Magnetocardiographic imaging of Tpeak-Tend magnetic field dynamics discriminates between ventricular repolarization disorders due to mitral valve prolapse and to ischemic heart disease

Abstract

Abstract Background Several etiopathogenetic mechanisms, including ischemia of the papillary muscles, abnormal catecholamine regulation, baroreflex modulation, and activation of atrial natriuretic peptide induced by abnormal stretch of the prolapsing mitral leaflets, have been suggested as possible causes of ventricular repolarization abnormalities (VRab) in patients (pts) with mitral valve prolapse (MVP) [1-3], especially in those with chest pain (CP). Purpose Since magnetocardiography (MCG) is a sensitive alternative to improve the detection of VRab, this study aimed to evaluate its discrimination accuracy to differentiate VRab due to MVP from those due to ischemic heart disease (IHD). Methods MCG recordings of 32 female patients (age 40.3±13.3 years) with MVP (at echocardiography), 20 of them with CP and/or palpitations, were retrospectively compared with those of 35 pts with IHD (at least one vessel stenosis >70%) (age 66.2±10.6 years), and with those of 32 age-matched (age 40.8±11.5 years) healthy females (HF) without MVP. The cardiac magnetic field (MF) component perpendicular to the anterior chest wall (Bz) was recorded with a 36-channel DC-SQUID MCG system (sensitivity ~30 fT/VHz). Thirteen MCG parameters, five derived from the analysis of the T-wave MF extrema dynamics, and eight from the effective magnetic vector (EMV) dynamics, were automatically calculated with proprietary software during the Tpeak-Tend interval (T3-T4 in Figure 1). Discriminant analysis (DA) was applied to separate groups. Results At univariate analysis, 11 MCG parameters were significantly different (p< 0.05) between MVP and IHD pts (Table 1). After multivariate analysis, 9 parameters (AzimuthMeanA, TrajectoryLengthRangeD, AngleDerivativeRangeD, AzimuthdiffAD, Q2AnalysisScore, AngleMinimum, AngleDynamics, DistanceDynamics, RatioDynamics) differentiated MVP and IHD pts’ VRab with 80% accuracy (cross-correlated), at DA. Moreover, in IHD pts abnormality of EMV dynamics extended also along the whole T-wave [4]. Three EMV parameters of the Tpeak-Tend interval (TrajectoryLengthRangeD, AzimuthdiffAD, Q2AnalysisScore), and three T-wave MF extrema parameters (AngleMinimum, Distance Dynamics, and Ratio Dynamics) were abnormal in 11 MVP pts, 10 of them with CP but normal ECG, and only one asymptomatic. Discussion: MCG EMV and MF dynamics calculated from rest-MCG data are reliable to identify VRab in pts with MVP and with IHD, differentiating them with a good discrimination accuracy. MCG VRa abnormality was mostly confined in the Tpeak-Tend interval in pts with MVP (in agreement with previous ECG findings [5]), while extended to the whole ST interval in IHD pts. Rest MCG is more sensitive than ECG in detecting VRab in pts with MVP and CP. Due to the limited number of investigated cases, the potential arrhythmogenicity of MVP-related VRab detected with MCG was not evaluated.Figure 1.MCG imaging of Tpeak-Tend MFTable 1