Antihistamines do an excellent job of keeping allergy symptoms at bay. Antidepressants can help a person suffering from mental-health conditions get back to a normal life. For most people, the positive qualities of medications like these outweigh their (usually few) risks. But for some people—those who suffer from certain autoimmune diseases—these normally benign drugs can cause potentially fatal cardiac arrhythmias, or abnormal heart rhythms.

In recent years, researchers have established that some people who suffer from autoimmune conditions such as Sjögren's syndrome, systemic lupus erythematosus (lupus), rheumatoid arthritis, and other connective tissue diseases (diseases of the tissues that give structure and support to joints, tendons, blood vessels, and ligaments) have certain antibodies in their blood called anti-SSA/Ro antibodies. These antibodies may cause a heartbeat irregularity called Long QT syndrome, or QT interval prolongation.

A team of scientists at SUNY Downstate Medical Center in Brooklyn, along with international colleagues, recently conducted a study that identified the exact mechanisms by which SSA/Ro antibodies can result in an irregular heartbeat. What happens is that the antibodies prevent potassium ions from leaving the cells of the heart, thus causing a prolonged QT interval that can result in palpitations, fainting and possibly death. And when combined with specific medications, which themselves may cause Long QT syndrome, the risk of cardiac arrhythmia is even greater.

Not everybody with an autoimmune disease has SSA/Ro antibodies, but up to 90 percent of those with Sjögren's syndrome do, as do up to 50 percent of those with lupus. Up to 11 percent of people with rheumatoid arthritis also have the antibodies. A simple blood test can tell you whether you do or not.

Mohamed Boutjdir, Ph.D., a professor at SUNY Downstate and the lead author of the study, says, “It is recommended that anyone with SSA/Ro antibodies should get regular cardiac screenings, and those with abnormal electrocardiograms, or ECGs (a simple test that displays heart rhythms), should consult with their healthcare providers before taking antihistamines or antidepressants.”

In the United States, at least four million people have Sjögren's syndrome; 1.5 million have lupus; and 1.5 million have rheumatoid arthritis.

Mohamed Boutjdir, Ph.D. reviewed this article on August 12, 2015.


Boutjdir, Mohamed, Ph.D. Email conversation with source. August 9, 2015.

“About Sjögren's Syndrome.” Sjögren's Syndrome Foundation. Accessed on August 11, 2015.

“Statistics on Lupus.” Lupus Foundation of America. Accessed on August 11, 2015.

Hajj-ali RA. “Overview of Autoimmune Disorders of Connective Tissue.” Merck Manual (Consumer Version). Accessed on August 10, 2015.