End-systolic Pressure–Dimension Relationship ofin situMouse Left Ventricle

The increasing popularity of genetically engineered mice in cardiovascular research has made it important to evaluate cardiac function in small animals. We have developed a system to enable simultaneous pressure–dimension analysis of the mouse left ventricle. The chest was opened under anesthesia, and a 1.4 F micromanometer catheter was inserted into the left ventricle through the apex. A pair of sonomicrometry crystals were attached to the anterior and posterior walls using tissue adhesive. Pressure and dimension were recorded simultaneously at baseline and after isoproterenol injection (1μg, intraperitoneally). The ascending aorta was occluded transiently to estimate the end-systolic pressure–dimension relationship (ESPDR), which was parameterized subsequently by the quadratic equation: Pes=C2×(Des−D0)2+E0×(Des−D0), where Pesis end-systolic pressure, Desis end-systolic dimension, D0is the dimension axis intercept, E0is the local slope at D0, and C2is the curvilinearity coefficient. The maximum and minimum external dimensions at baseline were 5.82±0.50 ( ) mm and 5.49±0.46 mm with fractional shortening of 0.057±0.014 (n=12). The ESPDR was significantly curvilinear and increased convexity after isoproterenol injection (C2, −444±281 to −1113±780 mmHg/mm2,P<0.05; E0, 536±175 to 889±276 mmHg/mm,P<0.001), while the dimension axis intercept remained relatively constant (D0, 5.39±0.46 to 5.37±0.52 mm). In conclusion, the combination of miniature piezo-electric crystals and a micromanometer enables continuous measurement of pressure and dimension ofin situmouse left ventricle. This technology may be useful in evaluating the cardiac phenotype of genetically engineered mice.