Premature cardiac contractions produced efficiently by external high-intensity focused ultrasound

Exposure of myocardium to a mechanical impact may produce premature ventricular contractions (PVCs). High-intensity focused ultrasound was reported to generate PVCs, while microbubbles at the target increased absorption, thus, promoting energy localization and decreased PVC threshold. The objective was to investigate the benefit of a two-stage ultrasonic transmission: (1) asymmetric mostly negative waveform at the focus (microbubbles generation) and (2) asymmetric mostly positive waveform at the microbubbles (impact generation). Optimization of transmission parameters was performed by measuring passive cavitation and attenuation. In vivo intact rat studies were performed while measuring electrocardiograph (ECG) and blood pressure. Most PVCs with blood injection were created while applying 3.06 MPa peak negative pressure during 1 ms, followed by 5.1 MPa peak positive pressure during 50 ms. Increasing the second stage from 5 ms to 50 ms increased the occurrence of PVCs. This study demonstrates that creation of localized microbubble population at the target promotes generation of PVCs without the need to inject contrast agents.