Magnetocardiography Using a Magnetoresistive Sensor Array.

In previous magnetocardiography studies, magnetocardiograms (MCGs) have been obtained using superconducting quantum interference device (SQUID) systems. SQUID is the most sensitive instrument for measuring low-frequency magnetic fields, but it requires liquid helium for cooling, so operating costs are high. In contrast, magnetoresistive (MR) magnetometers function by detecting the change in resistance, caused by an external magnetic field, and have much lower costs. This study was aimed to evaluate feasibility of the MR sensor array for acquiring MCGs.We used an MR sensor array, which was developed for measuring magnetic fields in the picotesla range, with a reduced noise level (TDK Corporation, Tokyo, Japan). A 30-channel MR sensor array was placed in a magnetically shielded room, and the cardiac magnetic field over the anterior chest walls of five healthy subjects was recorded.For all five subjects, MCGs were successfully recorded using the MR sensor array. The cardiac magnetic field corresponding to P, QRS, and T waves on an electrocardiogram (ECG) was detectable by signals averaging 272 ± 27.5 beats.An MR sensor array can be used to measure cardiac magnetic fields. Our results will contribute to the development of low-cost devices for recording MCGs, which will help develop non-invasive diagnostics in cardiovascular medicine.

Aortic root replacement for prosthetic aortic valve detachment without regurgitation and with enlarged Valsalva's sinuses and complete atrioventricular block caused by Takayasu's aortitis.

We replaced the aortic root in a 43-year-old woman with Takayasu's aortitis associated with prosthetic aortic valve detachment. The patient's aortic valve had been replaced when she was 31 years old with a mechanical prosthesis to treat aortic regurgitation. Though C-reactive protein was kept almost normal with prednisolone, complete atrioventricular block suddenly appeared 12 years after the first operation. After the implantation of an artificial pacemaker, we closely followed up aortic root status. Aortography and echocardiography showed that the valve moved up and down, probably due to enlargement of the sinuses of Valsalva, without perivalvular leakage. We removed the prosthetic aortic valve, which was partially detached from the aortic valve ring at the right- and non-coronary cusps and successfully replaced the aortic root with a mechanical prosthesis inserted into a 26 mm woven graft. Although the postoperative course was uneventful, we closely continue to observe the case and to administer of antiinflammatory medication.