Thursday 4th February 1993 Morning surgery 10:00

“Does anyone know why we get atrial fibrillation?”
Dilys shook her head. Even Dylan looked puzzled. “Is it due to a re-entry circuit or an automatic focus?” he asked.
“No one really knows,” said Dr Lewis, “there are lots of theories. It is the commonest cardiac arrhythmia and it has been suggested that it might be due chronic damage to the heart and the left atrium, in particular. Can you think of any conditions that lead to atrial fibrillation?”
“High blood pressure,” said Dilys.
“Good,” said Dr Lewis. “If you look through the records of our patients with atrial fibrillation, you will find that many of them also have hypertension. High blood pressure puts a constant strain on the heart. It damages the atrial muscle cells leading to inflammation and scarring. The electrical activity of these damaged cells is affected and they generate impulses chaotically. We think this can lead to atrial fibrillation.”
“Mitral stenosis causes increased left atrial pressure,” said Dylan. “Is that why patients with mitral stenosis are susceptible to atrial fibrillation?”
“Excellent, Dylan, that’s right,” said Dr Lewis. Even Dilys looked impressed. “It also means,” Dr Lewis continued, “that if we convert a patient with atrial fibrillation due to chronic heart damage back into a normal heart rhythm they are very likely to slip back into atrial fibrillation again. That’s why we often try to control the atrial fibrillation rather than get rid of it completely.”
“Don’t you get atrial fibrillation in young, healthy patients?” asked Dilys.
“Yes, you do,” said Dr Lewis. “I imagine it is a different mechanism in young patients without any obvious underlying heart disease. Now, let’s assume that we’ve got an elderly man who has chronic heart damage due to a 10 year history of hypertension and angina. He is probably susceptible to atrial fibrillation. Can you think of anything that might set it off?”
“Mmm . . . I know . . . an overactive thyroid, Dr Lewis.” Dilys smiled.
“Good . . . anything else, Dylan?”
“Pneumonia and I think it can be set off by a clot on the lung, a pulmonary embolism.”
“I am sure you can get it after cardiac surgery,” added Dilys.
“Very good, both of you,” said Dr Lewis. “In patients that are susceptible to atrial fibrillation there are lots of things that can set it off. You can look the rest of those up this evening.”

Does anyone know why we get atrial fibrillation?