Thoracic Massage Permits Use of Echocardiography in Unanesthetized Rats

Purpose: The objective of the study reported here was to investigate whether massage-like stroking of the thorax and cranial portion of the abdomen might relax unanesthetized rats sufficiently to permit in vivo echocardiography.

Methods: Nine-month-old spontaneously hypertensive rats (SHR) were first conditioned to being held by hand for 10 to 15 min twice a day for seven to 10 days. During each session, the animal was placed in supine position, and the thorax and cranial abdominal area were gently stroked (approx. 5 cm/s, 12 to 14 times/min). After the conditioning period, echocardiography was initiated. We obtained serial transthoracic two-dimensional (2-D) and M-mode echocardiograms from nine-month-old SHR that were treated with isoproterenol (60 mg/kg of body weight, s.c., x 1, followed by 30 mg/kg/d x3), and from old (20 to 24 months old) SHR, studied when labored breathing, suggestive of heart failure, was evident (SHR-F). Measurements included end-diastolic volume (EDV) and end-systolic volume (ESV).

Results: In the isoproterenol-treated SHR, mean ± SD echocardiographically derived EDV (2-D, 0.29 ± 0.05; M-mode, 0.28 ± 0.01 ml) was not significantly different from volume at necropsy (0.33 ± 0.04 ml). Measurements of EDV and ESV by use of M-mode and 2-D echocardiography were significantly correlated (EDV R ² = 0.48, P = 0.05; ESV R ² = 0.39, P = 0.02). Echocardiography revealed pleuropericardial effusions (4/6), atrial thrombi (5/6), and left and right ventricular enlargement (6/6). The EDV and ESV were increased fivefold (P < 0.01) and threefold (P < 0.05), respectively, versus values for SHR not in heart failure (SHR-NF). Left ventricular ejection fraction of hearts from SHR-F was markedly decreased, compared with that in SHR-NF (44 ± 7 versus 74 ± 2%, respectively; P < 0.05). The presence or absence of left atrial thrombi and fluid in the thoracic cavity was confirmed at necropsy in SHR-F and SHR-NF.

Conclusion: Thoracic massage permits use of echocardiography in unanesthetized rats, thereby providing a simple, non-invasive technique for assessment of cardiac structure and function in rats without the potentially adverse effects of anesthesia.