Smartphone-based ECG screening detects previously unknown atrial fibrillation in American Indians A smartphone-based electrocardiogram (ECG) screening accurately detected previously unknown atrial fibrillation in American Indians, and more than half who were diagnosed with the irregular heart rhythm were younger than the recommended screening age of 65, according to new research published today in the Journal of the American Heart Association, an open access journal of the American Heart Association. About one-third of ischemic strokes, those triggered by blood clots, are caused by atrial fibrillation, the most common heart rhythm disorder. Since many people don't have symptoms and are unaware of its presence, atrial fibrillation often goes undiagnosed. In some cases, a stroke is the first sign that a person has the disorder. American Indians are more at risk for atrial fibrillation than people in other racial and ethnic groups. As a population, American Indians also have substantially higher rates of obesity, diabetes and high blood pressure - all risk factors for atrial fibrillation.