Digital cellular telephone interaction with implantable cardioverter-defibrillators.

OBJECTIVES: This study sought to determine, in vivo, whether electromagnetic interference (EMI), generated by North American Digital Communications (NADC)/Time Division Multiple Access-50-Hz (TDMA-50) mobile cellular digital telephone model AT&T 6650, disturbs normal implantable cardioverter-defibrillator (ICD) operation and to verify these observations in vitro by testing a selection of telephones representing worldwide systems. METHODS: The effects of cellular phone interference on the operation of various models of market-released ICDs from a single manufacturer, Medtronic, Inc., were tested. The in vivo clinical test was undertaken in 41 patients using the AT&T 6650 digital telephone with the NADC/TDMA-50 technology. The in vitro component of the study was examined twofold: 1) antenna generated far field; and 2) analog/digital cellular telephone near field. RESULTS: None of the ICDs tested in 41 patients were affected by oversensing of the EMI field of the cellular telephones during the in vivo study. Therefore, the binomial upper 95% confidence limit for the failure rate of 0% is 7%. The in vitro antenna-generated field testing showed that telephone modulation frequencies used in the international Global System Mobile and TDMA-50 cellular telephone technologies did not result in ICD sensing interference at the predicted electric field intensity. The in vitro near field tests were performed using both analog and digital cellular telephones in service, or in the test mode, and indicated no interaction with normal operation. However, the static magnetic field generated by the cellular telephone placed over the ICD at a distance < or = 0.5 cm will activate the internal reed switch, resulting in temporary suspension of ventricular tachycardia and fibrillation detection. CONCLUSIONS: We conclude that TDMA-50 cellular telephones did not interfere with these types of ICDs. However, we recommend that the patient not carry or place the digital cellular telephone within 15 cm (6 in.) of the ICD.

Cardiac pacemakers and implantable cardioverter defibrillators are unaffected by operation of an extremity MR imaging system.

OBJECTIVE: The objective of our investigation was to determine whether an MR imaging system designed to obtain images of the extremities affects the safety and functionality of pacemakers or that of implantable cardioverter defibrillators (ICDs). MATERIALS AND METHODS: Ex vivo experiments were conducted in which seven pacemakers and seven ICDs were exposed to a 0.2-T extremity MR imaging system. Magnetic field attraction was assessed at three positions relative to the MR imaging system. In addition, the devices were placed into a test apparatus that was oriented parallel and perpendicular relative to the MR imaging system while imaging was performed on a phantom using T1-weighted spin-echo and gradient-echo sequences. Various functional aspects of the pacemakers and ICDs were evaluated before, during (pacemakers only), and after MR imaging. RESULTS: Magnetic field attraction was relatively minor for all devices. The quality of the MR images was unaffected by the devices. Operation of this MR system did not alter any of the functional aspects of the pacemakers or ICDs evaluated in this study. CONCLUSION: According to these data and in consideration of how patients are positioned during examinations--that is, positioned so that the thorax (where the pacemaker or ICD and the corresponding leads are located) does not enter the magnet bore--the results suggest that it should be safe to perform MR imaging in patients with the pacemakers and ICDs evaluated in this study.