What indices quantify regional myocardial function during supine bicycle in healthy subject: natural strain and strain rate?

BACKGROUND: Evaluation and quantification of regional myocardial function remain a challenge for imaging techniques in stress test. Strain and strain rate can be calculated from velocity gradients in time and space. This new technique has been developed to allow quantifiable stress echocardiography. The aim of this study was to define normal regional strain rate and strain values for both radial and deformation longitudinal myocardial deformation during supine bicycle. METHODS: Real-time color Doppler myocardial velocities were acquired as data superimposed on an underlying two-dimensional (2D) grey-scale image at a frame rate > 150/s, a depth of 16 cm, and a sector angle of 60 degrees in 18 healthy volunteers, mean age 34+/-7 years (25-43 years). During acquisition, a complete cardiac cycle of each view was acquired at rest and during supine bicycle (from 25 W to maximal charge). Maximal systolic velocity, strain rate, and strain were processed offline for both radial (basal posterior wall segment) and longitudinal (septum, lateral, inferior, anterior walls) function. For analysis, each wall was divided into three segments (basal, mid, apical). All the velocity and SR/S values were averaged over three consecutive cycles. RESULTS: During exercise, heart rate and systolic blood pressure increased significantly from rest to peak stress (69+/-14 vs. 152+/-7 beats/min, p < 0.0001 and 118+/-9 vs. 178+/-28 mm Hg, p < 0.001). For the Lax view, both the mean velocity and mean strain rate increased significantly between rest and peak exercise, respectively, for the velocity and for the strain rate. Similarly is said for the Sax view. In contrast, the systolic strain response was biphasic during exercise, basal, mid, and apical segments of walls showed a significant increase of velocity in each workload step. The resting base-apex velocity gradient observed at rest remained in all walls throughout supine bicycle. The mean peak systolic SR data were homogeneous throughout in all segments analysed at rest. This homogeneity remained at peak exercise. The SR increased significantly between rest and peak exercise, respectively, p < 0.0117. The segmental systolic strain response was biphasic. CONCLUSION: This study demonstrated that strain rate imaging may represent a new and interesting method for quantifying regional myocardial function during supine bicycle, which appears to be less influenced by tethering than Doppler tissue imaging. Further studies are needed to determine whether this approach will be clinically useful.