UK doctors have come upon a swallowing reflex that could make the heart stop momentarily. They detected the problem while examining a 25-year-old woman who regularly fainted after eating sandwiches or taking fizzy drinks.
She was eventually fitted with a pacemaker in January, which stopped her fainting. Her case has been explained in detail in a Lancet article by a team from the University of Birmingham hospital.
She experienced the episodes for around 10 years, but numerous medical tests had failed to find an explanation.
The episodes, lasted up to 10 seconds, making her feel suddenly and alarmingly light-headed and nauseous and she would sometimes have several episodes a week.
The problem first began when she was 15 and remained unexplained, despite hospital admissions between 2001 and 2007.
The patient did not smoke, drank little alcohol and had never used illicit drugs.
The 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, although she was in stationary traffic at the time.
She had undergone a full range of tests over the decade, including checks for thyroid and pituitary gland disorders, but medics could find nothing amiss.
And even though she weighed only 7st 2lbs (46.5 kg), she had no symptoms of anorexia and her pulse rate and blood pressure were normal.
Intrigued, doctors from the University Hospital of Birmingham then chose to monitor her as she ate a sandwich. And an electrocardiogram (ECG) test showed her heart stopped beating for around 2.5 seconds.
At times of light-headedness, she was found to have a complete block of the electrical impulse that regulates heartbeat.
They diagnosed her with "swallow syncope", where swallowing causes the abnormal feedback to the heart.
It can be associated with oesophageal or gastric disorders, or sometimes with heart and lung disorders, although this patient had no such problems.
She was fitted with a pacemaker to overcome this, and had stopped fainting when she was last seen in June.
Dr Howard Marshall, one of the cardiologists who treated her, said the reason sandwiches triggered attacks was because bread could form clumps and be hard to swallow.
"Fizzy drinks were also a problem, because of the bubbles of gas."
Dr Marshall, who said he had seen just one other case of the condition during his 20-year career, said the patient had been delighted that the pacemaker had relieved the symptoms.
"When she came back for her follow-up appointment, she was pleased we had discovered the cause of her faints and that we had found a treatment.
"But she wasn't so pleased that she had started to put on weight."
Writing in the Lancet, he and his colleagues added: "Patients with swallow syncope can languish for years because the diagnosis is little known - although a case report on it was published in The Lancet, 50 years ago."