Am Meloni

Contactless magnetocardiographic study of ventricular repolarization in intact Wistar rats: Evidence of gender-related differences

Abstract.Introduction:Magnetocardiographic (MCG) mapping is increasingly usednfor the non-invasive study of coronary artery disease (CAD),ncardiomyopathy (CMP) and arrhythmias. MCG study of small animalsnwith ischemia or CMP would provide useful experimental modelsnfor the interpretation of abnormal human patterns. The aim ofnthis study was to assess the range of normality of MCGnventricular repolarization parameters, in intact adultnrats.Methods and results:10 adult Wistar rats (weight 250 – 350 grams) wereninvestigated with a 36-channel MCG mapping instrumentationn(sensitivity is 20 fT/ √Hz, at 1 Hz), designed for clinicalnrecordings in unshielded hospital laboratories. To assessnventricular repolarization, MCG Q-Tpeak,nQ-Tend, J-Tpeak,nJ-Tend,nTpeak-Tendnintervals were measured. MCG imaging was obtained by automaticncalculation of isofield contour maps, and with inverse sourcenlocalization based on the Equivalent Current Dipole andnEffective Magnetic Dipole models, in a semi-infinite space withnhomogeneous conductance. Magnetic field (MF) orientation,ndynamics and stability during the J-Tendnsegment were also calculated. After averaging 300 s ofncontinuous MCG recording, the S/N ratio was good enough fornreproducible reconstruction of both atrial and ventricularnmagnetic maps and for three-dimensional localization of thenunderlying cardiac generators. Clear gender-related differencesnin ventricular repolarization duration were found, evidenced bynsignificantly longer Q-Tend,nJ-Tend andnTpeak-Tendnintervals in females. The differences in MF orientation, andnstability during the J-Tend segment werennot significant. For J-Tpeak MF dynamics,nonly the ratio between the strengths of the positive andnnegative poles was significantly lower in the female groupn(p < 0.05).Conclusions:Contactless MCG recording is a novel approach, whichnsimplifies non-invasive mapping in small animals. In normalnrats, gender-related differences of ventricular repolarizationnparameters equivalent to those reported in previous ECG studiesnwere demonstrated.

Magnetocardiographic imaging of ventricular repolarization in rett syndrome

Rett syndrome (RS) is a severe neurological disorder, predominant in females, with higher risk of sudden death (SD). So far for risk-assessment, heart rate variability (HRV), QT duration and its dispersion (QTd) were measured with ECG. However SD has occurred in RS also in absence of ECG abnormality. We aimed to evaluate the feasibility of magnetocardiographic (MCG) mapping as an alternative to study ventricular repolarization (VR) alteration in RS patients. 9 female (age: 1-34 years) RS patients were studied with an unshielded 36-channels MCG system. To assess VR, heart rate (HR)-corrected JTpeak, JTend, QTend, Tpeak−−endintervals and QTd, were measured from both MCG and ECG signals. Moreover the magnetic field (MF) gradient orientation (α-angle) during the ST segment and three MF dynamic parameters were automatically evaluated from MCG T-wave. HRV parameters were evaluated from 12-lead Holter ECG. 15 age-matched normal controls (NC) were studied for comparison. HR-corrected JTpeak, JTend, QTend and Tpeak−−end intervals, and QTd were longer in RS than in NC. The differences were more evident with clinical impairment (stage IV). MF gradient orientation and MF dynamic parameters were abnormal in RS patients. As compared to NC, HRV parameters were altered in the time-domain, although still within normal range in the frequency-domain. In RS, ECG recordings are often noisy and BSPM is difficult. On the contrary MCG mapping is easily feasible and discovers VR alteration not evident at the ECG. The diagnostic value of MCG in RS remains to be defined.