Noncontact Endocardial Mapping in the Human Left Ventricle

ABSTRACT & COMMENTARY

Synopsis: This system has potential use in patients undergoing mapping of complex arrhythmias since the system provides rapid analysis of real-time electrograms over the entire tachycardia circuit.

Source: Schilling RJ, et al. Circulation 1998; 98:887-898.

Schilling and associates report the first clinical use of a multielectrode catheter that was developed to permit noncontact mapping of electrical activity in cardiac chambers. This study describes results obtained in 13 patients who were undergoing endocardial left ventricular mapping prior to catheter ablation of hemodynamically well-tolerated ventricular tachycardia. The system consists of a catheter containing a multielectrode array, a custom-built amplifier system, and a Silicon Graphics workstation to process and analyze the signals. The electrode catheter is a woven grid of thin wires mounted on an ellipsoidal balloon at the tip of a 9 Fr catheter. Each wire has a 0.025-inch break in insulation, making it a noncontact unipolar electrode. A ring electrode is located on the proximal shaft of the catheter in the aorta as the reference. The catheter is placed over a guide wire into the left ventricle, and the balloon is inflated with saline after it is in position. A second catheter is then used for determining chamber dimensions and ablation. A low current "locator signal" is passed between this roving catheter and the ring electrodes on the noncontact catheter. The electrode array detects and determines the locator signal angles and determines the other catheter’s positions. This determines the geometry of the chamber and generates a series of coordinates for the endocardium. Electrical activity is detected by the multiple electrode array but it is of lower amplitude and frequency than the source on the endocardium. These signals must, therefore, be enhanced and resolved using a complex process involving an inverse solution to Laplace’s equation by use of the boundary element method. This inverse solution of Laplace’s equation allows computation of multiple endocardial electrograms from the potential sensed on the noncontact electrode. Mathematical techniques are used to minimize noise. This methodology computes the relationship between the 64 electrodes on the noncontact balloon and 3360 points on the endocardium. The signal processing for this analysis is done in real time using a Silicon Graphics workstation. This paper assesses the accuracy and timing of the reconstructed unipolar electrograms compared with traditional contact unipolar electrograms from the same endocardial site recorded by the roving catheter.

Contact electrograms were compared at 76 points equatorial and 32 points nonequatorial to the noncontact electrode array with respect to both morphology and timing. At points distant from the equator, the correlations were lower, but acceptable recordings were still made.

Schilling et al consider this system to have potential use in patients undergoing mapping of complex arrhythmias since the system provides rapid analysis of real-time electrograms over the entire tachycardia circuit.

Comment by John P. DiMarco, MD, PhD

Catheter ablation is now the preferred treatment for many cardiac arrhythmias. However, catheter ablation remains highly effective only in situations where a small critical portion of the circuit can be accurately mapped and identified. This is almost always possible in patients with accessory pathways and in patients with AV nodal reentry. It is usually possible in classic atrial flutter since the circuit in that arrhythmia passes through a known anatomic isthmus in almost all patients. Automatic rhythms usually arise from single foci and can be mapped using simple activation sequence mapping. For other arrhythmias, such as reentrant ventricular tachycardia in the setting of coronary artery disease or arrhythmogenic right ventricular dysplasia or in atrial reentrant arrhythmias, more complex mapping procedures have been necessary. Prior techniques have required catheter manipulation to reach various points within the circuit and then confirmation of participation of that site in the circuit using entrainment mapping or analysis of electrogram characteristics. This often required difficult catheter manipulation with the patient during tachycardia. This approach was severely limited in patients with unstable arrhythmias, or in those with several different arrhythmias that were difficult to sequentially map. Other techniques to map large numbers of sites simultaneously have been developed. Contact electrode arrays using various types of expandable baskets have been devised but they have been difficult to manipulate, and appropriate software for analysis of the signals has often not been available. An electroanatomic system that uses magnetic positioning has allowed accurate mapping of chamber contours and storage of signals but still requires that the catheter be moved to multiple places to generate the initial map. The system described in this paper is the first analysis recording system that permits the entire circuit of the arrhythmia to be analyzed in real time and permits positioning of an ablation catheter within that circuit guided by the electrical signals.

In this paper, no results of ablation are reported. One can anticipate that the ablation results are currently being analyzed. If the results are as good as might be expected, we should be a long way further toward the use of ablation as primary therapy for many patients with monomorphic ventricular and atrial tachycardias.


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