What is the main idea of the news item? [br] [originaltext] Since the first

Since the first artificial heart was implanted in a human here in Houston in 1969, the field has advanced steadily. But it hasn’ t kept pace with the need for devices that can keep patients alive until they can get a real organ transplant: Heart disease remains the number one killer of Americans each year. Of the estimated 5 million people in the United States with failing hearts, only around 2,000 are likely to get a transplant this year.
    That is where various types of artificial pumps have come into play. Last month, at the Texas Children’s Hospital here in Houston, Jordan Merecka, 17, became the first patient in a US pediatric hospital to have his congenitally deformed heart removed and replaced with an external mechanical heart pump. Meeting with reporters a few days ago, he told how he almost ran out of time, waiting to have the procedure.
    Merecka, who now awaits a transplant, has limited mobility in the hospital as he remains tethered to the artificial heart beating loudly beside him.
    But nearby, at the Texas Heart Institute, doctors and researchers are working with another type of artificial heart, one that is much smaller, much more efficient and does not beat.
    The artificial heart Frazier and his colleague, Dr. William Conn, developed is small enough to be implanted in the human chest. But, unlike an animal or human heart, it produces no pulse because it is a continuous-flow mechanism. It uses a small spinning turbine to keep blood flowing at a steady rate rather than a pump that mimics the action of the heart found in humans or in the calves the doctors have used for trials.
    To provide the blood flow of a natural human heart, vibrating pumps must beat 100,000 times a day, 35 million times a year, leading to mechanical breakdowns. The continuous-flow pumps are much more durable and can last years without a problem.