Asian Cardiovasc Thorac Ann 1999;7:345-348
© 1999 Asia Publishing EXchange Pte Ltd
Biosense Left Ventricular Electromechanical Mapping
Balram Bhargava, MD, DM,
Ran Kornowski, MD
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Cardiology Research Foundation Washington, DC, USA
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For reprint information contact: Ran Kornowski, MD Tel: 1 202 877 3321 Fax: 1 202 877 2715 email: rxk3{at}mhg.edu Cardiology Research Foundation, Washington Cardiology Center, Suite 4B-1, 110 Irving St. NW, Washington, DC 20010, USA.
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Abstract
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Biosense is a new technology for left ventricular endocardial mapping and catheter-based intramyocardial therapeutics. The system reconstructs electromechanical maps of the left ventricle without using x-ray fluoroscopy. The 3-dimensional electromechanical maps generated by the system are utilized to precisely identify viable target zones based on integration of endocardial electrical and mechanical signals for online diagnosis of myocardial viability in the catheterization laboratory. It may be used for guidance of radiofrequency ablation and may potentially be used to apply intramyocardial therapy by its integration with a laser fiber for transmyocardial laser revascularization procedures.
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Introduction
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Biosense is a novel technology for left ventricular endocardial mapping and catheter-based intramyocardial therapeutics. This left ventricular mapping system has been derived from a new diagnostic and navigational guidance tool that uses an ultra-low magnetic-field energy source and sensor-tipped catheter electrodes to locate the exact catheter position in 3-dimensional space. The system reconstructs electromechanical maps of the left ventricle without using x-ray fluoroscopy. Compared to standard fluoroscopic techniques, the Biosense system provides a reduction in fluoroscopy exposure time, more accurate detection of arrhythmic foci, and subsequent guidance for ablation treatment and reassessment of the therapy. In addition, this system has been used for online diagnosis of myocardial viability in the catheterization laboratory and for percutaneous endomyocardial revascularization procedures. The 3-dimensional electromechanical maps generated by the system are used to precisely identify viable target zones based on integration of endocardial electrical and mechanical signals. This technology may be potentially used to apply intramyocardial therapy by its integration with a laser fiber for transmyocardial laser revascularization procedures.
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The Mapping System Components
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The Biosense system (Johnson & Johnson, Warren, NJ, USA) uses a harmless electromagnetic field generated from a triangular location pad, interfaced with a 7F deflectable-tip catheter containing a miniature location sensor to provide real-time 3-dimensional electrical and anatomical maps of the endocardial surface.1–3 The system uses the following components for cardiac chamber navigation and mapping: a triangular location pad with three coils (Figure 1A
) generating an ultra-low magnetic field (5 x 10–6 to 5 x 10–5 tesla units); a stationary reference catheter with a miniature magnetic field sensor located either in the right heart or externally on the body surface; a 7F navigation mapping catheter with a deflectable tip and electrodes that provide unipolar or bipolar endocardial signals when inserted into the left ventric
a miniature passive location sensor within the mapping catheter; and a NOGA workstation (Biosense-Webster, Tirat-HaCarmel, Israel) processing the information obtained from the mapping catheter and constructing 3-dimensional left ventricular geometry (Figure 1B).
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Figure 1. (A) The Biosense system uses magnetic field emitters (location pad) and sensor-tipped catheter electrodes to locate precisely the catheter position in 3-dimensional space. The location pad is composed of 3 coils that generate a magnetic field energy that decays as a function of distance from the coils. (B) A Silicon-Graphics screen and a NOGA processing unit are located in a workstation to process and exhibit mapping data.
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The temporal relationship of left ventricular mapping is derived from the intracardiac electrogram recordings. The electromagnetic field generated by the system contains the information necessary to resolve the location and orientation of the sensor in 6 degrees of freedom. The sensor measures the strength of the magnetic field, thus enabling determination of the distance from each of its sources. These distances determine the radii of theoretical spheres around each coil. The intersection of these spheres determines the location of the sensor in space (Figure 1A
). From the electromechanical information during systole and diastole, and by using a classical triangular reconstruction algorithm, the Biosense system can provide accurate global and regional myocardial functional data that include end-diastolic and end-systolic volumes, ejection fraction, local endocardial shortening, electrical activation time, unipolar and bipolar endocardial electrical signals, and electromechanical delay.
Advantages of the Biosense System
There are several unique features of the Biosense left ventricular mapping system: the navigation and mapping rely solely on the electromagnetic field generated from the location pad for real-time 3-dimensional reconstruction of the cardiac chamber, with only minimal need for fluoroscopy or contrast administration; because the system collects endocardial electrical data (unipolar and bipolar voltages), myocardial viability (presence of normal or reduced voltage) can be accurately determined; the local activation map can distinguish the normal activation sequence from abnormal (arrhythmogenic) foci; and the mechanical map (end-systolic and end-diastolic volumes, ejection fraction, and local shortening) can provide global and regional contractility data for the left ventricle.
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The Mapping Procedure
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The mapping catheter is introduced through an 8F femoral sheath and placed in the left ventricle. A fixed location reference catheter (also with a tip sensor) can be placed either externally (securely taped to the patient's back) or introduced through a venous access to a stationary point in the right side of the heart (e.g., coronary sinus or inferior vena cava). The location of the mapping catheter is gated to end-diastole and recorded relative to the location of the fixed reference catheter at that time, thus com-pensating for subject or cardiac motion. By moving the mapping catheter tip to multiple left ventricular endocardial sites, the NOGA processing system uses a triangular algorithm to reconstruct the left ventricular anatomy that is presented in real time on a Silicon Graphics (Silicon Graphics, Inc., Mountain View, CA, USA) workstation (Figure 1B). Local activation time or unipolar and bipolar intracardiac electrical recordings are acquired simultaneously, color-coded, and superimposed on the 3-dimensional anatomical map. The maximum peak-to-peak voltage of the unipolar or bipolar electrogram (QS or QRS complex) is measured by the software. The stability of the catheter wall contact is evaluated at every site in real time and points are deleted from the map whenever electrical or mechanical stability parameters do not meet criteria pre-specified in the software.
Analysis of Mapping Data
Unipolar and bipolar endocardial potentials are recorded from the catheter-tip electrode and converted into 3-dimensional electrical maps by displaying the voltage potentials on a graded color scale. A 3-dimensional mechanical endocardial map is then reconstructed to represent the local shortening function. This function quantifies regional wall motion by averaging the change in distance of each sampled endocardial site from its neighboring points at end-systole, relative to end-diastole. The electrical (voltage amplitudes) and mechanical (local shortening) functions are not necessarily concordant, especially when electrical activity is preserved despite impaired mechanical activity, commonly seen experi-mentally and clinically in severe ischemic syndromes associated with hibernating myocardium.
In patients, endocardial zones with high electrical activity and local shortening are interpreted to represent normal regional myocardial function. Endocardial zones with abnormal or low electrical activity (5 mV) and impaired mechanical activity (usually local shortening 6%) are interpreted to represent abnormal electromechanical activity, probably in previously infarcted areas.4,5 If mechanical activity is impaired and different from what would be expected from the normal electrical activity (e.g., electromechanical dissociation), the area of interest may represent ischemic or hibernating myocardium.6
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Animal Validation Studies
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The Biosense system has been used in various animal models to verify its accuracy and to detect electro-mechanical changes during myocardial ischemia or infarction.2–6 In a canine model with left anterior descending coronary artery occlusion, a significant reduction (50% to 70%) was found in measured unipolar and bipolar voltage potentials and local endocardial shortening in the infarcted zone following 3 weeks of coronary occlusion compared to baseline or noninfarcted areas.4,5 These findings confirm that the Biosense electromechanical mapping system can distinguish zones of prior myocardial infarction from normal myocardium by a reduction in both electrical and mechanical endocardial signals.
In a pig model of chronic myocardial ischemia (rather than infarction) in the left circumflex myocardial territory, electrical signals were found to maintain normal values compared to nonischemic zones. However, mechanical activity, as manifested by the local shortening map, was found to be reduced and significantly impaired compared to nonischemic zones.6
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Electromechanical Mapping in Patients
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The ability to distinguish between normal, infarcted, and ischemic myocardium makes the Biosense electro-mechanical mapping system a potential clinical tool for online detection in the catheterization laboratory of myocardial viability in patients with ischemic coronary syndromes. Preliminary data from the catheterization laboratory at the Washington Hospital Center, indicate that infarcted myocardium could be accurately diagnosed, located, and distinguished from healthy myocardium by a reduction in both electrical voltage and mechanical activity, and that ischemic myocardium could be diagnosed by subtle changes observed in electromechanical functions when compared to normal myocardial territories in the same patient.4,7 A normal electro-anatomical map is presented in Figure 2A. Figure 2B shows an electrical map obtained from a patient with prior anteroapical myocardial infarction. Note the reduction in voltage amplitudes in the anteroapical territory (red zone, unipolar voltage 5 mV) compared to the normal map.
Clinical Utility
The Biosense left ventricular mapping system can function both as a diagnostic tool and as platform technology for intramyocardial therapy. For the electrophysiology application, this system can provide the normal and abnormal (arrhythmogenic foci) electrical activation sequence and ablate the abnormal foci.8–11 The electrical signals derived from ischemic or infarcted regions can be measured to differentiate between normal, necrotic, and ischemic myocardium. Using the location sensors to obtain the combination of intracardiac electrical recordings with mechanical data seems to be a sensitive clinical tool for the assessment of myocardial viability. Clinical studies are underway to evaluate the use of electromechanical mapping as a novel diagnostic approach for online assessment of myocardial viability in the catheterization laboratory.
The use of Biosense electromechanical mapping technology should allow precise localization of an integrated mapping-laser catheter within the left ventricle and accurately identify ischemic target sites for trans-myocardial laser revascularization procedures.12,13 Ongoing studies in the USA and Europe are evaluating the safety and efficacy of the Biosense guided trans-myocardial laser revascularization approach in patients with refractory ischemic coronary syndromes who are poor candidates for conventional revascularization techniques such as angioplasty or coronary artery bypass surgery.14
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References
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Abstract
Introduction
