WASHINGTON (AP) – Scientists created virtual replicas of patients' diseased hearts so precise that blocking a dangerous irregular heartbeat in these digital "twins" showed doctors how to better treat the real thing. One of the first clinical trials of these custom models suggests it might improve care for ventricular tachycardia , a notoriously difficult-to-treat arrhythmia that is a major cause of sudden cardiac arrest, blamed for about 300,000 U.S. deaths a year. The study, by researchers at