In experiments with dogs, Johns Hopkins
researchers successfully used a 3-D map
of the heart and a sensor-guided catheter
to perform cardiac ablation, a mainstay
treatment that stops abnormally fast and
potentially fatal heartbeats, or arrhythmias.
The Johns Hopkins findings, presented
in November at the American Heart Association's
Scientific Sessions 2005 in Dallas,
provided information and technology used
by the U.S. Food and Drug Administration
to approve the system for testing in humans,
now under way.
The Johns Hopkins team created its
own 3-D models of each heart from images
obtained by integrating and superimposing
CT and MRI scans. Using an upgraded computer
software program known as electroanatomic
mapping, the scientists were able
to color code the heart models' structures.
The scientists safely ablated, or destroyed,
tiny areas of diseased heart tissue that facilitate
rhythm disturbances, guided only by
these anatomically precise, reconstructed
3-D maps.
During the procedure, a catheter containing
a magnetic sensor in its tip was inserted
through a vein in the dog's leg, then guided
to the heart, where it was used to burn off
the small part of heart muscle that gives rise
to the errant signaling responsible for the
arrhythmia.
A magnetic location pad was placed under
the operating table and situated directly
beneath the animal's body to detect the
position of the catheter and compare it to
the computer-generated image of the heart
displayed on a screen.
"This is a significant improvement for
patient safety and the performance of minimally
invasive procedures in the heart," said
study senior investigator and cardiologist
Timm Dickfeld, an adjunct assistant professor
at the School of Medicine and its Heart
Institute. Current methods for visualizing
the heart, using X-rays and fluoroscopy, are
potentially hazardous, Dickfeld said, because
they involve radiation and produce only
two-dimensional images, which are not as
accurate as 3-D images.
"Our study proves the effectiveness of
3-D mapping in guiding and pinpointing
the catheter's tip during a procedure, giving
the electrophysiologist a more concrete
awareness of the placement of lesions, and
it eliminates the need for an X-ray, reducing
the amount of radiation exposure for the
patient," he said.
As part of the study, the Johns Hopkins
scientists performed catheter ablation in
nine dogs who had nearly 50 CT markers,
small waferlike targets that could be seen
by a scanner, surgically implanted on the
outside of their heart's muscle wall. The
placement of the wafers covered all regions
of the heart, especially those where arrhythmias
are known to occur. Three-dimensional
maps of the heart, made shortly before the
procedure, were then used to guide the catheter
to its targets.
After the procedure, analysis of heart
tissue showed that the 3-D maps worked
very well and were extremely precise and
safe, Dickfeld said. The range of errors in
pinpointing therapy to a lesion was between
1.9 millimeters and 4.9 millimeters, and well
within lesion boundaries, which average 6
millimeters in diameter.
"A physician really needs precise anatomical
information during ablation because
one move in the wrong direction could
damage healthy heart tissue or puncture
the organ," said study lead investigator Jun
Dong, a postdoctoral research fellow. Previous
research by Dong and colleagues showed
that such complications occur in nearly 5
percent of catheter ablation procedures for
atrial fibrillation.
Funding for this study was provided by
Biosense Webster of Haifa, Israel, the manufacturer
of the electro-anatomic mapping
system.