Two months after federal regulators approved the first defibrillator that can be placed under the skin instead of connecting directly to the heart, doctors at Brigham and Women’s Hospital implanted three of the new devices Monday in patients at risk of cardiac arrest.

The procedures marked the first New England implantations of the subcutaneous heart defibrillator, or S-ICD, built by Natick-based Boston Scientific Corp. Doctors call it a breakthrough treatment in preventing sudden cardiac fatalities, the most common cause of death in the United States.