Major influence of a ‘smoke and mirrors’ effect caused by wave reflection on early diastolic coronary arterial wave intensity

Abstract

Coronary arterial wave intensity analysis (WIA) is thought to provide clear insight into upstream and downstream forces on coronary flow, with a large early-diastolic surge in coronary flow accompanied by a prominent backward decompression wave (BDW ), as well as a forward decompression wave (FDW ) and forward compression wave (FCW ). The BDW is believed to arise from distal suction due to release of extravascular compression by relaxing myocardium, while FDW and FCW are thought to be transmitted from the aorta into the coronary arteries. Based on an established multi-scale computational model and high-fidelity measurements from the proximal circumflex artery (Cx) of 18 anaesthetized sheep, we present evidence that wave reflection has a major impact on each of these three waves, with a non-linear addition/subtraction of reflected waves obscuring the true influence of upstream and downstream forces through concealment and exaggeration, i.e. a 'smoke and mirrors' effect. We also describe methods, requiring additional measurement of aortic WIA, for unravelling the separate influences of wave reflection versus active upstream/downstream forces on coronary waves. Distal wave reflection accounted for ∼70% of the BDW in sheep, but had a lesser influence (∼25%) in the computer model representing a hypertensive human. Negative reflection of the BDW at the coronary-aortic junction attenuated the Cx FDW (by ∼40% in sheep) and augmented Cx FCW (∼5-fold), relative to the corresponding aortic waves. We conclude that wave reflection has a major influence on early-diastolic WIA, and thus needs to be considered when interpreting coronary WIA profiles.

Measurement, Analysis and Interpretation of Pressure/Flow Waves in Blood Vessels

“…On the other hand, although atrial contraction aids ventricular filling, the absence of an atrial inflow valve means that this contraction also generates a BCW that propagates into the systemic/pulmonary veins in a direction that is opposite to mean blood flow ( Hellevik et al, 1999 ; Smiseth et al, 1999 ; Hobson et al, 2007 ; Mynard, 2011 ). Other pump phenomena that generate BCWs in arteries include the active compression of the coronary microvasculature by contracting myocardium ( Davies et al, 2006a ; Mynard et al, 2018 ) and the inflation of an intra-aortic or para-aortic balloon pump ( Kolyva et al, 2009 ; Lu et al, 2012 ).…”

“…After a pump has contracted, relaxation causes pressure to fall and therefore generates a decompression wave (sometimes called a ‘suction wave’) ( Figure 7B ). Decompression waves are generated by atrial relaxation ( Smiseth et al, 1999 ; Mynard, 2011 ), release of extravascular pressure on intramyocardial vessels by the relaxing ventricle ( Davies et al, 2006a ; Mynard et al, 2018 ) and deflation of aortic balloon pumps ( Kolyva et al, 2009 ; Lu et al, 2012 ). In the first paper utilizing wave intensity analysis, entitled “What stops the flow of blood from the heart?”, Parker et al (1988) showed that a forward decompression wave (FDW) is primarily responsible for the deceleration of systolic flow in arteries, not a reflected wave as had been widely believed.…”

“…When interpreting wave patterns, one of the mechanisms responsible for generating waves mentioned above may be responsible for a given wave, but it is also possible that multiple mechanisms act together to produce a particular wave. This issue was recently identified in the context of coronary arterial wave intensity analysis, which is characterized by a large backward decompression wave (BDW) that is mainly responsible for the early diastolic surge in coronary flow ( Mynard et al, 2018 ). It was previously thought that this BDW arose solely from an active suction effect in the intramyocardial circulation caused by myocardial relaxation ( Davies et al, 2006a ; Lee et al, 2016 ; Raphael et al, 2016 ).…”

“…It was previously thought that this BDW arose solely from an active suction effect in the intramyocardial circulation caused by myocardial relaxation ( Davies et al, 2006a ; Lee et al, 2016 ; Raphael et al, 2016 ). However, evidence from experimental and modeling data suggested that the coronary BDW actually arises from a combination of (1) the active relaxation effect and (2) simultaneous reflection of the aortic FDW that is transmitted into coronary arteries ( Mynard et al, 2018 ).…”

Usefulness of Proximal Coronary Wave Speed for Wave Intensity Analysis in Diseased Coronary Vessels

“…It has previously been speculated that distal reflection is not a confounding factor for the sum-of-squares method ( 5 ), whereas in vitro experiments have shown that wave speed is altered within a stenosis or aneurysm ( 27 ). The influence of wave reflections on wave intensity in coronary vessels was recently investigated ( 28 ). These authors also used a fixed wave speed assessed by the sum-of-squares method.…”