JACC: ICD electrograms can identify VT in ablation patients
Implantable cardioverter-defibrillators (ICD) electrograms provide a practical approach to identifying ventricular tachycardias (VTs), and can differentiate clinical VTs from inducible VTs of uncertain clinical relevance in patients referred for catheter ablation, based on a study published Sept. 14 in the Journal of the American College of Cardiology (JACC).

“Patients who receive frequent appropriate shocks from ICDs often are referred for catheter ablation of VT,” the authors wrote. “Stored ICD electrograms (EGMs) of spontaneously occurring VTs often are the only documentation of VT in patients undergoing VT ablation.”

Because previous studies have not evaluated ICD EGMs as a surrogate for 12-lead ECGs to differentiate clinical VTs from undocumented VTs, Kentaro Yoshida, MD, of the University of Michigan, Ann Arbor, Mich., and colleagues studied 21 patients referred for catheter ablation of post-infarction VT.

The 21 patients (two women) had an average age of 70 and a mean ejection fraction of 0.25. All had a previous history of MI and all failed to respond to anti-arrhythmic drug treatment.

In 15 of the 21 patients, clinical VT was detected via a 12-lead ECG. In the remaining six patients seven-lead telemetry recordings were available for at least one VT. Prior to ablation, 10 patients were treated with amiodarone (Cordarone), three were treated with mexiletine (Mexitil), three with metoprolol (Lopressor), two with dofetilide (Tikosyn), one with sotalol (Betapace), one with procainamide (Pronestyl) and one with lidocaine (Xylocaine).

Of the 21 patients, 10 were implanted with Medtronic ICDs, nine with Boston Scientific and two with St. Jude Medical devices.

In order to compare clinical VTs to other VTs and for comparison of pace maps (corresponding ICD EGMs) with targeted VTs, the researchers constructed receiver-operating characteristics. To do so, the researchers took the ICD EGM recordings during induced VT and pace mapping and placed the recordings into an electrophysiologic recording system.

After the researchers identified the clinical VT on the basis of ECGs, the ICD EGMs recorded during the clinical VT were compared to ICD EGMs or all inducible VTs. Patients were followed up every three to six months.

During the trial, Yoshida and colleagues induced 124 VTs via programmed stimulation. In 13 or 15 patients whose VTs were documented on 12-lead ECGs, VTs with matching configurations were inducible by programmed stimulation; in two patients VTs could not be induced.

Pace mapping was performed at 1,296 sites in low-voltage areas and 62 exit sites were detected. According to the researchers, the mean procedure time was recorded to be 383 ±97 minutes. After ablation procedures, 10 VTs remained inducible while none of the clinical VTs remained inducible. Yoshida et al reported that 14 patients (67 percent) had no inducible VTs post-ablation.

“The ICD EGMs were almost as accurate as the 12-lead ECGs for differentiating the clinical VT from previously undocumented VTs,” the authors wrote. While all clinical VTs were identified by a 12-lead ECG of the clinical VT, 98 percent were distinguished from clinical VT on the basis of computerized analysis of the ICD EGMs.

In 67 percent of patients, who had clinical VT induced, the cycle length of the clinical VT was within 10 percent of the cycle length of at least one other induced VT that was not previously documented.

Additionally, the researchers said that clinical VT differed by more than 50 ms compared to previously documented VT in eight of the 13 patients. And, while the cycle length of clinically documented VTs was reported to be 433 ms, the difference in cycle length between the documented VT and induced clinical VT was 75 ms.

The authors also found that 96 percent of the clinical VTs were accurately differentiated from the 64 previously undocumented VTs, which they said showed that these simple visual analysis of the ICD EGMs were as accurate as computerized analysis.

The researchers also found no significant differences in spatial resolution between ICD manufacturers.

“When ECG documentation of clinical VTs is not available in patients with ICDs, the ICD EGMs can be used to discriminate the clinical VTs from other VTs that are induced in post-infarction patients,” the authors said. “Furthermore, ICD EGMs may be helpful for pace mapping when a clinical VT is not inducible during a mapping procedure.”

While the researchers noted that spatial resolution of pace mapping based on ICD EGMs is inferior to the spatial resolution of 12-lead ECGs, they may be beneficial in determining whether or not an ablation catheter is located at a VT exit site.

“Therefore, during mapping of VTs in the electrophysiology laboratory, visual comparisons of stored and real-time ICD EGMs provide a simple and practical technique for identifying clinical VTs,” the authors concluded.

In an accompanying JACC editorial, Jesus Almendral, MD, and Francis Marchlinski, MD, wrote that "signal analysis could be established, independently of symptoms, if device therapy was appropriate for a ventricular arrhythmia or inappropriate for a nonventricular arrhythmia event or abnormal lead-related activity."

And, despite what the authors called a small sample size and the fact that the recording system used in the study was not filtered for standard ICD EGM tracings and instead used between 0.05 and 300 Hz, they called Yoshida and colleagues work “seminal in nature and certainly a welcome investigation.

“Their work [Yoshida et al] suggests that in the management of VT with catheter ablation procedures, ICD EGMs could become the new ‘standard’ link between spontaneous phenomena and induced arrhythmias,” the authors concluded.