The feasibility of ultrasonic regional strain and strain rate imaging in quantifying dobutamine stress echocardiography.

Abstract

Ultrasonic strain rate and strain can characterize regional one-dimensional myocardial deformation at rest. In theory, these deformation indices could be used to quantify normal or abnormal regional function during a dobutamine stress echo test. The aims of our pilot study were threefold: (1) to determine the percentage of segments in which interpretable strain rate/strain data could be obtained during routine dobutamine stress echo, (2) to establish whether either the increase in heart rate or artefacts induced by respiration during dobutamine stress echo would influence analysis by degrading the data and (3) to determine the optimal frame rate vs image sector angle settings for data acquisition. Furthermore, although the detection of ischaemia was not to be addressed specifically in this study, we would describe the findings on the potential clinical role of regional deformation vs velocity imaging in detecting ischaemia-induced changes. A standard dobutamine stress echo protocol was performed in 20 consecutive patients with a history of chest pain (16 with angiographic coronary artery disease and four with normal coronary angiograms). DMI velocities were acquired at baseline, low dose, peak dose, and recovery. To evaluate radial function (basal segment of the left ventricle posterior wall segment), parasternal LAX, SAX views were used. For long axis function data were acquired (4-CH, 2-CH views) from the septum; lateral, inferior and anterior left ventricle walls. Data was acquired using both 15 degrees (>150 frames per second (fps) and 45 degrees (115fps) sector angles. During post-processing each wall was divided into three segments: basal, mid and apical. Strain rate/strain values were averaged over three consecutive heart cycles. Data was obtained from 1936 segments, of which only 54 had to be excluded from subsequent analysis (2.8%) because of suboptimal quality. An increase in heart rates (up to 150/min) was not associated with a significant reduction in the number of interpretable segments. There was a significant correlation between maximal systolic strain rate/strain values obtained at narrow and at wide sector angles (e.g. a correlation for the septal segments: r=0.73,P <0.001 for strain rate, and r=0.71; P<0.001 for strain). The correlation for the timing of events obtained from narrow and wide sector angles was weaker. This would indicate that there was the insufficient temporal resolution for the latter acquisition method. Normal and abnormal regional strain rate/strain responses to an incremental dobutamine infusion were defined. In normal segments, maximal systolic strain rate values increased continuously from baseline, reaching the highest values at the peak dose of dobutamine. The segmental strain response was different. For strain, there was an initial slight increase at low dose of dobutamine (5, 10 microg/kg/min), but no further increase with increasing dose. A pattern representing an ischaemic response was identified and described. The feasibility study would suggest that with appropriate data collection and post-processing methodologies, strain rate/strain imaging can be applied to the quantification of dobutamine stress echo. However, appropriate post-processing algorithms must be introduced to reduce data analysis time in order to make this a practical clinical technique.