Feasibility of aortic wave intensity analysis from sequentially acquired cardiac mri and non-invasive central blood pressure

Abstract

BackgroundWave intensity analysis (WIA) in the aorta offers important clinical and mechanistic insights but is difficult non-invasively. We performed WIA by combining high temporal resolution cardiovascular magnetic resonance (CMR) flow velocity and non-invasive central blood pressure (BP) waveform data.Method206 healthy volunteers (36 ± 11 years, 47% male) underwent sequential phase contrast CMR (Siemens Aera 1.5T, 1.97 × 1.77 mm2, ~9 ms temporal resolution) and supra-systolic oscillometric central BP (Uscom Ltd BP+) measurement. Velocity (U) and central pressure (P) waveforms (200 Hz) were aligned using the wave foot, and local wave speed was calculated both from the P-U slope during early systole (c) and the sum of squares method (cSS) (Figure 1), and compared with CMR aortic arch pulse wave velocity (PWV) by transit time.ResultsThe peak intensity of the initial compression wave (dI+1), backward compression wave (dI-) and protodiastolic decompression wave (dI + 2) were 69.5 ± 28, −6.6 ± 4.2 and 6.2 ± 2.5 W/m2 respectively. PWV correlated with c or cSS (r = 0.60, and 0.68 respectively; bias −1.3 [limits of agreement: −3.8 to 1.2 m/s], and bias −0.64 [limits of agreement: −3.0 to 1.7 m/s] respectively), Figure 1.ConclusionWave intensity patterns and values are similar to those measured using invasive methods. Local wave speed showed good agreement with PWV. CMR and central blood pressure provides a novel non-invasive technique for performing wave intensity analysis and is feasible for large scale studies.Figure 1Calculation of wave speed from a pressure - velocity (P-U) loop and comparison with pulse wave velocity by transit time. Top left: alignment of scaled pressure (blue) and velocity (red) waveforms and example of wave intensity analysis showing initial compression (dl+1), backward compression (dl-)and protodiastolic decompression (dl+2) waves. Top right: P-U loop showing wave speed measurement in early systole (c); and using sum of squares (cSS). Bottom left and Bottom right: Correlation and Bland-Altman analysis of cSS and PWV from phase-contrast MRI showing good correlation and slight underestimation