A Simpler Approach For Assessing Left Ventricular Function Using Ultrafast Ultrasound Based Wave Intensity Analysis
Kevin M. Lichtenstein1, Ethan M. Rowland2, Kai Riemer2, Peter D. Weinberg2.
1University of British Columbia, Vancouver, BC, Canada, 2Imperial College London, London, United Kingdom.
Changes in pressure and flow travel throughout the arterial system in the form of forward and backward waves. Wave intensity analysis (WIA) can examine these waves and their relation to left ventricular (LV) function. Clinically, WIA can be performed at any site in the arterial system.
Initially, WIA was performed invasively using pressure and flow catheters introduced into the arterial system. The two WIA indices crucial to analyzing LV function are two positive peaks, W1 and W2. W1 a forward going compression wave correlates with the maximum rate of pressure rise, and LV systolic function. W2 is the second positive peak and represents a forward travelling decompression wave that decelerates blood flow, and reflects LV diastolic function. The literature supports W1 and W2 as useful clinical indicators for LV systolic and diastolic function in patients with heart failure with preserved ejection fraction (HFpEF) and reduced ejection fraction (HFrEF). Previous studies demonstrated an effective non-invasive method of WIA using one point echo-Doppler based ultrasound of the carotid artery combined with sphygmomanometer blood pressure measurements, which was used to examine how WIA indices change in heart failure. Though non-invasive, the synchronization of echo-Doppler with blood pressure measurements, make this method technically challenging, prone to timing errors, inaccuracies, time consuming, and overly complex.
We propose a novel approach to WIA using ultrafast ultrasound to simultaneously measure changes in velocity and diameter. Velocity is normally determined by tracking scatterers (microbubbles) within the blood; called ultrasound imaging velocimetry. However, the injection of microbubbles is invasive. Instead, we propose to non-invasively track the native blood speckle alone utilizing a method of ultrasound image decomposition called singular value decomposition (SVD) which is well suited for simultaneous calculation of blood velocity and vessel diameter via ultrafast ultrasound of the carotid artery.
The measurement of diameter and velocity through the proposed means is a simpler, and truly non-invasive method of WIA which could enable clinicians of varying specialties to evaluate LV systolic and diastolic function non-invasively and allow for more ubiquitous monitoring, and therefore treatment, of symptomatic and asymptomatic heart failure patients in the community, and in hospital.
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