Determinatino of right ventricular structure and function in normoxic and hypoxic mice: A transesophageal echocardiographic study

Background - Noninvasive cardiac evaluation is of great importance in transgenic mice. Transthoracic echocardiography can visualize the left ventricle well but has not been as successful for the right ventricle (RV). We developed a method of transesophageal echocardiography (TEE) to evaluate murine RV size and function. Methods and Results - Normoxic and chronically hypoxic mice (FIO₂=0.11, 3 weeks) and agarose RV casts were scanned with a rotating 3.5F/30-MHz intravascular ultrasound probe. In vivo, the probe was inserted in the mouse esophagus and withdrawn to obtain contiguous horizontal planes at 1-mm intervals. In vitro, the probe was withdrawn along the left ventricular posterior wall of excised hearts. The borders of the RV were traced on each plane, allowing calculation of diastolic and systolic volumes, RV mass, RV ejection fraction, stroke volume, and cardiac output. RV wall thickness was measured. Echo vlumes obtained in vitro were compared with cast volumes. Echo-derived cardiac output was compared with measurements of an ascending aortic Doppler flow probe. Echo-derived RV free wall mass was compared with true RV free wall weight. There was excellent agreement between cast and TEE volumes (y=0.82x+6.03, r=0.88, P < 0.01) and flow-probe and echo cardiac output (y=1.00x+0.45, r=0.99, P < 0.0001). Although echo-derived RV mass and wall thickness were well correlated with rule RV weight, echo- derived RV mass underestimated true weight (y=0.53x+2.29, r=0.81, P < 0.0001). RV mass and wall thickness were greater in hypoxic mice than in normoxic mice (0.78±0.19 versus 0.51±0.14 mg/g, P < 0.03, 0.50±0.03 versus 0.38±0.03 mm, P < 0.04). Conclusions - TEE with an intravascular ultrasound catheter, is a simple, accurate, and reproducible method to study RV size and function in mice.