Woman Who Regularly Fainted While Eating Sandwiches Or Fizzy Drinks

Here's a stumper from Pooch Hound for the medically interested among us. Read the first few paragraphs, guess the diagnosis, then read the article. Those who guess the correct diagnosis will be presented with a medical degree from South Harmon Institute of Technology...

The 25-year-old woman was seen at the hospital in January this year. She presented with episodes, typically lasting 10 second or less, of feeling suddenly and alarmingly light headed, and nauseous. She had collapsed on more than one occasion, but had no movements typical of epilepsy. Sometimes she would have several episodes a week. The problem first began when she was 15 and remained unexplained despite hospital admissions between 2001 and 2007. A full battery of blood and other tests had, more than once, revealed everything to be normal. However, an electrocardiogram (ECG) test had shown a pause of 2.5 seconds. She then had external-loop ECG tests, in which she was asked to press a button to record 1-2 minutes of the ECG each time she felt faint. At times of light-headedness, she was found to have complete atrioventricular block (a slowing of intracardiac conduction), with beat-to-beat pauses lasting up to 2.5 seconds.
On questioning, the patient revealed no history of note - she did not smoke, drank little alcohol and had never used illicit drugs. Her episodes tended to occur when she ate certain types of food, particularly sandwiches and fizzy drinks - and she had last collapsed when eating a sandwich while driving (in stationary traffic). Despite weighing only 46.5 kg, she had no symptoms of anorexia and her pulse rate and blood pressure were normal. Dr Boos and colleagues offered the woman a sandwich, which caused rapid onset of atrioventricular block and an associated 'heart pause' lasting two seconds - causing her to feel light headed again. She was diagnosed with...

What was the diagnosis?  Read on...

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