The Next Standard in ICD Lead Technology: The DF-4 ICD Lead Connector System
A recent ICD implant case used the new SJ4 connector system, an interesting advancement that represents the next standard in ICD lead technology. This article will discuss the history of the DF-4 technology as well as describe aspects of how this technology will alter the practice of electrophysiology.
While the exact incidence of pin-to-port mismatch is difficult to track, it will soon become much less common as the current standard in high voltage lead connections, the DF-1 connection and its low-voltage counterpart, the IS-1 connection are at least partially replaced by the draft standard IS-4/DF-4. The ritual of reading the last four digits of the serial numbers on the IS-1 leads before placing them in ports on the device should similarly become much less necessary. With multiple pace-sense leads utilizing an IS-1 connection, the atrial, right ventricular, and left ventricular leads can all look identical. Biventricular defibrillators, with five ports and three IS-1 connections, can similarly seem quite confusing, requiring careful attention to the diagram etched on the side of the device. When published, the IS-4/DF-4 draft standard will simplify and streamline the header connections for these devices. The new design incorporates four conductors into a quadpole connection replacing the defibrillation coil DF-1 and pace-sense IS-1 connections with the DF-4 connection. The IS-4 draft standard is similarly a quadpole connection for low-voltage applications. The result is that the three ports previously required for a defibrillation lead are now combined into a single port and connection. (See Figure 1.)
The DF-4 draft standard began in collaboration over seven years ago among the major device manufacturers to simplify the connection between the pulse generator and ICD lead. The physical specifications of the standard were agreed upon very early in the process: the quadpole connector would be in-line and the size, shape and specifications were established. The ICD header has one port to accommodate the dual-coil lead instead of three. The header is significantly smaller; the lead is 7 to 10 cm shorter because no yoke is required to bring the IS-1 and DF-1 connections to a single lead body. Recent developments have prompted close scrutiny of lead engineering and design, and approval of required bench-testing standards for the new lead design has been a long process.
The first-to-market version of the DF-4 draft standard lead in the U.S. has been available since June 10, 2009. The St. Jude Medical SJ4 lead connector system paired with the Durata lead and devices with compatible headers are available for use in the U.S. The Boston Scientific version of the DF-4 draft standard, the ENDOTAK RELIANCE® 4-SITE (Figure 2), is available in Europe; the first human implants were announced on May 12, 2009. Medtronic also has a version of the DF-4 draft standard, which is currently being evaluated by the FDA. The new standard moves the sealing rings from the lead to the device header where they are less likely to be damaged and are replaced at generator change. The new lead design simplifies the initial implant process as well as generator replacement procedures by reducing the total ports and set-screw connections and eliminating the possibility of inadvertently reversing high-voltage pins when connecting the lead. Dual chamber devices utilize the DF-4 draft standard for the ventricular lead and the smaller IS-1 for pace-sense lead in the atrium, eliminating inadvertent pace-sense lead reversal. Biventricular devices will use IS-1 connections for atrial and left ventricular pace-sense leads, and the RV lead uses the DF-4 design. With the advent of quadpole left ventricular leads, devices will use an IS-1 connection for the atrial lead, IS-4 connection for the left ventricular lead, and DF-4 for the RV pace-sense and coils.
Benefits of the Technology
Among the benefits of the new design is a reduction in lead length (reducing lead-on-can abrasion), smaller pocket volume (for lead as well as reduced pulse generator size owing to a smaller header design) and the potential for reduced implant time and lower risk of port mismatch. The draft standard, once published, will also allow compatibility with the leads across the industry and interchangeability of adaptors and accessories for lead placement.
The quadpole connector also allows for simpler VDD pacing systems, multipole atrial, right ventricular or left ventricular leads, and at least potentially multipole leads with defibrillation potential.
Having seen the design at the Heart Rhythm Society meeting in May 2009, I had been anxious to use the SJ4 lead system for my patients. My opportunity to use it for the first time coincided with its first use in the VA system. That implant was performed on July 30, 2009 at the Omaha VA Nebraska-Western Iowa Healthcare Center. The patient, a minister from Iowa, had ischemic cardiomyopathy and required a single-chamber ICD for primary prevention of sudden cardiac death. The procedure went smoothly and the lead handling characteristics are very familiar (as the lead is the Durata, based on the Riata platform). Stylets pass through the lead slightly more easily, but this may be due to a shorter overall length. The single set screw seemed anticlimactic, and the lead length seemed short due to the absence of a yoke and Hydra of lead connections.
The decision to use a lead conforming to the DF-4 draft standard must be made with care. Patients should be those in whom subcutaneous array or azygous or coronary sinus coil will not be required (as adaptors for adding these options are not yet available and would be so large as to obviate any benefit of the smaller lead design). Patients not expected to have elevated defibrillation thresholds would be preferred candidates for the new lead, though obviously elevated defibrillation thresholds cannot always be predicted a priori. Addition of an array or coil would currently require removal of the DF-4 lead, replacement with an IS-1/DF-1 lead and replacement of the device with the IS-1 design. The addition of a ventricular pace-sense lead, commonly necessary with older leads, is similarly not possible at this point due to a lack of a suitable adaptor. Lead replacement would currently be necessary if one of the conductors is damaged or fails. Replacing the defibrillation lead without extraction of the old lead can be especially problematic in an integrated bipolar design where long-term contact between coils can cause noise sensed as ventricular arrhythmia. Removing the SVC coil from the circuit can easily be done by programming the device, and single-coil leads are also available. If replacing the lead is necessary, and extraction of the malfunctioning lead is required, both the St. Jude Medical Durata and the Boston Scientific Endotak Reliance leads have been designed with consideration of extraction. The Durata (St. Jude Medical) lead utilizes a flat coil design that is backfilled and minimizes tissue ingrowth. The Endotak Reliance (Boston Scientific) lead uses an ePTFE coating on the coils, which helps to prevent tissue ingrowth. These designs are intended to facilitate removal should extraction be necessary.
The design of the DF-4 lead does not allow use of the alligator clips currently ubiquitous in device placement without an adaptor because the clips do not make contact well with the lead electrodes and may damage the lead. The SJ4 device (St. Jude Medical) utilizes plunge connectors, whereas the Boston Scientific device is packaged with an adaptor for use with alligator clips. The plunge connector or adaptor is required to avoid inadvertent connection with multiple electrodes simultaneously. The pin connection requires a different torque tool to extend the helix of the active-fixation lead as well, as the pin diameter is greater compared to the IS-1 standard, though the torque tool for DF-4 leads can also be used on the IS-1 pin.
The headers of the DF-1 and DF-4 standards are also different for obvious reasons. Representative device headers are shown in the figures, with the St. Jude Medical single chamber (VR) device in Figure 1 and biventricular (CRT-D) devices shown in Figure 3. The number of set screws and the complexity of the header are decreased by using the DF-4 lead design. Total header volume may also be decreased with the DF-4 draft standard.
The IS-4/DF-4 draft standard represents an incremental improvement in lead design and will simplify the implantation process and device replacement. The IS-4/DF-4 draft standard will also eliminate port mismatch with single chamber devices using this design. The pocket volume, length of redundant lead, and patient discomfort should all be reduced to varying degrees as well. This will add to the practice of electrophysiology a simpler option in single chamber ICD placement and a more streamlined option in dual and biventricular systems. It will also allow quadpole left ventricular leads, simplify VDD systems, may minimize revisions for loose set screws, and hopefully advance the field of research in multielectrode arrays for rhythm management. The IS-4/DF-4 draft standard is scheduled to be published on May 31, 2010.