The fact that WPW patients are young and do not have structural heart disease, lead to using catheter ablation of the APs with the elimination of the atrial fibrillation as well as the episodes of re-entrant ventricular tachycardia. This elimination of the atrial fibrillation with ablation implies APs have some pathophysiologic role in the development of a-fib in the WPW patient.Functionally defined re-entry does not require the alternative anatomically defined circuit accessory pathways and it may not reside in just one location. Ventricular fibrillation (VF) following ventricular tachycardia (VT) may be described as a functionally defined re-entry problem caused by multiple mini re-entrant circuits spontaneously created within the ventricular myocardium. The original re-entrant circuit breaks down into multiple mini reentrant circuits. (VF becoming the grand finale of a single prolonged VT larger circus movement, propagating change in the "functional core" of the ventricular myocardium, dissipating mini reentrant circuits, exhibited as ventricular fibrillation.) Ischemia, electrolyte, pH abnormalities, or bradycardia are potential causes of functionally defined re-entry due to changes in the properties of the cardiac tissues functional core. (No accessory pathway required). For reentry to occur, the path length of circuit should be greater than the wave length (ERP × conduction velocity) of impulse. See also
AV reentrant tachycardia
AV nodal reentrant tachycardia

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The tumor may be localized at the end of the long bone (commonly in the metaphysis). Most often it affects the proximal end of tibia or humerus, or distal end of femur. Osteosarcoma tends to affect regions around the knee in 60% of cases, 15% around the hip, 10% at the shoulder, and 8% in the jaw. The tumor is solid, hard, irregular ("fir-tree," "moth-eaten", or "sun-burst" appearance on X-ray examination) due to the tumor spicules of calcified bone radiating at right angles. These right angles form what is known as a Codman triangle, which is characteristic but not diagnostic of osteosarcoma. Surrounding tissues are infiltrated. Microscopically: The characteristic feature of osteosarcoma is presence of osteoid (bone formation) within the tumor. Tumor cells are very pleomorphic (anaplastic), some are giant, numerous atypical mitoses. These cells produce osteoid describing irregular trabeculae (amorphous, eosinophilic/pink) with or without central calcification (hematoxylinophilic/blue, granular)—tumor bone. Tumor cells are included in the osteoid matrix. Depending on the features of the tumor cells present (whether they resemble bone cells, cartilage cells, or fibroblast cells), the tumor can be subclassified. Osteosarcomas may exhibit multinucleated osteoclast-like giant cells. Diagnosis
X-rays is the initial imaging of choice to diagnose osteosarcoma. Some characteristics of osteosarcoma on X-rays are sunburst appearance and Codman triangle (elevation of bony cortex by the tumour that caused new bone formation). CT scan is helpful in defining the bony anatomy, the integrity of the bony cortex, detecting pathologic fracture, and assessing ossification (laying of new bone materials) and calcification of the cartilage.