156 Shear wave propagation velocity after aortic valve closure could be a novel parameter for myocardial contractility

Abstract

Background: Shear wave imaging is a novel ultrasound technique based on the detection of transverse waves travelling through the myocardium by using high frame rate (HFR) echocardiography. These waves can be induced by an external or internal stimulus, such as aortic valve closure (AVC). The propagation velocity of shear waves is directly dependent on myocardial stiffness. It has been previously suggested in animals that the shear wave propagation velocity at AVC might be related to myocardial contractility. Aim(s): The aim of this study was to validate if the shear wave propagation velocity after AVC (end-systole) is related to myocardial contractility. Method(s): Firstly, 11 healthy volunteers (age: 25 +/- 4 years; male: n = 11) performed a supine bicycle exercise test. Images were taken at rest and during 25%, 50% and 66% of maximal workload, as determined by previous upright bicycle exercise testing. Secondly, 9 patients (age: 63 +/- 10 years; male: n = 7) underwent a dobutamine stress echocardiography. The stress echo was negative in all patients. Images were taken at rest and after a dobutamine administration of 10mug/kg/min and 40mug/kg/min. Left ventricular (LV) parasternal long axis views were acquired with an experimental HFR ultrasound scanner (HD-PULSE) (average frame rate: 1217 +/- 233fps). Apical 4-chamber views were acquired with a conventional ultrasound machine. Non-invasive single beat end-systolic elastance (Ees) was used as a measure of contractility. Acceleration maps were created from HFR-datasets by drawing a M-mode line along the midline of the interventricular septum. Shear wave propagation speed at AVC (end-systole) was calculated by measuring the slope of the wave front on the acceleration maps (Figure A). Result(s): During the bicycle exercise, heart rate (61 +/- 11bpm vs. 146 +/- 13bpm; p < 0.001), systolic blood pressure (125 +/- 12mmHg vs. 173 +/- 15mmHg; p < 0.001), LV ejection fraction (55 +/- 3% vs. 70 +/- 5%; p < 0.001), Ees (1.8 +/- 0.3mmHg/ml vs. 3.6 +/- 1.0mmHg/ml; p < 0.001) and propagation velocity of the shear waves (3.3 +/- 0.5m/s vs. 6.2 +/- 1.7m/s; p < 0.01) (Figure B) increased significantly from rest to exercise. Likewise, dobutamine administration significantly increased the heart rate (68 +/- 10bpm vs. 131 +/- 14bpm; p < 0.001), LV ejection fraction (57 +/- 5% vs. 74 +/- 7%; p < 0.001), as well as the shear wave velocity after AVC (4.4 +/- 0.6m/s vs. 7.2 +/- 1.7m/s; p < 0.01) (Figure C) and Ees (2.1 +/- 0.4mmHg/ml vs. 3.3 +/- 0.8mmHg/ml; p < 0.001). Independent from the stressor, shear wave propagation velocity had a good and significant correlation with Ees (Figure D). Conclusion(s): Shear wave propagation velocity after AVC increases with increasing level of exercise or dobutamine dose. Shear wave velocities at AVC show a good correlation with Ees. Our data indicate that end-systolic shear wave velocity is related to myocardial contractility and might therefore be a potential novel parameter for the non-invasive assessment of myocardial function.(Figure Presented).