Acoustic radiation force impulse and ultrasound contrast agent evokes arrhythmias in the rabbit heart

Abstract

Introduction Acoustic Radiation Force Impulse[ARFI] ultrasound elastography has been widely introduced as a diagnostic modality for liver and breast masses. We previously reported that arrhythmias were observed at a mechanical index [MI] of 1.8 with ARFI and concomitant administration of an ultrasound contrast agent[UCA] in rabbits. The aim of this study was to identify the location of the arrhythmias in a heart using a new system (Microsonic co., Tokyo, Japan) which transmits ARFI from the probe used for B-mode imaging of the heart. Methods Under general anesthesia, seven rabbits were exposed to ARFI. Using the new transducer, cardiac B-mode images (4 chamber view, left ventricle long-axis view) were obtained through the intercostal space. We chose three points along the impulse conduction system of the heart: (1) right ventricle, (2) right atrium and (3) left ventricular wall.We confirmed the occurrence of arrhythmias and the shape of arrhythmias with and without UCA (perfluorobutane (SonazoidTM)). (at double the clinical dose). Two minutes after intravenous injection of the UCA, ARFI was transmitted with a 1.0 msec pulse duration delayed 200msec after the R wave. Thirty exposures were synchronized with one exposure per three heart beats. The MI of the ARFI exposure ranged from 0.84 to 1.16. Results Arrhythmias were not observed using ARFI without UCA. For ARFI exposure with UCA, an average of 2.85 arrhythmias were observed (range 0-7). There were no fatal arrhythmias. Arrythmias tend to occur from (1) and (2) rather than (3). The shape of arrhythmias were single ventricular or supraventricular extra-systolic waves. Arrhythmias from the right (1), (2) and left (3) heart had a reversed shape. Discussion Using this new system, the rabbit heart exposed to ARFI had more reliable focal positions. The MI used in this study was similar to that used in clinical setting of ARFI. There was no significant difference in the frequency of arrhythmias among the three points of ARFI exposure. However, reversed shape arrhythmias may indicate that ARFI exposure actually stimulated the right or left-sided impulse conduction system. Conclusion Extra-systolic activity at different origins was observed under similar clinical conditions using ARFI with infusion of an UCA. Ultrasound practitioners should know this adverse reaction, even if the MI is below the previously determined value of 1.9, especially when imaging near the conduction system.