The coronary flow velocity reserve measured by stress transoesophageal echocardiography evaluates the success of coronary interventions – Results of a 5-year follow-up

Fluid structure interaction modelling of aortic valve stenosis: Effects of valve calcification on coronary artery flow and aortic root hemodynamics

BACKGROUND AND OBJECTIVE

Coronary artery diseases and aortic valve stenosis are two of the main causes of mortality and morbidity worldwide. Stenosis of the aortic valve develops due to calcium deposition on the aortic valve leaflets during the cardiac cycle. Clinical investigations have demonstrated that aortic valve stenosis not only affects hemodynamic parameters inside the aortic root but also has a significant influence on the coronary artery hemodynamics and leads to the initiation of coronary artery disease. The aim of this study is to investigate the effect of calcification of the aortic valve on the variation of hemodynamic parameters in the aortic root and coronary arteries in order to find potential locations for initiation of the coronary stenoses.

METHODS

Fluid structure interaction modelling methodology was used to simulate aortic valve hemodynamics in the presence of coronary artery flow. A 2-D model of the aortic valve leaflets was developed in ANSYS Fluent based on the available echocardiography images in literature. The k-ω SST turbulence model was utilised to model the turbulent flow downstream of the leaflets.

RESULTS

The effects of calcification of the aortic valve on aortic root hemodynamics including transvalvular pressure gradient, valve orifice dimeter, vorticity magnitude in the sinuses and wall shear stress on the ventricularis and fibrosa layers of the leaflets were studied. Results revealed that the transvalvular pressure gradient increases from 792 Pa (∼ 6 mmHg) for a healthy aortic valve to 2885 Pa (∼ 22 mmHg) for a severely calcified one. Furthermore, the influence of the calcification of the aortic valve leaflets on the velocity profile and the wall shear stress in the coronary arteries was investigated and used for identification of potential locations of initiation of the coronary stenoses. Obtained results show that the maximum velocity inside the coronary arteries at early diastole decreases from 1 m/s for the healthy valve to 0.45 m/s for the severely calcified case.

CONCLUSIONS

Calcification significantly decreases the wall shear stress of the coronary arteries. This reduction in the wall shear stress can be a main reason for initiation of the coronary atherosclerosis process and eventually results in coronary stenoses.

The effect of aortic wall and aortic leaflet stiffening on coronary hemodynamic: a fluid-structure interaction study

Pathologies of the aortic valve such as aortic sclerosis are thought to impact coronary blood flow. Recent clinical investigations have observed simultaneous structural and hemodynamic variations in the aortic valve and coronary arteries due to regional pathologies of the aortic valve. The goal of the present study is to elucidate this observed and yet unexplained phenomenon, in which a local pathology in the aortic valve region could potentially lead to the initiation or progression of coronary artery disease. Results revealed a considerable impact on the coronary flow, velocity profile, and consequently shear stress due to an increase in the aortic wall or aortic leaflet stiffness and thickness which concur with clinical observations. The cutoff value of 0.75 for fractional flow reserve was reached when the values of leaflet thickness and aortic wall stiffness were approximately twice and three times their normal value, respectively. Variations observed in coronary velocity profiles as well as wall shear stress suggest a possible link for the initiation of coronary artery disease.

Long-term prognostic value of coronary flow reserve in patients without significant left anterior descending coronary artery stenosis: results from the SZEGED Study

A coronariaáramlási rezerv (CFR) a bal coronaria leszálló szárában (LAD) szignifikáns szűkület hiánya esetén a microvascularis (disz)funkció jellemzésére használható hemodinamikai index. Célkitűzés: Jelen tanulmány célja a LAD-ban mért CFR prognosztikus értékének tisztázása lenne, amennyiben a koronarográfia során a LAD-ban szignifikáns szűkület nem volt igazolható. Módszerek: A jelen tanulmányban 166 olyan beteg eredményeit elemeztük, akiknél a CFR-vizsgálatok idején elvégzett koronarográfia a LAD-ban szignifikáns szűkületet (>50%) nem mutatott ki. Valamennyi esetben transthoracalis és terheléses transoesophagealis echokardiográfia (CFR-mérés), valamint koronarográfia történt. Eredmények: A továbbkövetés átlagos ideje 93±34 hónap volt, sikeressége 75%-osnak bizonyult (124/166). A továbbkövetés időszaka alatt 27 beteg hunyt el, 16 beteg esetén hirtelen szívhalál, 3 esetben akut szívelégtelenség, 2 esetben stroke volt a halál oka, míg 6 beteg pulmonalis, illetve gastrointestinalis tumoros folyamat miatt halt meg. A ROC-analízis során a CFR ≥ 2,13-t találtuk a legnagyobb pontosságú cut-off (határ-) értéknek a túlélés előrejelzésében (szenzitivitás 67%, specificitás 60%, görbe alatti terület 62%, p = 0,046). A 2,13-nál alacsonyabb CFR-rel bíró betegekben a továbbkövetés során szignifikánsan több esemény történt, mint az annál nagyobb értékkel bíróknál (32% vs. 13%, p < 0,05). A multivariáns logisztikus regressziós modell során a CFR [hazard ratio (HR) 2,43, p = 0,04] és a bal kamrai végszisztolés térfogatérték [HR 1,49, p = 0,03] bizonyult a túlélés független prediktorának. Következtetések: Hosszú távú továbbkövetéses vizsgálataink alapján megállapíthatjuk, hogy a CFR a túlélés független prediktora a LAD szignifikáns szűkületét nem mutató betegekben.

Long-term prognostic value of coronary flow velocity reserve in patients with hypertrophic cardiomyopathy: 9-year follow-up results from SZEGED study

Reduction in coronary flow velocity reserve (CFR) is a recognized feature in hypertrophic cardiomyopathy (HCM). We sought to assess the long-term prognostic value of CFR by pulsed-wave Doppler transesophageal echocardiography (TEE) in HCM patients. The study comprised 20 patients with typical features of HCM. The patients were enrolled in 1999. All patients underwent a standard transthoracic echo-Doppler study to evaluate left ventricular function and a stress vasodilator TEE study to evaluate CFR. The success rate of follow-up was 18 out of 20 (90%). During a mean follow-up of 90 +/- 24 months, four patients suffered cardiovascular death (2 sudden cardiac deaths and 2 strokes). The other seven patients underwent invasive procedures (coronary angiography, implantable cardioverter defibrillator implantation, percutaneous transluminal septal myocardial ablation) or showed cerebrovascular events. Using receiver operator characteristic analysis, CFR < 2.35 was a significant predictor for cardiovascular event-free survival (sensitivity 91%, specificity 71%, area under the curve 74%, P = 0.05). Multivariable regression analysis showed that only CFR (hazard ratio (HR) 4.21, P < 0.05) was an independent predictor of cardiovascular event-free survival. Despite the relatively small number of patients involved in the study, results could suggest that CFR should be considered as an independent predictor for future cardiovascular events in HCM patients. However, further studies with larger HCM patient populations are warranted.

Simultaneous echocardiographic evaluation of coronary flow velocity reserve and aortic distensibility indices in hypertension

The coronary flow velocity reserve (CFVR), a measure of endothelial function in coronary circulation, can be measured semi-invasively in the left anterior descending coronary artery by using stress transesophageal echocardiography (TEE). During the same stress TEE, aortic distensibility indices (elastic modulus [E(p)] and Young's circumferential static elastic modulus [E(s)]) can be assessed. The purpose of the present study was to examine whether stress TEE is valuable method for parallel evaluation of CFVR, E(p), and E(s) in patients with hypertension. A total of 38 patients with chest pain but with a negative coronary angiogram were enrolled into the present study, which included examination of the presence or absence of hypertension. Significant coronary stenosis was considered present in the event of a luminal diameter reduction of >50% on use of the "worst view method." Patients with significant coronary or valvular heart disease, atrial fibrillation, heart failure, unstable angina pectoris, acute myocardial infarction, or diabetes mellitus were excluded from the study. Stress TEE was performed in each case to evaluate CFVR, E(p), and E(s). Coronary flow velocity reserve and diastolic coronary flow velocities measured at peak stress were decreased in hypertensive patients as compared with normotensive subjects. E(p) and E(s) were significantly increased in hypertensive patients. In conclusion, it can be stated that Stress TEE is a useful tool for the simultaneous evaluation of the CFVR, E(p), and E(s) in hypertension. The CFVR and aortic distensibility are decreased in hypertension.