Abstract 2740: Heterogeneous Zones in Magnet Resonance Images Are the Critical Areas for Ventricular Tachycardia and for Successful Ablation
Introduction: Magnetic Resonance Imaging (MRI) can reveal the complex structures of a scar that develops after a myocardial infarct. Parts of the scar can contain islands of viable issue, resulting in a mixture of scar and viable tissue (heterogeneous zone - HZ). We hypothesized that (1) successful ablation of ventricular tachycardia (VT) would include ablation in the HZ, and (2) incomplete ablation of the HZ can result in changes of the VT morphology and/or cycle length by changing the substrate of the VT circuit.
Methods Myocardial infarction was induced by mid-left anterior descending coronary artery occlusion in 17 pigs. MRI and then invasive electrophysiology (EP) intervention (3-dimensional voltage mapping, VT inducibility, pace and entrainment mapping, and ablation) were performed 55±18 days later. Ablations were done blinded to the MRI and guided by standard EP criteria. A second MRI was performed after the ablations, and in five animals, a second EP study was performed one week after ablation, followed by high-resolution MR imaging.
Results In 8 animals, a total of 22 sustained monomorphic VTs with a mean cycle length of 235±48 ms were induced. The remaining 9 animals were not inducible. In the non-inducible animals, the HZ encompassed 22±2 % of the total scar, compared to 62±16 % in inducible animals (p < 0.05). All VTs were successfully ablated at 13 ablation sites. Post-procedure analysis showed that in all animals, at least one ablation site was in the HZ. One week after the initial procedure, only one of the previously present VTs could be induced. In 3 cases, however, there was a prolongation of the cycle length of a previously induced VT morphology, and there were 3 new VT morphologies induced. In these animals with inducible VT a week post ablation, MRI confirmed that the HZ had not been completely ablated.
Conclusion These findings support the hypothesis that tissue heterogeneity serves as the critical slow conduction substrate to generate and maintain VT. The HZ detected by MRI may be a promising ablation target to cure ischemic VTs. In addition, remnants of HZ after ablation may lead to VTs with different morphologies and/or cycle lengths, and thus to clinical relapses.