Arthritis sufferers have 40 per cent higher risk of developing erratic heartbeat which can trigger heart attacks and death, warn researchers. The researchers believe the inflammation of joints in arthritis may cause irregular heartbeat, known as atrial fibrillation, besides formation of blood clots and stroke. Rheumatoid arthritis tends to strike between the ages of 40 and 70 years and is more common amongst women than men. It is the result of the immune system attacking cells lining the joints, making them swollen, stiff and very painful, reported online journal BMJ.com. Copenhagen University scientists studied more than four million people of whom 18,250 had rheumatoid arthritis over a period of five years, and found those afflicted were 40 per cent at higher risk of atrial fibrillation and 30 per cent higher risk of strokes than the general public. In a group of 1,000 normal patients, six would likely suffer from atrial fibrillation in any given year while 5.7 would be likely to have a stroke. However, amongst a group of 1,000 rheumatoid arthritis sufferers, eight would be expected to have atrial fibrillation while 7.6 would be likely to have a stroke.