WHAT'S NEXT THE familiar electrocardiograms of yearly medical checkups are the routine way to record electrical activity of the heart and detect disorders in its rhythms. But the test is relatively insensitive at pinpointing small areas where there may be problems, since a standard EKG machine samples electrical potential only at a handful of points on the body's surface. But a new computer-based method developed by a researcher seeks to deliver far more detailed information about the electrical activity of the heart. Instead of a dozen or so electrodes, the technique uses 224 of them, all woven into a chain...