Characterization of Anatomic Ventricular Tachycardia Isthmus Pathology After Surgical Repair of Tetralogy of Fallot

Abstract

The autopsy and surgical pathology databases at UCLA were searched for cases of TOF and its major variants (including TOF with pulmonary atresia and TOF with absent pulmonary valve). Baseline demographic and clinical data were obtained from the medical records. All specimens were evaluated for the presence of naturally or surgically related anatomic isthmuses corresponding to those that have been previously described. In addition, isthmus 1 was redesignated as 1A, 12 and © 2013 American Heart Association, Inc. Original ArticleBackground-Although catheter ablation has been used to target the critical isthmuses for re-entrant monomorphic ventricular tachycardia in tetralogy of Fallot, the anatomy and histology of these regions have not been fully characterized. Autopsy hearts with tetralogy of Fallot were evaluated to clarify the pathological substrate. Methods and Results-Twenty-seven hearts with the diagnosis of tetralogy of Fallot were examined. Anatomically defined isthmuses included (1A) ventriculotomy-to-tricuspid annulus, (1B) ventriculotomy-to-ventricular septal defect patch, (2) ventriculotomy-to-pulmonary annulus, (3) pulmonary annulus-to-ventricular septal defect patch, and (4) ventricular septal defect patch-to-tricuspid annulus. Length and wall thickness were measured for all specimens, and light microscopy was performed for those surviving surgery. For subjects ≥5 years at death, isthmuses 1A and 1B were present in 88%, isthmus 2 in 25%, isthmus 3 in 94%, and isthmus 4 in 13%. Isthmus 1A had the greatest dimensions (mean length, 3.9±1.08; thickness, 1.5±0.3 cm), isthmus 1B intermediate dimensions (mean length, 2.4±0.8; thickness, 1.1±0.4 cm), and isthmuses 2, 3, and 4 the smallest dimensions (mean length, 1.5±0.5, 1.4±0.8, and 0.6±0.4 cm; thickness, 0.5±0.2, 0.6±0.2, and 0.3±0.04 cm, respectively). Histological examination (n=7) revealed increased fibrosis in anatomic isthmuses relative to nonisthmus controls. Conclusions-Consistencies in isthmus dimensions and histology are found among patients with repaired tetralogy of Fallot. Isthmus 1A is associated with the largest morphological dimensions, whereas the nearby newly described isthmus 1B is significantly smaller. Of isthmuses with the smallest dimensions, isthmus 3 is the most common. (Circ Arrhythm Electrophysiol. 2013;6:905-911.)

Assessing Ventricular Scar in Tetralogy of Fallot

“…Again, the data from the article of Moore et al 7 are helpful here, reinforcing the Zeppenfeld et al 9 finding that isthmus 4 is rarely present. However, we know that the native atrioventricular conduction tissue in TOF runs inferior and posterior to the VSD, thus deep ablations on the inferior rim of the VSD should be conducted cautiously.…”

“…Antiarrhythmic medications and defibrillator therapies are offered to those patients with the highest risk of lifethreatening VT. Ablation serves as a useful adjunct therapy, either to prevent future arrhythmia or to reduce implantable cardioverter-defibrillator shocks. In this issue of Circulation: Arrhythmia and Electrophysiology, Moore et al 7 report the results of gross and microscopic evaluation from 27 postmortem specimens with TOF. The authors' goal was to describe the dimensions of the right ventricular muscular isthmuses and quantify the degree of fibrosis.…”

“…The data of Moore et al 7 on the length and thickness of each isthmus may become a helpful reference in designing potential lesion sets. However, despite their useful description of macroreentry corridors, these data have important limitations.…”

“…Successful ablation requires the best possible understanding of anatomic substrate. Moore et al 7 offer another layer of anatomic data in hearts with TOF, which may improve ablation strategies. However, TOF is just 1 lesion in congenital heart disease.…”

Challenges and Pitfalls of Entrainment Mapping of Ventricular Tachycardia

“…Exits may be multiple 9,10 and patterns other than loop reentry around scar are likely. Channels of preserved myocardium are frequently not "normal" in voltage (>1.5 mV) as described in the anatomic isthmuses in Tetralogy of Fallot, 11,12 but rather recorded as dense scar (<0.5 mV). Entrainment mapping is influenced by the current strength and size of the virtual electrode that both paces and records the local response to continuous resetting.…”