Cardiac arrhythmia and injury induced in rats by burst and pulsed mode ultrasound with a gas body contrast agent.
OBJECTIVE
Premature complexes (PCs) in the electrocardiogram (ECG) signal have been reported for myocardial contrast echocardiography and also for burst mode (physical therapy) ultrasound with gas body contrast agents at lower peak rarefactional pressure amplitudes (PRPAs). For contrast echocardiography, irreversibly injured cardiomyocytes have been associated with the arrhythmia. The objective was to determine whether cardiomyocyte injury is associated with the PCs induced by the burst mode at lower PRPAs.


METHODS
Anesthetized rats were exposed to focused 1.5-MHz ultrasound in a water bath. Evans blue dye was injected intraperitoneally to stain injured cardiomyocytes, and a perflutren lipid microsphere ultrasound contrast agent was infused intravenously. The continuous burst mode simulated physical therapy ultrasound. Intermittent 2-millisecond bursts, or envelopes of pulses simulating diagnostic ultrasound, were triggered 1:4 at end systole. Premature complexes were observed on ECG recordings, and stained cardiomyocytes were counted in frozen sections.


RESULTS
The continuous burst mode produced variable PCs and stained cells above a 0.3-MPa PRPA. The triggered bursts above 0.3 MPa and pulse envelopes above 1.2 MPa produced statistically significant (P < .01) PCs and stained cardiomyocytes.


CONCLUSIONS
Irreversible cardiomyocyte injury was associated with the development of PCs for the burst mode and occurred at substantially lower PRPAs than for pulsed ultrasound.
Department of Radiology, University of Michigan Health System, 1301 Catherine St, Ann Arbor, MI 48109-5667, USA. douglm@umich.edu
Douglas L
DL
Miller
Chunyan
C
Dou
Benedict R
BR
Lucchesi
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology*; D003287:Contrast Media / Q000009:adverse effects; D005466:Fluorocarbons / Q000009:adverse effects*; D005740:Gases / Q000009:adverse effects; D006335:Heart Injuries / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology*; D051381:Rats; D054772:Rats, Hairless; D013010:Sonication / Q000009:adverse effects*
D003287:Contrast Media; D005466:Fluorocarbons; D005740:Gases; C042852:perflutren