No abstract

Objective The critical mass hypothesis for atrial fibrillation (AF) was proposed in 1914; however, there have been few studies defining the relationship between atrial surface area and AF. This study evaluated the effect of tissue area and effective refractory period (ERP) on the probability of sustaining AF in an in vivo model. Methods Domestic pigs (n=9) underwent median sternotomy. Epicardial activation maps were constructed from bipolar electrograms recorded from form fitting electrode templates placed on the atria. Baseline ERPs were determined. ERP was lowered with a continuous infusion of acetylcholine (0.005-0.04 mg/kg/min) until AF could be sustained after burst pacing. The atria were sequentially partitioned using bipolar radiofrequency ablation. ERPs were lowered using acetylcholine until AF could be sustained in each subdivision of atrial tissue. Each subdivision was further divided until AF was no longer inducible. At study completion, the heart was excised and the surface area of each section was measured. Results Over a range of ERPs from 75 to 250ms, the probability of AF was correlated with increasing tissue area (range 19.5 to 105 cm2) and decreasing ERP. Logistic regression analysis identified shorter ERP (p < 0.001) and larger area (p = 0.006) as factors predictive of an increased probability of sustained AF (AUC of ROC = 0.878). Conclusions The probability of sustained AF was significantly associated with increasing tissue area and decreasing ERP. These data may lead to a greater understanding of the mechanism of AF and help to design better interventional procedures.

Giant cell tumor of tendon sheath is one of the most common soft tissue tumors of the hand. These tumors typically occur in the third or fourth decade of life and present as solitary nodules on a single digit. Currently, the greatest reported number of lesions found within a single digit is five. Although uncommon, giant cell tumor of tendon sheath does occur in the pediatric population. Herein we present a report of a rare case of GCTTS in a child in which seven lesions were identified within a single digit—the greatest number of lesions within a single digit reported to date.

Diagnostic Level V. See Instructions for Authors for a complete description of levels of evidence.