Atrial Remodeling After the Fontan Operation

Abstract

Hemodynamics following Fontan surgery are notable for right atrial (RA) hypertension and dilation. The effect of this stress on atrial cytoarchitecture has not been studied systematically, and may be relevant to arrhythmias and their treatment. Morphologic and histopathologic analysis was performed on RA and left atrial (LA) tissue from post-mortem specimens of Fontan hearts (n = 47) and compared to control samples from young patients with normal atrial hemodynamics (n = 15). Most Fontan specimens were from young patients who expired after a relatively short duration of Fontan physiology. Tissues were analyzed for wall thickness, fibrosis content, and fibrosis pattern. Mean wall thickness for both RA (3.0±1.0 mm) and LA (2.3±0.6 mm) in Fontan hearts was significantly greater than in control hearts (RA = 1.8±0.4 mm and LA = 1.8±0.5 mm, p<0.001 and p=0.024, respectively). Predictors for RA thickening included: a) older age at Fontan surgery, b) older age at death, and c) longer duration of Fontan circulation. Fontan hearts and controls exhibited nearly identical RA and LA fibrosis patterns. Neither wall thickness nor fibrosis varied with underlying heart defect or style of Fontan connection. In conclusion, atrial remodeling after Fontan surgery for univentricular heart physiology involves increased wall thickness in both the RA and LA. Interstitial fibrosis was also observed in Fontan atria, but because a similar pattern was present in control tissue, this likely represents normal fibroelastic atrial structure rather than a specific response to Fontan hemodynamics. The degree of wall thickening observed in Fontan atria was not so excessive as to preclude transmural lesions during catheter or surgical ablation of reentrant arrhythmias.

Evolving Electroanatomic Substrate and Intra‐Atrial Reentrant Tachycardia Late After Fontan Surgery

“…A recent histopathological study in a predominantly pediatric cohort of Fontan patients who died shortly after surgery (mean, 1.7 years after Fontan surgery), demonstrated that the amount of atrial fibrosis was not significantly different compared to patients with a normal heart. 5 In contrast, electroanatomic mapping data in older Fontan patients (mean, 18 years after Fontan surgery) showed extensive abnormal atrial endocardium (bipolar voltage ≤ 0.5 mV) in those patients with atrial tachyarrhythmias. 6 Stephenson et al recently demonstrated that the prevalence of IART declines in the initial 4-6 years after Fontan surgery but then increases with age irrespective of the type of Fontan operation, with the highest hazard 10 years post-Fontan and beyond.…”

“…The contribution of adverse atrial mechano‐electrical remodeling, including right atrial (RA) dilatation, fibrosis, and atrial wall thickening, to the pathogenesis of IART is less clear. A recent histopathological study in a predominantly pediatric cohort of Fontan patients who died shortly after surgery (mean, 1.7 years after Fontan surgery), demonstrated that the amount of atrial fibrosis was not significantly different compared to patients with a normal heart 5 . In contrast, electroanatomic mapping data in older Fontan patients (mean, 18 years after Fontan surgery) showed extensive abnormal atrial endocardium (bipolar voltage ≤ 0.5 mV) in those patients with atrial tachyarrhythmias 6 .…”

State-of-the-Art CT Imaging of the Left Atrium

“…Evidence from pathological studies suggests that the thickness of the atrial myocardium changes with age as well as a variety of pathological conditions [60][61][62]. Myocyte hypertrophy is seen in animal models used to study AF [63].…”

The Clinical Course and Incidence of Supraventricular Tachyarrhythmias After Extra-Cardiac Conduit Fontan Procedures in Relation to an Atrial Situs

“…This speculation is supported by a histopathologic report of atrial remodeling after Fontan procedures; the wall thickness for both the RA and LA was greater than that in the control hearts, and neither the wall thickness nor fibrosis varied with the underlying heart defects or type of Fontan connection. 24 …”