In-vitro mapping of E-fields induced near pacemaker leads by simulated MR gradient fields.
BACKGROUND
Magnetic resonance imaging (MRI) of patients with implanted cardiac pacemakers is generally contraindicated but some clinicians condone scanning certain patients. We assessed the risk of inducing unintended cardiac stimulation by measuring electric fields (E) induced near lead tips by a simulated MRI gradient system. The objectives of this study are to map magnetically induced E near distal tips of leads in a saline tank to determine the spatial distribution and magnitude of E and compare them with E induced by a pacemaker pulse generator (PG).


METHODS
We mapped magnetically induced E with 0.1 mm resolution as close as 1 mm from lead tips. We used probes with two straight electrodes (e.g. wire diameter of 0.2 mm separated by 0.9 mm). We generated magnetic flux density (B) with a Helmholtz coil throughout 0.6% saline in a 24 cm diameter tank with (dB/dt) of 1 T/sec (1 kHz sinusoidal waveform). Separately, we measured E near the tip of leads when connected to a PG set to a unipolar mode. Measurements were non-invasive (not altering the leads or PG under study).


RESULTS
When scaled to 30 T/s (a clinically relevant value), magnetically-induced E exceeded the E produced by a PG. The magnetically-induced E only occurred when B was coincident with or within 15 msec of implantable pacemaker's pulse.


CONCLUSIONS
Potentially hazardous situations are possible during an MR scan due to gradient fields. Unintended stimulation can be induced via abandoned leads and leads connected to a pulse generator with loss of hermetic seal at the connector. Also, pacemaker-dependent patients can receive drastically altered pacing pulses.
Bassen
Howard I
HI
Division of Physics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, FDA, 10903 New Hampshire Avenue Silver Spring, MD 20993-0002, USA. howard.bassen@fda.hhs.gov
Mendoza
Gonzalo G
GG
D002138:Calibration; D004553:Electric Conductivity; D004566:Electrodes; D004574:Electromagnetic Fields; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging / Q000009:adverse effects; D010138:Pacemaker, Artificial; D012965:Sodium Chloride; D012996:Solutions
D012996:Solutions; D012965:Sodium Chloride