Premature cardiac contractions produced by ultrasound and microbubble contrast agents in mice

This study investigated the effects of microbubble contrast agents on the production of premature cardiac contractions in mice exposed to ultrasound. Acoustic exposures consisted of a single pulse of 1.2-MHz ultrasound delivered to the murine heart during diastole. Two contrast agents (Albunex®, Optison®) and two pulse durations (5 ms, 10 μs) were investigated. The threshold for producing a premature contraction with a single 10-μs duration pulse was ∼1 MPa. Using a 5-ms pulse, the threshold with contrast was an order of magnitude less than the threshold without contrast. These results are consistent with cavitation as a mechanism for this bioeffect.