomenclature—a standardized 5-letter code, recently designated "NBG", has been developed to indicate various pacemaker functions.

    1. The first letter refers to the chamber(s) to which pacing stimuli are delivered

      1. A = atrium

      2. V = ventricle

      3. D = dual or both chambers

      4. O = no pacing support (early implantable defibrillators, which also used this coding system, had no pacing function)

    2. The second letter refers to the chamber(s) in which sensing can occur

      1. A = atrium

      2. V = ventricle

      3. D = dual or both chambers

      4. O = no sensing

    3. The third letter refers to the mode of sensing or how the pacemaker reacts to a detected event

      1. I = inhibited, the system inhibits the output and resets the timers in response to a detected event.

      2. T = triggered, the system delivers an output in response to a detected event.

      3. D = dual mode of sensing

        1. This action is specific for a dual chamber pacemaker.

        2. It can both inhibit and trigger, depending on how it is programmed and what happens in the two chambers.

      4. O = no mode response (this is the only option if there is no sensing).

    4. The fourth letter refers to a hierarchy of increasingly more complex capabilities

      1. O = no programmability, no communicating capability and no rate modulation.

      2. P = simple programmability (one or two parameters).

      3. M = multiparameter programmability (three or more programmable options).

      4. C = communicating or telemetric capability; these devices all have multiparameter programmability and are also able to transmit stored and real time intracardiac electrograms.

      5. R = rate modulation; these devices incorporate all of the above and add the capacity to vary heart rate according to programmed algorithms.

    5. The fifth letter previously referred to antitachycardia functions such as overdrive pacing or the delivery of a shock, but currently refers to multisite pacing, thus:

      1. A = multisite pacing in the atria

      2. V = multisite pacing in the ventricles (as in biventricular pacemakers for heart failure)

      3. D = multisite pacing in the atria and ventricles

      4. O = no multisite pacemakers

    6. Implantable cardiac defibrillators (ICDs) now have a separate coding system that is not covered in this text.

  2. Pacemaker development

    1. VOO (Day 10-01) (Day 10-02)

      1. The first pacemakers, developed in the late 1950s, had no sensing circuitry and paced in the ventricle at a rate set by the factory.

      2. The advantage of this system was that it was better than asystole.

         

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        DAY 10-1

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        DAY 10-2

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      3. A modern pacemaker can still be programmed to this modality, which may be useful under certain circumstances (e.g., during surgery when signals from electrocautery might be inappropriately inhibit the pacemaker).

    2. VVT (Day 10-03)

      1. This pacemaker sensed in the ventricle, but was committed to firing.

      2. This technology solved the potential problem of possible initiation of a ventricular arrhythmia by avoiding firing on the upslope of the T wave.

      3. The problems of distortion of the QRS complexes and constant use of the battery remained.

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