Adding functional imaging to structural imaging of patients with ventricular tachycardia (VT) has the potential to improve current VT ablation strategies, according to newly published research (Imanli H et al. Ventricular Tachycardia (VT) Substrate Characteristics: Insights from Multimodality Structural and Functional Imaging of the VT Substrate Using Cardiac MRI Scar, 123I-Metaiodobenzylguanidine SPECT Innervation, and Bipolar Voltage. J Nucl Med. 2019; 60: 79. doi: 10.2967/jnumed.118.211698). Iodine-123 metaiodobenzylguanidine (123I-MIBG) SPECT imaging, when combined with cardiac magnetic resonance imaging (MRI), helped to identify specific subsets of heart tissue more prone to arrhythmia, which may allow physicians to achieve improved VT suppression and shorter procedure times.
Ventricular arrhythmias, are the main cause of sudden cardiac death in the United States and are responsible for up to 300,000 deaths each year. Ablation of ventricular tachycardia is a proven treatment for arrhythmias in patients with a history of heart attacks. Identifying the area of the increased scar tissue that is responsible for the current arrhythmia and possible future arrhythmias has been challenging, with up to 50% of patients suffering a recurrence during the 6 months following the ablation. “The amount of scar tissue can often account for more than half of the left ventricle myocardium,” noted Dr. Timm Dickfeld, of the University of Maryland School of Medicine. “Ablating such a large amount of the myocardium is often not desirable and very time-intensive.”
In the study, researchers followed 15 patients with ischemic cardiomyopathy who were scheduled for radiofrequency ablation for drug-refractory VT. Each patient underwent imaging with 123I-MIBG SPECT and cardiac MRI, as well as high-resolution bipolar voltage mapping. These three mapping tools assessed various adaptations found in VT: abnormal innervation, tissue scarring and low-voltage area, respectively. The adaptations were then compared to determine which were present in the affected heart tissue.
Areas with abnormal innervation, cardiac tissue scar and low bipolar voltage were seen in all patients. While approximately 25 percent of patients had abnormalities found by all three mapping tools, researchers found that significant areas of the affected heart tissue showed adaptations only noted by one or two of the tools. The largest of these areas had abnormal innervation only (18.2 percent), cardiac scar tissue and abnormal innervation (14.9 percent), and MRI scar only (14.6 percent). “Results from this study show that nuclear medicine can be used to develop novel, cutting-edge strategies for risk stratification and arrhythmia treatment,” said Dickfeld.