Measurements and Main Results: Voltage generated by saline 0.9% flowing through a magnetic field and distribution of current from a catheter tip within a sheep heart model were measured in a 0.15 Tesla MRI system. Resistance of loops formed by pacing wires, a pacing electrode, and a thermistor wire were measured in saline 0.9%. Effects of rapidly changing magnetic fields and the movement of the beating heart on epicardial pacing wires were calculated theoretically. A flow of 200 mL/min of saline 0.9% induced a current of 0.1 microampere (uA) (at 0.15 Tesla). From magnetic resonance images we derived a current density of -0.004 [mu]A/mm2 (at 0.15 Tesla). Internal resistance of pacing catheters and thermistor wires was >1 megaohm (M[OMEGA]). The maximum currents calculated (for a higher field strength of 1.5 Tesla) in a circuit formed by epicardial pacing wires were 80 [mu]A, induced by the beating heart moving the wires through the magnetic field and 46 [mu]A, induced by the rapidly changing magnetic fields.
Conclusions: Current generated by flow of conducting fluid should be safe. Pacing catheters and thermistor wires should be safe if well insulated and disconnected from external electric connections. However, current induced in epicardial pacing wires may be a hazard, and precautions should be taken. External wire tips must be separated, insulated, and coiled to lie along the axis of the magnetic field. Electrocar-diography is required, and defibrillation equipment should be available.
Xanya Sofra Weiss
Xanya Sofra Weiss
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