Non-invasive mapping of ventricular action potential waveforms reconstructed from clinical unshielded magnetocardiography. Potential diagnostic application and current limitations

Abstract

Objective: To evaluate the feasibility and limitations of reconstructing ventricular action potential waveforms using non-invasive, unshielded magnetocardiographic mapping (uMCG), highlighting differences between healthy individuals and patients, even at the current level of precision.

Methods: Clinical uMCG was performed using a 36-channel DC-SQUID system. The mathematical reconstruction method developed by Kandori et al. was applied to derive reconstructed ventricular action potential waveforms (rVAPw) from uMCG data in 10 healthy volunteers and 12 patients with various cardiac abnormalities. In four cases, simultaneous recordings of uMCG and right ventricular monophasic action potentials (RVMAP) were obtained using an amagnetic catheter technique.

Results: Reconstruction of rVAPw from uMCG signals was feasible in all subjects. Waveforms derived from 90-s averaged uMCG signals were comparable to those obtained with 300-s averages. The rVAPw closely matched the simultaneously recorded RVMAP waveforms. Compared to healthy individuals, patients showed a significant prolongation of rVAPw phase-0 (p < 0.01) and a trend toward increased total duration (p = 0.06), demonstrating the method's sensitivity to electrophysiological abnormalities.

Conclusions: While incomplete rVAPw at some MCG mapping sites reflects the current spatial resolution limitations of the uMCG array, the close alignment between rVAPw and RVMAP recordings suggests that 90-s uMCG acquisitions may suffice for reliable, non-invasive imaging of ventricular action potentials in clinical practice. These findings support further development of MCG technology as a medical device uniquely suited to bridge experimental and clinical applications by enabling non-invasive rVAPw mapping in patients. Future improvements in sensor technology, mathematical modelling, and multimodal imaging may allow for near-cellular spatial resolution.

Keywords: Current arrow map; Magnetic reconstruction of ventricular action potential; Magnetocardiography; Magnetoionography; Monophasic action potential; Non-invasive multimodal imaging of electrophysiologic events.

Fig. 1

(A) Example of Ventricular MultiMAP recording with a single amagnetic catheter. (B) One MAP signal (MAP1) is connected to the CardioMag system to synchronize the MCG with the intracardiac electrophysiological mapping. (C) The three-dimensional model of the patient's heart is shown, with superimposed the recording sensor array and the current arrows map trajectory calculated after the QRS onset.

Fig. 2

Examples of magnetic field distribution, effective magnetic dipole inverse localization, and current arrow map, computed at the onset of the QRS complex, showing the reproducibility between 90-s (A) and 300-s (B) MCG signal averages.

Fig. 3

Example of reproducibility of rVAPw (blue) and superimposed averaged MCG waveforms (purple) obtained from 90-s (A) and 300-s (B) MCG signal averages (same healthy subject as ih Fig. 2). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

Patient # 200525.z8 in Table 1. (A) Simultaneous MCG (butterfly overlay) and RVMAP signals during the electrophysiologic study. (B) Comparison between RVMAP (green waveform) and rVAPw (blue waveform) The amplitude of the rVAPw is normalized to that of the RVMAP. A good agreement is observed at 19 recording positions, whereas some misalignment is evident at several MCG recording sites (highlighted by red squares). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

Patient #200592.z15, in Table 1. (A) Simultaneous MCG (butterfly overlay) and RVMAP recordings during the electrophysiological study in sinus rhythm. (B) Comparison between RVMAP (green waveform) and RAP (blue waveform). The amplitude of the rVAPw, normalized to that of the RVMAP, shows a good alignment at 11 recording positions. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Example of unsuccessful action potential reconstruction during right ventricular pacing (same patient as in Fig. 5). (A) Simultaneous unshielded MCG signals (butterfly overlay) and right ventricular monophasic action potential (RVMAP) recordings. (B) In comparison to the RVMAP waveform, the reconstructed ventricular action potential waveform (rVAPw) appears unreliable, showing delayed and incomplete repolarization, specifically, the absence of a distinct phase 3 across all MCG recording sites.

Fig. 7

Patient #200532.z13 in Table 1. (A) Simultaneous unshielded MCG signals (butterfly overlay) and right ventricular monophasic action potential (RVMAP) recordings during sinus rhythm. (B) Comparison between the RVMAP (green waveform) and the reconstructed action potential (rVAPw; blue waveform), after amplitude normalization, shows a fair alignment, particularly in the overall waveform morphology and repolarization phase. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 8

Same patient as in Fig. 7. (A) Simultaneous unshielded MCG signals (butterfly overlay) and right ventricular monophasic action potential (RVMAP) recordings during right ventricular pacing. (B) Reconstructed ventricular action potential waveforms (rVAPw) show unreliable results, with delayed and incomplete repolarization (specifically the absence of a clear phase 3 across all MCG recording sites).

Fig. 9

Examples of rVAPw reconstructed in patients with ventricular conduction abnormalities. (LBBB: left bundle branch block; RBBB: right bundle branch block, LAFB: Left anterior fascicular block; LVH: left ventricular hypertrophy; WPW: ventricular preexcitation (right posterolateral).