Qualitative und quantitative Beschreibung von myokardialen Ischämien mittels Magnetokardiographie / Qualitative and Quantitative Description of Myocardial Ischemia by means of Magnetocardiography

Case report: Magnetocardiography as a potential method of therapy monitoring in amyloidosis

Amyloidosis is characterized by a disorder of protein conformation and metabolism, resulting in deposits of insoluble fibrils in various organs causing functional disturbances. Amyloidosis can also affect the heart. Cardiac amyloidosis tends to have a poor prognostic outcome if diagnosed at a late stage. Therefore, early diagnosis and initiation of therapy as well as monitoring of treatment response are crucial to improve outcomes and to learn more about its pathophysiology and clinical course. We present an 83-year-old woman with cardiac transthyretin amyloidosis (ATTR) who was treated with tafamidis. The patient significantly improved 18 months after initiation of therapy with regards to exercise capacity and quality of life. In addition to standard diagnostic methods, we used magnetocardiography (MCG) to monitor potential treatment response by detecting changes in the magnetic field of the heart. MCG is a non-invasive method that detects the cardiac magnetic field generated by electrical currents in the heart with high sensitivity. We have recently shown that this magnetic field changes in various types of cardiomyopathies may be used as a non-invasive screening tool. We determined previously that an MCG vector ≥0.052 was the optimal threshold to detect cardiac amyloidosis. The patient's MCG was measured at various time points during therapy. At the time of diagnosis, the patient's MCG vector was 0.052. After starting therapy, the MCG vector increased to 0.090, but improved to 0.037 after 4 months of therapy. The MCG vector reached a value of 0.017 after 5 months of therapy with tafamidis, and then increased slightly after 27 months to a value of 0.027 (<0.052). Data from this case support our previous findings that MCG may be used to monitor treatment response non-invasively. Further research is needed to understand the unexpected changes in the MCG vector that were observed at the beginning of therapy and later in the course. Larger studies will be necessary to determine how these changes in the electromagnetic field of the heart are related to structural changes and how they affect clinical outcomes.

Magnetocardiography for the detection of myocardial ischemia

Ischemic heart disease (IHD) continues to be a significant global public health concern and ranks among the leading causes of mortality worldwide. However, the identification of myocardial ischemia in patients suspected of having coronary artery disease (CAD) remains a challenging issue. Functional or stress testing is widely recognized as the gold standard method for diagnosing myocardial ischemia, but it is hindered by low diagnostic accuracy and limitations such as radiation exposure. Magnetocardiography (MCG) is a non-contact, non-invasive method that records magnetic fields produced by the electrical activity of the heart. Unlike electrocardiography (EKG) and other functional or stress testing, MCG offers numerous advantages. It is highly sensitive and can detect early signs of myocardial ischemia that may be missed by other diagnostic tools. This review aims to provide an extensive overview of the available evidence that establishes the utility of MCG as a valuable diagnostic tool for identifying myocardial ischemia, accompanied by a discussion of potential future research directions in this domain.

Myocardial Ischemia Detection by a Sensitive Pump-Probe Atomic Magnetometer

Introduction: Magnetocardiography (MCG) based on optical atomic magnetometers has shown promise for detecting heart diseases accurately. Different methods were introduced to improve the sensitivity of detecting magnetic fields during cardiac activity. Methods: In this paper, an optical pump-probe magnetometer operated on the ground-state Hanle effect based on the zero-field level crossing technique was developed and the laser output signal was optimized in an unshielded environment. Then, the optical magnetometer was utilized to record the simulated MCG trace of different stages of myocardial ischemia. Results: The probe output light intensity followed the variation of cardiac magnetic field (MCG trace) generated by Helmholtz coil accurately. Conclusion: Based on the results, the feasibility of our highly sensitive optical magnetometer in tracing showed no change in the P-QRS-T waveform associated with ischemic heart disease (IHD), where P indicates atrial depolarization, QRS is responsible for ventricular depolarization, and T represents ventricular repolarization.

Detection of coronary artery disease in patients with chest pain: A machine learning model based on magnetocardiography parameters

BACKGROUD

Patients with chest pain and suspected of coronary artery disease(CAD) need further test to confirm the diagnosis. Magnetocardiography (MCG) is a non-invasive and emission-free technology which can detect and measure the weak magnetic fields created by the electrical activity of the heart.

OBJECTIVE

This study aimed to investigate the usefulness of the 10 MCG parameters to detect CAD in patients with chest pain by means of a machine learning method of multilayer perceptron(MLP) neural network.

METHODS

209 patients who were suffering from chest pain and suspected of CAD were enrolled in this cross-sectional study. In all patients, 12-lead electrocardiography(ECG) and MCG test were performed before percutaneous coronary angiography(PCA). 10 MCG parameters were analyzed by MLP neural networks.

RESULTS

11 diagnostic models(M1 to M11) were established after MLP analysis. The accuracies ranged from 71.2% to 90.5%. Two models(M10 and M11) were further analyzed. The accuracy, sensitivity, specificity, PPV, NPV, PLR and NLR were 89.5%, 89.8%, 88.9%, 92.7%, 84.7%, 11.10 and 0.11, of M10, and were 90.0%, 91.4%, 87.7%, 92.1%, 86.6%, 7.43 and 0.10, of M11.

CONCLUSIONS

By a method of MLP neural network, MCG is applicable in identifying CAD in patients with chest pain, which seems beneficial for detection of CAD.

Diagnostic accuracy of the magnetocardiograph for patients with suspected acute coronary syndrome

Background

We aimed to estimate the diagnostic accuracy of the VitalScan magnetocardiograph (MCG) for suspected acute coronary syndrome (ACS).

Methods

We undertook a prospective cohort study evaluating the diagnostic accuracy of the MCG in adults with suspected ACS. The reference standard of ACS was determined by an independent adjudication committee based on 30-day investigations and events. The cohort was split into a training sample, to derive the MCG algorithm and an algorithm combining MCG with a modified Manchester Acute Coronary Syndrome (MACS) clinical probability score, and a validation sample, to estimate diagnostic accuracy.

Results

We recruited 756 participants and analysed data from 680 (293 training, 387 validation), of whom 96 (14%) had ACS. In the training sample, the respective area under the receiver operating characteristic (AUROC) curves were the following: MCG 0.66 (95% CI 0.58 to 0.74), MACS 0.64 (95% CI 0.54 to 0.73) and MCG+MACS 0.70 (95% CI 0.63 to 0.77). MCG specificity was 0.16 (95% CI 0.12 to 0.21) at the threshold achieving acceptable sensitivity for rule-out (>0.98). In the validation sample (n=387), the respective AUROCs were the following: MCG 0.56 (95% CI 0.48 to 0.64), MACS 0.69 (95% CI 0.61 to 0.77) and MCG+MACS 0.64 (95% CI 0.56 to 0.72). MCG sensitivity was 0.89 (95% CI 0.77 to 0.95) and specificity 0.15 (95% CI 0.12 to 0.20) at the rule-out threshold. MCG+MACS sensitivity was 0.85 (95% CI 0.73 to 0.92) and specificity 0.30 (95% CI 0.25 to 0.35).

Conclusion

The VitalScan MCG is currently unable to accurately rule out ACS and is not yet ready for use in clinical practice. Further developmental research is required.

Unshielded magnetocardiography: Repeatability and reproducibility of automatically estimated ventricular repolarization parameters in 204 healthy subjects

BACKGROUND

Magnetocardiographic mapping (MCG) provides quantitative assessment of the magnetic field (MF) induced by cardiac ionic currents, is more sensitive to tangential currents, and measures vortex currents undetectable by ECG, with higher reported sensitivity of MCG ventricular repolarization (VR) parameters for earlier detection of acute myocardial ischemia. Aims of this study were to validate the feasibility of in-hospital unshielded MCG and to assess repeatability and reproducibility of quantitative VR parameters, considering also possible gender- and age-related variability.

METHODS

MCG of 204 healthy subjects [114 males-mean age 43.4 ± 17.3 and 90 females-mean age 40.2 ± 15.7] was retrospectively analyzed, with a patented proprietary software automatically estimating twelve VR parameters derived from the analysis of the dynamics of the T-wave MF extrema (five parameters) and from the inverse solution with the effective magnetic dipole model giving the effective magnetic vector components (seven parameters). MCG repeatability was calculated as coefficient of variation (CV) ±standard error of the mean (SEM). Reproducibility was assessed as intraclass correlation coefficient (ICC).

RESULTS

The repeatability of all MCG parameters was 16 ± 1.2 (%) (average CV ± SEM). Optimal (ICC > 0.7) reproducibility was found for 11/12 parameters (mean values) and in 8/12 parameters (single values). No significant gender-related difference was observed; six parameters showed a strong/moderate correlation with age.

CONCLUSION

Reliable MCG can be performed into an unshielded hospital ambulatory, with repeatability and reproducibility of quantitative assessment of VR adequate for clinical purposes. Wider clinical use is foreseen with the development of multichannel optical magnetometry.

Incremental diagnostic value of combined quantitative and qualitative parameters of magnetocardiography to detect coronary artery disease

BACKGROUND/OBJECTIVES

Magnetocardiography (MCG) has been proposed as a non-invasive and functional technique with high accuracy for diagnosis of myocardial ischemia. This study sought to investigate the incremental diagnostic value of combined quantitative and qualitative parameters of MCG to detect coronary artery disease (CAD).

METHODS

Ninety six patients with suspected CAD who underwent coronary angiography were enrolled in the analysis to test the diagnostic accuracy of 2 MCG parameters (a quantitative parameter of the percent change of ST-segment fluctuation score and a qualitative parameter of non-dipole phenomenon).

RESULTS

The best cut-off value for the percent change of ST-segment fluctuation score was -51.0%. The accuracy, sensitivity, specificity, positive predictive value, and negative predictive value were 78.1, 73.9, 82.0, 79.1, and 77.4, in the percent change of ST-segment fluctuation score and 86.5, 84.8, 88.0, 86.7, and 86.3 in non-dipole phenomenon. The area under the curve of receiver-operating characteristics was 0.79 for the percent change of ST-segment fluctuation score and 0.86 for non-dipole phenomenon (p<0.001). However, the incorporation of non-dipole phenomenon into a model with the percent change of ST-segment fluctuation score significantly improved C-statistics, indicating the enhancement of diagnostic performance in the detection of significant CAD (0.790 to 0.930; p<0.001).

CONCLUSIONS

Qualitative assessment of non-dipole phenomenon has a better diagnostic value than the quantitative parameter of percent change of ST-segment fluctuation score in the detection of significant CAD. Furthermore, this study found that the incorporation of non-dipole phenomenon into the percent change of ST-segment fluctuation score significantly improved the diagnostic performance of CAD detection.

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.

Repolarization spatial-time current abnormalities in patients with coronary heart disease

BACKGROUND

Magnetocardiography (MCG) is a new technique for visualizing a current distribution in the myocardium. In recent years, current distribution parameters (CDPs) have been developed based on the distribution. The CDPs reflect spatial-time current abnormalities in patients with coronary heart disease (CHD). However, the criteria and scoring method of the abnormalities using CDPs are still controversial.

METHOD

We measured MCG signals for 101 normal controls and 56 CHD patients (single-, double-, and triple-vessel diseases) using a MCG system. The CDPs (maximum current vector [MCV], total current vector [TCV], current integral map, and current rotation) during ventricular repolarization were analyzed. To evaluate the CDPs that are effective in distinguishing between normal controls and CHD patients, the areas under the receiver operating characteristic curve (A(z)) are calculated. Furthermore, the total scores ("0" to "4") of four CDPs with high A(z) values are also calculated.

RESULTS

MCV and TCV angles at the T-wave peak had the highest A(z) value. Furthermore, TCV angular differences between the ST-T segment also had high A(z) values. Using the four CDPs, the averaged total score for patients with triple-vessel disease was the highest ("2.67") compared to the other groups (normal controls: 0.53). Furthermore, based on the assumption that subjects with a total score over "1" were suspected of having CHD, sensitivity and specificity were 85.7% and 74.3%, respectively.

CONCLUSION

We concluded that the score and criteria using MCV and TCV during repolarization in CHD patients can reflect lesion areas and time changes of electrical activation dispersion due to ischemia.

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.

Resting magnetocardiography predicts 3-year mortality in patients presenting with acute chest pain without ST segment elevation

OBJECTIVE

Magnetocardiography (MCG) as a noninvasive, noncontact and risk-free diagnostic method predicts ischemic coronary artery disease (CAD) in patients with acute chest pain at admission with high accuracy. However, it remains unclear whether MCG findings can add prognostic information.

METHOD

A cohort of 402 consecutive patients presenting at the intensive care unit (ICU) with acute chest pain without ST segment elevation (NSTEMI) were included in a prospective registry. In order to prove the prognostic value of MCG a head-to-head comparison of the admission MCG, ECG, TnI, and ECHO tests was made.

RESULTS

In 43 patients (10.7%) the MCG could not be analyzed due to insufficient signal-to-noise ratio. Complete follow-up over a period of up to 3 years was obtained in 355 out of the 359 patients (98.9%). Age at admission was 67.2 +/- 10.3 years, 59.7% males. In the group of patients with an abnormal MCG at admission, 43 out of 249 patients (17.3%) died in the follow-up period, while in the group of patients with a normal MCG at admission only 4 out of 106 patients died (3.77%). The relative risk was 4.58 (95% confidence intervals: 1.68-12.42). A multivariate regression analysis revealed the highest mortality risk for patients with diabetes mellitus and an abnormal MCG at admission (RR = 18.0; 95% CI: 2.49-133.3).

CONCLUSION

Resting MCG at hospital admission predicts 3-year mortality in patients presenting with acute chest pain without ST segment elevation in the ECG. MCG seems to be valuable in identifying chest pain patients at highest risk.

Corrected body surface potential mapping

In the method for body surface potential mapping described here, the influence of thorax shape on measured ECG values is corrected. The distances of the ECG electrodes from the electrical heart midpoint are determined using a special device for ECG recording. These distances are used to correct the ECG values as if they had been measured on the surface of a sphere with a radius of 10 cm with its midpoint localized at the electrical heart midpoint. The equipotential lines of the electrical heart field are represented on the virtual surface of such a sphere. It is demonstrated that the character of a dipole field is better represented if the influence of the thorax shape is reduced. The site of the virtual reference electrode is also important for the dipole character of the representation of the electrical heart field.

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.