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Cardiovascular magnetic resonance guided electrophysiology studies
Journal of Cardiovascular Magnetic Resonance
Cardiovascular magnetic resonance guided electrophysiology studies
Aravindan Kolandaivelu 0
Albert C Lardo 0
Henry R Halperin 0
0 Address: Johns Hopkins Hospital, Division of Cardiology , Baltimore, MD 21205 , USA
Catheter ablation is a first line treatment for many cardiac arrhythmias and is generally performed under x-ray fluoroscopy guidance. However, current techniques for ablating complex arrhythmias such as atrial fibrillation and ventricular tachycardia are associated with suboptimal success rates and prolonged radiation exposure. Pre-procedure 3D CMR has improved understanding of the anatomic basis of complex arrhythmias and is being used for planning and guidance of ablation procedures. A particular strength of CMR compared to other imaging modalities is the ability to visualize ablation lesions. Post-procedure CMR is now being applied to assess ablation lesion location and permanence with the goal of indentifying factors leading to procedure success and failure. In the future, intra-procedure real-time CMR, together with the ability to image complex 3-D arrhythmogenic anatomy and target additional ablation to regions of incomplete lesion formation, may allow for more successful treatment of even complex arrhythmias without exposure to ionizing radiation. Development of clinical grade CMR compatible electrophysiology devices is required to transition intra-procedure CMR from pre-clinical studies to more routine use in patients.
Introduction
Radiofrequency (RF) catheter ablation has advanced over
the last 25 years from an experimental procedure to the
first line treatment for a number of cardiac arrhythmias
including atrio-ventricular reentrant tachycardia,
accessory pathway associated tachycardias, and typical atrial
flutter [
1
]. These procedures are typically guided by
positioning electrode catheters using x-ray fluoroscopy and
using these catheters to observe the propagation of
electrical activity through the heart. Successful targeting of
ablation primarily to the anatomic arrhythmia substrate, as
opposed to mapping and targeting ablation based on
electrogram characteristics, began with recognition that
common atrial flutter passes through a narrow structure
known as the cavo-tricuspid isthmus [
2
]. By directing
ablation to interrupt conduction through this region, high
cure rates have been achieved with a low risk of
complications [
3
].
The clinical indications for anatomy based catheter
ablation have since expanded to more complex arrhythmias
such as atrial fibrillation and scar based ventricular
tachycardia [
4,5
]. The basis of these strategies is to target
specific anatomic regions and often to create extended
ablation "lines" by aligning multiple point lesions or by
dragging the catheter along the endocardial surface while
applying ablative energy. While the feasibility of x-ray
fluoroscopy guidance has been demonstrated for these
complex arrhythmias, precise targeting of ablation lesions
is limited by fluoroscopy's inherently poor ability to
visualize cardiovascular soft tissue anatomy. Electrospatial
mapping systems, which locate the catheter tip in 3-D
space relative to magnetic or electric field transmitters,
were rapidly adopted to create surface maps of electrical
characteristics from multiple regions of the heart and
mark the location of ablation attempts so that more
elaborate ablation patterns could be created (Figure 1a,b).
Electrospatial mapping, however, does not provide direct
visualization of the complex underlying arrhythmogenic
anatomy (Figure 2a,b). The persistence of suboptimal
cure rates, prolonged procedure and radiation exposure
times, and the risk of serious complications have
motivated new approaches to facilitate anatomy-based
catheter ablation for complex arrhythmias.
Modern imaging techniques such as Cardiovascular
Magnetic Resonance (CMR), intra-cardiac ultrasound, and
xray computed tomography (CT) are increasingly used to
approach the shortcomings of current mapping and
ablation systems. CMR is a particularly flexible imaging
modality that offers excellent soft tissue contrast, well
characterized gadolinium enhancement techniques for
myocardial scar visualization, 3-D imaging of complex
cardiovascular anatomy, real-time 2-D imaging along
arbitrary imaging planes, and the ability to quantify
cardiac motion and blood flow. This article will review the
application of CMR to current clinical procedures and
ongoing advances toward full CMR guidance of
electrophysiology procedures.
The present: Ablation planning and guidance using pre-procedural CMR
Atrial fibrillation
CMR has been used most extensively to assist planning
and guidance of atrial fibrillation (AF) ablation
procedures. AF is the most common clinically relevant
arrhythmia affecting 0.4% of the general population [
6
]. The
principle morbidities related to AF are stroke due to
embolization of atrial thrombus and symptoms related to
poor he (...truncated)