Magnetocardiographic Mapping Research Articles

Magnetocardiographic electroanatomical imaging for pre-interventional evaluation of arrhythmogenic substrates

Catheter ablation has significantly changed the diagnostic approach and the treatment of cardiac arrhythmias. Being the appropriate localization of the arrhythmogenic target a key-point for effective ablation, new technologies have been recently developed, for three-dimensional (3D) electroanatomical imaging during ablation procedures. However all of them are invasive and cannot be used for preoperative assessment and localization of arrhythmogenic substrates. Magnetocardiographic mapping (MCG) on the contrary is a feasible method, which provide 3D electroanatomical imaging of cardiac sources non-invasively, therefore it can be repeated on ambulatory patients, to define the characteristics of the arrhythmogenic substrate before intervention. MCG detection of electrophysiologic (EP) abnormalities and 3D electroanatomical imaging of arrhythmogenic substrates can be enhanced by simultaneous EP study with amagnetic trans-esophageal atrial pacing. Alternatively minimally invasive, single-catheter multiple monophasic action potential recordings (Multi-MAP) can be aimed at the arrhythmogenic targets identified by MCG. The MCG-guided Multi-MAP EP study is also useful for direct validation of MCG estimate of atrial and ventricular de-repolarization by comparison with simultaneous MAP recordings in sinus rhythm and under pacing. Future robotic navigation of an ablation catheter guided by 3D MCG coordinates of the arrhythmogenic target is foreseeable.

Study of ventricular repolarization changes after carnitine deprivation in rats by contactless magnetocardiography

Carnitine deficiency can be associated with cardiomyopathy and life-threatening arrhythmias. The aim of this study was to assess changes of ventricular repolarization (VR) intervals by contactless magnetocardiographic mapping (MCG), in a rat model of carnitine deficiency. 21 anesthetized Wistar rats (WR), 11 males and 10 females, were investigated, with an unshielded 36-channel MCG instrumentation. After a basal recording 10 animals were randomized to carnitine-deprivation induced by a 3-weeks diet containing N-trimethyl-hydrazine-3-propionate (THP). All WR were restudied 1 week after the end of THP treatment. RR, QRS, QT peak, QT end, JT peak, JT end and T peak-end intervals were measured from MCG waveforms. A prolongation of all HR-corrected VR intervals was observed in THP-treated animals (range 7.6–12.8%), as compared to their basal values. However, only the lengthening of QT end and T peak-end was statistically significant ( p < 0.05). Compared to untreated age-matched controls, the cardiac intervals of TPH-treated WR values were longer, but the differences were not significant. After 3 weeks of THP-induced reduction of cardiac and plasma levels of carnitine, abnormalities in myocardial function are expected. In this study we have found only a prolongation of HR-corrected QT end and T peak-end in THP-treated animals. The lack of significance versus age-matched controls could be either due to too early re-evaluation after deprivation, or to the effect of aging. In fact, age-related prolongation of VR intervals has been reported in WR at the age of 14 months.

Percutaneous method for multiple epicardial monophasic action potential recordings during magnetocardiographic mapping in intact rats

A surgical approach for subdiaphragmatic-programmed electrical stimulation (PES) in mice has been reported by Gutstein et al. [D.E. Gutstein, S.B. Danik, J.B. Sereysky, G.E. Morley, G.I. Fishman, Subdiaphragmatic murine electrophysiological studies: sequential determination of ventricular refractoriness and arrhythmia induction, Am J Physiol Heart Circ Physiol. 285 (3) (2003) H1091-96.]. We developed a percutaneous method to drive a patented magnetocardiography-compatible amagnetic catheter (AC), specifically designed for multiple monophasic action potentials (Multi-MAP) recording, at the epicardium of spontaneously breathing small animals. The aim of this study was to test the feasibility of simultaneous magnetocardiographic (MCG) estimate of ventricular repolarization (VR) and Multi-MAP recording in 5 rats. Under fluoroscopic control, the AC was introduced with a sub-xyphoid puncture, in all animals, and moved at several epicardial sites until 4 stable MAPs were recorded, with a fixed inter-electrode distance of 1 mm. An unshielded 36-channel DC-SQUID system (sensitivity 20 fT/Hz 1 / 2) was used to record the MCG. MAP signals, differentially amplified and filtered at DC-500 Hz, were digitized at 1 kHz. The same AC was used for programmed PES at pacing cycles between 200 and 250 ms. Ventricular effective refractory period (VERP) was evaluated with the accuracy of 2 ms. MAP duration (MAPd) was measured, at 90% levels of repolarization. Simultaneous MCG and MAP recordings were successful in all animals. One rat died for respiratory arrest. Four animals tolerated well the procedure and survived. In WRs, MAPd 90% and VERP were 67 ± 9.4 ms and 69.6 ± 5.6 ms, respectively. This minimally invasive method is well tolerated, avoids animal sacrifice, can be used to validate the accuracy of surface MCG estimate of dispersion of VR and for assessment of arrhythmogenic potential of new drugs.

Contactless magnetocardiographic study of age- and gender-related variability of ventricular repolarization parameters in guinea pigs

Guinea pigs (GPs) are used for preclinical investigation of the ability of new drugs to induce QT alterations and arrhythmias. The aim of this study was to evaluate the accuracy of multi-site magnetocardiographic mapping (MCG) for the assessment of age-related variation of ventricular repolarization (VR) maps in GPs. 18 adult GPs (8 males and 10 females) were investigated with an unshielded 36-channel MCG instrumentation, at the age of 5 months. Only 12 survived until the age of 14 months and were restudied. RR, PR, QRS, QT peak, QT end, JT peak, JT end and T peak-end intervals were measured from MCG waveforms. Magnetic field (MF) maps and the Equivalent Current Dipole (ECD) inverse solution were automatically computed. At the age of 5 months, average values of VR intervals were slightly longer in males. At the age of 14 months, a statistically significant age-related prolongation of the PR ( p < 0.05) and of the QRS ( p < 0.01) intervals was found. Neither significant age- nor gender-related variations of VR intervals were appreciable. Statistically significant ( p < 0.01) age-related differences were found for the JT α angle, T peak α angle and for the distance dynamics. At the same age, the strength of the ECD at the peak of the P, QRS and T waves, was stronger ( p < 0.01) than at 5 months. MCG is reliable for VR assessment in GPs. In contrast with findings in rats, age-related changes and gender-related differences of VR parameters were not statistically significant in GPs. More complex variability of MF patterns was observed, which deserves further investigation.

Assessment of atrial repolarization by magnetocardiographic mapping in patients

Assessment of atrial repolarization by magnetocardiographic mapping in patients

Bridging noninvasive and interventional electroanatomical imaging: role of magnetocardiography

Abstract New “magnetic” technologies for intracardiac three-dimensional electroanatomical imaging (3D-EAI) have been recently developed, which have proven useful to localize the arrhythmogenic targets, to improve the outcome of ablation procedures and to reduce patient irradiation. However their 3D imaging capability cannot be used for preoperative localization of arrhythmogenic substrates. Magnetocardiographic mapping (MCG) is a more feasible and reproducible method to provide non-invasive 3D-EAI of cardiac sources. MCG detection and 3D study of arrhythmias can be enhanced by simultaneous electrophysiologic study with trans-esophageal atrial pacing and by combining MCG with minimally invasive single-catheter, multiple monophasic action potential recording, which provides a better understanding of local arrhythmogenic mechanisms underlying abnormal MCG patterns. MCG is also feasible for non-fluoroscopic imaging of amagnetic catheters in the heart. Furthermore providing 3D numerical coordinates of arrythmogenic targets, MCG could be used to program robotic magnetic navigation and to automatically guide ablation catheters or aimed endomyocardial biopsy.

Magnetocardiography provides non-invasive three-dimensional electroanatomical imaging of cardiac electrophysiology

Objective More than two decades of research work have shown that magnetocardiographic mapping (MCG) is reliable for non-invasive three-dimensional electroanatomical imaging (3D-EAI) of arrhythmogenic substrates. Magnetocardiographic mapping is now become appealing to interventional electrophysiologists after recent evidence that MCG-based dynamic imaging of atrial arrhythmias could be useful to classify patients with atrial fibrillation (AF) before ablation and to plan the most appropriate therapeutic approach. This article will review some key-points of 3D-EAI and discuss what is still missing to favor clinical applicability of MCG-based 3D-EAI. Methods Magnetocardiographic mapping is performed with a 36-channel unshielded mapping system, based on DC-SQUID sensors coupled to second-order axial gradiometers (pick-up coil 19 mm and 55-70 mm baselines; sensitivity of 20 fT/Sqrt[Hz] in above 1 Hz), as part of the electrophysiologic investigation protocol, tailored to the diagnostic need of each arrhythmic patient. More than 500 arrhythmic patients have been investigated so far. Results The MCG-based 3D-EAI has proven useful to localize well-confined arrhythmogenic substrates, such as focal ventricular tachycardia or preexcitation, to understand some causes for ablation failure, to study atrial electrophysiology including spectral analysis and localization of dominant frequency components of AF. However, MCG is still missing software tools for automatic and/or interactive 3D imaging, and multimodal data fusion equivalent to those provided with systems for invasive 3D electroanatomical mapping. Conclusion Since there is an increasing trend to favor interventional treatment of arrhythmias, clinical application of MCG 3D-EAI is foreseen to improve preoperative selection of patients, to plan the appropriate interventional approach and to reduce ablation failure.

P6-20: Age-related changes of cardiac electrical activity in Wistar rats. A longitudinal study with contactless magnetocardiographic mapping

P6-20: Age-related changes of cardiac electrical activity in Wistar rats. A longitudinal study with contactless magnetocardiographic mapping

Contactless magnetocardiographic mapping in anesthetized Wistar rats: evidence of age-related changes of cardiac electrical activity

Magnetocardiography (MCG) is the recording of the magnetic field (MF) generated by cardiac electrophysiological activity. Because it is a contactless method, MCG is ideal for noninvasive cardiac mapping of small experimental animals. The aim of this study was to assess age-related changes of cardiac intervals and ventricular repolarization (VR) maps in intact rats by means of MCG mapping. Twenty-four adult Wistar rats (12 male and 12 female) were studied, under anesthesia, with the same unshielded 36-channel MCG instrumentation used for clinical recordings. Two sets of measurements were obtained from each animal: 1) at 5 mo of age (297.5 +/- 21 g body wt) and 2) at 14 mo of age (516.8 +/- 180 g body wt). RR and PR intervals, QRS segment, and QTpeak, QTend, JTpeak, JTend, and Tpeak-end were measured from MCG waveforms. MCG imaging was automatically obtained as MF maps and as inverse localization of cardiac sources with equivalent current dipole and effective magnetic dipole models. After 300 s of continuous recording were averaged, the signal-to-noise ratio was adequate for study of atrial and ventricular MF maps and for three-dimensional localization of the underlying cardiac sources. Clear-cut age-related differences in VR duration were demonstrated by significantly longer QTend, JTend, and Tpeak-end in older Wistar rats. Reproducible multisite noninvasive cardiac mapping of anesthetized rats is simpler with MCG methodology than with ECG recording. In addition, MCG mapping provides new information based on quantitative analysis of MF and equivalent sources. In this study, statistically significant age-dependent variations in VR intervals were found.

Non-invasive detection of conduction defect in bachman’s bundle by magnetocardiographic mapping in patients with paroxysmal lone atrial fibrillation

Non-invasive detection of conduction defect in bachman’s bundle by magnetocardiographic mapping in patients with paroxysmal lone atrial fibrillation

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.

Fetal magnetocardiographic mapping using independent component analysis

Fetal magnetocardiography (fMCG) is the only noninvasive technique allowing effective assessment of fetal cardiac electrical activity during the prenatal period. The reconstruction of reliable magnetic field mapping associated with fetal heart activity would allow three-dimensional source localization. The efficiency of independent component analysis (ICA) in restoring reliable fetal traces from multichannel fMCG has already been demonstrated. In this paper, we describe a method of reconstructing a complete set of fetal signals hidden in multichannel fMCG preserving their correct spatial distribution, waveform, polarity and amplitude. Fetal independent components, retrieved with an ICA algorithm (FastICA), were interpolated (fICI method) using information gathered during FastICA iterations. The restored fetal signals were used to reconstruct accurate magnetic mapping for every millisecond during the average beat. The procedure was validated on fMCG recorded from the 22nd gestational week onward with a multichannel MCG system working in a shielded room. The interpolated traces were compared with those obtained with a standard technique, and the consistency of fetal mapping was checked evaluating source localizations relative to fetal echocardiographic information. Good magnetic field distributions during the P-QRS-T waves were attained with fICI for all gestational periods; their reliability was confirmed by three-dimensional source localizations.

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

In the framework of this study quantitative parameters are presented which, derived from magnetocardiographic maps, aid in making a conclusion about ischemia in the myocardium. The analysis is based on the examination of 86 patients with unstable angina, of which 53 exhibited myocardial ischemia with high probability (Group I: angiographically proven stenosis of at least 50% in a coronary artery of first or second order and positive troponin), while in the 33 other patients myocardial ischemia could be ruled out with high probability (Group II: angiographically clean coronary bed and normal troponin values). The negative predictive value (the probability that there is no myocardial ischemia when the magnetocardiogram (MCG) is negative) is 96.2%; the positive predictive value (the probability that there is actually coronary heart disease when the magnetocardiogram is positive) is 91.2%. A 12-lead ECG taken at the same time as the MCG achieved a positive predictive value of 92.8%, but a negative predictive value of 53.4%. Consequently, the boundary values of the parameters selected lead to a markedly distinct separation between patients with myocardial ischemia from those without. For ruling out coronary heart disease in patients with unstable angina the MCG is superior to 12-lead ECG.

P1642 Multichannel magnetocardiographic mapping of small animals in an unshielded laboratory

P1642 Multichannel magnetocardiographic mapping of small animals in an unshielded laboratory

Magnetocardiographic mapping of QRS fragmentation in patients with a history of malignant tachyarrhythmias.

The identification of patients at increased risk for ventricular tachycardia or ventricular fibrillation (VT/VF) and sudden cardiac death has consequences for therapeutic options and thus may reduce mortality in patients with coronary artery disease (CAD). We hypothesized that the intra-QRS fragmentation in magnetocardiographic recordings is increased in patients with CAD and with a history of VT/VF. Multichannel magnetocardiography (MCG) was carried out in 34 healthy controls, 42 patients with CAD without a history of VT/VF, and 43 patients with CAD and with a history of VT/VF. The intra-QRS fragmentation was quantified by a new fragmentation score. Its spatial distribution was investigated using two-dimensional (2-D) contour maps according to the sensor position of the 49-channel magnetogradiometer. Patients with CAD and with a history of VT/VF had significantly increased QRS fragmentation compared with patients with CAD without VT/VF or controls (72.9+/-37.5, 48.5+/-14.3, and 42.5+/-7.8, respectively: p <0.05). The area of high fragmentation in 2-D contour maps was twice as large in patients with than in those without a history of VT/VF (represented by the number of MCG channels with high fragmentation: 26.3+/-15.5 vs. 12.4+/-9.9, p<0.0001). Patients prone to VT/VF could be identified with a sensitivity of 64% and a specificity of 90%. In patients with CAD and with a history of VT/VF, intra-QRS fragmentation is increased and the area of high fragmentation in 2-D contour maps is enlarged. These findings may be helpful in identifying patients with CAD at risk for malignant tachyarrhythmias.

Electrocardiographic and magnetocardiographic body surface mapping

The spread of electrical endo- and epicardial activation is projected also to body surface and can be deducted from various numbers of recording points at the front or the back of the thorax. The resulting data are visualized in a body surface map (BSM).

Noninvasive visualization of multiple simultaneously activated regions on torso magnetocardiographic maps during ventricular depolarization

The time course and instantaneous distribution of the electrophysiologic processes of the human heart were analyzed by using a multichannel superconducting quantum interference device (SQUID) system, enabling the tangential components of the cardiac magnetic fields to be measured. By visualizing the changing magnetic field pattern in a two-dimensional presentation of the anterior and posterior torso during depolarization, the existence of more than one simultaneously activated region and the effective intracardiac current distribution were estimated without using a mathematical algorithm. The mid-to-late QRS complex when the myocardium has widespread depolarizing regions was analyzed using this technique. Even in an early stage of the QRS, two discrete active regions were observed in the magnetic field maps, in all nine subjects (adults with normal hearts). Furthermore, differences in the current distribution between the front and back active region were observed.

Nonfluoroscopic localization of an amagnetic catheter in a realistic torso phantom by magnetocardiographic and body surface potential mapping.

This study was performed to evaluate the accuracy of multichannel magnetocardiographic (MCG) and body surface potential mapping (BSPM) in localizing three-dimensionally the tip of an amagnetic catheter for electrophysiology without fluoroscopy. An amagnetic catheter (AC), specially designed to produce dipolar sources of different geometry without magnetic disturbances, was placed inside a physical thorax phantom at two different depths, 38 mm and 88 mm below the frontal surface of the phantom. Sixty-seven MCG and 123 BSPM signals generated by the 10 mA current stimuli fed into the catheter were then recorded in a magnetically shielded room. Non-invasive localization of the tip of the catheter was computed from measured MCG and BSPM data using an equivalent current dipole source in a phantom-specific boundary element torso model. The mean 3-dimensional error of the MCG localization at the closer level was 2 +/- 1 mm. The corresponding error calculated from the BSPM measurements was 4 +/- 1 mm. At the deeper level, the mean localization errors of MCG and BSPM were 7 +/- 4 mm and 10 +/- 2 mm, respectively. The results showed that MCG and BSPM localization of the tip of the AC is accurate and reproducible provided that the signal-to-noise ratio is sufficiently high. In our study, the MCG method was found to be more accurate than BSPM. This suggests that both methods could be developed towards a useful clinical tool for nonfluoroscopic 3-dimensional electroanatomical imaging during electrophysiological studies, thus minimizing radiation exposure to patients and operators.

Dispersion of the repolarization can be quantified by magnetocardiographic mapping in patients with malignant tachyarrhythmias

Dispersion of the repolarization can be quantified by magnetocardiographic mapping in patients with malignant tachyarrhythmias

Magnetocardiographic localization of the origin of ventricular ectopic beats.

Magnetocardiographic mapping opens new perspectives for three-dimensional localization of cardiac electrical activation. Using a 37-channel SQUID magnetometer equipment with high shielding, the origin of abnormal ventricular activation was investigated in 18 patients with Wolff-Parkinson-White syndrome prior to catheter ablation and in 5 of 31 patients with coronary artery disease having a sufficient number of monomorphic ventricular extrasystoles to enable evaluation. In all WPW-patients, the site of the earliest delta-wave activation was projected onto the AV-valve plane in accordance with the MR images. The result of magnetocardiographic localization was then compared to the site of successful catheter ablation determined by digital imaging processing. After optimization of the algorithms, both sites were in the various planes at the following distance from each other: X-plane: 0.8 +/- 0.9 cm, Y-plane: 1.1 +/- 1.0 cm and Z-plane: 1.5 +/- 1.0 cm. In three-dimensional projection, the mean difference in space between both positions was calculated to be 2.1 +/- 1.7 cm. After this validation ventricular premature beats were localized in another group of patients. In 4 of 5 patients their origin was found at the border of infarct areas. In each case, the progression of the ventricular activation could be pursued. The detected structure of the magnetic field distribution of the VBP's exhibited a stable bipolar pattern, which is comparable to that of ventricular tachycardia, and its algorithms may be used to localize the origin of ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)