Abstract 2857: Identification of Substrate of Ventricular Tachycardia by Regional Strain MR Imaging in Infarct Porcine Heart.
Background; It has been difficult to identify the substrate of arrhythmia by non-invasive methods. Recent progression of strain analysis by cardiac magnetic resonance imaging (MRI) can characterize regional myocardial contractile properties, and may serve to index activation. To identify the substrate of ventricular tachycardia (VT) after myocardial infarction (MI), we performed strain analysis and delayed enhancement (DE) MRI in porcine MI-VT model.
Methods; Eight domestic pigs weighing 25–35kg were studied. All pigs had a baseline MRI in a 3T clinical scanner followed by induction of anteroseptal MI by balloon occlusion of the left anterior descending artery. Subsequently, they underwent MRI 4 – 6 weeks after MI. MRI protocol included cine, scar detection with DE by gadolinium, and regional 2D strain analysis by grid tagging. Invasive electrophysiologic study including induction of VT was performed within 1 week of MRI.
Results; All pigs had anteroseptal MI with a ejection fraction of 35 ± 3%. Segmental strain analysis was performed in each short axis slice. All segments were classified as normal, borderzone, and infarct scar based on DE image. We measured endsystolic strain value (ES), time to peak strain (TP) as a fraction of whole cardiac cycle, systolic strain rate (SSR), and early diastolic strain rate (DSR) from grid tagging data. ES after MI was reduced in scar and borderzone (-13 ± 4, -11 ± 6, and -5 ± 6 % in normal, borderzone, and scar, respectively, p = .02). TP was mildly prolonged in borderzone, as well as scar (0.49 ± 0.06, 0.53 ± 0.08, and 0.61 ± 0.13, p < .01). Though SSR did not show difference, DSR was reduced in borderzone (2.0 ± 1.1, 1.4 ± 0.8, and 1.3 ± 0.3 %/frame, p = .04). Five of 8 pigs had inducible VT by programmed pacing. Earliest activation site of VT was located at borderzone. The identical borderzone of VT origin had significantly larger TP compared to remaining borderzone (0.64 ± 0.09 vs 0.55 ± 0.08, p = .04).
Conclusions; Regional strain analysis by MRI identified that the infarct borderzone had delayed peak of contraction and reduced early diastolic function at 4 weeks after MI. Origin of VT is correlated with borderzone with delayed peak of contraction. These findings represent a first step towards the noninvasive identification of sites of VT origin.