Pacemakers and internal cardioverter defibrillators

1

What are the common indications for placement of a permanent pacemaker?

Common indications are as follows: symptomatic bradycardia that is not reversible, third-degree heart block (sometimes referred to as complete heart block ) is a problem of the atrioventricular (AV) node and requires permanent pacing, second-degree type II heart block (even in an asymptomatic patient), as it can progress to third-degree heart block.

2

What is the origin of the NBG coding system for permanent pacemakers? What do positions I, II, III, IV, and V in the NBG code stand for?

The North American Society of Pacing and Electrophysiology and the British Pacing and Electrophysiology Group combined to produce the Generic (NBG) code. Positions I, II, and III define the chamber in which pacing or sensing occurs and the mode of the response to the sensed or triggered event. Position IV indicates the presence (R) or absence (O) of an adaptive-rate mechanism and whether it is simple (P) or multiprogrammable (M). Position V refers to multisite and antitachycardiac permanent pacemaker (PM) functions ( Table 29.1 ).

3

What are asynchronous pacing modes and how would you describe them in the NBG code?

The asynchronous pacing modes are often used for temporary pacing. The PM will be programmed to pace at a fixed rate, without the ability to sense or react to any underlying intrinsic cardiac activity. The NBG codes are AOO, VOO, or DOO. In these modes, the atrium, ventricle, or both are paced, and the PM has no sensing capability.

4

When is it advantageous to use asynchronous pacing?

A PM may be reprogrammed into an asynchronous mode perioperatively to allow for the safe use of surgical electrocautery. If not reprogrammed, electrocautery used during surgery could be sensed by the PM and misinterpreted as underlying intrinsic cardiac activity, thereby inhibiting the pacing function and possibly resulting in bradycardia or even asystole in a PM-dependent patient.

5

Define DDD pacing.

From the NBG code, DDD describes a situation in which the atria and ventricles are paced, the atrial and ventricular response to the pacing is sensed, and the dual mode of the response is both inhibited and triggered. This form of pacing is common and allows for an underlying sensed event from the atria to occur, and if it does not, for the atrium to be paced. An appropriately set AV delay will then be allowed to occur, and if no ventricular sensed event occurs within a preset time interval, the ventricle will be also paced. DDD mode is sometimes referred to as physiological pacing because it allows for AV synchrony that closely approximates normal cardiac function.

6

What are the advantages and disadvantages of DDD pacing?

There is reduced incidence of atrial fibrillation with the use of DDD pacing. In addition, maintaining AV-synchrony with DDD pacing reduces atrial pressures and increases ventricular end-diastolic volumes, resulting in increased stroke volume, better cardiac output, and improved arterial blood pressure and coronary perfusion. DDD pacing has also been shown to decrease thromboembolic events, which may be related to the reduction in atrial fibrillation seen.

However, if used too frequently, chronic right ventricular pacing in DDD mode results in adverse left ventricular (LV) remodeling, LV dysfunction, congestive heart failure, and increased incidence of atrial fibrillation.