Using select data from 3D contrast-enhanced (CE) CT imaging can better locate areas to be ablated in patients with ventricular tachycardia (VT), compared with standard voltage mapping, according to a small study published online July 24 in Circulation: Arrhythmia and Electrophysiology.
“An increasing number of patients with internal cardiac defibrillators (ICD) present with frequent and appropriate shocks for VT,” and most undergo radiofrequency ablation of VT rather than antiarrhythmic medications, due to their side effects," the authors wrote. However, “suboptimal catheter contact can result in falsely low voltage tomography.”
To better understand the practicality of integrating 3D CT scar/border zone reconstruction into clinical mapping systems to guide VT ablation, Jing Tian, MD, PhD, of the University of Maryland School of Medicine in Baltimore, and colleagues compared CT-derived anatomic, dynamic and perfusion characteristics of scar/border zones with standard voltage mapping in 11 patients.
The 11 male patients had a mean age of 65 years, had a previous MI and ischemic cardiomyopathy, were implanted with ICDs and were all scheduled to undergo VT ablation. The study had a mean follow-up of 12 months. Researchers used a 64-slice CT scanner to obtain CT images. Data sets were extracted and reconstructed into 3D images and compared to clinical electrical mapping systems.
Investigators reported that 40 percent (n=71) of segments were homogeneous—43 had normal segments and 28 were abnormal. There was an average of 14 mapping points in each segment.
When compared to areas under the curve, end-systole wall thickness had better discrimination value then wall motion in identifying abnormal voltage segments.
The researchers found no significant difference between end-systole wall thickness and wall thickness in predicting voltage categories. “Successful reconstruction of the left ventricle anatomy and scar/border zone was achieved in all cases,” the authors wrote.
Results showed that 3D scar reconstruction from CT imaging predicted abnormal electrical activity in 81.7 percent of the heart segments analyzed.
"The imaging also correctly displayed the location and extent of cardiac scar tissue, determined by voltage mapping--the gold standard for scar definition in current clinical practice," said Tian. "Curative ablations were located within tissue that CT had identified as abnormal in 82 percent of the cases."
Of the 11 patients, all had perfusion defects, and 3D CE-CT reconstructions from hypoperfused myocardium was successfully embedded in the left ventricle myocardium mapping.
“After 3D reconstruction of endo/epicardial borders and integration of 3D hypoperfused myocardium, this provided a detailed appreciation of the 3D scar anatomy during the VT ablation,” the authors noted.
No complications were reported during ablation procedures, but one death occurred within six months of follow-up period due to chronic heart failure and four deaths occurred within 12 months.
The novel findings of the study are:
- Anatomic, dynamic and perfusion parameters derived from a single CE-CT scan allow a comprehensive characterization of scar/border zone;
- Among anatomic and dynamic parameters, end-systole wall thickness and wall thickness jointly were the best predictors for the presence of the abnormal voltage segments;
- Areas of CT hypoperfusion correlate best with areas of abnormal voltage ( <1.5 mV rather than scar ( <0.5 mV) alone; and
- 3D CT-defined abnormal myocardium can be accurately extracted and embedded in clinical mapping systems displaying areas of abnormal anatomic, dynamic and perfusion parameters to guide substrate-guided VT ablations.
According to the researchers, the “gold standard” of voltage mapping holds limitations due to the fact that a single endocardial voltage measurement “incompletely” describes complex intramural scar anatomy. Integrating scar imaging into VT ablations can eliminate such limitations.
“Our results indicate that regional LV anatomic, dynamic and perfusion parameters can be utilized to correctly predict abnormal voltage locations in advance of the mapping procedure,” the authors concluded. “This may allow the electrophysiologist to concentrate on areas of likely myocardial scar and identify false low voltage recordings in areas of normal perfusion due to suboptimal catheter contact. This novel approach has the potential to significantly facilitate substrate-based VT ablations.”