Hamburg - There is new evidence that a virus could be the cause of irregular heartbeat in millions of patients who otherwise exhibit no diagnosed reason for atrial or ventricular fibrillation, according to a team of German scientists.

The researchers at the Max Delbruck Center for Molecular Medicine (MDC) in Berlin say they have uncovered the first firm evidence of the molecular mechanism whereby virus infections cause cardiac arrhythmia.

While many patients suffer from irregular heartbeat for reasons which are clearly diagnosed, millions of others have sudden bouts of atrial or ventricular fibrillation for no apparent reason. It has long been thought that a virus could be responsible.

The German researchers now say that a virus is indeed the most likely cause.

They have discovered that the receptor used by the virus to infect heart cells is necessary for regular heartbeat in mice, they noted.

Writing about their observations in the Journal of Experimental Medicine, the researchers say that arrhythmia occurs in the absence of the receptor.

They believe that both the virus infection and the autoimmune disease can block the receptor, which in turn disrupts the heart's normal rhythm.

The heart consists of two ventricles and two atria. In order to beat correctly and to pump blood through the body, specialized heart fibres generate electric signals that control the heart beat. Cardiac arrhythmia occurs when these signals are not correctly generated or forwarded. There, a receptor, which scientists call CAR, plays an important role.

CAR stands for Coxsackievirus-Adenovirus-Receptor. It is embedded in specific cell-cell-contacts (tight junctions) of the specialized heart fibres. CAR was discovered as the critical protein responsible for virus entry during infection with Coxsackie and Adenoviruses. Its role in the adult heart was previously unknown.

To investigate CAR's task in a healthy organism, the MDC-scientists switched off the CAR-gene in adult mice. As a result, the rodents could no longer produce the receptors and developed cardiac arrhythmia.

"That is an interesting observation because these special cell-cell-contacts, the tight junctions, have not been connected to arrhythmia so far", says Professor Michael Gotthardt, a team member.

The researchers also observed that the transfer of electric signals from the atria to the ventricles did not work properly.

"When CAR is missing, the signal cannot be passed on and the heart does not beat properly," according to Dr. Yu Shi, another researcher.

Gotthardt now wants to investigate whether CAR is blocked in patients with arrhythmia.

"However, it does not always have to be connected to a virus infection. The body's own antibodies directed against CAR could cause the disease as well," he was quoted as saying. (dpa)