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Real-ECG extraction and stroke volume from MR-Compatible 12-lead ECGs; testing during stress, in PVC and in AF patients

  • 1,
  • 2,
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Journal of Cardiovascular Magnetic Resonance201113 (Suppl 1) :P6

https://doi.org/10.1186/1532-429X-13-S1-P6

  • Published:

Keywords

  • Stroke Volume
  • Atrial Fibrillation Patient
  • Processing Block
  • Vary Heart Rate
  • Subject Result

Background

Due to the Magneto-Hydro-Dynamic (MHD) effect, blood flow within the MRI’s magnetic field (B0) produces a large voltage during the S-T cardiac segment [1]. The peak MHD voltage (VMHD) can be comparable, in higher-field MRIs, to the R-wave amplitude of the real Electrocardiogram (ECGreal), so that VMHD reduces ECG-gating reliability and prevents ischemia-monitoring during cardiac imaging/interventions. We hypothesized that (1) separation of ECGreal and VMHD from 12-lead ECGs acquired within a 1.5T MRI could be achieved, using adaptive filtering, based on a set of ECG calibration measurements, and (2) a non-invasive beat-to-beat stroke-volume estimation could be achieved from time-integrated systolic VMHD.

Methods

Fig.1 shows 3 sets of 20-sec breath-held ECGs measured at positions (i), (ii) and (iii), utilizing an MRI-compatible Cardiolab-IT digital ECG-recording system [2]. The adaptive filtering procedure was tested in 5 healthy subjects, and 2 patients with Premature Ventricle Contractions (PVCs) and Atrial Fibrillation (AF). Validation was based on comparing the filter-derived ECGreal with ECGs measured periodically outside the MRI. The data processing block diagram (Fig. 2) includes training of adaptive Least-Mean-Square filters with ECGreal input (i), application of the trained filters to ECGs acquired in (ii) and (iii), which separates the VMHD from ECGreal.
Figure 1
Figure 1

ECGs measured at 3 positions; outside the field (i) and at isocenter with head-in (ii) and feet-in (iii).

Figure 2
Figure 2

Adaptive filtering diagram used for intermittent PVC patients, with beats separated and then processed independently at abnormal/normal beat filters.

Results

PVC patient’s results (Fig. 3): (a) unprocessed surface-lead V6, (b) extracted ECGreal, and (c) VMHD. In (b) S-T segment voltage is restored, and the R-wave dominates for gating. Aortic-flow vortices (c) generate oscillating-polarity VMHD, with VMHD peaking during S-T segment. Cardiac beat-to-beat stroke volume (d) was estimated from time-integrated systolic VMHD. PVC beats produce substantially lower stroke volume than during sinus-rhythm. AF patient results (Fig. 4): (c) Irregular VMHD and (d) irregular stroke volume are due to ventricular-filling differences at varying heart rates (100-140bpm). Athlete subject results (Fig. 5): Filter tracking of rapid heart-rate changes from 44bpm to 87bpm is shown during a treadmill stress test performed inside the MRI. VMHD (b) and stroke volume (c) increase with heart rate, suggesting that the cardiac output matches higher demand. A stroke-volume comparison of all subjects (Fig 6), derived from time-integrated systolic VMHDs, demonstrates the measurement’s sensitivity to pathology.
Figure 3
Figure 3

Results from a PVC patient (Ejection Fraction 20-25%, mitral regurgitation.

Figure 4
Figure 4

Results from AF patient (100-150 bpm)

Figure 5
Figure 5

Results from athlete subject during treadmill stress test (44-87 bpm)

Figure 6
Figure 6

Stroke-volume comparison (cardiac cycles n=20 per subject). Athlete (+24%), PVC (-54%) and AF (-23%), relative to average of volunteers.

Conclusions

The filtering extracts ECGreal from measured 12-lead ECG, preserving ECGreal for ischemia monitoring and MRI gating. Stroke volume can be non-invasively derived from the time-integrated systolic VMHD.

Authors’ Affiliations

(1)
Brigham and Women's Hospital, Boston, MA, USA
(2)
University of Cincinnati College of Medicine, Cincinnati, OH, USA
(3)
University of Oxford, Oxford, UK

References

  1. Gupta : IEEE Trans. BioMed. Eng. 2008Google Scholar
  2. Dukkipati. Circulation. 2008Google Scholar

Copyright

© Ho Tse et al; licensee BioMed Central Ltd. 2011

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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