Author + information
- Rohit Mehta, MD⁎ (, )
- Amit A. Doshi, MD,
- Ayesha K. Hasan, MD,
- Charles J. Love, MD,
- Marg Pizzuto, RN,
- Chittoor Sai-Sudhakar, MD and
- David P. Chan, MD
- ↵⁎Division of Cardiovascular Medicine, The Ohio State University College of Medicine, 473 West 12th, HLRI Room 200, Columbus, Ohio 43210
To the Editor: Device therapy for advanced cardiac failure has created the potential for device interactions and raised a significant clinical consideration before implementation of therapy. Here we present 2 case vignettes where implantation of an approved left ventricular assist device (LVAD) interfered with remote telemetry of previously implanted cardioverter defibrillators.
A 30-year-old woman with a nonischemic cardiomyopathy, American College of Cardiology Stage D status after implantable cardioverter-defibrillator (ICD) for primary prevention of sudden cardiac death, presented for implantation of a LVAD (Thoratec Heartmate II, Thoratec, Pleasanton, California) due to progressive congestive heart failure (CHF) while awaiting transplantation. Before surgery, ICD detections were suspended to minimize interactions with electrocautery. Initial LVAD motor settings were 9,400 revolutions/min (RPMs). Post-operatively, communication with the ICD (St. Jude Atlas VR Model V-193, St. Jude Medical, Sunnyvale, California) was unavailable and therapies remained off. She improved during the hospital stay with chronic LVAD therapy and presented for ICD change out. The Atlas V-193 ICD was removed from the pocket with restoration of wand communications. Reconfirmation of loss of communication within the pocket was accomplished. A newer ICD (St. Jude Atlas II VR Model V-168) was placed, and communication was confirmed on the field and in the pocket. Defibrillation testing was successful, and the patient was discharged the following day. Further evaluation of the original ICD generator was performed with no evidence of structural abnormalities.
A 67-year-old woman suffered an acute myocardial infarction in the left anterior descending coronary artery distribution after subacute stent thrombosis. Her post-infarction course was complicated by CHF, and post-gadolinium cardiac magnetic resonance imaging demonstrated nonviable myocardium precluding revascularization. After 6 months of aggressive medical therapy, she was referred for primary prevention ICD implantation with a single chamber ICD (St. Jude Medical Epic + VR V-196). Over the following 3 months, the patient had progressive decompensation with resultant admission to the hospital in cardiogenic shock. After failure of medical therapy, she underwent placement of Heartmate II LVAD with post-operative settings of 9,500 RPMs. Pre-operatively, ICD therapies were suspended. Post-operatively, her ICD remained off, owing to an inability to communicate with the device. She is scheduled to undergo ICD generator replacement.
Federal Communications Commission (FCC) regulations govern the use of wireless technology in the medical arena (1). Specific operating bands exist to minimize the interactions from a multitude of ever-expanding wireless devices. The Medical Implant Communications Service (MICS) band and the Industrial, Scientific and Medical (ISM) are the 2 primary frequency bands used medically (2). Primary use of the MICS band includes: Meteorological Aids Service, the Meteorological Satellite Services, and the Earth Satellite Service (2). The MICS band (300 to 420 MHz) supports diagnostic and therapeutic functions of implantable medical devices as a secondary use (2). The ISM band (902 to 928 MHz) confers primary use for the application of radiofrequency (RF) energy for heating, ionization of gases, and similar scientific applications with secondary use to medical devices/wireless telemetry (also allowing amateur radio operators as a secondary use) (2). The tissue penetration necessary for implantable devices has made frequencies over 2 GHz impractical for medical device telemetry (2).
Older-generation St. Jude devices use 8-kHz telemetry frequency for data transfer and programming, which is outside of the MICS and ISM bands described in the previous text (St. Jude Medical, Inc. technical support, Sunnyvale, California, e-mail communication May 1, 2007). The HeartMate II uses variable input power frequencies of 100 to 250 Hz when operating between 6,000 and 15,000 RPMs, respectively, on the basis of use of a 2 pole motor (Thoratec, Inc. technical support, e-mail communication, June 7, 2007). However, the Heartmate II uses a 12-Volt battery input to power the controller and substantially less voltage to power the motor. To facilitate operation of both components with a single battery, a pulse-width modulator (PWM) is used to reduce the 12-Volt battery that powers the controller, to facilitate motor power. The HeartMate II PWM operates at a constant frequency of 7.2 kHz and specifically produces the interaction in question. This constant output renders ineffective any manipulation in LVAD speed to overcome the device interaction. Thoratec's in-lab animal testing has been able to bypass the PWM by eliminating the controller and reducing the voltage input directly to the motor and has eliminated this interaction with the older St. Jude devices. According to Thoratec product support, manipulation of the LVAD motor speed will not change the interaction in question and has been confirmed with laboratory product testing (Thoratec, Inc. technical support [September 28, 2006], e-mail communication, June 7, 2007).
In our experience, explantation of the ICD is the only clinical option, although sporadic anecdotal reports of barrier methods (cast iron cookware shielding both components independently) to circumvent the interaction exist. Clinical testing of the Atlas II VR demonstrated no significant interaction with the HeartMate II, owing to the change in programmer telemetry to 64 kHz, well out of the range of interaction (e-mail communication May 1, 2007 with St. Jude Medical, Inc. technical support; Sunnyvale, California). No interactions with other manufacturers have been identified. The telemetry frequencies of other manufacturers (Table 1) will likely prevent a specific interaction with the Heartmate II. Interactions with other LVAD manufacturers and types are unknown, and the information provided is based on Food and Drug Administration approved or pending approval LVADs (Heartmate XVE and Heartmate II, respectively).
Implantable cardioverter defibrillator therapy is a primary option for prevention of sudden cardiac death in advanced cardiomyopathies and CHF (3,4). In the post-LVAD patient, ventricular arrhythmias are associated with a more malignant course both by the frequency and timing of their appearance (5). This adverse association has theoretically justified the use of ICDs in the setting of LVAD-supported cardiomyopathy, with more studies necessary to assess their role in outcomes. As device therapy becomes commonplace with more complex disease, device interactions will need to be factored into the complex nature of patient management (6). Careful planning by the FCC and device manufacturers will play a major role in their avoidance.
Please note: Financial support to Dr. Sai-Sudhakar from St. Jude Medical, Speakers' Honorarium: <$10,000. The authors thank Nirav Patel, Erich Stohr, Gregg Deutsch (Medtronic, Inc. technical support); Kevin Schilling (Boston Scientific, Inc. technical support); Timothy A. Rooney, Al Schwartz (St. Jude Medical technical support); Doug Thomas, Lynda Kessler (Thoratec, Inc.); Barb Besancon, RN, Marc Dutro, RN (The Ohio State University Pacer Clinic); and Sherri Wissman, RN, CCTC (The Ohio State University Transplantation Program) for their help with technical information and/or manuscript preparation.
- American College of Cardiology Foundation
- ↵Medtronic Technical Services Communication: “Radiofrequency Considerations for the Use of Wireless Telemetry with the Medtronic CareLink Programmer and Implanted Medical Devices.”
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