Mapping and ablation of ventricular tachycardia guided by virtual electrograms using a noncontact, computerized mapping system
S. Adam Strickberger, MD, FACCa,
Bradley P. Knight, MDa,
Gregory F. Michaud, MDa,
Frank Pelosi, MDa and
Fred Morady, MD, FACCa
a Division of Cardiology, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, Michigan, USA
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Figure 1 Display of virtual electrograms. Multiple virtual electrograms were simultaneously viewed in a linear or grid format after being selected at the area of interest with the computer mouse. An isopotential map during ventricular tachycardia (VT) (cycle length 380 ms) is shown in these three panels. In each panel, the left ventricular reconstruction is shown with the septum, base and apex indicated. The chamber is shown in an open view of the entire endocardial reconstruction. The anterior septum on the far left of each endocardial reconstruction is anatomically continuous with the anterior septum on the far right of each model. In each panel, the isopotential map identifies the site of endocardial activation associated with the onset of the QRS complex during VT. The maximum negative potential, representing the leading edge of the wave of depolarization, is shown in white. A wireframe depiction of the inflated noncontact balloon catheter is shown in the top panel but not in the lower panels. In the top panel, eight closely-spaced virtual electrograms have been selected for viewing in a linear format. In the middle panel, a linear format of eight virtual electrograms with a larger interelectrode distance is displayed. An example of 16 virtual electrograms in a grid format is provided in the bottom panel. The letters on the isopotential map correspond to the virtual electrograms. Surface ECG lead I also is shown.
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Figure 2 Identification of sites of endocardial activation 0–30 msec preceding the onset of the QRS complex during ventricular tachycardia (VT). The VT depicted in this example had a cycle length of 240 ms, was associated with severe hypotension and loss of consciousness and, therefore, was induced only once. The data provided by the mapping system were based on a single 3 s sample of the VT. The top panel shows an open view of the left ventricular reconstruction, with the septum, base and apex as labeled; the inflated noncontact balloon catheter is shown only in the top panel. The letters A, B, C and D in the left ventricular reconstruction designate the sites at which the virtual electrograms in the top panel were computed. The instantaneous isopotential maps are shown in panels 1–4 at the time points designated by the vertical lines through the electrograms. This VT was no longer inducible and did not recur spontaneously after delivery of radiofrequency energy at sites A–D, as guided by the locator signal.
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Figure 3 Virtual electrograms and superimposed isopotential maps of a reentrant ventricular tachycardia (VT) that had a cycle length of 670 ms. The location of the distal electrode of a conventional catheter was determined with a locator signal, and the green locator line extends from the center of the balloon to the distal electrode of the conventional catheter. (A) Identification of the entire diastolic component of the reentry circuit. Shown are leads I, V1, V6 and aVF, along with the virtual and actual electrograms recorded at site 3, as depicted by the green locator signal in the left ventricular reconstruction. Note that the virtual electrogram faithfully reproduces the fractionated endocardial electrogram and the diastolic potentials recorded at site 3 with the conventional catheter. The instantaneous isopotential maps at the five time points depicted by the vertical lines through the electrograms have been superimposed on the left ventricular reconstruction to depict the path of the VT wavefront during diastole and at the onset of the QRS complex. (B) Isopotential maps during concealed entrainment with varying stimulus-QRS intervals. Shown are leads I, V1, V6 and aVF. Pacing was performed at a cycle length of 630 ms during VT at the two sites designated by the green locator signal, and, at both sites, the QRS complexes were identical to the QRS complexes during VT. In the top panel, the stimulus-QRS interval is 520 ms, and the path traveled by the wavefront (blue arrow) corresponds to the path of activation during the undisturbed VT depicted in (A). In the bottom panel, the stimulus-QRS interval is 190 ms, and, as expected, the wavefront originates at a site closer to the exit site of the VT and also follows the same activation path (blue arrow) as during VT. Successful ablation was achieved at the location depicted in the bottom figure.
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Figure 4 An example of virtual and actual electrograms recorded during sinus rhythm and ventricular tachycardia (VT). Also shown is lead I. The top panel shows the virtual and actual electrograms recorded during sinus rhythm. The bottom panel shows the virtual and actual electrograms recorded during VT.
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