High-Frame-Rate Speckle Tracking for Echocardiographic Stress Testing

Stress echocardiography helps to diagnose cardiac diseases that cannot easily be detected or do not even manifest at rest. In clinical practice, the assessment of the stress test is usually performed visually, therefore in a qualitative and subjective way. Although speckle tracking echocardiography (STE) has been proposed to quantify function during stress, its time resolution is inadequate at high heart rates. Recently, high frame rate (HFR) imaging approaches have been proposed together with dedicated speckle tracking (STE) algorithms capable of handling small interframe displacements. Therefore, the aim of this study was to determine if HFR STE is effective to assess strain and strain rate parameters during echocardiographic stress testing. Specifically, stress echocardiography, at four different workload intensities, was performed in 25 healthy volunteers. At each stress level, HFR images from the apical 4-chamber (A4C) view were recorded using the ULA-OP 256 experimental scanner. Then, the myocardium was tracked with HFR STE and strain and strain rate biomarkers were extracted to further analyse systolic and diastolic (early and late) peaks, as well as a short-lived isovolumic relaxation peak during stress testing. The global systolic strain response was monophasic, showing a significant (p<0.001) increase at low stress but then reaching a plateau. In contrast, all strain rate indices linearly increased (p<0.001) with increasing stress level. These findings are in line with those reported using tissue Doppler imaging and, thus, show that HFR STE can be a useful tool to assess cardiac function during stress echocardiography.