Insights into the mechanism of sustained ventricular tachycardia after myocardial infarction in a closed chest porcine model using a multielectrode "basket" catheter

Introduction: Accurate analysis of the arrhythmia substrate is important fo r successful radiofrequency ablation of sustained ventricular tachycardia ( VT) after myocardial infarction (MI). Methods and Results: A multielectrode "basket" catheter capable of endocard ial recording and pacing was inserted percutaneously into the left ventricl e of post-MI swine for analysis of the mechanism of sustained VT. Sustained VT was induced in 42 of 61 pigs that survived an acute MI produced by perc utaneous transluminal coronary angioplasty balloon occlusion of the left an terior descending coronary artery and injection of agarose gel beads. A mul tielectrode "basket" catheter (Constellation(TM)) with 61 electrodes was in serted in 35 of these animals for analysis of the VT. Induced VT had a cycl e length of 179 +/- 25 msec at control and 230 +/- 43 msec after administra tion of intravenous procainamide. Presystolic electrical activity was recor ded from at least 1 of 32 bipolar pairs of electrodes at a mean 40.7 +/- 23 .6 msec prior to QRS onset. Isolated mid-diastolic potentials were recorded in 26 of 35 animals, In 22 animals, there were multiple isolated potential s recorded from adjacent electrode pairs. Isochronal maps demonstrated that these potentials returned to the systolic site of origin, Resetting of sus tained VT by single premature ventricular stimuli was observed in 6 of 12 a nimals. Entrainment with overdrive pacing was seen in 19 of 26 animals with induced VT. Concealed entrainment was observed in ten animals, The mean st imulus to QRS interval was 45 +/- 28 msec, Concealed entrainment was observ ed from adjacent electrode pairs with different stimulus to QRS intervals. Conclusion: These data suggest that sustained VT in this model is due to re entry with an excitable gap. A multielectrode "basket" catheter is useful f or analyzing the zone of slow conduction participating in the tachycardia c ircuit. Such analysis mag provide useful information to guide successful ca theter ablation of sustained VT after MI.