IEEE Spectrum November, 2014 - 38

Pinpointing the Problem

nOv 2014

nORTh aMERICan

Some patients who've had heart attacks develop life-threatening
arrhythmias, which doctors try to stop by burning away problematic
tissue. A computer model can precisely identify the target.

the personalized 3-d model
of a patient's heart shows its unique
anatomy and pattern of scar tissue, which
determine how electrical signals move
through the heart.

doctors can simUlate an electrical signal that produces an abnormal
heartbeat and can thus cause cardiac arrest. By
observing how it moves through the tissue, they
can determine where the signal must originate.

in the standard treatment,
doctors use a catheter to probe for tissue
with abnormal electrical activity. They then burn
away a large patch of that tissue [blue dotted
line] in hopes of destroying the point of origin.

hoWever, the computer model reveals
that just one small piece of tissue [red circle]
is the key to the faulty signal. If doctors base their
treatment on the model, they can burn less tissue
and leave more of the heart intact.

parts of the heart that aren't responsible
for the faulty electric pulse. In one clinical study of patients with an accelerated
rhythm called ventricular tachycardia,
researchers found that ablation stopped
the arrhythmia in only 54 percent of
patients, and 8 percent of patients experienced complications.
For people in Jim's situation, a virtual
heart could offer a better way. Indeed, at
Johns Hopkins my colleagues and I are
now testing the first clinical application of

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our models in post-heart-attack patients
who have developed ventricular tachycardia, which can be life threatening. We
want to determine whether our models
can help physicians make better decisions
about which tissue to burn away-and let
them make those decisions without long
sessions of probing patients' hearts.
Using our system on Jim, we'd build
a three-dimensional model of his heart,
which would display its unique structural quirks and | co nti n u e d o n pag e 58

JoHns HopkIns UnIversIty/Heart rHytHm (4)

tor described above. Those devices can
lower patients' risk of dying from sudden cardiac arrest, but they don't "cure"
patients by preventing arrhythmias
altogether. So for some patients with
dangerous arrhythmias, such as people who receive frequent and painful
shocks from their implanted defibrillators, doctors set out to find sources
of the problems and fix them.
Let's imagine that our patient, Jim,
is a candidate for this treatment. First,
his doctors must study the electrical
pulses that are creating his irregular
heartbeat. These pulses sweep through
Jim's cardiac muscle in patterns that look
like spiraling electrical tornadoes. If the
doctors can locate the spot where these
disruptions originate, they can burn it
away (ablate it, in medical speak) and
restore a regular rhythm to Jim's heart.
Sounds sensible-but the task isn't easy.
To find that critical spot, they bring Jim
to an electrophysiology lab and sedate
him. Specialists insert a catheter into
his leg and slowly guide it through a
vein until it enters the heart's chambers. Then they begin the painstaking
process of "interrogating" the heart
with the electrode on the catheter's tip.
They slowly navigate the tool around
the inner surface of the heart to measure the electric signals in the tissue,
trying to piece together a map showing
how the irregular electric signal moves
through Jim's heart.
This painstaking procedure typically
takes between 4 and 12 hours, and it carries numerous risks, including the possibility that the electrode will pierce the
heart wall. The dangers are justified by
Jim's medical condition, but unfortunately
this intervention may not help him much.
Maps constructed by this point-by-point
interrogation method have poor resolution and are sometimes inaccurate. When
the doctors use these maps to plan their
ablation procedures, they simply don't
have the best information.
For arrhythmias originating in the
heart's primary pumps-the ventricles-
ablation isn't always successful. Doctors
may scorch the wrong tissue, damaging

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Table of Contents for the Digital Edition of IEEE Spectrum November, 2014