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*

* 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

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

AV, Atrioventricular.

Modified from Parsonnet V, Furman S, Smyth NPD: Revised code for pacemaker identification. PACE 4:400, 1981.

NASPE/BPEG Generic (NBG) Pacemaker Code

The Mode Code Committee of the North American Society of Pacing and Electrophysiology (NASPE), now known as the Heart Rhythm Society, in cooperation with the British Pacing and Electrophysiology Group (BPEG), developed a code in 1987 (Table 8-5).⁴ The one change still used today is the letter R in the fourth position to represent rate-modulated pacing to treat chronotropic incompetence. The R in the fourth position was developed in response to the many sensors available to help the pacemaker mimic sinus nodal function in response to external or internal stimuli. The other development in the nomenclature is the use of the letter S for shock delivery for tachyarrhythmias with the fifth position in the code.

The NASPE/BPEG Generic (NBG) Pacemaker Code retains all the characteristics of the 1974 ICHD Code and some of those of the later five-position codes. To deal with the increasing complexity of later devices, however, it was considered necessary to clarify several features and to define more explicitly how the code was to be used. Positions I, II, and III were still used exclusively for antibradycardia pacing, but position IV had the option of describing either programmability or rate-responsive pacing. With establishment of programmability in almost all devices, position IV evolved to denote the presence or absence of rate-response pacing. Position V is for describing the ability to deliver antitachycardia therapy, as either antitachycardia pacing or a shock. As of 1987, shocks were described as either low-energy cardioversions or high-energy defibrillation. No distinction was made between low-energy and high-energy shocks in the nomenclature. The original code of 1981 allowed for different letters to describe different forms of pacing trains used in tachycardia termination, such as burst (B), scanning (S), or external (E). The update of 1987 simplified the descriptors to pacing (P), shock (S), or pacing and shocks (D).^4,5

Revised NBG Code

In light of evolving pacemaker technology and increasing interest in multisite pacing, the 1987 NBG Code was modified by a multinational task force under the chairmanship of David Hayes, MD. Three major changes were made that simplified the code. It was assumed that all pacemakers were communicative and programmable, eliminating the need for those codes. Further, this revised code established a system to describe the function of ICDs.

The structure of the revised NBG Code is summarized in Table 8-6, with examples of its use in Table 8-7.⁶ Note that with each modification, the first three positions continue to describe antibradycardia pacing, but in this update, no mention of antitachycardia pacing is made.⁷ Positions I, II, and III indicate the chambers in which pacing and sensing occur and the effect of sensing on the triggering or inhibition of subsequent pacing stimuli. In this context, “sensing” refers specifically to the detection of spontaneous cardiac depolarizations (or spurious interference signals interpreted as spontaneous cardiac depolarizations) outside the refractory periods of the pulse generator. Position IV is now used only to indicate the presence (R) or absence (O) of an adaptive-rate mechanism (rate modulation). This position is also used to denote that changes can occur in pacing parameters, such as changes in the atrioventricular (AV) delay in response to increased heart rates.

TABLE 8-7 Examples of Revised NBG Code

MUSTIC, Multisite Stimulation in Cardiomyopathy.

* Leclerq C, Walker S, Linde C, et al. Comparative effects of permanent biventricular and right-univentricular pacing in heart failure patients with chronic atrial fibrillation. Eur Heart J 23:1780-1787, 2002.

† Revault d’Allonnes G, Pavin D, Leclerq C, et al. Long-term effects of biatrial synchronous pacing to prevent drug-refractory atrial tachyarrhythmias: a nine-year experience. J Cardiovasc Electrophysiol 11:1081-1091, 2000.

‡ Fitts SM, Hill MR, Meral R, et al. Design and implementation of the Dual Site Atrial Pacing to Prevent Atrial Fibrillation (DAPPAF) clinical trial. J Interv Card Electrophysiol 2:139-144, 1998.

§ Cazeau S, Leclerq C, Lavergne T, et al. Effects of multisite biventricular pacing in patients with heart failure and intraventricular conduction delay. N Engl J Med 344:873-880, 2001.

Modified from Bernstein AD, Daubert J-C, Fletcher RD, et al. The Revised NASPE/BPEG Generic Code for antibradycardia, adaptive-rate, and multisite pacing. PACE 25:260-264, 2000.

Position V indicates whether multisite pacing, as described earlier, is present in none of the cardiac chambers (O); in one or both of the atria (A), with stimulation sites in each atrium or more than one stimulation site in either atrium; in one or both of the ventricles (V), with stimulation sites in both ventricles or more than one stimulation site in either ventricle; or in dual chambers (D), in one or both of the atria and in one or both of the ventricles. Resynchronization pacing is often used to treat congestive heart failure in patients with a wide QRS, but the device is rarely described using a fifth letter to denote ventricle (V) as the site of pacing in both ventricles. In reality, a biventricular pacemaker with rate-responsive pacing “on” would be categorized as DDDRV pacing in both atrium and ventricle, sensing in atrium and ventricle, inhibition or triggered activity dependent on intrinsic activation rates, with rate-responsive pacing and the presence of pacing leads in the right and left ventricle.

As multisite pacing and physiologic pacing with leads in specific positions (e.g., Bachman bundle) are further investigated, use of the fifth letter may become more prevalent.^8,9

NASPE/BPEG Defibrillator (NBD) Code

On January 23, 1993, the NASPE (now Heart Rhythm Society) Board of Trustees approved the adoption of the NASPE/BPEG Defibrillator (NBD) Code (Table 8-8).¹⁰ It was developed by the NASPE Mode Code Committee, composed of members of NASPE and BPEG, and was intended for describing cardiac-defibrillator capabilities and operation. The resultant code for ICDs is similar in form to the long-established pacing code. Although the pacing code described antibradycardia pacing in detail and then acknowledged the presence of antitachycardia therapy, the ICD code describes the antitachycardia therapy in detail and then acknowledges the presence of antibradycardia pacing.

No indication is made to distinguish between low-energy cardioversion and high-energy defibrillation. Position (potential) I denotes the chamber where the shock is delivered; position II indicates antitachycardia pacing function; position III reports how the tachycardia is detected, i.e. based on electrograms or hemodynamic changes, and position IV reports the presence of antibradycardia pacing.

In current practice, given the lack of a selective atrial defibrillator, the first letter will always be V for ventricle as the location of the shock and the third letter will always be E for electrogram because all ICDs are using electrograms for determination of arrhythmia. The second position will be rarely used because antitachycardia pacing is so widely prevalent on ICDs, and with so many combinations of therapies, a single letter cannot reliably describe them. Given the state of current practice, an ICD is still described most often using the same four letters (including rate-responsive pacing) as in the pacing realm.

NBD Code, Short Form

As an additional means of concisely distinguishing among devices limited to cardioversion or defibrillation and those that incorporate antitachycardia and antibradycardia pacing, a short-form code was defined (Table 8-9). It is intended for use only in conversation and again rarely used given the widespread prevalence of both antitachycardia pacing and shocking across platforms and manufacturers.

TABLE 8-9 The NASPE/BPEG Defibrillator Code, Short Form

ICD, Implantable cardioverter-defibrillator.

Modified from Bernstein AD, Camm AJ, Fisher JD, et al. The NASPE/BPEG Defibrillator Code. PACE 16:1776, 1993.

NASPE/BPEG Pacemaker-Lead (NBL) Code

In 1996 the NASPE Board of Trustees voted to adopt a generic code for pacemaker leads, to be known as the NASPE/BPEG Pacemaker-Lead (NBL) Code. The code was approved subsequently by BPEG, and its definition and usage conventions were published as a NASPE Policy Statement. The NBL Code is a four-position generic code intended for use in conversation, record keeping, writing, and labeling. All four positions (potentials), as defined in Table 8-10, are used in every circumstance, unlike the NBG Code, for which only three or four of the five positions are often used. Table 8-11 provides examples of the use of the simple NBL Code.¹¹

TABLE 8-11 Examples of the NBL Code

Modified from Bernstein AD, Parsonnet V. The NASPE/BPEG Pacemaker-Lead Code. PACE 19:1535, 1996.

The NBL Code is designed so that it cannot be confused with the NBG or NBD Codes. As with those earlier codes, the characteristics were chosen in terms of clinical priority to describe characteristics with significant influence on the behavior of the device under consideration. For this reason, the NBL Code does not address such features as connector design and electrode location. Moreover, until there was emergence of clearer patterns in the electrode configurations used for cardioversion and defibrillation, with or without the pulse generator housing serving as part of the electrode system, it was believed that attempts to design a practical code encompassing leads used for cardioversion and defibrillation as well as pacing would be premature.¹²