By Kit Yee Au-Yeung
In 1963, in a remote field in Syracuse, New York, Gerhard Baule and Richard McFee twisted a wire two million times around a ferrite core rod and hovered it over someone’s chest. It wasn’t a magic trick. Baule and McFee were trying to do something no one had done before: measure the heart’s magnetic signature.
Up until that point, researchers had long known the heart generates electrical activity that can be measured on the body – that’s the basis for the electrocardiogram (ECG). But ECG isn’t without its shortcomings. For one, it can only pick up electrical currents flowing toward or away from the recording leads, leaving it blind to important lateral activity across the heart’s surface. And because it relies on direct contact with the body, the signals it captures can sometimes get blurred, making it harder for doctors to make sense of what’s really going on inside the heart. While it’s a great clinical tool, ECG can still struggle to make the correct diagnoses of critical heart diseases when used on certain patients with underlying conditions.
Baule and McFee wanted to take it a step further. Since fluctuating currents produce magnetic fields, they figured the heart must be emitting its own tiny magnetic pulse with every beat. The challenge? That magnetic field is one million times weaker than the Earth’s. Picking it up was like trying to hear a whisper in a hurricane.
Baule and McFee’s experiment worked, but just barely. The signal was too noisy to be useful, even in that quiet field in Syracuse. Four years later at MIT, David Cohen took the work done by Baule and McFee further. Armed with a smaller coil and an electromagnetically shielded room that resembled an Apollo-era Lunar Module, Cohen cleaned up the magnetocardiography (MCG) signal enough to begin studying the basic physics behind it.
For a long time, MCG stayed in the realm of physics labs. You needed a giant room to shield the sensors, and the equipment was too sensitive to bring into busy hospital environments. But that’s changing fast. Thanks to better sensors, smarter software, and some help from AI, MCG is starting to hold its own and will soon be working alongside mainstream heart diagnostics. It's quick, high resolution, radiation-free, and non-invasive, making it truly valuable in real-world medicine. In fact, there is already increasing proof of its utility coming from a number of clinical studies.
Instead of relying on ECG and waiting a few hours for a biomarker test to be ordered and processed, patients can be assessed for ischemia with MCG in minutes after arriving at the ER. That’s a big deal. For people with chest pain, this means faster answers, fewer invasive follow-ups, and potentially avoiding an unnecessary overnight stay. Proving MCG’s impact in the ER is still a work in progress, and the bar is very high to avoid incorrectly sending someone home who should be receiving care. We’ll unpack this more in future blog posts.
MCG is also showing promise in another tricky area: heart rhythm disorders. For people with arrhythmias, especially those being prepped for procedures like catheter ablation, MCG can help map out where those irregular rhythms are starting. It’s even been used to decode fetal arrhythmias, which are complex and hard to pin down with traditional techniques.
In small studies, MCG may also help spot inflammatory heart conditions like myocarditis. In particular, MCG might be useful for monitoring the response to treatment over time. For example, if someone is receiving immunosuppressants to treat myocarditis, MCG could offer an early sign of whether the inflammation is improving, possibly several weeks earlier than an echocardiogram, according to one study by Dr. Bettina Heidecker. It’s not going to fully replace biopsies or MRI yet, but it could become a solid supporting actor now.
To put it in familiar context, MCG has progressed past its “infancy” stage and is now in its formative teenage years. Its accuracy can vary depending on how it’s set up, what system is used, and even the type of analysis applied. Larger studies are still needed to pinpoint exactly where it fits into clinical care, but the potential is real. In cases where traditional ECGs don’t give a clear picture, other techniques are costly and/or cumbersome, MCG might help fill in the gaps. Its success depends a lot on robust data and smart interpretation, but scientists are steadily figuring out where it shines.
It’s taken six decades, countless wires, and a lot of shielding, but the heart’s magnetic whisper is finally being heard.
Note: This is the first in a series exploring the evolving world of magnetocardiography – what it is, where it shines, and where it still needs work. Along the way, we’ll also share what we’re learning firsthand as we build our own MCG system at AQMed. More soon.
