Substrate characterization of ventricular tachycardia in a porcine model of tetralogy of Fallot using noncontact mapping

BACKGROUND: Ventricular tachycardia (VT) in patients following tetralogy of Fallot (TOF) repair is challenging to map because of the presence of scar, patch material, and hemodynamic residua of surgery. This study investigates whether noncontact mapping can identify the arrhythmia substrate in a porcine model that involves a right ventricular outflow tract (RVOT) patch and either chronic volume or pressure load on the right ventricle. METHODS: Nine infant pigs (3-5 kg) underwent surgery involving an RVOT patch and creation of pulmonary insufficiency (PI, n = 4) or pulmonary stenosis (PS, n = 5). After a mean of 4.2 months, pigs underwent invasive electrophysiology studies (EPS) with noncontact mapping (Ensite, St. Jude Medical, St. Paul, MN USA) of the right ventricle. Automated, unipolar voltage maps (VM) were constructed during sinus rhythm. Threshold for substrate was set at -0.5 mV and incrementally adjusted to higher values until a contiguous region of low voltage was delineated. Programmed stimulation was performed to induce VT. VT activation was correlated to location of VM defined substrate. Three control pigs underwent EPS and VM. RESULTS: Free-wall RVOT substrate was identified in each of the model animals, correlating to location of the patch. The mean voltage threshold was -1.1 mV. VT was induced in 6/9 animals. Diastolic activation approximated the inferior or lateral border of the substrate in all animals. No RVOT substrate was identified in the control pigs. CONCLUSION: Automated voltage mapping of sinus beats identifies substrate for VT in a porcine model of TOF. Consistent diastolic activation of the substrate border was found during VT. Targeting this area may be useful in the ablation of VT after repair of TOF.