Pacemaker, Defibrillator, and Lead Codes and Headers

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8 Pacemaker, Defibrillator, and Lead Codes and Headers

Robert Andrew Pickett, George H. Crossley, III

In the continuing pursuit of therapy for the arrhythmia patient, tremendous strides have been made in pacing and defibrillation platforms. Along with these advances, much standardization has been introduced to limit differences and disparities among device types and to allow for compatibility. In the 1960s, pacemakers served to stimulate one chamber at a fixed rate. By the 1980s, implantable cardioverter-defibrillators (ICDs) offered lifesaving therapy by way of shock only, without supportive pacing for bradycardia. However, many patients require both antibradycardia and antitachycardia therapies. Later, cardiac resynchronization therapy (CRT) for congestive heart failure was developed and has become the standard of care for these patients. With each of these advances in device therapy, the traditional means of describing device function have become inadequate, requiring new standardized terminology.

Devices are used for more indications in the treatment of patients with bradyarrhythmias, tachyarrhythmias, and congestive heart failure, and more algorithms are developed either to stimulate multiple chambers (cardiac resynchronization) or to minimize unnecessary pacing when possible.^1,² It is noteworthy that, unlike some therapies, the generic pacemaker codes have withstood the test of time.

Pacemaker Codes

Three-Position Ichd Code (1974)

In 1974 the Inter-Society Commission for Heart Disease Resources (ICHD) proposed a three-position code to allow a uniform system to describe the functionality of a pacemaker platform.³ The goal was to create a generic code that would work among all platforms; it would also allow for concise description of what was becoming a more complex issue. The first letter of the code was to distinguish the chamber(s) being paced. The second letter was to determine the chamber(s) that were sensed for intrinsic electrical depolarizations and to start the timer for determining the next paced beat delivery. The third letter of the code was to describe how the pacing was to be affected by a sensed event (i.e., inhibiting pacing or triggering pacing in response to sensing).

Position one can be the atrium (A), the ventricle (V), or both atrium and ventricle (D) for location of pacing. Position two again represents atrium (A), the ventricle (V), or both (D), meaning sensing can occur for spontaneous electrical depolarizations in either chamber. The third position describes whether sensing leads to inhibition of pacing (I), triggering the delivery of a pacing stimulus (T), or both inhibition and triggering (D). Tables 8-1 and 8-2 outline the options and different pacing configurations.

TABLE 8-1 The 1974 Three-Position ICHD Code or Three-Letter Identification Code *

First Letter	Second Letter	Third Letter
Chambers paced	Chambers sensed	Mode of response

* Letters used: A, atrium; D, double-chamber; I, inhibited; O, not applicable; T, triggered; V, ventricle.

Adapted from Parsonnet V, Furman S, Smyth NPD: Implantable cardiac pacemakers: Status report and resource guideline. Pacemaker Study Group, Inter-Society Commission for Heart Disease Resources (ICHD). Circulation 50:A-21, 1974. Copyright 1974 American Heart Association.

TABLE 8-2 Pacing Modes Described by the Three-Position ICHD Code

Mode	Description
VOO	Asynchronous ventricular pacing; no sensing function
AOO	Asynchronous atrial pacing; no sensing function
DOO	Dual-chamber (AV-sequential) asynchronous pacing; no sensing function
VVI	Ventricular pacing inhibited by ventricular sensing
VVT	Ventricular pacing triggered instantaneously by ventricular sensing
AAI	Atrial pacing inhibited by atrial sensing
AAT	Atrial pacing triggered instantaneously by atrial sensing
VAT	Ventricular pacing triggered after a delay by atrial sensing
DVI	Dual-chamber (AV-sequential) pacing inhibited by ventricular sensing

AV, Atrioventricular.

Modified from Parsonnet V, Furman S, Smyth NPD: Implantable cardiac pacemakers: status report and resource guidelines. Pacemaker Study Group, Inter-Society Commission for Heart Disease Resources (ICHD). Circulation 50:A21, 1974. Copyright 1974 American Heart Association.

The outstanding feature of this code is its utility in describing pacemaker function despite all the therapeutic advances since its introduction. Changes have been proposed, but this code endures with the addition of a letter to indicate rate-responsive pacing.

Five-Position Ichd Code (1981)

In 1981, in response to changes in the technology of pacing, two more positions were added. The first three positions remained unchanged, and position four was developed to convey the ability to program the pacemaker. With advancements in pacing, it became important to determine if a pulse generator could be programmed. As the ability to reprogram the pacing rate, pacing output, and mode were introduced into pacemakers, the fourth position could be listed as programmable (P), which generally implied one feature, or multiprogrammable (M), which implied multiple parameters, or none (O). A fifth letter was included to determine if the device had the capability of antitachycardia pacing. Interestingly, this fifth letter was used in the pacing platform and was not for ICD platforms, which were not available at the time this code was developed.

A second modification of the ICHD nomenclature occurred in 1983 to distinguish, in the fourth letter, if a device had the ability to internally store data such as battery voltage, serial numbers, or electrograms. This was designated communicating (C).

Table 8-3 shows the different options for all five positions, but as one would surmise, it is now assumed all devices can store information and can be programmed, thus obviating the need for that nomenclature. Currently, pacing platforms that provide antitachycardia pacing are typically identified based on the specifics of the device platform rather than an additional letter in the code (e.g., Medtronic EnRhythm pacing platform allows atrial antitachycardia pacing therapy). Using this convention, a single-chamber pacing system today would be described as VVIM to designate multiprogrammability or VVIC to designate the presence of telemetry (communication). In reality, this fourth letter is implied due to the presence of telemetry and multiprogrammability in all of our current platforms. Table 8-4 provides examples of the many different ways to describe pacemaker function that are highly descriptive of the available features on pacing systems, but not readily used in day-to-day management of pacemakers.

TABLE 8-3 The 1981 Five-Position ICHD Code

TABLE 8-4 Pacing Modes Described by the Five-Position ICHD Code

Mode	Description
VDD,M (VDDM)	Ventricular antibradycardia pacing inhibited by ventricular sensing, triggered after delay by atrial sensing; multiprogrammable device; no antitachyarrhythmia (antitachycardia) function.
DDD,M (DDDM)	Dual-chamber (AV-sequential) antibradycardia pacing inhibited by sensing in either chamber, with ventricular pacing triggered after delay by sensing in atrium after ventricular event; multiprogrammable device; no antitachycardia function.
VVI,MB (VVIMB)	Ventricular antibradycardia pacing inhibited by ventricular sensing; multiprogrammable device; pacing bursts for ventricular tachycardia, means of activation unspecified.
AAR,ON (AARON)	No antibradycardia function; nonprogrammable device; normal-rate competition for termination of atrial tachycardia, activated by atrial sensing.
AOO,OE (AOOOE)	Asynchronous atrial antibradycardia pacing; nonprogrammable device; externally activated atrial antitachycardia pacing, nature unspecified.