Download Electrophysiology research includes MR

Electrophysiology
research includes MR
Use of MR imaging is studied in atrial fibrillation and cardiac resynchronization therapy
at Beth Israel Deaconess Medical Center.
Electrophysiology (EP), the study, diagnosis and treatment of heart rhythm disorders, has replaced
coronary stenoses as the fastest growing segment of invasive cardiology today. While the main tool
of EP physicians is the electrocardiograph (ECG), the use of diagnostic imaging is increasing to help
assess the causes and severity of EP conditions.
Because MR offers high quality cardiac anatomical and
functional imaging without the radiation or iodinated
contrast exposure of interventional x-ray, Philips has
dedicated a new Business Unit to EP. Philips supports
MR-EP research at Beth Israel Deaconess Medical
Center (BIDMC, Boston, Massachusetts, USA), where
clinicians are using a Philips Achieva 1.5T to research
in cardiovascular applications of MR since 1995,” says
Warren J. Manning, M.D., Professor of Medicine and
Radiology at Harvard Medical School and Section
Chief of Non-Invasive Cardiac Imaging at BIDMC.
“Most recently we are combining MR imaging with
electrophysiology in two distinct areas: atrial fibrillation
(AF) and cardiac resynchronization therapy (CRT).”
MR imaging in two important cardiac procedures.
“We have had a very strong relationship with Philips
Mark Josephson, M.D.
Reza Nezafat, Ph.D.
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Warren Manning, M.D.
Dana C. Peters, Ph.D.
FieldStrength – Issue 34 – May 2008
MR aids in RF ablation research
There are 2.5 million AF patients in the United States
alone, and risk increases with age. In paroxysmal and
some persistent forms of AF, abnormal electrical activity,
often originating in the pulmonary veins, causes electrical
and mechanical dysfunction of the atria. Blood pools in
the atria, thereby promoting clot formation and raising
the risk of stroke. One solution is to electrically isolate
the pulmonary veins from the atria with radiofrequency
(RF) ablation of the tissue surrounding the veins.
MR imaging can benefit AF patients before, during and
after treatment. “Pulmonary vein MR angiography helps
identify the location of the pulmonary veins, their size
and their orientation,” says Dr. Manning. “We send this
information to the electrophysiologist, who can use it for
planning before and during the RF ablation procedure.”
Mark Josephson, M.D., chief of the Cardiovascular Division
at BIDMC and author of the definitive text on cardiac
electrophysiology (Clinical Cardiac Electrophysiology,
Third Edition, Lippincott 2002), has a global reputation
as a pioneer in arrhythmia research. He explains how
a
b
c
d
“We have had a very strong
relationship with Philips
in cardiovascular applications
of MR since 1995”
post-ablation imaging with MR can be used to assess the
results of RF ablation: “The biggest reason for failure
of ablation is incomplete circumferential isolation of
the pulmonary veins. The lesions don’t appear to be
permanent; there is reconnection. If we can demonstrate
scarring around the pulmonary vein, it is more likely
that the vein is permanently isolated.” An additional
area of research should focus on the use of MR imaging
to delineate scar tissue in the left ventricle in order to
optimize very complex VT ablation procedures.
Pre- and post-ablation MRI
MR angiography (a) and pre- and post-ablation MR imaging
(b,c). On the reformatted image (d) ablation around the left
inferior pulmonary vein is seen.
Dana C. Peters, Ph.D., Assistant Professor of Medicine
at Harvard and Scientific Director of the BIDMC Cardiac
MR Center, has developed an MR protocol for research
studies imaging post-RF ablation scars that has led to
a better understanding of catheter ablation patterns.
“MR, unique among modalities, can help identify post-RF
ablation scars using a 3D navigator-gated method,” says
Dr. Peters. “And MR does not give additional radiation
to patients who otherwise would have repeated high
doses of ionizing radiation in pre-procedure, postprocedure and follow-up CT imaging,” she adds.
Dr. Josephson says preliminary study data suggests
that the MR protocol, performed 30 days after RF
ablation, may help to predict which patients will have
clinical success and which will have a recurrence of
atrial fibrillation.
John Wylie, M.D., junior faculty member in electro­
physiology, has helped to create the bridge between
imaging and electrophysiology at BIDMC. Dr. Wylie has established a collaboration between EP and the Cardiac
MR Center that has resulted in important developments
in imaging of AF patients, and CRT patients as well.
Pre-CRT vein imaging using MR
CRT is used to treat patients with impaired left
ventricular contraction and ventricular dyssynchrony,
which impairs the pump function of the heart and the
Pre-CRT coronary vein MRI
Example of pre-CRT coronary vein imaging with MRI, as
performed to help identify dissimilarities in vein anatomy to
help clinicians choose the most favorable veins for CRT leads.
Dr Nezafat received the ISMRM Young investigator award 2007
for this work.
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subsequent blood flow to the body. In CRT, a pacemaker
or cardioverter defibrillator is implanted in the patient,
with lead wires to effectuate electrical communication
to the cardiac tissue. Typically, one lead is placed in the
right atrium (RA), one in the right ventricle (RV) and one
through the coronary veins to the left ventricle (LV).
Reza Nezafat, Ph.D., Associate Scientific Director of
the BIDMC Cardiac MR Center is researching innovative
MR imaging protocols and techniques for patients
under­going CRT. Since one-third of CRT procedures
in patients with congestive heart failure involve
hemodynamic failure or implantation failure, Dr. Nezafat
and his group have developed a novel MR imaging
technique for assessing coronary vein anatomy, based
on a free-breathing, non-contrast imaging sequence with
magnetization transfer prepulse for improvement of
tissue contrast. Studies have shown that the MR images
may help to identify dissimilarities in vein anatomy
so clinicians can choose the most favorable veins for
CRT leads.
EP research continues
As the population ages and EP disorders become more
common, MR will likely play a larger role in assisting
EP clinicians. Philips continues to support MR research
that will benefit both clinicians and patients with
innovative diagnostic and treatment options.
References
ME Josephson
Clinical Cardiac Electrophysiology, 3rd Edition, Lippincott 2002.
R Nezafat, Y Han, DA Herzka, DC Peters, JV Wylie, B Goddu,
KV Kissinger, SB Yeon, PJ Zimetbaum, WJ Manning.
Magn Reson Med, 2007; 58:1196-206.
JV Wylie, DC Peters, V Essebag, WJ Manning, ME Josephson,
TH Hauser.
Heart Rhythm, 2008 (in press)
DC Peters, Wylie JV, TH Hauser, KV Kissinger, RM Botnar,
V Essebag, ME Josephson, WJ Manning.
Radiology, 2007; 243(3):690-695.
EP-Navigator
Ablation is usually done under x-ray fluoroscopic guidance,
enabling doctors to see the catheters, but x-ray does
not show the heart tissue well. For optimal navigation
physicians need to see the left atrium outline, including
the pulmonary veins. With Philips’ EP Navigator, a 3D
roadmap CT image is superimposed on the live x-ray
fluoroscopy. Philips is currently developing a similar
procedure using MR. The 3D MR dataset acquired prior
to the procedure is automatically segmented into the
different chambers of the heart. After selecting the
left atrium the doctor can immediately start navigation
for the ablation process. The EP Navigator tool will
facilitate more accurate assessment of 3D anatomy in
relation to the electrical signals helping physicians to
perform ablation procedures with more accuracy and
more confidence.
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FieldStrength – Issue 34 – May 2008
3D image data
Automatic segmentation
3D images combined with x-ray
of 3D data set
fluoroscopy show the exact position
of all catheters