Microvascular function/dysfunction downstream a coronary stenosis

Endothelial-cell-mediated mechanism of coronary microvascular dysfunction leading to heart failure with preserved ejection fraction

Although the prevalence of heart failure with preserved ejection fraction (HFpEF) is growing worldwide, its complex pathophysiology has yet to be fully elucidated, and multiple hypotheses have all failed to produce a viable target for therapeutic action or provide effective treatment. Cardiac remodeling has long been considered an important mechanism of HFpEF. Strong evidence has been reported over the past years that coronary microvascular dysfunction (CMD), manifesting as structural and functional abnormalities of coronary microvasculature, also contributes to the evolution of HFpEF. However, the mechanisms of CMD are still not well understood and need to be studied further. Coronary microvascular endothelial cells (CMECs) are one of the most abundant cell types in the heart by number and active players in cardiac physiology and pathology. CMECs are not only important cellular mediators of cardiac vascularization but also play an important role in disease pathophysiology by participating in the inception and progression of cardiac remodeling. CMECs are also actively involved in the pathogenesis of CMD. Numerous studies have confirmed that CMD is closely related to cardiac remodeling. ECs may serve a critical function in mediating the connection between CMD and HFpEF. It follows that CMECs participate in the mechanism of CMD leading to HFpEF. In this review article, we focus on the role of CMD in the pathogenesis of HFpEF resulting from cardiac remodeling and highlight the subsequent complexity of the EC-mediated correlation between CMD and HFpEF.

Risk Stratification by Coronary Perfusion Pressure in Left Ventricular Systolic Dysfunction Patients Undergoing Revascularization: A Propensity Score Matching Analysis

Background

Coronary perfusion pressure (CPP) and coronary artery stenosis are responsible for myocardial perfusion. However, how CPP-related survival outcome affects revascularization is unclear.

Objective

The aim of this study is to investigate the prognostic role of CPP in patients with left ventricular systolic dysfunction (LVSD) undergoing percutaneous coronary intervention (PCI) with complete revascularization (CR) or reasonable incomplete revascularization (RIR).

Methods

We retrospectively screened 6,076 consecutive patients in a registry. The residual synergy between percutaneous coronary intervention with Taxus and cardiac surgery (SYNTAX) score (rSS) was used to define CR (rSS = 0) and RIR (0<rSS≤8). Propensity score matching was performed to reduce bias between RIR and CR. The primary endpoint was all-cause mortality.

Results

In total, 816 patients with LVSD who underwent CR or RIR were enrolled. After a mean follow-up of 4.6 years, 134 patients died. Both CPP and RIR independently predicted mortality in the total population. After 1:1 matching, 175 pairs of RIR and CR were found in patients with CPP > 42 mmHg. Moreover, 101 pairs of RIR and CR were present in patients with CPP ≤ 42 mmHg. In patients with CPP > 42 mmHg, RIR was not significantly different from CR in long-term mortality [hazard ratio (HR) 1.20; 95% confidence interval (CI):0.70–2.07; p = 0.513]; However, in patients with CPP≤42 mmHg, RIR had a significantly higher mortality risk than CR (HR 2.39; 95% CI: 1.27–4.50; p = 0.007).

Conclusions

The CPP had a risk stratification role in selecting different revascularization strategies in patients with LVSD. When patients with LVSD had CPP > 42 mmHg, RIR was equivalent to CR in survival. However, when patients with LVSD had CPP ≤ 42 mmHg, RIR had a significantly higher mortality risk than CR.

Computational Assessment of Hemodynamic Significance in Patients With Intramural Anomalous Aortic Origin of the Coronary Artery Using Virtually Derived Fractional Flow Reserve and Downstream Microvascular Resistance

Anomalous aortic origin of a coronary artery (AAOCA) is the second most common cause of sudden cardiac death in young athletes. One of the hypothesized mechanisms of ischemia in these patients is the lateral compression of the anomalous artery with an intramural or interarterial course. The presence of a narrowing in the anomalous artery will cause physiologic changes in downstream resistance that should be included for computational assessment of possible clinical ramifications. In this study, we created different compression levels, i.e., proximal narrowing, in the intramural course of a representative patient model and calculated hyperemic stenosis resistance (HSR) as well as virtual fractional flow reserve (vFFR). Models also included the effect of the distal hyperemic microvascular resistance (HMR) on vFFR. Our results agreed with similar FFR studies indicating that FFR is increased with increasing HMR and that different compression levels could have similar FFR depending on the HMR. For example, vFFR at HSR: 1.0-1.3 and HMR: 2.30 mmHg/cm/s is 0.68 and close to vFFR at HSR: 0.6-0.7 and HMR: 1.6 mmHg/cm/s, which is 0.7. The current findings suggest that functional assessment of anomalous coronary arteries through FFR should consider the vascular resistance distal to the narrowing in addition to the impact of a proximal narrowing and provides computational approaches for implementation of these important considerations.

Effect of microcirculatory resistance on coronary blood flow and instantaneous wave-free ratio: A computational study

BACKGROUND AND OBJECTIVE

The instantaneous wave-free ratio (iFR) has been proposed to estimate the hemodynamic severity of atherosclerotic stenosis in coronary arteries. The atherosclerotic stenosis in a proximal coronary artery could change its distal microcirculatory resistance (MR). However, there is a lack of investigation about the effect of MR variation on the blood flow and iFR of stenotic coronary arteries. We aim to investigate the changes of blood flow and iFR caused by distal MR variation.

METHODS

Four three-dimensional models of coronary arteries were reconstructed from the computed tomography images of two normal cases and two cases with 74.9% and 96.4% (in area) stenoses in a large branch of left anterior descending artery (LAD). Computational fluid dynamics simulation was performed on each model under 6 MR situations: hyperemia as the reference situation, resting when MR was multiplied by 8/3 in all outlet branches, h-one-1.5 and h-one-2 when MR was multiplied by 1.5 and 2.0 in one branch (the stenotic, or the corresponding branch in normal case) of LAD, h-branches-1.5 and h-branches-2 when MR was multiplied by 1.5 and 2.0 in the stenotic/corresponding and its cognate branches. Flow rate and iFR of each outlet branch were then calculated and compared between different MR situations to investigate the effect of MR variation on flow rate and iFR.

RESULTS

In the 74.9% stenosed and normal cases, referring to the hyperemia situation, the increase of MR in any branch significantly decreased its flow rate and increased its iFR, with limited effect on the flow rate (<3%) and iFR (<0.01) of other branches. However, in the 96.4% stenosed case, the doubled MR in the stenosed branch (h-one-2) significantly increased the flow rate (>10%) and iFR (>0.05) of its cognate branches.

CONCLUSION

The increase of MR in a normal or mildly stenosed branch of coronary artery decreases its blood flow and increases its iFR, with limited effect on other branches. Whereas, the increase of MR in a severely stenotic large branch could significantly increase the flow velocity and iFR of its cognate branches.

Influence of microcirculation load on FFR in coronary artery stenosis model

BACKGROUND

The coronary artery hemodynamics are impacted by both the macrocirculation and microcirculation. Whether microcirculation load impact the functional assessment of a coronary artery stenosis is unknown. The purpose of this study is to investigate the effect of porous media of the microcirculation on fractional flow reserve (FFR) in stenotic coronary artery model.

METHODS

A three dimensional computational simulation of blood flow in coronary artery symmetric stenotic model was constructed. The computational fluid dynamics (CFD) model was developed with Fluent 16.0. Blood was modeled as a shear thinning, non-Newtonian fluid with the Carreau model. A seepage outlet boundary condition and transient inlet conditions were imposed on the model. Coronary physiologica diagnostic parameter such as pressure, velocity and fractional flow reserve (FFR) were investigated in the model and compared with the microcirculation load (ML) and constant pressure load (PL) condition.

RESULTS

The present study showed the different hemodynamics in the ML and PL condition. The pre-stenotic pressure is almost the same in the two model. However the pressure in the post-stenotic artery domain is much lower in the PL model. The fluctuation range of the pressures is much higher in ML model than those in PL model. The velocity flow was more steady and lower in the ML model. For the PL model with 75% artery stenosis the FFR was 0.776, while for the ML model with the same stenosis, the FFR was 0.813.

CONCLUSIONS

This study provides evidence that FFR increased in the presentation of ML condition. There is a strong hemodynamic effect of microcirculation on coronary artery stenosis.

Potential Applications of Remote Limb Ischemic Conditioning for Chronic Cerebral Circulation Insufficiency

Chronic cerebral circulation insufficiency (CCCI) refers to a chronic decrease in cerebral blood perfusion, which may lead to cognitive impairment, psychiatric disorders such as depression, and acute ischemic stroke. Remote limb ischemic conditioning (RLIC), in which the limbs are subjected to a series of transient ischemic attacks, can activate multiple endogenous protective mechanisms to attenuate fatal ischemic injury to distant organs due to acute ischemia, such as ischemic stroke. Recent studies have also reported that RLIC can alleviate dysfunction in distant organs caused by chronic, non-fatal reductions in blood supply (e.g., CCCI). Indeed, research has indicated that RLIC may exert neuroprotective effects against CCCI through a variety of potential mechanisms, including attenuated glutamate excitotoxicity, improved endothelial function, increased cerebral blood flow, regulation of autophagy and immune responses, suppression of apoptosis, the production of protective humoral factors, and attenuated accumulation of amyloid-β. Verification of these findings is necessary to improve prognosis and reduce the incidence of acute ischemic stroke/cognitive impairment in patients with CCCI.

A narrative overview: Have clinical trials of PCI vs medical therapy addressed the right question?

BACKGROUND

In RCTs about revascularization, the terms "coronary artery disease" and "ischemic heart disease" are sometimes used interchangeably. This can create confusion concerning inclusion and exclusion criteria, which may lead to uncertain results.

OBJECTIVE

Our purpose is to investigate whether the study populations in randomized controlled trials (RCTs) which compared percutaneous coronary revascularization to medical therapy for stable ischemic heart disease specifically enrolled patients with demonstrable ischemia, and how many patients were included in trials with evidence of coronary atherosclerosis but without evidence of ischemia.

METHODS

Trial published data were obtained from ACME I, ACME II, RITA I, RITA II, MASS I, MASS II, AVERT, ACIP, COURAGE and FAME2. Published data were used to calculate the number of patients included in the trials with a negative stress test but significant coronary artery stenosis and the number of patients excluded from the trials with a positive stress test or angina, but without significant coronary artery stenosis at the time of angiography.

RESULTS

A total of 196,433 patients were screened between 1998 and 2011. Overall about 30% of patients were excluded if they did not meet the angiographic criteria, even though the presence of inducible ischemia or angina, and, about 20% of patients were included without inducible ischemia.

CONCLUSION

RCTs have contributed to the confusion between coronary artery disease and ischemic heart disease. This may limit the ability to interpret the results and apply them in practice.

Increased hyperaemic coronary microvascular resistance adds to the presence of myocardial ischaemia

AIMS

It has been argued that hyperaemic microvascular resistance (HMR), defined as the ratio of mean distal coronary pressure to flow velocity, is overestimated in the presence of a coronary stenosis compared to actual microvascular resistance (MR), due to neglecting collateral flow. We aimed to test the hypothesis that HMR allows accurate identification of microvascular functional abnormalities by evaluating the association between high or low HMR and the presence of myocardial ischaemia on non-invasive stress testing.

METHODS AND RESULTS

Myocardial perfusion scintigraphy was performed in 228 patients, with 299 lesions to identify reversible myocardial ischaemia. Intracoronary distal pressure and flow velocity were assessed during adenosine-induced hyperaemia (20-40 µg, intracoronary) to determine hyperaemic stenosis resistance (HSR) and HMR. HMR >1.9 mmHg/cm/s was defined as high. The diagnostic odds ratio (OR) for myocardial ischaemia for lesions associated with high compared to low HMR was 2.6 (95% confidence interval [CI]: 1.5-4.4; p<0.001) overall, 3.3 (95% CI: 1.2-9.0; p=0.02) for lesions with HSR >0.8 mmHg/cm/s, and 1.3 (95% CI: 0.6-2.9; p=0.52) for lesions with HSR ≤0.8 mmHg/cm/s.

CONCLUSIONS

The increased risk of myocardial ischaemia in the presence of high HMR, uncorrected for collateral flow, demonstrates that HMR is reflective of an increase in actual MR, identifying pertinent pathophysiological alterations in the microvasculature.

Impact of hyperaemic microvascular resistance on fractional flow reserve measurements in patients with stable coronary artery disease: insights from combined stenosis and microvascular resistance assessment

BACKGROUND

Fractional flow reserve (FFR) aims to identify the extent of epicardial disease, but may be obscured by involvement of the coronary microvasculature. We documented the impact of hyperaemic stenosis resistance (HSR) and hyperaemic microvascular resistance (HMR) on FFR, and its relationship with myocardial ischaemia in patients with stable coronary artery disease.

METHODS AND RESULTS

We evaluated 255 coronary arteries with stenoses of intermediate severity by means of intracoronary pressure and flow measurements to determine FFR, HSR and HMR. Myocardial perfusion scintigraphy (MPS) was performed to identify inducible myocardial ischaemia. In 178 patients, HMR was additionally determined in a reference coronary artery. Target vessel HMR was stratified according to reference vessel HMR tertiles. The diagnostic OR for inducible ischaemia on MPS of a positive compared with a negative FFR was significantly higher only in the presence of a high HMR (at the 0.75 and 0.80 FFR cut-off). Among stenoses with a positive FFR, the prevalence of ischaemia was significantly higher when HMR was high despite equivalent FFR across the HMR groups. This was paralleled by a concomitant significant increase in HSR with increasing HMR across groups. The relation between FFR and HSR (r(2)=0.54, p<0.001) was modulated by the magnitude of HMR, and improved substantially after adjustment for HMR (adjusted-r(2)=0.73, p<0.001), where, for epicardial disease of equivalent severity, FFR increased with increasing HMR.

CONCLUSIONS

Identification of epicardial disease severity by FFR is partly obscured by the microvascular resistance, which illustrates the necessity of combined pressure and flow measurements in daily practice.

Phosphodiesterase-5 activity exerts a coronary vasoconstrictor influence in awake swine that is mediated in part via an increase in endothelin production

Nitric oxide (NO)-induced coronary vasodilation is mediated through production of cyclic guanosine monophosphate (cGMP) and through inhibition of the endothelin-1 (ET) system. We previously demonstrated that phosphodiesterase-5 (PDE5)-mediated cGMP breakdown and ET each exert a vasoconstrictor influence on coronary resistance vessels. However, little is known about the integrated control of coronary resistance vessel tone by these two vasoconstrictor mechanisms. In the present study, we investigated the contribution of PDE5 and ET to the regulation of coronary resistance vessel tone in swine both in vivo, at rest and during graded treadmill exercise, and in vitro. ETA/ETB receptor blockade with tezosentan (3 mg/kg iv) and PDE5 inhibition with EMD360527 (300 μg·min(-1)·kg(-1) iv) each produced coronary vasodilation at rest and during exercise as well as in preconstricted isolated coronary small arteries. In contrast, tezosentan failed to produce further coronary vasodilation in the presence of EMD360527, both in vivo and in vitro. Importantly, EMD360527 (3 μM) and cGMP analog 8-Br-cGMP (100 μM) had no significant effects on ET-induced contractions of isolated porcine coronary small arteries, suggesting unperturbed ET receptor responsiveness. In contrast, PDE5 inhibition and cGMP blunted the contractions produced by the ET precursor Big ET, but only in vessels with intact endothelium, suggesting that PDE5 inhibition limited ET production in the endothelium of small coronary arteries. In conclusion, PDE5 activity exerts a vasoconstrictor influence on coronary resistance vessels that is mediated, in part, via an increase in endothelial ET production.