Perspectives in noninvasive imaging for chronic coronary syndromes

Both the latest European guidelines on chronic coronary syndromes and the American guidelines on chest pain have underlined the importance of noninvasive imaging to select patients to be referred to invasive angiography. Nevertheless, although coronary stenosis has long been considered the main determinant of inducible ischemia and symptoms, growing evidence has demonstrated the importance of other underlying mechanisms (e.g., vasospasm, microvascular disease, energetic inefficiency). The search for a pathophysiology-driven treatment of these patients has therefore emerged as an important objective of multimodality imaging, integrating "anatomical" and "functional" information. We here provide an up-to-date guide for the choice and the interpretation of the currently available noninvasive anatomical and/or functional tests, focusing on emerging techniques (e.g., coronary flow velocity reserve, stress-cardiac magnetic resonance, hybrid imaging, functional-coronary computed tomography angiography, etc.), which could provide deeper pathophysiological insights to refine diagnostic and therapeutic pathways in the next future.

Coronary flow reserve and cardiovascular outcomes: a systematic review and meta-analysis

AIMS

This meta-analysis aims to quantify the association of reduced coronary flow with all-cause mortality and major adverse cardiovascular events (MACE) across a broad range of patient groups and pathologies.

METHODS AND RESULTS

We systematically identified all studies between 1 January 2000 and 1 August 2020, where coronary flow was measured and clinical outcomes were reported. The endpoints were all-cause mortality and MACE. Estimates of effect were calculated from published hazard ratios (HRs) using a random-effects model. Seventy-nine studies with a total of 59 740 subjects were included. Abnormal coronary flow reserve (CFR) was associated with a higher incidence of all-cause mortality [HR: 3.78, 95% confidence interval (CI): 2.39-5.97] and a higher incidence of MACE (HR 3.42, 95% CI: 2.92-3.99). Each 0.1 unit reduction in CFR was associated with a proportional increase in mortality (per 0.1 CFR unit HR: 1.16, 95% CI: 1.04-1.29) and MACE (per 0.1 CFR unit HR: 1.08, 95% CI: 1.04-1.11). In patients with isolated coronary microvascular dysfunction, an abnormal CFR was associated with a higher incidence of mortality (HR: 5.44, 95% CI: 3.78-7.83) and MACE (HR: 3.56, 95% CI: 2.14-5.90). Abnormal CFR was also associated with a higher incidence of MACE in patients with acute coronary syndromes (HR: 3.76, 95% CI: 2.35-6.00), heart failure (HR: 6.38, 95% CI: 1.95-20.90), heart transplant (HR: 3.32, 95% CI: 2.34-4.71), and diabetes mellitus (HR: 7.47, 95% CI: 3.37-16.55).

CONCLUSION

Reduced coronary flow is strongly associated with increased risk of all-cause mortality and MACE across a wide range of pathological processes. This finding supports recent recommendations that coronary flow should be measured more routinely in clinical practice, to target aggressive vascular risk modification for individuals at higher risk.

Assessment of the functional significance of borderline stenosis by determining coronary flow reserve, after primary percutaneous infarct artery intervention by stent implantation

Introduction: Patients with myocardial infarction who are effectively treated with primary percutaneous coronary intervention (PCI) may have significant coronary artery stenosis that is not responsible for current myocardial infarction. Non-infarction artery stenosis can cause serious adverse cardiac events, which can be avoided by performing PCI. Coronary flow reserve (CFR) is defined as the ratio of the hyperemic mean blood flow velocity to the resting blood flow velocity for a given coronary artery. Coronary flow reserve decreases with increasing severity of the lesion. Aim: Determination of CFR prognostic value in patients with residual intermediate stenosis on non-infarcted artery after PCI. Material and methods: The prospective study included 106 patients treated at the University Clinical Center of Serbia in the period from July 2007 to December 2014. Coronary flow reserve was performed on a non-infarcted coronary artery with intermediate stenosis (40-70%). Adenosine was administered intravenously for two minutes to induce hyperemia at a dose of 140 mcg/kg/min. It was calculated as the ratio of the maximum diastolic flow rate under hyperemia and the maximum flow rate under basal conditions. Patients were invited for follow-up at 6, 12, 18, and 24 months to determine the occurrence of composite adverse events, which included: cardiac death, stroke, myocardial infarction, and myocardial revascularization (non-infarction lesion). Results: In our group of patients, 18 adverse events were reported during follow-up. A statistically highly significant difference (p < 0.001) in CFR values was found in patients with adverse events compared to patients without adverse events. The CFR >2 value had a high negative predictive value (95%) for the absence of adverse events. Conclusion: In patients with CFR > 2, revascularization can be safely delayed with continued optimal drug therapy.

Should we routinely assess coronary artery Doppler in daily echocardiography practice?

A lot of people with coronary artery disease do not have specific symptoms, and myocardial infarction or death are the first manifestation of the disease. New accurate, non-invasive and safe screening methods are required that can assess the prognosis of patients during routine examinations performed on millions of people. The aim of this review was to discuss the current literature regarding the utility of non-invasive ultrasound imaging of the coronary artery in assessing a patient's prognosis in daily practice. Assessment of coronary artery flow during common stress echocardiography or echocardiography can provide additive incremental prognostic information without the burden of radiation. Exercise or pharmacologic stress echocardiography tests combined with coronary flow velocity reserve assessment has advantages over stress tests based only on regional wall motion abnormalities. Scanning of main coronary arteries as an addition to routine echocardiography can reveal patients at high risk of adverse cardiac events in the near future.

Prognostic Value of Transthoracic Doppler Echocardiography Coronary Flow Velocity Reserve in Patients with Nonculprit Stenosis of Intermediate Severity Early after Primary Percutaneous Coronary Intervention

BACKGROUND

Treatment of nonculprit coronary stenosis during primary percutaneous coronary intervention in patients with ST-segment elevation myocardial infarction may be beneficial, but the mode and timing of the intervention are still controversial. The aim of this study was to examine the significance and prognostic value of preserved coronary flow velocity reserve (CFVR) in patients with nonculprit intermediate stenosis early after primary percutaneous coronary intervention.

METHODS

Two hundred thirty patients with remaining intermediate (50%-70%) stenosis of non-infarct-related arteries, in whom CFVR was performed within 7 days after primary percutaneous coronary intervention, were prospectively enrolled. Twenty patients with reduced CFVR and positive results on stress echocardiography or impaired fractional flow reserve underwent revascularization and were not included in further analysis. The final study population of 210 patients (mean age, 58 ± 10 years; 162 men) was divided into two groups on the basis of CFVR: group 1, CFVR > 2 (n = 174), and group 2, CFVR ≤ 2 (n = 36). Cardiac death, nonfatal myocardial infarction, and revascularization of the evaluated vessel were considered adverse events.

RESULTS

Mean follow-up duration was 47 ± 16 months. Mean CFVR for the whole group was 2.36 ± 0.40. There were six adverse events (3.4%) related to the nonculprit coronary artery in group 1, including one cardiac death, one ST-segment elevation myocardial infarction, and four revascularizations. In group 2, there were 30 adverse events (83.3%, P < .001 vs group 1), including two cardiac deaths, two ST-segment elevation myocardial infarctions, and 26 revascularizations.

CONCLUSIONS

In patients with CFVR > 2 of the intermediate nonculprit coronary lesion, deferral of revascularization is safe and associated with excellent long-term clinical outcomes.

Assessment of left anterior descending artery stenosis of intermediate severity by fractional flow reserve, instantaneous wave-free ratio, and non-invasive coronary flow reserve

To test the usefulness of non-invasive coronary flow reserve (CFR) by transthoracic Doppler echocardiography by comparison to invasive fractional flow reserve (FFR) and instantaneous wave-free ratio (IFR), a new vasodilator-free index of coronary stenosis severity, in patients with left anterior descending artery (LAD) stenosis of intermediate severity (IS) and stable coronary artery disease. 94 consecutive patients (mean age 68 ± 10 years) with angiographic LAD stenosis of IS (50-70 % diameter stenosis), were prospectively studied. IFR was calculated as a trans-lesion pressure ratio during the wave-free period in diastole; FFR as distal pressure divided by mean aortic pressure during maximal hyperemia (using 180 μg intracoronary adenosine); and CFR as hyperemic peak LAD flow velocity divided by baseline flow velocity using intravenous adenosine (140 μg/kg/min over 2 min). The mean values of IFR, FFR, and CFR were 0.88 ± 0.07, 0.81 ± 0.09, and 2.4 ± 0.6 respectively. A significant correlation was found between CFR and FFR (r = 0. 68), FFR and IFR (r = 0.6), and between CFR and IFR (r = 0.5) (all, p < 0.01). Using a ROC curve analysis, the best cut-off to detect a significant lesion based on FFR assessment (FFR ≤ 0.8, n = 31) was IFR ≤ 0.88 with a sensitivity (Se) of 74 %, specificity (Sp) of 73 %, AUC 0.81 ± 0.04, accuracy 72 %; and CFR ≤ 2 with a Se = 77 %, Sp = 89 %, AUC 0.88 ± 0.04, accuracy 85 % (all, p < 0.001). In stable patients with LAD stenosis of IS, non-invasive CFR is a useful tool to detect a significant lesion based on FFR. Furthermore, there was a better correlation between CFR and FFR than between CFR and IFR, and a trend to a better diagnostic performance for CFR versus IFR.

Coronary Artery Imaging with Transthoracic Doppler Echocardiography

Coronary artery imaging with transthoracic Doppler echocardiography is a simple and useful technique to diagnose significant coronary artery stenosis. The visualization of mosaic flow in the proximal left coronary artery provides a direct indication of the presence of significant stenosis at the corresponding site during routine echocardiography. Coronary flow velocity reserve (CFVR) has a high diagnostic accuracy and feasibility in detecting the presence of functionally significant coronary stenosis in the left anterior descending coronary artery (LAD) and in the right coronary artery. The measurement of CFVR in the LAD also provides prognostic information in patients with intermediate coronary stenosis. This review summarizes the utility of transthoracic coronary artery imaging.

Positive effects of aggressive vasodilator treatment of well-treated essential hypertensive patients

Increased systemic vascular resistance and coronary microvascular dysfunction are well-documented in essential hypertension (EH). We investigated the effect of additional vasodilating treatment on coronary and peripheral resistance circulation in EH patients with high systemic vascular resistance index (SVRI) despite well-treated blood pressure (BP). We enroled patients on stable antihypertensive treatment that were given intensified vasodilating therapy (ACE inhibitor, angiotensin II receptor blocker or calcium channel blocker). Before and following 6 months of intensified therapy, coronary resting and maximal artery flow were measured by transthoracic Doppler echocardiography to calculate coronary flow reserve (CFR) and minimum vascular resistance (C-R_min). Cardiac output was estimated by inert gas rebreathing to calculate SVRI. Maximal forearm blood flow was determined by venous occlusion plethysmography to calculate minimum vascular resistance (F-R_min). Patients were assigned into two groups: high-SVRI and low-SVRI subgroups, based on a median split at baseline. Following additional treatment SVRI decreased more in the high-SVRI group than in the low-SVRI group (14.4 vs -2.2%: P=0.003), despite similar baseline ambulatory BP (132/81 mm Hg) and BP reduction (6.5 and 4.6%: P=0.19). F-R_min remained unchanged (6.5 vs -2.0%: P=0.30), while C-R_min decreased by 22 and 24% (P=0.80) and CFR increased by 23 and 17% (P=0.16). Thus, intensified vasodilating therapy improved SVRI more in patients with high SVRI than in those with low SVRI. Regardless of SVRI status, the treatment improved cardiac but not forearm dilatation capacity. The substantial improvement of the hypertensive cardiac microvascular dysfunction was not related to the reduction in SVRI.

Feasibility of 3D4D echocardiography for the detection of colour-coded flow in the left anterior descending artery

The aim of this study was to test the feasibility of the visualisation of 3D4D coronary flow in detectable segments of coronary arteries. Regarding the feasibility of this new approach, the hypothesis was proposed that the flow signals of the course of detectable coronary arteries can be better visualised by 3D4D echocardiography than by the conventional 2D approach. A total of 30 consecutive patients with sinus rhythm, in whom the distal left anterior descending artery (LAD) was visualised by 2D colour-coded Doppler echocardiography, were selected for 3D4D scanning procedures. All measurements were performed using a Vivid 7 or E9. All segments visualised by 2D colour-coded Doppler echocardiography were also examined by 3D4D echocardiography. Using defined settings, the width of the colour-coded flow signal differs significantly between 2D- and 3D4D echocardiography. The length of larger segments of the visualised colour-coded flow signal of the coronary flow could be better detected with 2D imaging. Small segments of coronary artery flow (<11 mm), however, could be significantly better visualised by 3D4D echocardiography. The main advantage of 3D4D echocardiography of the coronary artery flow is the visualisation of the proportions of vessels with complex morphology. 3D4D echocardiography of LAD flow by colour-coded Doppler echocardiography raises new possibilities for the direct flow visualisation of the detectable segments of coronaries. With its sufficiently high spatial and temporal resolution, this new method has the potential to be implemented in clinical scenarios. The possible application to the quantification of stenoses by the flow visualisation has to be evaluated in further studies.

Coronary flow reserve predicts cardiopulmonary fitness in patients with coronary artery disease independently of systolic and diastolic function

AIMS

Despite revascularization and optimal medical treatment, patients with coronary artery disease (CAD) have reduced exercise capacity. In the absence of coronary artery stenosis, coronary flow reserve (CFR) is a measure of coronary microvascular function, and a marker of future poor outcome in CAD patients. The aim of this study was to examine the relationship among CFR, systolic and diastolic function, peripheral vascular function, and cardiopulmonary fitness in CAD patients.

METHODS AND RESULTS

Forty patients with median left ventricular ejection fraction (LVEF) 49 (interquartile 46-55) with documented CAD without significant left anterior descending artery (LAD) stenosis underwent cardiorespiratory exercise test with measurement of VO2 peak, digital measurement of endothelial function and arterial stiffness, and an echocardiography with measurement of LVEF using the biplane Simpson model, mitral early (E) and late (A) inflow velocities, and tissue Doppler diastolic (e') and systolic (s') velocities. Peak coronary flow velocity (CFV) was measured in the LAD using pulse-wave Doppler. CFR was calculated as the ratio between peak CFV at rest and during vasodilator stress. Median CFR was 2.22 (1.90-2.62) and VO2 peak was 21.8 (17.6-25.5). VO2 peak correlated significantly with CFR (r = 0.57, P < 0.001), E/e' (r = -0.35, P = 0.04), and s' (r = 0.41, P = 0.01) and with LVEF (r = 0.35, P = 0.03). CFR remained independently associated with VO2 peak after adjustment for systolic and diastolic function.

CONCLUSIONS

Coronary flow reserve measured noninvasively predicts cardiopulmonary fitness independently of resting systolic and diastolic function in CAD patients, indicating that cardiac output during maximal exercise is dependent on the ability of the coronary circulation to adapt to the higher metabolic demands of the myocardium.

Comparison of 5-Year Outcomes for Patients With Coronary Artery Disease in Groups With and Without Revascularization With Different Results of Stress Echocardiography

BACKGROUND

There is conflicting data in contemporary literature concerning the best way to treat patients with stable coronary artery disease; specifically, whether medical treatment alone or invasive strategies combined with medical treatment are better. The purpose of this study was to evaluate the clinical outcomes of patients with and without revascularization after stress echocardiography and to create formulas for detecting patients with a very high risk of cardiac death/major adverse cardiac event (MACE) in their present conditions.

METHODS

We assessed 323 patients (53.9 ± 8.4 years, 247 men), undergoing upright bicycle stress echocardiography in 2006 - 2007. During a median follow-up of 5.2 ± 0.2 years, 21 cardiovascular and 5 confirmed non-cardiac deaths occurred. Eighty-three patients underwent revascularization.

RESULTS

Stress echocardiography was normal in 32% and abnormal in 68%. All the patients with CAD were prescribed acetylsalicylic acid, statins, beta-blockers and ACE inhibitors. Eighty-seven percents of the patients took medication regularly. The percentage taking medication didn't significantly differ in the subgroups. Two formulas were created for detecting a very high risk of cardiac death (25%) or MACE (68%) within 5 years. All the patients with abnormal stress tests were divided into two subgroups: 80 patients with revascularization and 138 subjects without revascularization. There was a significant difference in 5 year cardiac mortality if the patients had an index of wall motion abnormality (IWMA) after exercise greater than or equal to 1.3.

CONCLUSION

It is possible to identify during stress echocardiography subjects with a very high risk for cardiac death/MACE. Patients with IWMA ≥ 1.3 had improved outcomes following revascularization.

[Interest of coronary flow reserve of the LAD during dobutamine stress echocardiography]

AIM OF THE STUDY

To assess the value of the coronary flow reserve (CFR) in the left anterior descending artery (LAD) during dobutamine stress echocardiography in the diagnosis of significant LAD stenosis (more than 70%).

METHOD

Retrospective study of 81 patients with a positive stress echocardiography who underwent a coronarography.

RESULTS

Measurement of coronary flow reserve was able in half echocardiographic exams. Medium Pic diastolic velocity was 0.33 m/s (SD 0.20), medium maximal diastolic velocity during stress was 0.62 m/s (SD 0.20), medium CFR was 2.25 (SD 0.65). In 50 patients LAD was not seen; in five of them LAD was occluded. The predictive positive value (PPV) of a low coronary flow reserve to detect LAD stenosis is 66.7% and the negative predictive value (NPV) is 65.4%. An abnormal anterior contraction during stress echo with a low reserve has a PPV of 75% for the diagnosis of significant IVA stenosis and a normal contraction during stress with normal coronary flow reserve means a NPV of 65%. We did not show a significant correlation between low coronary flow and abnormal contraction during stress echocardiography (kappa 0.51).

CONCLUSION

Coronary flow reserve of LAD during stress echo is feasible but does not really improve exam performance to detect significant IVA stenosis. This measurement remains to be clear in coronary patients management.

Disproportionally impaired microvascular structure in essential hypertension

BACKGROUND

Increased microvascular resistance and small artery remodelling are key abnormalities in the pathophysiology of essential hypertension. We investigated the relation between the impairment of coronary and forearm minimum vascular resistances (C-Rmin and F-Rmin) and the degree of hypertension.

METHOD

Seventy-five never-treated essential hypertension patients with 24-h systolic blood pressure (BP) at least 130 mmHg or diastolic BP at least 80 mmHg were assigned into grade 1 (office BP 140/90-159/99 mmHg) and grade 2 (office BP 160/100-179/109 mmHg) hypertension and compared to normotensive controls (n = 25). The patients were (48 years, 60% men) without cardiovascular disease. C-Rmin and coronary flow reserve (CFR) were derived from flow measurements in the left anterior descending artery using transthoracic echocardiography. F-Rmin was measured using venous occlusion plethysmography. Resting systemic vascular resistance index (SVRI) was measured with a gas rebreathing technique.

RESULTS

Compared to normotensive controls: 24-h mean BP was raised 14% in grade 1 essential hypertension and 28% in grade 2 essential hypertension, whereas F-Rmin and C-Rmin were elevated by 58 and 87% in grade 1 essential hypertension and 72 and 125% in grade 2 essential hypertension. C-Rmin and F-Rmin were thus both increased more than expected from the BP level. SVRI and left-ventricular mass were increased proportionally to the BP. CFR was decreased by approximately 30% in both essential hypertension groups.

CONCLUSION

The results demonstrate excessive microvascular structural abnormalities in hypertension suggesting microvascular alterations occur early and not just as an adaptation to the BP level. Thus the level of BP elevation does not give an accurate indication of the microvascular involvement and impairment in essential hypertension.

Circulating vaspin levels and epicardial adipose tissue thickness are associated with impaired coronary flow reserve in patients with nonalcoholic fatty liver disease

BACKGROUND

Patients with nonalcoholic fatty liver disease (NAFLD) have a reduced coronary flow reserve (CFR) and an increased risk of cardiovascular disease. The fat cells that surround coronary arteries may play a central and underrecognized role in development of cardiovascular disease through the systemic secretion of adipokines. We therefore evaluated the relation of epicardial fat thickness, serum levels of epicardial fat-related adipokines (chemerin and vaspin), and CFR in patients with NAFLD.

METHODS

We investigated 54 patients with biopsy-proven NAFLD and 56 age- and sex-matched controls. CFR and epicardial fat thickness (EFT) were measured by transthoracic echocardiography. Serum levels of chemerin and vaspin were measured by ELISA.

RESULTS

EFT was significantly higher (0.64 ± 0.13 vs. 0.54 ± 0.10 cm, P<0.001) and CFR significantly lower (2.11 ± 0.45 vs. 2.52 ± 0.62, P < 0.001) in patients with NAFLD than in controls. Serum levels of vaspin and chemerin were both significantly increased in patients with NAFLD compared with controls. Stepwise regression analysis showed that EFT (β=-0.53, t=-3.7, P<0.001), serum vaspin levels (β=-0.30, t=-2.5, P=0.014), and liver fibrosis (β=-0.31, t=-2.11, P=0.041), in the order they entered into the model, were independent predictors of CFR in NAFLD patients.

CONCLUSION

Our data suggest the presence of a complex interplay between EFT, serum vaspin, and liver histology in promoting an impaired hyperemic stimulation of coronary blood flow in patients with NAFLD.

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.