Beat-to-beat analysis method for magnetocardiographic recordings during interventions

Enhancing the efficiency and cost-effectiveness of magnetocardiography by optimal channel selection for cardiac diagnosis

Background. Magnetocardiography (MCG) is a non-invasive and non-contact technique that measures weak magnetic fields generated by the heart. It is highly effective in the diagnosis of heart abnormalities. Multichannel MCG provides detailed spatio-temporal information of the measured magnetic fields. While multichannel MCG systems are costly, usage of the optimal number of measurement channels to characterize cardiac magnetic fields without any appreciable loss of signal information would be economically beneficial and promote the widespread use of MCG technology.Methods. An optimization method based on the sequential selection approach is used to choose channels containing the maximum signal information while avoiding redundancy. The study comprised 40 healthy individuals, along with two subjects having ischemic heart disease and one subject with premature ventricular contraction. MCG measured using a 37 channel MCG system. After revisiting the existing methods of optimization, the mean error and correlation of the optimal set of measurement channels with those of all 37 channels are evaluated for different sets, and it has been found that 18 channels are adequate.Results. The chosen 18 optimal channels exhibited a strong correlation (0.99 ± 0.006) between the original and reconstructed magnetic field maps for a cardiac cycle in healthy subjects. The root mean square error is 0.295 pT, indicating minimal deviation.Conclusion. This selection method provides an efficient approach for choosing MCG, which could be used for minimizing the number of channels as well as in practical unforeseen measurement conditions where few channels are noisy during the measurement.

Clinical application of magnetocardiography

Magnetocardiography is a noninvasive contactless method to measure the magnetic field generated by the same ionic currents that create the electrocardiogram. The time course of magnetocardiographic and electrocardiographic signals are similar. However, compared with surface potential recordings, multichannel magnetocardiographic mapping (MMCG) is a faster and contactless method for 3D imaging and localization of cardiac electrophysiologic phenomena with higher spatial and temporal resolution. For more than a decade, MMCG has been mostly confined to magnetically shielded rooms and considered to be at most an interesting matter for research activity. Nevertheless, an increasing number of papers have documented that magnetocardiography can also be useful to improve diagnostic accuracy. Most recently, the development of standardized instrumentations for unshielded MMCG, and its ease of use and reliability even in emergency rooms has triggered a new interest from clinicians for magnetocardiography, leading to several new installations of unshielded systems worldwide. In this review, clinical applications of magnetocardiography are summarized, focusing on major milestones, recent results of multicenter clinical trials and indicators of future developments.

Usefulness of magnetocardiogram to detect unstable angina pectoris and non-ST elevation myocardial infarction

Electrophysiologic information as well as anatomic information to detect coronary artery disease is important for accurate diagnosis. A diagnostic tool that can detect patients with unstable angina pectoris (UAP) or non-ST elevation myocardial infarction (NSTEMI) with severe stenosis would be beneficial for patients and clinicians. Magnetocardiography has been recognized as a noncontact, noninvasive, fast tool to detect ischemic coronary artery disease and provide direct electrophysiologic information from the heart. In this study, 10 magnetocardiographic (MCG) parameters from 4 groups, including 185 young controls, 19 age-matched controls (AMCs), 110 patients with UAP, and 83 patients with NSTEMIs, were analyzed. A 64-channel MCG system in a magnetically shielded room was used. All 10 parameters showed significant differences (p <0.001) between controls and patients with NSTEMIs, and 6 parameters showed significant differences (p <0.01) between AMCs and patients with UAP. MCG parameters significantly increased when ischemic heart conditions worsened. Of the 10 parameters, the magnetic field map was among the easiest ways to detect the severity of coronary artery disease. Abnormal magnetic field maps were observed frequently with worsening ischemic coronary artery disease (70% of patients with UAP and 92.5% of those with NSTEMIs had abnormal maps). The combination of the binary boundaries of the 10 parameters had 96.4% sensitivity and 85% specificity to detect NSTEMI. In conclusion, the MCG parameters and magnetic field maps may detect UAP and NSTEMI easily when they are considered together.

Detection of non-ST-elevation myocardial infarction using magnetocardiogram: new information from spatiotemporal electrical activation map

BACKGROUND AND AIM

Non-ST-segment elevation myocardial infarction (NSTEMI) cannot be easily detected in the emergency room. We evaluate a method to detect NSTEMI using 64-channel magnetocardiography (MCG).

METHODS

MCG recordings were made in 20 NSTEMI patients (aged 59.7+/-12.4 years), 15 young (aged 26.8+/-3.4 years), and 13 age-matched control subjects (aged 57.3+/-3.6). We evaluated three approaches to analysis, including 1) determination when individual subjects' MCG results fell outside normal ranges for ten MCG parameters, 2) the magnetic field map at the T-wave peak (T-MFM), and 3) a pair of spatiotemporal activation graphs (STAGs) showing two projections of electrical excitation during repolarization.

RESULTS

Significant differences were found between normal controls and patients for all MCG parameters. None of the healthy controls had more than four MCG abnormal parameters, whereas 19 NSTEMI patients (95%) were abnormal in more than four parameters. STAGs and T-MFM also showed clear differences between healthy controls and NSTEMI patients.

CONCLUSIONS

These results suggest that the MCG is sensitive to changes in the cardiac electrical pathway after myocardial infarction as described by these graphs and parameters, and therefore MCG may be a useful tool to detect severe ischemic patients.

Can magnetocardiography detect patients with non-ST-segment elevation myocardial infarction?

BACKGROUND AND AIM

Magnetocardiography (MCG) has been proposed as a noninvasive diagnostic tool to risk-stratify patients with myocardial infarction (MI) and ischemia. The purpose of this study is to find the MCG parameters that are sensitive enough to detect the non-ST-segment elevation myocardial infarction (NSTEMI) patients.

METHODS

MCG data were recorded and analyzed from 165 young controls (mean age = 27.2 +/- 9.0 years), 57 age-matched controls (mean age = 55.9 +/- 10.5 years) and 83 NSTEMI patients (mean age = 59.7 +/- 11.1 years). The MCG recordings were obtained using a 64-channel MCG system in a magnetically shielded room. Statistical analyses were performed for 24 parameters derived from QRS-, R-, T-wave, and ST-T period. Binary boundaries to detect NSTEMI patients out of control subjects were found using the receiver operating characteristic (ROC) curve for each parameter.

RESULTS

Fifteen parameters showed a significant difference (P < 0.05 and P < 0.01) between NSTEMI and both of the control groups. For detection of NSTEMI, the angle of the maximum current and the filed map angle on T-wave peak showed the highest diagnostic performance from 75% to 92% including accuracy, sensitivity, specificity, positive predictive value, and negative predictive value (area under ROC curve = 0.87 approximately 0.93).

CONCLUSIONS

Our study showed that MCG has potential clinical application for detection of NSTEMI and should be further investigated.

Reproducibility of Quantitative Estimate of Magnetocardiographic Ventricular Depolarization and Repolarization Parameters in Healthy Subjects and Patients with Coronary Artery Disease

Magnetocardiography (MCG) has been introduced as an innovative non-invasive diagnostic tool to identify various heart diseases. However, there have been little data on the reliability of MCG parameters. The purpose of this study is to examine the test-retest reliability of different diagnostic parameters derived from MCG. We investigated short-, intermediate-, and long-term reliability of nine parameters from T (max/3)-T (max) interval, and five parameters from each time point such as QRS-wave, the peak of R-, and T-wave were evaluated. Short-term reliability was tested in the youngest 20 subjects (mean age = 26.3 +/- 4.9 years) in three sessions separated by 5 min. Intermediate-term reliability was tested in the 35 subjects with coronary artery disease (CAD) (65.1 +/- 7.1 years) with two recording sessions each in the morning and afternoon, separated by more than four hours. Long-term reliability was tested in seven subjects (37.1 +/- 8.8 years) using seven daily sessions. Interclass correlation coefficients (ICC) showed that test-retest reliability was good to excellent (0.99 > or = ICC > or = 0.80) for six out of nine parameters within T (max/3)-T (max). In addition, all parameters on the peak of R-wave, T-wave, and QRS-wave integrated were good to excellent (0.99 > or = ICC > or = 0.80) except for one parameter of CAD patients showing lower ICC values under 0.7. In conclusion, our study showed that the test-retest characteristics of the studied MCG parameters are generally stable and reliable over periods of minutes to days in subjects with different age spectrums.

Identification of patients with coronary artery disease using magnetocardiographic signal analysis / Identifizierung von Patienten mit koronarer Herzkrankheit anhand magnetokardiographischer Signalanalyse

INTRODUCTION

Magnetocardiography (MCG), which measures the magnetic component of the heart's electrical activity, offers an alternative approach for analyzing changes induced by coronary artery disease (CAD). This study examines several parameters that quantify spatial and temporal aspects of cardiac magnetic signals in CAD.

MATERIALS AND METHODS

MCGs were registered at rest in 144 subjects, aged 58.3 +/- 9.8 years: 50 healthy subjects, 43 CAD patients without myocardial infarction (MI), 36 with MI, and 15 with spontaneous episodes of ventricular tachycardia (VT). Spatial characteristics of magnetic field maps (MFM), quantified using their centers of gravity, included MFM orientation and trajectory plots. Spatio-temporal analysis was performed by determining the spatial distribution of the QT interval.

RESULTS

In CAD patients, MFM orientation during the QT interval deviated from normal in 67% of patients without MI and in 85% of patients with MI. Trajectory plots deviated from those of the normal group, with deviation increasing with disease severity. Quantifying the distribution of QT interval duration using a smoothness index demonstrated a significant difference between the values for healthy subjects and non-MI patients, as well as MI patients with and without VT (p < 0.001).

CONCLUSION

The results reported demonstrate that disturbances in cardiac electrogenesis resulting from CAD may be assessed using MCG signal analysis.

Detection of spatial repolarization abnormalities in patients with LQT1 and LQT2 forms of congenital long-QT syndrome

The aim of this study is to detect the spatial current dispersion that appears in the T-wave of patients with congenital long-QT syndrome (LQTS). To observe this dispersion, magnetocardiograms (MCGs)--which have a high spatial resolution--of LQT1 patients (n = 7), LQT2 patients (n = 9) and a control group (n = 33) were recorded. The dispersion was evaluated by plotting current-arrow maps (CAMs) calculated from the MCG signals. In the case of LQT1, abnormal current arrows in the CAMs appeared above the inferior part of the heart in two LQT1 patients with a long corrected QT interval (QTc) (>0.6), and the current direction was from the left (origin side) to the right ventricular muscle (110 degrees). In six out of nine LQT2 patients, abnormal current arrows with angles below 20 degrees were observed above the right inferior part or lower septum; the current direction was from the right (origin side) to the left ventricular muscle. However, in the case of the LQT2 patients, the QTc values did not correlate with the abnormal current. These findings suggest that the origin of abnormal repolarization in LQT1 is the left ventricular muscle and the origin of that in LQT2 is the right ventricular muscle or lower septum. The estimation of the origin in LQTS patients can provide important information such as the risk factor of sudden death.