A 63-year old man presented with abdominal pain, of sudden onset. the pain was situated across the central abdomen and whilst initially mild, had increased in severity, being continuously present with little fluctuation in it's intensity, . soon after the onset of pain he developed an urge to defecate, the stools appearing normal . the patient had atrial fibrillation ; there was little abdominal tenderness and on other intra-abdominal abnormality. investigations showed a leucocytosis of 15.7 thousand and mild metabolic acidosis. chest X-ray showed no abnormality but electrocardiogram revealed atrial fibrillation.
what is the diagnosis?
what further investigations may be helpful