Abstract 2354: Low-Voltage Multiple Pulse Termination of Ventricular Tachycardia in 4-day Infarct Canine Hearts
Introduction: ICD therapy is the most reliable treatment of ventricular arrhythmias in high-risk post-myocardial infarction (MI) patients. However, high-voltage shocks may induce local injury current and contribute to the progression of heart failure. Previously, we achieved a significant reduction in the cardioversion threshold (CVT) by applying five monophasic (MP) shocks within one ventricular tachycardia (VT) cycle length (CL) via maintaining depolarization of a small excitable gap instead of exciting a large area by a high-voltage shock in a rabbit model of chronic infarct. In this study, we aimed to extend these findings to a more clinically relevant canine model of healing infarct and to optimize the number of the multiple pulses.
Methods: The left anterior descending artery of mongrel dogs (n=6) was occluded for two hours via a left lateral thoracotomy and then blood flow was re-established. One dog died of congestive heart failure after reperfusion. Four days later, a medial sternotomy was performed and cardiopulmonary bypass was maintained. Loading (2 mg/kg) and maintenance (0.05 mg/kg/min) infusions of Flecainide were used to induce sustained VTs. Epicardial multielectrode mapping was performed. Through a right ventricle (RV) ICD lead, 3 to 8 MP shocks and 10 MP shocks were applied within one and two VT CLs, respectively. Antitachycardia pacing (ATP: 8 pulses, CL=70–95% of VT CL) was applied from a RV endocardial electrode.
Results: We were unable to induce sustained VT in two dogs. In the remaining three dogs, monomorphic figure-of-eight reentry pinned to the epicardial border zone was the main mechanism of VT. There was only one predominant ECG morphology with CL of 167±15.0 ms for each heart. Multiple pulses reduced CVT by 93% that of a single shock, which was 0.43±0.13 vs. 6.1±1.0 J, respectively (p <0.05). Compared to 3~8 MP shocks that applied in 1 VT CL, 10MP applied in 2 VT CLs had the lowest CVT of 0.11±0.08 J. The success rate of ATP was 8.1±9.6% (n=3).
Conclusions: Our results suggest that a 14-fold reduction in energy can be achieved by the multiple pulse therapy compared to the conventional high-energy defibrillation. And for stable reentry VT, multiple shocks are much more efficient than ATP in destabilizing the reentrant circuit.