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The role of the duty factor in ultrasound-mediated cardiac stimulation.

The role of the duty factor (DF) in ultrasound-mediated cardiac stimulation is studied. Five 3-month-old female rats were exposed transthoracically to 3.5-MHz ultrasonic pulses of 2.0-MPa peak rarefactional pressure amplitude, variable DF, and variable pulse repetition frequency. A change in the heart rate was not observed following the 0.25%-DF sequence. A decrease of ∼4% in the heart rate was observed following the 0.50%-DF and 1.00%-DF sequences. Outcomes suggest a possible DF threshold for cardiac pacing.