Experimental and theoretical investigation of implantable cardiac pacemaker exposed to low frequency magnetic field.

This paper presents in vitro investigation of an implantable cardiac pacemaker exposed to low frequency magnetic fields. The method used in this study is based on the interaction by inductive coupling through the loop formed by the pacemaker and its loads and the surrounding medium. This interaction results in an induced electromotive force between the terminals of the pacemaker, which can potentially disturb its operation. The studied frequencies are 50/60 Hz and 10/25 kHz. The experimental tests were carried out on several cardiac pacemakers, single chamber, and dual chamber. The results show a window effect of the detection circuits of cardiac pacemakers for the four studied frequencies. The modelling of the test bed requires studying the effects of the induced currents generated by the application of a magnetic field. Analytical calculations and Numerical simulations were carried out. We modelled the interactions of the magnetic field with a simplified representation of pacemaker embedded in the medium. The comparison of the results in the air and in vitro enabled us to make an equivalent electric model. The results obtained in experimental and theoretical studies allowed us to validate the test bed. The method applied is valid for other medical implants such as cardiac defibrillators, implant hearing aids system...etc.

Adalimumab for Crohn's disease with intolerance or lost response to infliximab: a 3-year single-centre experience.

BACKGROUND: Adalimumab is effective in inducing clinical remission in patients with Crohn's disease who lost response or became intolerant to infliximab. AIM: To evaluate long-term efficacy and safety of adalimumab as a second line therapy in luminal and fistulizing Crohn's disease. METHODS: We report our single-centre experience in 53 patients. We evaluated maintenance of clinical response defined as the absence of adverse events leading to drug withdrawal, no major abdominal surgery and no loss of clinical response in initial responders. Major abdominal surgery, steroid sparing, complete fistula closure and safety were also assessed. RESULTS: The probability of maintaining clinical response was 77.2%, 67.8% and 50.8% at 26, 52 and 130 weeks respectively. The probability of remaining major abdominal surgery-free was 82.3% at 26, 52 and 130 weeks. Complete fistula closure occurred in six of 10 patients, and eight of 10 patients were able to taper steroid therapy. Adverse events occurred in 31 patients (58.5%) leading to adalimumab withdrawal in nine patients (17%). CONCLUSION: Adalimumab therapy may be effective in the long term in both luminal and fistulizing Crohn's disease in infliximab-failure patients, half of patients maintaining clinical response and potentially avoiding major abdominal surgery in 80% of cases.

Long-term outcome of adalimumab therapy for ulcerative colitis with intolerance or lost response to infliximab: a single-centre experience.

BACKGROUND: Adalimumab may be effective in inducing remission in patients with mild-to-moderate ulcerative colitis who had secondary failure to infliximab. AIM: To evaluate long-term efficacy and safety of adalimumab in patients with ulcerative colitis who previously responded to infliximab, and then lost response or became intolerant. METHODS: We report our single-centre experience in 13 patients. The patients received a loading dose of 160 mg of adalimumab subcutaneously in week 0, followed by 80 mg at week 2 and then 40 mg every other week starting at week 4. The primary efficacy measure was the proportion of patients on adalimumab therapy during the study. RESULTS: Median duration of follow-up was 42 weeks (range, 10-100). The mean number of adalimumab infusions was 21 (range, 5-50). The probability of maintaining adalimumab was 92.3%, 84.6%, 60.6% and 32.5% at 1, 3, 6 and 23 months respectively. Six of 13 patients (46.2%) underwent colectomy during the study. No serious toxicities occurred in the study. CONCLUSION: Adalimumab is well-tolerated and may be effective in maintaining clinical remission in a subgroup of patients with ulcerative colitis and lost response or intolerance to infliximab, potentially avoiding colectomy in about half of the patients.

In vitro investigation of eddy current effect on pacemaker operation generated by low frequency magnetic field.

This paper presents in vitro investigation of the eddy current induction effects to the cardiac pacemaker exposed to low frequency magnetic fields. The method used in this study is based to the interaction by inductive coupling through the loop formed by the pacemaker and its leads and the surrounding medium. This interaction results in an induced electromotive force between the terminals of the pacemaker which can potentially disturb the operation of this last. In this article we present experimental results, analytical calculations and numerical simulations using the finite element method.

The behavior of dual-chamber pacemakers exposed to a conducted low-frequency disruptive signal.

This paper presents a study of the behavior of dual-chamber cardiac pacemakers submitted to low-frequency conducted disruptions. The disruptive signal is sinusoidal, operating at 50 Hz, 60 Hz, 10 kHz and 25 kHz. The behavior of the pacemakers is described by statistical data obtained with a telemetry system and by visualization of the pacemaker signal during the application of the interfering signal. The pacemakers were tested in two configurations. The first one consists of direct application of the interfering signal between the pacemaker terminals. In the second, these attempts are completed by in vitro tests using an electromagnetic model which allow us to take into account the interface which constitutes the human body. The pacemaker under test is inserted into a gelatine phantom mimicking the electrical conductivity of tissues. This study allowed us to define the pacemaker detection thresholds for the two test configurations. For the in vitro approach, which constitutes a complementary approach to a realistic implantation situation, oversensing is noticed for 10 kHz and 25 kHz interfering signal frequencies. Detection thresholds vary from a few tens to a few hundreds of mV, depending on the interfering signal frequency, the device and its programmed detection sensitivities.