Technology that aims to keep congestive heart failure patients out of the hospital is gaining traction. The idea is for heart patients to take readings like their weight, blood pressure and other key metrics using wireless and other technologies; the data are then transmitted to a case manager or medical care giver. That way health care givers can catch, and address, warning signs before the patient lands in the ER with shortness of breath or a heart attack. In the past, patients have found such technology difficult to use. But a number of managed-care companies are experimenting with electronic devices meant to make the process easier.