I had become accustomed to making the necessary tradeoffs when choosing the appropriate defibrillator for my patients and until recently thought that these choices were ones that I would always have to make. But the options have increased and matching the unique capabilities of devices, lead systems and remote monitoring has become easier now that there are more than two distinct categories of defibrillator systems available — single and double lead implants and now, the DX system.
I recently attended a local educational program where the new DX defibrillator systems were explained along with the rationale for their development. The presenters in this program reviewed the evolution of the debate, which began in early 2011, regarding appropriate use of implantable cardiac defibrillators (ICDs), and showed several case study examples that took the audience through patient selection, implant techniques and the utilization of home monitoring.
Many readers may recall this dispute beginning with the Journal of the American Medical Association (JAMA) article, “Non-Evidence Based ICD Implantations in the United States,” authored by Al-Khatib (et al).A panel discussion between doctors Al-Khatib and Brian Olshansky quickly followed at Heart Rhythm Society’s 2011 Annual Scientific Session in San Francisco. Although there was no clear winner coming out of the exchange, pressure in the system increased as U.S. Department of Justice investigations and Recovery Audit Contractor (RAC) reviews of ICD implantation ensued.
Byron Lee, M.D., from the University of California San Francisco gave a presentation that took the audience on a journey through the many studies published over the intervening years. These subsequent analyses have a common denominator — the National Cardiovascular Device Registry’s Implantable Cardiac Device Registry (NCDR). ICD implanters nationwide have been contributing data since May of 2006. Although the data collected for the NCDR registry is not entered with the greatest level of rigor, the numbers are impressive, and the trends are hard to ignore. The data reveals widely disparate regional and even local trends in device utilization along with relative rates and the accompanying costs associated with the use of dual versus single-chamber ICDs. As you can see from the chart above depicting the number of de novo ICD implants in the US over the most recent four years, there appear to be at least two notable effects from this attention to appropriate use. First, overall use of ICDs has decreased, from a high in March of 2010 (7,684) to a low in September 2012 (5,285), by over 30%. There also appears to have been diminished utilization of dual-chamber devices from a high of 65% to the current 53%, and a corresponding increase in the number of single chamber implants.
Prior to this presentation, and for the past several years, I have made the decision between single and dual-chamber ICD primarily based on the ACC/AHA guidelines according to the patient’s condition. For patients with demonstrated pacing indications, dual-chamber ICD’s have been, and continue to be, the best choice. However, for my patients that do not require atrial pacing, I have another option to consider, the DX. The challenge has always been to obtain valuable atrial signal information. Atrial signals can enable device algorithms to discriminate self-terminating rhythms, or those otherwise determined inappropriate to warrant shock therapy, and can provide valuable post shock clues as to what underlying condition caused the device to shock.
Single chamber devices simply cannot perform the former, and while far-field signals can and have been used for the latter, they are sometimes hard to interpret and can mislead the interpreter. DX systems solve this issue by producing high-fidelity atrial signals that, once conducted by the lead to the can, are augmented 4X by on-board amplifiers and further clarified by sophisticated band-pass filters before being interpreted and acted on by the device’s algorithms.
DX systems are designed to obtain the atrial signal (p-Waves) utilizing a ventricular lead with a pair of sensors (dipoles) in the right atrium. There are two 65 cm lead options with different dipole spacing (15 and 17 cm) measured from the distal active fixation tip to the center of the dipoles. The operator simply chooses based on measurements of the heart size and expected heart drop for the individual patient. A mid to lower atrial location for the dipole is ideal.
The Biotronik DX systems have been available since May of 2013. The previous version (Lumax DX) had the same capabilities, but with a larger form factor. The newest version (Ilesto DX) is significantly downsized and now competes effectively in terms of size and longevity to other single and dual-chamber ICDs. The reasons for considering this therapy will certainly vary between implanters. I prefer to get the most information (atrial signal) with the least amount of hardware (leads) and accompanying patient risk such as dislodgement or infection requiring system or lead revision, or even long term lead failure and removal of the atrial lead.
Editor's note: Richard Chang, M.D., FACC, FSCAI, CCDS is a practicing physician with John Muir Health Physician Network, Division of Cardiology in Walnut Creek, California. He completed his interventional cardiology fellowship training at the Houston Methodist, DeBakey Heart and Vascular Center in conjunction with the University of Texas Medical Branch and completed general cardiology at Loma Linda University Medical Center.