Abstract
Increased wave reflection is an independent predictor of cardiovascular events, possibly due to effects on left ventricular (LV) function. We investigated the relationship between reflected waves in early systole, the forward decompression wave in mid-late systole and LV mechanical behavior. Invasively acquired ascending aortic velocity, pressure, and LV long and minor axes’ dimensions were measured simultaneously in 11 anesthetized dogs during both control conditions and aortic occlusion to cause additional early wave reflection. Wave intensity analysis (WIA) was used to identify the arrival of the reflected wave and the onset of a forward decompression wave in mid-late systole. The arrival time of the reflected wave coincided with the time when minor axis shortening began to decline from its peak, even during aortic occlusion when this time is 12 ms earlier. The initial decline in long axis shortening corresponded to the time of the peak of the reflected wave. The forward decompression wave was consistently observed to have a slow and then rapid phase. The slow phase onset coincided with time of maximum shortening velocity of the long axis. The onset of the later larger rapid phase consistently coincided with an increased rate of deceleration of both axes during late systole. Forward decompression waves are generated by the LV when the long axis shortening velocity falls. Reflected wave arrival has a detrimental effect on LV function, particularly the minor axis. These observations lend support to suggestions that therapies directed toward reducing wave reflection may be of value in hypertension and cardiovascular disease.
Highlights
Increased wave reflection is an independent predictor of cardiovascular events in hypertension (London et al, 2001; Manisty et al, 2010) and has been proposed as a therapeutic target in cardiovascular disease (O’Rourke and Safar, 2005)
The onset of the decline in long axis velocity corresponded with the onset time of the forward decompression wave (FDW) (D1) (x ± SDdiff = 2 ± 4 ms, correlation coefficients (CCC) = 0.97, p < 0.001; Figures 3, 4A)
By employing aortic clamping as an intervention to cause a defined reflection site, we provide strong evidence for a causal link between arrival of the reflected wave, slowing of minor axis shortening, and peak volume rate of decline with a lesser effect on long axis function
Summary
Increased wave reflection is an independent predictor of cardiovascular events in hypertension (London et al, 2001; Manisty et al, 2010) and has been proposed as a therapeutic target in cardiovascular disease (O’Rourke and Safar, 2005). Reflected waves arrive at the left ventricle (LV) during systole (Baksi et al, 2009) and impose an additional load on the LV, which is exaggerated in WIA and LV Function hypertension (Merillon et al, 1983; Westerhof and O’Rourke, 1995) and heart failure (Curtis et al, 2007). Systolic LV function involves shortening of myocardial fibers oriented in circumferential, longitudinal, and oblique directions (Greenbaum et al, 1981; Henein and Gibson, 1999). This arrangement optimizes work (Torrent-Guasp et al, 2005) and has a major influence on intramural stress distribution (Arts et al, 1991). Velocity and strain patterns of various myocardial components have provided valuable information on cardiac function (Nagueh et al, 1997; Wang et al, 2005); the relationship between arterial wave reflection, LV mechanical function, and aortic flow remains modestly understood
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