Delineation of cardiac twist by a sonographically based 2-dimensional strain analysis method - An in vitro validation study

Objective. Normal left ventricular contraction involves a twisting component that helps augment stroke volume, the unwinding of which also very usefully contributes to early diastolic filling. Abnormalities of cardiac twist have been related to abnormal cardiac function. We sought to quantify the twisting action using a new sonographically based angle-independent motion-detecting echo method. Methods. A twist model was developed with a variable-speed motor to rotate a wheel in water bath. A freshly harvested pig heart was mounted on it as a twist phantom. Short axis views were acquired with a GE/VingMed Vivid 7 system (GE Healthcare, Milwaukee, WI) at 3.5 MHz and more than 100 frames/s. Eight different speeds (30-100 cycles/min of winding and unwinding) were studied at 5 degrees of rotation (10 degrees, 20 degrees, 30 degrees, 40 degrees, and 50 degrees). Data were analyzed off-line for twist analysis with a new 2-dimensional speckle-tracking-based program (2-dimensional strain rate method [2DSR]) embedded in EchoPac software (GE Healthcare). Ten freshly harvested pig hearts were studied in this model. Results. The 2DSR program tracked the twist well (mean determination at 10 degrees = 16.88 degrees +/- 1.81 degrees [SD]; at 20 degrees = 26.5 degrees +/- 1.05 degrees; at 30 degrees = 36.47 degrees +/- 1.31 degrees, at 40 degrees= 44.03 degrees +/- 1.39 degrees, and at 50 degrees = 54.1 degrees +/- 1.96 degrees). Conclusions. The 2DSR program can be used to study twisting action of the heart.