Noninvasive quantification of aortic wave reflection timing indices in aging: a study combining MRI and applanation tonometry.

Objective: To study associations of newly proposed noninvasive central arterial wave reflection timing indices with age and reference indices of reflection magnitude, using superimposed MRI aortic flow and applanation tonometry carotid pressure waveforms.

Methods: Consecutively acquired MRI flow and tonometry pressure waveforms were superimposed in 113 volunteers [56 women, age: 43 ± 16 (19-81) years] free from overt cardiovascular disease except for hypertension, after registration and interpolation to averaged cardiac cycle duration using a custom interface to derive time to peak flow ( TQmax ) and pressure ( TPmax ). Conventional time to return of reflected pressure wave ( Ti ), augmentation index (AIx) and reflection magnitude (RM) were further measured and used as reference.

Results: TQmax occurred slightly earlier, whereas TPmax appeared later in the cardiac cycle with age, resulting in significant, independent age-related decrease in TQmax to Ti ( r  = -0.63, P  < 0.0001) and increase in TQmax to TPmax ( r  = 0.61, P  < 0.0001) delays. Such delays were further significantly and independently related to reference AIx ( Ti  -  TQmax : r  = -0.66, P  < 0.0001; TPmax  -  TQmax : r  = 0.78, P  < 0.0001) and RM ( Ti  -  TQmax : r  = -0.55, P  < 0.0001; TPmax  -  TQmax : r  = 0.76, P  < 0.0001). Correlations obtained with TPmax  -  TQmax were overall higher than those obtained with conventional Ti timing (age: r  = -0.52, P  < 0.0001; AIx: r  = -0.77, P  < 0.0001; RM: r  = -0.42, P  < 0.0001).

Conclusion: Combination of noninvasive flow and pressure time domain waveforms was able to reliably capture central wave reflection timing indices as demonstrated by strong and independent associations with age and gold standard measures of reflection magnitude. Such timing, which was based on straightforward peaks detection, could be used to explore and better understand left ventricular-aortic coupling in cardiovascular conditions presenting increased reflections.