A test that picks up a nearly undetectable variation in the heartbeat helps single out heart attack survivors who are likely to develop potentially deadly heart rhythms, reports the June issue of the Harvard Heart Letter. These are the people who would most benefit from getting a device called an implantable defibrillator, which shocks the heart back into a normal rhythm if it goes astray. Defibrillators help some heart attack survivors who have damage to the left ventricle live longer. The problem is that doctors can't easily tell which survivors are most likely to suddenly develop lethal heart rhythms — and so would benefit from a defibrillator — and which aren't. The new test, called the T wave alternans test, may fill that need. Originally designed for the space program, the test detects beat-to-beat changes in the heartbeat that are too small to be seen on a standard electrocardiogram
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