Article

Determinants of gradient field-induced current in a pacemaker lead system in a magnetic resonance imaging environment

Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA. <>
Heart Rhythm (Impact Factor: 4.92). 04/2008; 5(3):462-8. DOI: 10.1016/j.hrthm.2007.12.022
Source: PubMed

ABSTRACT The determinants of low-frequency-induced current by magnetic resonance imaging (MRI) gradient fields in a pacemaker lead system are largely unknown.
The purpose of this study was to determine the magnitude of MRI low-frequency-induced current in an implanted pacemaker lead system and to investigate in vivo determinants of low-frequency-induced current in an animal model.
Six mongrel dogs underwent conventional single-chamber pacemaker implantation with a current recorder connected in series. Pulse generator (PG) was programmed to VOO 120 bpm with subthreshold output. MRI was performed in a 1.5-T scanner. Low-frequency-induced current was recorded during unipolar pacing, bipolar pacing, and bipolar pacing with the PG case electrically isolated from the pocket. In each mode, low-frequency-induced current was recorded with and without a large loop of additional lead connected in series.
With a conventional implant, low-frequency-induced current was < or =0.5 mA in all three pacing modes. With five external loops, the magnitude of low-frequency-induced current increased to >30 mA, with consistent myocardial capture in unipolar and bipolar pacing. However, in bipolar pacing with the PG electrically isolated from the pocket, low-frequency-induced current decreased to <0.5 mA with no myocardial capture even with additional looped leads.
Under conventional implant conditions, the magnitude of low-frequency-induced current is <0.5 mA and is unlikely to cause myocardial capture; however, arrhythmia induction cannot be excluded. With sufficient increase in effective loop area (additional looped leads), direct myocardial capture by the low-frequency-induced current is possible. In this study, breaking the return pathway by electrically isolating the PG case from the circuit abolished low-frequency-induced current.

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    • "However, in [15] and [2], no experimental verification is performed and in [4], experiments are only performed for the Helmholtz coil. On the other hand, in [3], experiments were performed on six mongrel dogs and the induced current was measured with a current recorder. However, no analytical explanation about the stimulation risk is carried out. "
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