New Approach to Non-invasive Visualisation of Cardiac Function - Risk-free Test Can Provide Fast, Cost-effective Diagnosis

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Citation
European Cardiovascular Disease 2006 - Issue 1;2006:2(1):1-4
DOI
http://dx.doi.org/10.15420/ecr.2006.1.1t
Cardiovascular Disease - A Global Challenge

Heart disease is the single largest medical problem in the US, according to the American Heart Association (AHA), and costs over US$300 billion per year. Every year, of the millions of people in the US who have heart disease, at least 300,000 die because of late or inadequate diagnosis. The statistics show that the majority of the developed countries worldwide have a similar situation. Coronary heart disease (CHD) is projected, by the British Heart Foundation, to cost the UK a total of ┬ú7 billion per year. The World Health Organization (WHO) estimated, in 2003, that over 16 million people around the world die of cardiovascular disease (CVD) each year. It is remarkable that this is over 29% of all deaths internationally. To give some perspective, the AHA statistics indicate that, for example, a Canadian dies of stroke and heart disease every seven minutes. This is not just a 'manÔÇÖs diseaseÔÇÖ. There are predictions that, by 2040, women (in the study countries of Russia, Brazil, China and South Africa) will account for a higher proportion of CVD fatalities than men.

Regarding the specific socioeconomic consequences of CVD, WHO and the British Heart Foundation (among others) site the following.

  • Clinical care of CVD can be quite prolonged and, hence, costly, diverting earned precious family dollars to medical care.
  • CVD impacts wage earners in their prime mid-life years, disrupting family income and nationsÔÇÖ productivity.
  • There is increased risk of CVD correlated with lowered socioeconomic status.

Countries need faster, more reliable, more effective means of preventing, detecting and treating CVD. This article will focus on magnetocardiography as a non-invasive medical imaging technique to detect and monitor CVD.

About CardioMag Imaging

CardioMag Imaging (CMI), founded in 1999, has developed a magnetocardiograph (MCG) non-invasive heart-function diagnostic piece of equipment (see Figure 1). In a procedure lasting less than 10 minutes, the MCG provides accurate, highly reproducible information about cardiac electric function in realtime. Magnetocardiography procedures are expected to augment or even replace more invasive, lengthy procedures for the diagnosis of coronary artery disease (CAD), the leading cause of death for both men and women. As a result, resources in hospitals and private clinics may be more effectively utilised and, in the emergency room setting, the risk of malpractice from inadvertent discharge mitigated. As magnetocardiography enters standard clinical practice, the number of uses will grow for heart-health diagnostics.

CMI is the leader in clinical MCG-based diagnostics. As a functional imaging display modality. The MCG will sell into the diagnostic imaging market, which in the US alone exceeds US$12 billion and is experiencing double-digit growth. CMI has already sold systems in China and Europe. Short-term growth (years two-five) relies on meeting the worldwide need for more rapid diagnosis of acute chest pain. Growth thereafter will be fuelled by additional products that are highly suitable for routine screening of heart-health conditions in the general population.

Using the most advanced software technology and proprietary electronics, an MCG system utilises the worldÔÇÖs most sensitive magnetic field sensors - Superconducting Quantum Interference Devices (SQUIDs) - to measure true cardiac electric activity without touching the patient. This is the only non-invasive way to obtain such information. The heart can pump blood because heart muscle cells carry electric current (that produce magnetic fields outside the body). The MCG sees the magnetic 'heart printÔÇÖ created each millisecond by these cells.

CMIÔÇÖs application for market clearance in the US has been approved by the US Food and Drug Administration (FDA). Its systems also carry the European CE Mark. Further clinical trials in the US aimed at demonstrating the broader benefits of an MCG test for patients with chest pain and many other cardiac defects are under way at the following luminary sites: Mayo Clinic, John Hopkins Hospital and Cedars-Sinai Medical Center in the US, as well as centres in Germany, Italy and China.

In the US alone, there are over 6,000 primary hospitals and 1,500 chest pain centres that will need one or more MCGs. CMIÔÇÖs first targets are the chest pain centres, where a fast, accurate and non-invasive patient evaluation is required. In parallel, the company will serve similar markets in Europe and Asia - the latter requiring individual country regulatory approvals, which are facilitated by FDA market clearance in the US. CMI will reach all markets through established medical equipment dealers.

The company has recruited a world-class staff of 28 employees, including:

  • Carl H Rosner, President & Chief Executive Officer (CEO) - Chm-Emeritus InterMagnetics General Corporation;
  • Alexander A Bakharev, Senior Vice President - New Products - world-class expert in magnetocardiography;
  • Dr Robert S Sokolowski, Vice President, Business Development - experienced in international sales;
  • Barbara R Polidore, Controller - over 18 years of financial expertise; and
  • Dr Afshin Abedi, Vice President, Clinical and Regulatory Affairs.
A Brief History of Magnetocardiography

Magnetocardiography was first introduced in the 1970s as a non-invasive technique to detect the weak magnetic signals emanating from the heart with each heartbeat. The technology has continued to evolve and improve to a level where multichannel systems are now available that produce a dynamic image of the magnetic field produced by the heart are available. The MCG device is a passive system, emitting no ionising radiation or mechanical energy. Most, but not all, commercially available systems require a shielded room to operate. The CMI 2409 MCG operates without the need for an expensive shielded room, permitting placement of the system in clinical environments. The CMI 2409 MCG is a multichannel device composed of an array of sensors that are positioned over the torso for a simultaneous recording of the magnetic signals from the sensors, with no contact to the patient. In this manner an image is created of the magnetic field produced by the heart throughout the cardiac cycle at a typical time resolution of one millisecond. Proprietary medical analysis techniques have been developed by CMI to determine the presence or absence of ischemia using the magnetic signals.

Some clinical applications of magnetocardiography are detection of the following:

  • myocardial ischaemia (using rest or stress magnetocardiography),
  • risk stratification after myocardial infarction (MI),
  • monitoring rejection after heart transplantation,
  • detection of ventricular hypertrophy,
  • ventricular repolarisation study,
  • fetal MCG,
  • localisation of arrhythmogenic sites (ventricular tachycardia, premature ectopic heatbeats, supraventricular arrhythmias),
  • localisation of pre-excitation sites (Wolff- Parkinson-White (WPW) syndrome).

Several good sources are available to learn more about the field of magnetocardiography. A paper by Koch1 highlights recent developments, and presents a brief overview of the subject. A thorough review covering physical principles, instrumentation and clinical applications can be found in Tavarozzi et al.2,3

Description of Device

Figure 1 shows the major components of the CMI 2409 system. As previously mentioned, the MCG system operates without the burden of a shielded room, making the system well suited for use in the clinical domain. The strength of cardiac magnetic fields is several orders of magnitude lower compared with other magnetic field-creating sources that are usually present in typical hospital environments.

Examples for such sources include moving elevators, metal doors and metal chairs, as well as spinning fans, air conditioners or other clinical apparatus, and power supplies, monitors or other electronic devices. Magnetic fields produced by those sources are hereby referred to as 'noiseÔÇÖ. The 2409 uses sophisticated hardware and software techniques to suppress this unwanted, environmental noise and achieve acceptable signal quality. The SQUID sensors are located in the tower, each capable of measuring magnetic fields millions of times smaller than the magnetic field of the earth. The SQUIDs are kept at liquid helium temperature in a low noise dewar for the sensitive magnetic field detection.

An array of nine channels (3 x 3 grid) senses the heart magnetic fields, three additional channels are used for referencing and one channel for a reference electrocardiogram (ECG). MCG data are acquired at 36 locations above the torso by making four sequential measurements in mutually adjacent positions. The sensor housing is moved between four measurement positions, producing a total of 36 MCG measurements covering a 20cm x 20cm plane over the chest. In each position the nine sensors measure the cardiac magnetic field for 90 seconds using a sampling rate of 1,000Hz leading to 36 individual time series (see example in Figure 2). The inter-channel spacing is 4cm on a side.

The electrical activity during repolarisation gives rise to effective magnetic vectors, the dynamic motion of which describes the displacement of the electrical source. The software calculates 40 magnetic vectors at equally spaced time intervals around the peak of the T-wave (pre- and post-peak repolarisation). The detection of repolarisation abnormalities is directly related to the direction and dynamic motion of the magnetic vector around the peak of the T-wave. The magnitude and strength of motion of the vector can be described by seven predefined parameters: Pre-peak T-wave mean frontal angle, trajectory, angle deviation and post-peak T-wave mean frontal angle, trajectory, angle deviation and difference in mean frontal angle between pre- and post peak T-wave. If any of the seven parameters lie in the abnormal range, then the patientÔÇÖs repolarisation pattern is consistent with ischaemia.

Figure 3 is an illustration (using patient data) comparing the magnetic field map with the effective magnetic dipole vector (EMDV) for a normal healthy subject versus that of a patient with ischaemia.

Clinical Results

A discussion of recent clinical results using the CMI 2409 MCG can be found in a Touch Briefings article entitled ÔÇ£Non-invasive resting magnetocardiographic imaging for the rapid detection of ischemiaÔÇØ, written by Dr Kirsten Tolstrup, a cardiologist and assistant director of the cardiac non-invasive laboratory at the Cedars-Sinai Medical Center.4 Dr TolstrupÔÇÖs article highlights the use of CMIÔÇÖs proprietary EMDV analysis for the application of resting magnetocardiography in chest pain syndrome. Detailed results can also be found in Park et al.,5,6 Fenici et al.7 and Tolstrup et al.8,9,10 Ôûá

This document contains confidential and proprietary information of CardioMag Imaging, Inc. It is for use only as directed by CardioMag, and may not be used for any other purpose.

References
  1. Koch H, Recent Advances in Magnetocardiography, J Electrocardiology (Oct. 2004);37: suppl. 1: pp. 117-122.
    Crossref | PubMed
  2. Tavarozzi I, Comani S, Del Gratta C et al., Current perspective, magnetocardiography: current status and perspectives. Part I: physical principles and instrumentation, Ital Heart J (2002);3, No. 2: pp. 75-85.
  3. Tavarozzi I, Comani S, Del Gratta C et al., Current perspective, magnetocardiography: current status and perspectives. Part II: clinical applications, Ital Heart J (2002);3, No. 3: pp. 151-165.
    PubMed
  4. Tolstrup K, Non-invasive resting magnetocardiographic imaging for the rapid detection of ischaemia, European Cardiovascular Disease 2006 (May 2006); London.
  5. Park J W, Hill P M, Tolstrup K et al., Magnetocardiography Predicts Coronary Artery Disease in Bundle Branch Block Patients with Acute Chest Pain, poster P3447, Abstract Supplement of the Eur Heart J (2005);26: p. 567.
  6. Park J W, Hill P M, Chung N, Hugenholtz P G, Jung F, Magnetocardiography Predicts Coronary Artery Disease in Patients with Acute Chest Pain, ANE (July 2005);Vol. 10, No.3: pp. 312-323.
    Crossref | PubMed
  7. Fenici R, Brisinda D, Nenonen J, Mäkijärvi M, Fenici P, Study of ventricular repolarization in patients with myocardial ischemia, using unshielded multichannel magnetocardiography, Proceedings of 13th Intrnl Conf on Biomagnetism, Biomag (2002); pp. 537-539.
  8. Tolstrup K, Riuz J A, Greenwood S, Flores S et al., Cedars-Sinai Medical Center, Los Angeles, CA, Resting Magnetocardiography Accurately Detects Myocardial Ischemia in Chest Pain Patients Even When 12 Lead ECG is Normal, Circulation (2004);110: P III-743.
  9. Tolstrup K, Rashti S, Cheung B,et al., Resting Magnetocardiography Detects Ischemia with High Accuracy in Patients with Acute Coronary Syndrome, J Am Coll Cardiol. (2006);47: p. 182A.
  10. Tolstrup K, Brisinda D, Meloni A M et al., Comparison of Resting Magnetocardiography with Stress Single Photon Emission Computed Tomography in Patients with Stable and Unstable Angina, J Am Coll Cardiol (2006);47: p.176A.