Noninvasive coronary flow reserve assessed by transthoracic coronary Doppler ultrasound in patients with left anterior descending coronary artery stents

A knowledge graph-based analytical model for mining clinical value of drug stress echocardiography for diagnosis, risk stratification and prognostic evaluation of coronary artery disease

The three major techniques for clinically diagnosing coronary heart disease, including angina associated with myocardial ischemia, are coronary angiography, myocardial perfusion imaging, and drug stress echocardiography. Compared to the first two methods, which are invasive or involve the use of radionuclides, drug stress echocardiography is increasingly used in clinical practice due to its non-invasive, low-risk, and controllable nature, and wide applicability. We developed a novel methodology to demonstrate knowledge graph-based efficacy analysis of drug stress echocardiography as a complement to traditional meta-analysis. By measuring coronary flow reserve (CFR), we discovered that regional ventricular wall abnormalities (RVWA) and drug-loaded cardiac ultrasound can be used to detect coronary artery disease. Additionally, drug-loaded cardiac ultrasound can be used to identify areas of cardiac ischemia, stratify risks, and determine prognosis. Furthermore, adenosine stress echocardiography(ASE) can determine atypical symptoms of coronary heart disease with associated cardiac events through CFR and related quantitative indices for risk stratification. Using a knowledge graph-based approach, we investigated the positive and negative effects of three drugs - Dipyridamole, Dobutamine, and Adenosine - for coronary artery disease analysis. Our findings show that Adenosine has the highest positive effect and the lowest negative effect among the three drugs. Due to its minimal and controlled side effects, and high sensitivity for diagnosing coronary microcirculation disorders and multiple lesions, adenosine is frequently used in clinical practice.

Evaluation of the coronary circulation and calcification in children on regular hemodialysis

BACKGROUND

The objective of this study was to evaluate the coronary circulation and calcification in children with end-stage renal disease (ESRD) on hemodialysis.

METHODS

A total of 50 children with ESRD and 50 healthy controls were enrolled in the study. Cardiac functions and coronary blood flow were evaluated with conventional and tissue Doppler echocardiography. Coronary artery calcification (CAC) was evaluated using high-resolution multidetector computed tomography (CT).

RESULTS

The hyperemic coronary flow volume (CFV) and coronary flow reserve were significantly lower in the patient group than in the controls, while there was no significant difference in the baseline CFV between the two groups. Hypertension was present in 60% and CAC was observed in 20% of the children in the patient group. CAC was present in 30% of the children in the hypertensive subgroup. The left ventricle myocardial performance index (LV MPI), CAC score, duration of hypertension and level of diastolic blood pressure were independent predictors of the coronary blood flow, and LV MPI, serum parathyroid hormone, duration of dialysis and E'/A' mitral valve were independent predictors of coronary calcification.

CONCLUSION

High diastolic blood pressure, long duration of hypertension, high LV MPI and increased CAC scores are independent risk factors for impaired coronary blood flow in children with ESRD.

Diabetes mellitus and coronary microvascular function in asymptomatic patients with severe aortic stenosis and nonobstructed coronary arteries

BACKGROUND AND AIM

Coronary flow reserve is impaired in asymptomatic patients with aortic stenosis and has a prognostic value. We investigated whether the type II diabetes mellitus additionally impairs microvascular circulation assessed by coronary flow reserve in patients with asymptomatic severe aortic stenosis, normal left ventricular ejection fraction and nonobstructed coronary arteries.

METHODS

A total of 128 patients, mean age of 66.35 ± 10.51 (58.6% males), with severe aortic stenosis and normal left ventricular ejection fraction were enrolled in this study. Patients with diabetes mellitus, those who were treated for diabetes mellitus or had documentation confirming the diagnosis of diabetes mellitus, were considered. All patients underwent coronary angiography and had no obstructive coronary disease (defined as having no stenosis >50% in diameter), standard transthoracic Doppler-echocardiographic study and adenosine stress transthoracic echocardiography for coronary flow reserve measurement.

RESULTS

Diabetes mellitus was present in 26 patients (20.31%). There was no significant difference in aortic stenosis severity between diabetic and non-diabetic patients [aortic valve area (0.81 ± 0.18 vs 0.85 ± 0.15 cm(2)) and Vmax (4.20 ± 0.57 vs 4.21 ± 0.48 m/s)]. Mean coronary flow reserve in diabetic patients was 1.98 ± 0.48, while mean coronary flow reserve in non-diabetic patients was 2.64 ± 0.54 (p < 0.01). Diabetes mellitus was independent predictor of coronary flow reserve [B = -0.636, 95% confidence interval (-0.916 to -0.368), p < 0.001].

CONCLUSION

Diabetes mellitus additionally impairs coronary microvascular function in asymptomatic patients with severe aortic stenosis and nonobstructed coronary arteries.

Transthoracic Doppler for detection of stenoses in the three main coronary arteries by use of stenotic to prestenotic velocity ratio and aliased coronary flow

AIMS

Our aim was to determine the feasibility and accuracy of diagnosing significant coronary artery stenoses using peak stenotic to prestenotic velocity ratio (pSPVR) measurements when compared with results from quantitative coronary angiography and coronary flow velocity reserve (CFVR) assessed by transthoracic echocardiography (TTE).

METHODS AND RESULTS

One hundred and eight patients scheduled for coronary angiography were studied using transthoracic Doppler echocardiography. Stenoses were identified by local colour aliasing by colour flow Doppler, and further evaluated by pSPVR, using a pSPVR of ≥2.0 as a cut-off for significant stenosis. When pSPVR could not be measured, local mosaic coronary flow pattern at Nyquist limit ≥0.48 m/s was used. Sixty-five lesions suggestive of stenosis were found by TTE. Combining findings of pSPVR ≥2.0 and local mosaic flow at Nyquist limit ≥0.48 m/s, the sensitivity and specificity of demonstrating significant stenoses (diameter stenosis, 50-99%) in the left main coronary artery (LM), left anterior descending coronary (LAD), left circumflex coronary (Cx), and right coronary artery (RCA) were 75 and 98%, 74 and 95%, 40 and 87%, and 34 and 98%, respectively. The pSPVR did not differ significantly between arteries with reduced and normal CFVR, with a cut-off of CFVR <2.0.

CONCLUSIONS

Findings of pSPVR ≥2.0 or localized colour flow aliasing are useful in the non-invasive diagnosis of significant coronary disease in the three main coronary arteries, with high specificity for detecting significant stenoses. These findings showed high sensitivity for identifying significant stenoses in the LM and LAD, but showed lower ability to detect those lesions in the Cx and RCA.

Feasibility of proximal right coronary artery imaging by 2D and 3D echocardiography in comparison to coronary angiography

The present study was carried out to test the feasibility of proximal right coronary artery (RCA) imaging and to detect proximal RCA narrowing and occlusion by 2D and 3D transthoracic echocardiography in comparison to coronary angiography (CA). Standardised 2D and 3D echocardiography were performed prior to CA in 97 patients with sinus rhythm. The following parameters were determined: the longest longitudinal detectable RCA segment, the minimum and maximum width of the RCA, the area and number of detectable narrowing >50% of the proximal RCA and the correlation between the echocardiographic and angiographic findings. The visualisation of the proximal RCA and the detection of coronary artery narrowing in the proximal RCA are generally possible. Differences in width and area were not statistically significant between 2D and 3D echocardiography, but showed significant differences between echocardiography and CA. For the detection of proximal RCA narrowing, higher sensitivity and specificity values were obtained by 2D than by 3D echocardiography. However, in patients with sufficient image quality 3D echocardiography permits a more detailed visualisation of the anatomical proportions and an en-face view into the RCA ostium. The visualisation of the proximal RCA is feasible and narrowing can be detected by 2D and 3D echocardiography if image quality is sufficient. CA is the gold standard for the detection of coronary artery stenoses. However, the potential of this new approach is clinically important because crucial findings of the proximal RCA can be presumably detected non-invasively prior to CA.

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.

Prediction of long-term ischemic events by noninvasively assessed coronary flow reserve

BACKGROUND

Coronary flow reserve (CFR) by adenosine echocardiography in left anterior descending (LAD) or posterior descending coronary arteries may predict clinical outcome.

METHODS

We used models accounting (Cox's model) or not (logistic regression and neural network) for time to event and either considered (forced models) or not (stepwise logistic regression and neural network models) all among 21 covariates to predict 1-year composite events after LAD CFR.

RESULTS

There were 553 consecutive patients with coronary artery disease (CAD): 89 patients had also posterior descending CFR. During 1-year follow-up 328 patients were event-free, 35 had composite ischemic events and 190 underwent short-term revascularization. LAD and posterior descending CFR (respectively, 1.53 ± 0.83, N = 225 and 1.84 ± 0.80, N = 42) were significantly (P < 0.0001) lower in patients with events (or with revascularization following CFR measurement) than in those without (respectively, 3.13 ± 0.84, N = 328, and 2.53 ± 0.72, N = 47). Using LAD CFR as a continuous covariate, by both forced Cox's and logistic regression, coefficients (t values, respectively, -14.11 and -10.19) were significant (both P < 0.00001) to predict outcome. Global predictive accuracies by neural network, adopting a receiver operating characteristic areas under the curve (ROC) assessment, were excellent (>0.91) and the role of LAD CFR among predictors was overwhelming. Other indices of myocardial ischemia and the presence of coronary stenoses or previous infarction did not modify the multivariable predictive role of LAD CFR. When patients with revascularization were discounted, the LAD CFR predictive role was the same.

CONCLUSIONS

Thus, adenosine echocardiography-based LAD CFR predicts 1-year composite ischemic events in patients with CAD, independent of the multivariable model adopted. Posterior descending CFR also has a role.

New method to measure coronary velocity and coronary flow reserve

Coronary flow reserve (CFR) is an important index of coronary microcirculatory function. The objective of this study was to validate the reproducibility and accuracy of intravascular conductance catheter-based method for measurements of baseline and hyperemic coronary flow velocity (and hence CFR). The absolute coronary blood velocity was determined by measuring the time of transit of a saline injection between two pairs of electrodes (known distance) on a conductance catheter during a routine saline injection without the need for reference flow. In vitro validation was made in the velocity range of 5 to 70 cm/s in reference to the volume collection method. In 10 swine, velocity measurements were compared with those from a flow probe in coronary arteries at different CFR attained by microsphere embolization. In vitro, the mean difference between the proposed method and volume collection was 0.7 ± 1.34 cm/s for steady flow and −0.77 ± 2.22 cm/s for pulsatile flow. The mean difference between duplicate measurements was 0 ± 1.4 cm/s. In in vivo experiments, the flow (product of velocity and lumen cross-sectional area that is also measured by the conductance catheter) was determined in both normal and stenotic vessels and the mean difference between the proposed method and flow probe was −1 ± 12 ml/min (flow ranged from 10 to 130 ml/min). For CFR, the mean difference between the two methods was 0.06 ± 0.28 (range of 1 to 3). Our results demonstrate the reproducibility and accuracy of velocity and CFR measurements with a conductance catheter by use of a standard saline injection. The ability of the combined measurement of coronary lumen area (as previously validated) and current velocity and CFR measurements provides an integrative diagnostic tool for interventional cardiology.

Usefulness of coronary flow reserve measured by echocardiography to improve the identification of significant left anterior descending coronary artery stenosis assessed by multidetector computed tomography

Multidetector computed tomography (MDCT) detects coronary artery disease. However, an overestimation of coronary artery stenosis and artifacts can prevent accurate identification of significant coronary narrowing. The combination of MDCT with coronary flow reserve (CFR), the hyperemic/baseline peak flow velocity ratio, measured by transthoracic Doppler echocardiography might be helpful. We studied 144 consecutive patients with CFR and quantitative coronary angiography, obtained using both MDCT and invasive coronary angiography (reference method). It was hypothesized that the CFR might provide an incremental value to MDCT in detecting significant (> or =70%) left anterior descending (LAD) coronary artery stenosis. A CFR cutoff of <2 was used to discriminate significant stenosis. CFR was feasible in 141 (98%) of 144 patients, and MDCT was feasible in 131 (91%) of 144 patients (p <0.02). In a univariate model, the prediction of significant LAD stenosis was slightly, but significantly (p <0.0001), better with CFR (sensitivity 90%, specificity 96%, positive predictive value 84%, negative predictive value 97%, and diagnostic accuracy 94%, chi-square = 97.5) than with MDCT (sensitivity 80%, specificity 93%, positive predictive value 71%, negative predictive value 95%, diagnostic accuracy 90%, chi-square = 63.2). When the findings from transthoracic Doppler echocardiography and MDCT agreed, the diagnostic accuracy increased (96%; chi-square = 86.1, p <0.0001). In a multivariate prediction of significant LAD stenosis using a logistic neural network, CFR overshadowed MDCT, and the area under the receiver operating curve was 0.99. Of the 13 patients missed by MDCT, the diagnostic accuracy of transthoracic Doppler echocardiography to predict significant LAD stenosis was 100%. Thus, CFR could improve the diagnostic accuracy of MDCT to detect significant LAD stenosis.

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

OBJECTIVES

The aim of the present study was to examine the long-term prognostic value of coronary flow velocity reserve (CFR) evaluated by means of stress transoesophageal echocardiography (STEE) in patients who have undergone percutaneous coronary intervention (PCI).

DESIGN

The study comprised 31 patients with significant LAD stenosis who underwent LAD-PCI. In consequence of their clinical signs, 11 subjects required rePCI or coronary artery bypass graft (CABG) operation within six months. The clinical status of the remaining 20 cases improved during the follow-up. STEE examinations were performed before LAD-PCI and after it.

RESULTS

The CFR of patients in a stable clinical condition improved during the follow-up, while the CFR of those who required rePCI or CABG remained unchanged. From this patient population, two subjects died during the 5-year follow-up.

CONCLUSIONS

Most of the patients who displayed an improved CFR after PCI suffered no major clinical events during the 5-year follow-up; in contrast, in those who a priori had a low CFR and did not show any improvement after PCI, major events did occur during this period.

Detection of severe stenosis and total occlusion in the left anterior descending coronary artery with transthoracic Doppler echocardiography in the emergency room

BACKGROUND

The noninvasive measurement of coronary flow velocity in the left anterior descending artery (LAD) has recently been realized by using the transthoracic Doppler echocardiography (TTDE). A couple of investigations demonstrated that the diastolic-to-systolic peak velocity ratio (DSVR) by TTDE is a simple and noninvasive method for the detection of severe stenosis in the elective settings. However, the usefulness of DSVR by TTDE in the emergency settings has not been evaluated.

OBJECTIVE

The purpose of this study was to assess the clinical feasibility to document the LAD flow by TTDE in emergency patients who complained of chest pain.

METHODS

We studied 49 consecutive patients with acute coronary syndrome who were going to undergo emergency coronary angiography (CAG) for the anatomical diagnosis and the facilitated percutaneous coronary intervention (PCI). Prior to CAG, we recorded the LAD flow by TTDE and measured the diastolic peak velocity (DVp), systolic peak velocity (SVp), and their ratio, DSVR (DVp/SVp) of LAD flow.

RESULTS

By CAG, the culprit lesions actually resided in the proximal LAD in 36 patients. Among the 36 patients, we detected the Doppler LAD flow in 29. Five out of 7 patients who were unable to detect the LAD flow revealed total occlusions by CAG. DSVR of the LAD is significantly lower in 17 patients who showed severe stenoses (>90%) than those in the rest of 12 patients who did not show such critical stenoses (1.44 +/- 0.16 vs 2.10 +/- 0.26, P < 0.0001).

CONCLUSION

In the emergency settings, a noninvasive assessment of the LAD flow by TTDE accurately estimates the critical stenotic lesions of the LAD.

Coronary flow reserve dysfunction in hemodialysis and kidney transplant patients

BACKGROUND

The assessment of coronary flow reserve (CFR) by trans-thoracic echocardiography has recently been introduced into clinical studies. Impairment of coronary microvascular functions and decreased CFR detected by trans-thoracic Doppler harmonic echocardiography (TTDE) has recently been reported in hemodialysis (HD) patients, but there is no comparative study between HD patients and renal transplant recipients.

METHODS

The aim of our study was to evaluate coronary microvascular circulation in chronic HD patients and renal transplant recipients. Forty-eight chronic HD patients, 27 renal transplant patients and 39 normotensive healthy controls were studied for the assessment of CFR by TTDE. The carotid artery intima media thickness (IMT) and areas of focal plaque formation were also evaluated in all subjects.

RESULTS

CFR values were significantly lower in both the HD and renal transplant groups than in the control group (p = 0.00). CFR values (1.57 +/- 0.32 vs. 1.89 +/- 0.50, p = 0.01) were also significantly lower in the HD group than in the renal transplant group. In 43 of 48 (89.6%) HD patients, CFR was <2.0; however, in 16 of 27 (59.3%) renal transplant recipients it was <2.0 (p = 0.00). When the HD and renal transplant groups were divided into two subgroups, according to CFR measurements (CFR < 2 and > or =2), no significant differences were found with respect to coronary risk factors and left ventricular echocardiographic measurements. The IMT of the control group (0.586 +/- 0.163 mm) was significantly lower than the HD (0.799 +/- 0.218 mm) and renal transplant groups (0.681 +/- 0.148 mm; p = 0.00). The IMT of the HD patients (0.799 +/- 0.218 mm) was significantly higher than the renal transplant recipients (0.681 +/- 0.148 mm; p = 0.01).

CONCLUSIONS

Renal transplant and HD patients had lower CFR values detected by TTDE, which may be regarded as an early finding of an affected cardiovascular system. CFR is more impaired in HD patients than renal transplant recipients. Uremia-associated microvascular disease may be responsible for CFR impairment in HD patients.

Clinical value of echocardiographic assessment of coronary flow reserve after left anterior descending coronary artery stenting in an unselected population

BACKGROUND

Transthoracic Doppler echocardiography is a valuable tool to measure coronary flow reserve (CFR) and detect in-stent restenosis (ISR) after percutaneous coronary angioplasty in selected series of patients.

OBJECTIVES

To assess the usefulness of coronary flow reserve measured by echocardiography in detecting significant (> or =70%) ISR of the left anterior descending coronary artery in a large unselected population.

METHODS

Two hundred and twenty-three patients (age 61 +/- 10 years; 168 men) treated with left anterior descending stenting underwent CFR measurement by transthoracic Doppler echocardiography and venous adenosine infusion 24-72 h before control coronary angiography. Coronary-active drugs were continued, and patients with multiple risk factors and old anterior-apical myocardial infarction were included.

RESULTS

Significant ISR occurred in 56 patients (25%). Patients with ISR had higher basal coronary flow velocity (27 +/- 10 cm/s vs. 24 +/- 7 cm/s; P < 0.002) and lower CFR (1.5 +/- 0.5 vs. 2.7 +/- 0.6; P < 0.0001) than those without ISR. A linear relation was found between ISR and CFR (r = -0.73; P < 0.0001) and remained significant after adjustment for blood pressure and heart rate (r = -0.74; P < 0.0001). A CFR less than two identified significant ISR (sensitivity 88%, specificity 88%, area under the curve = 0.943; P < 0.001). In a multivariate model of CFR prediction, myocardial infarction and heart rate were slightly contributory (ss = -0.19, P < 0.01; ss = -0.16, P < 0.03, respectively), whereas ISR had a large influence (ss = -0.66; P < 0.0001). The inverse correlation between ISR and CFR persisted in patients with myocardial infarction (r = -0.64; P < 0.0001) and in those treated with beta-blockers (r = -0. 71; P < 0.0001).

CONCLUSION

Echocardiographic measurement of CFR detects significant left anterior descending ISR in unselected patients with multiple risk factors, old anterior-apical myocardial infarction, and taking beta-blockers.

Transthoracic echocardiography in the detection of chronic total coronary artery occlusion

AIMS

The aim of our study was to detect chronic total occlusion of the left anterior descending coronary artery (LAD), circumflex coronary artery (Cx), and right coronary artery (RCA) using transthoracic echocardiography (TTE) in 110 consecutive patients who underwent coronary angiography for investigation of angina.

METHODS AND RESULTS

Coronary blood flow direction was assessed in the epicardial collaterals [distal LAD (dLAD), obtuse marginal branches and right posterior descending artery (PDA)] and intramyocardial collaterals [LAD septal branch (SB LAD) and RCA septal branch (SB RCA)]. The sensitivity and specificity of retrograde flow for identification of the occluded LAD by TTE in the dLAD only were 78 and 96%, respectively, and those in both dLAD and SB LAD were 89 and 96%, respectively. The retrograde SB LAD flow detects proximal LAD occlusion with 88% sensitivity and 75% specificity. The sensitivity and specificity of retrograde flow for identification of the occluded RCA by TTE in the PDA only were 79 and 97%, respectively, and those in both PDA and SB RCA were 89 and 97%, respectively. The retrograde SB RCA flow does not allow us to differentiate between proximal and non-proximal RCA occlusion. Transthoracic echocardiography is not a method for diagnosing Cx occlusions as the success in visualizing the Cx epicardial collaterals was achieved in 31% of cases only.

CONCLUSION

TTE is a sensitive and highly specific non-invasive method for diagnosis of LAD and RCA occlusions, based on the detection of the coronary blood flow direction in the epicardial and intramyocardial collaterals.

Distal left circumflex coronary artery flow reserve recorded by transthoracic Doppler echocardiography: a comparison with Doppler-wire

Background

Coronary flow reserve (CFR) recording by means of transthoracic echocardiography (TTDE) in all the main distal coronary arteries is a challenge for advanced echocardiography. Validation studies of TTDE versus Doppler-wire (DW) recordings are available for Left Anterior Descending artery (LAD) and the Posterior Descending coronary artery (PD), but lacking for the more technically challenging Left Circumflex coronary artery (LCx).

Aim

To evaluate the reliability of TTDE in assessing CFR in LCx when compared to the intracoronary Doppler flow-wire gold standard.

Methods

we evaluated 5 patients (age = 60 ± 9 years, 5 males) on LCx by TTDE and invasive CFR assessment. TTDE recording was performed using a low-frequency probe, with a four-chamber as a guiding 2D view. The 2 tests were performed on different days and in random order within 48 hours in a blind fashion. Vasodilator stimulus was adenosine, intravenously (140 γ/kg/min × 3–6 min) for TTDE and intracoronary (40 γ bolus) for DW recordings.

Results

CFR values on LCx ranged from 1.9 to 2.8 for DW, and from 2.0 to 3.0 for TTDE, with an overall correlation of R = 0,85 (p = 0,06); normal (CFR > 2.5) or abnormal (CFR < 2.5) value was concordantly identified by the 2 techniques in 4 out 5 cases (80%).

Conclusion

CFR of LCx artery can be obtained noninvasively with TTDE.

Functional assessment of the collateral-dependent circulation in chronic total coronary occlusion using transthoracic Doppler ultrasound and venous adenosine infusion

The measurement of collateral flow reserve (CFR; the hyperemic/baseline collateral flow velocity ratio) in patients with chronic total coronary occlusion requires invasive and expensive techniques. Noninvasive transthoracic coronary Doppler echocardiography may be an alternative option. Fifty-one patients with chronic total coronary occlusion were evaluated by transthoracic coronary Doppler echocardiography and venous adenosine infusion to measure CFR in occluded coronary arteries (the left anterior descending artery in 44 patients and the artery supplying the posterior descending artery in 7 patients). CFR data were plotted against 3 angiographic parameters: (1) grade of the epicardial filling of the occluded artery (1=absent, 2=partial, 3=complete), (2) stenosis of the donor artery, and (3) the extent of coronary artery disease (vessels with >or=70% stenosis). Collateral flow was maintained at stress in 34 patients (CFR>or=1, range 1.0 to 2.2) but was withdrawn in 17 patients (CFR<1, range 0.25 to 0.90). CFR increased with the degree of angiographic collateral flow (grade 1: 0.73+/-0.29; grade 2: 1.16+/-0.31; grade 3: 1.34+/-0.49; F=5.31, p=0.008). A multivariate model of CFR prediction showed a direct relation with angiographic collateral grade and the number of diseased vessels and an inverse relation with stenosis of the donor artery. In conclusion, CFR measurement is feasible by transthoracic coronary Doppler echocardiography. One third of the patients with chronic total coronary occlusion had collateral flow withdrawal at stress, which occurs when collateral circulation is poor and when the donor artery is stenotic. CFR correlates with angiographic collateral grade and with the extent of coronary artery disease.

Coronary flow reserve evaluation in stress-echocardiography laboratory

The assessment of coronary flow reserve by transthoracic echocardiography has recently been introduced into clinical practice with good results for the diagnosis of left anterior descending artery disease and fairly promising results for posterior descending coronary artery disease. By looking at what is behind wall motion, we may realize a sonographer's dream and, in particular, the addition of coronary flow reserve to regional wall motion analysis allows us to have - in the same sitting - high specificity (regional wall motion) and a highly sensitive (coronary flow reserve) diagnostic marker, with an improvement in overall diagnostic accuracy. Coronary flow reserve evaluation may shift the balance of stress choice in favor of vasodilators, which are easier to perform with dual imaging than dobutamine or exercise coronary flow reserve evaluation and may shift the choice in favor of dipyridamole or adenosine stress tests, which are also easier to perform with dual imaging than those using dobutamine or exercise. Lastly, it adds quantitative support to the exquisitely qualitative assessment of wall motion analysis, thereby facilitating the communication of stress echo results to the cardiological world outside the echo laboratory.

Direct demonstration by transthoracic Doppler echocardiography of adenosine-induced coronary steal in the collateral-dependent vessel

Coronary flow velocity reserve was measured to assess the frequency of coronary steal in the collateral-dependent coronary arteries using transthoracic Doppler echocardiography. Coronary steal occurred in half the vessels studied. There was no significant difference between coronary flow velocity reserve in poorly and well-developed collaterals.

Coronary flow reserve in stress-echo lab. From pathophysiologic toy to diagnostic tool

The assessment of coronary flow reserve by transthoracic echocardiography has recently been introduced into clinical practice with gratifying results for the diagnosis of left anterior descending artery disease simultaneously reported by several independent laboratories. This technological novelty is changing the practice of stress echo for 3 main reasons. First, adding coronary flow reserve to regional wall motion allows us to have - in the same sitting - high specificity (regional wall motion) and a high sensitivity (coronary flow reserve) diagnostic marker, with an obvious improvement in overall diagnostic accuracy. Second, the technicalities of coronary flow reserve shift the balance of stress choice in favour of vasodilators, which are a more robust hyperemic stress and are substantially easier to perform with dual imaging than dobutamine or exercise. Third, the coronary flow reserve adds a quantitative support to the exquisitely qualitative assessment of wall motion analysis, thereby facilitating the communication of stress echo results to the cardiological world outside the echo lab. The next challenges involve the need to expand the exploration of coronary flow reserve to the right and circumflex coronary artery and to prove the additional prognostic value - if any - of coronary flow reserve over regional wall motion analysis, which remains the cornerstone of clinically-driven diagnosis in the stress echo lab.

Feasibility of Measuring Coronary Flow Velocity and Reserve in the Left Anterior Descending Coronary Artery by Transthoracic Doppler Echocardiography in a Relatively Obese American Population

BACKGROUND

Transthoracic Doppler echocardiography (TTDE) assessment of coronary flow velocity reserve (CFVR) has been validated in Asian and European centers. This methodology has not gained acceptability in the United States due to the bias that coronary flow velocity (CFV) by TTDE might be difficult in an obese population with relatively poor acoustic windows.

METHODS

Baseline CFV in the left anterior descending coronary artery (LAD) by TTDE was obtained in 67 nonselected American patients. A subset of 38/67 received adenosine infusion for measuring CFVR of the LAD.

PURPOSE

The aim of this study was twofold: (1) to determine the feasibility of measuring CFV and CFVR in the LAD by TTDE in a relatively obese American population, and (2) to compare CFV and CFVR values in this population with those previously obtained in a group of Japanese patients.

RESULTS

The mean body mass index (BMI) of the American population (28 +/- 6 kg/m2, range: 18-46 kg/m2) was significantly higher than that of the Japanese group (23 +/- 4 kg/m2, range: 15-37 kg/m2). Twenty-five American patients were classified as obese (BMI >30 kg/m2). Baseline CFV was obtained in 60/67 patients (feasibility: 90%) with a 10% need for intravenous contrast agent to enhance the delineation of the CFV envelope. The success rate in recording CFVR in American patients (92%) was nearly identical to that of a Japanese group (99%). The time-averaged peak diastolic coronary flow velocity increased from 15.6 +/- 5.5 cm/sec at baseline to 47.1 +/- 17.9 cm/sec during adenosine infusion, and CFVR was calculated to be 3.22 +/- 1.15 (range: 0.94-5.69). Intraobserver and interobserver variability for the CFV recording was 4.7 and 6.2%, respectively.

CONCLUSIONS

These results suggest that the noninvasive measurement of CFV and CFVR of the LAD is feasible even in a relatively obese American population. Furthermore, the success rates for recording CFV and CFVR are similar to those measured in a Japanese population. This methodology has the potential to provide useful physiological information on the coronary circulation in American patients.

Evaluation of flow in the left anterior descending coronary artery but not in the left internal mammary artery graft predicts significant stenosis of the arterial conduit

OBJECTIVES

The purpose of this study was to evaluate which Doppler-derived flow index best predicts new distal left anterior descending coronary artery (LAD) stenosis in patients with left internal mammary artery (LIMA) graft.

BACKGROUND

The LIMA flow measurement has been proposed to assess graft function, but it may be misleading in case of new distal LAD stenosis and/or competitive flow from native LAD. Distal LAD coronary flow reserve (CFR: hyperemic/baseline peak flow velocity ratio) may be more appropriate.

METHODS

The LIMA and distal LAD flow was measured by transthoracic Doppler echocardiography in 96 patients undergoing diagnostic/therapeutic coronary angiography, 7 +/- 4 years after cardiac bypass surgery. The LIMA flow indexes (systolic-to-diastolic peak velocity ratio [SDPVr] >1, diastolic time velocity integral fraction [DTVIf] <0.5, and CFR <2) and LAD CFR <2 were used to predict > or =70% new LAD stenosis.

RESULTS

The LAD CFR <2 predicted new LAD stenosis, found in 21 of 77 patients without competitive flow from native LAD, with significantly higher diagnostic accuracy (98%) than LIMA flow indexes (SDPVr >1 = 61%, DTVIf <0.5 = 69%, and CFR <2 = 72%). The LIMA flow indexes were abnormal in 17 of 19 patients with competitive graft flow, but only 5 had graft restriction, and none had significant LAD stenosis. In a multivariate model of new distal LAD stenosis prediction, competitive flow from native LAD reduced the predictive role of LIMA but not of LAD CFR.

CONCLUSIONS

In patients without competitive flow from native LAD, LAD CFR is more accurate for the detection of LAD stenosis than LIMA CFR. In patients with competitive graft flow, abnormal LIMA flow patterns and blunted LIMA CFR do not reflect downstream LAD flow as LAD CFR does.

Coronary flow reserve of the angiographically normal left anterior descending coronary artery in patients with remote coronary artery disease

Coronary artery disease (CAD) has been suggested to alter coronary flow reserve (CFR; the ratio between hyperemic and baseline coronary flow velocities) not only in territories supplied by stenotic arteries but also in angiographically normal, remote regions. However, few data exist regarding the left anterior descending (LAD) coronary artery as the normal index artery. The influence of remote CAD on CFR of the angiographically normal LAD was evaluated with transthoracic Doppler ultrasound to measure CFR in the LAD during 90 seconds of venous adenosine infusion (140 microg/kg/min) in 122 subjects who were assigned to 1 group; group 1 comprised 49 controls without angiographically detectable CAD, and group 2 consisted of 73 patients with an angiographically normal LAD and remote CAD. Group 2 was divided into 4 subgroups: 16 patients with previous remote percutaneous coronary intervention (group 2A); 13 patients with significant remote stenosis (group 2B); 23 patients with previous remote myocardial infarction and percutaneous coronary intervention (group 2C); and 21 patients with previous remote myocardial infarction but no percutaneous coronary intervention (group 2D). CFR in the LAD was not significantly different in groups 1 and 2 (3.08 +/- 0.61 and 3.03 +/- 0.69, respectively, p = NS). Decreased ejection fraction and increased wall motion score index in patients with remote CAD (p < 0.00001) and multivessel CAD did not affect CFR in the LAD (group 2A 3.18 +/- 0.77; group 2B 3.05 +/- 0.65; group 2C 3.07 +/- 0.79; group 2D 2.86 +/- 0.50, respectively; F = 0.63, p = NS). In conclusion, CFR of an angiographically normal LAD is preserved in patients with remote CAD, even in the presence of previous remote myocardial infarction and wall motion abnormalities.

Measurement of coronary flow velocity reserve in the posterior descending coronary artery by contrast-enhanced transthoracic Doppler echocardiography

BACKGROUND

Although the measurement of coronary flow velocity (CFV) reserve (CFVR) in the left anterior descending coronary artery (LAD) by transthoracic Doppler echocardiography has been established, its success rate in the posterior descending coronary artery (PD) is still limited.

OBJECTIVE

This study reports the feasibility and diagnostic accuracy of measuring CFVR in the PD by transthoracic Doppler echocardiography.

METHODS

CFVR in both the distal LAD and the PD was measured in 151 consecutive patients before coronary angiography. PD flow was investigated under the guidance of a nondirectional Doppler color flow map with harmonic imaging in the modified apical 2-chamber view. Intravenous contrast agent, Levovist, was injected to enhance the CFV envelope at baseline and during hyperemia.

RESULTS

CFVR was obtained in 145 patients in the LAD and 126 patients in the PD (P <.001). The success rate of CFVR measurement in the PD was significantly higher in the last 50 patients (88%) than it was in the first 50 patients (72%) (P <.05). CFVR in the PD was significantly lower for patients with significant stenosis of the artery supplying the PD than it was in those without stenosis (1.58 +/- 0.59 vs 2.45 +/- 0.72, P <.001). CFVR in the distal LAD was 1.40 +/- 0.62 in patients with significant LAD stenosis and 2.45 +/- 0.80 in those without stenosis (P <.001). If a cut-off value of CFVR < 2 was used, sensitivity, specificity, and accuracy for the diagnosis of significant (>50%) stenosis of the artery supplying the PD were 84%, 83%, and 83%, respectively, whereas for the LAD they were 91%, 75%, and 80%, respectively.

CONCLUSIONS

Noninvasive measurement of CFVR in the PD could be obtained in the majority of unselected patients using a nondirectional Doppler color flow map and contrast-enhanced harmonic imaging. The diagnostic accuracy of CFVR in the PD is similar to that of the LAD and, hence, has a potential clinical use.

Magnetic resonance phase velocity mapping through NiTi stents in a flow phantom model

PURPOSE

To assess constant and pulsatile flow velocity within the lumen of a peripheral NiTi stent using phase velocity mapping for comparison with independent assessments of flow velocity in a phantom model.

MATERIALS AND METHODS

A 9 x 20-mm stent installed in flexible tubing was placed in a phantom filled with stationary fluid. Constant and pulsatile flow (produced by a pump programmed to produce a simulation of the carotid artery flow) was assessed using phase velocity mapping at 4.1 T (for constant flow) and at 1.5 T (for pulsatile flow). In all cases 256 x 256 gradient echo phase velocity maps were acquired. For the pulsatile flow condition, cine images with acquisition gated to the pump cycle were acquired with 40 msec temporal resolution across the simulated cardiac cycle. Computed flow volume rates were compared with fluid volume collection for the constant flow model, and with ultrasonic Doppler flow meter measurements for the pulsatile model.

RESULTS

The data showed that volume flow rate assessments by phase velocity mapping agreed with independent measurements within 10% to 15%.

CONCLUSION

Phase velocity mapping of the lumen of peripheral size NiTi stents is possible in an in vitro model.

Emerging, noninvasive surrogate markers of atherosclerosis

Noninvasive surrogate markers of atherosclerosis allow the physician to identify subclinical disease before the occurrence of adverse cardiovascular events, thereby limiting the need to perform invasive diagnostic procedures. Imaging modalities, such as carotid artery ultrasound, two-dimensional echocardiography, coronary artery calcium imaging, cardiac magnetic resonance imaging, ankle-brachial indices, brachial artery reactivity testing, and epicardial coronary flow reserve measurements, provide information that may improve the predictive value of a person's risk of developing clinically significant atherosclerotic disease. Newer imaging modalities have also emerged to bring insight into the pathophysiology and treatment of atherosclerosis.

Usefulness of coronary flow reserve measured by transthoracic coronary Doppler ultrasound to detect severe left anterior descending coronary artery stenosis

Transthoracic coronary Doppler ultrasound during venous adenosine infusion showed damped (<1) coronary flow velocity reserve in patients with severe left anterior descending coronary artery stenosis. Damped coronary flow reserve discriminated severe from nonsevere stenosis with high sensitivity, specificity, and positive predictive accuracy, and is a unique noninvasive tool to identify high-risk patients.

Value of echocardiography in predicting future cardiac events after acute myocardial infarction

Short- and long-term survival after acute myocardial infarction mainly depends on three factors: the amount of myocardium that had become necrotic, the area of myocardium at further risk of becoming necrotic, and the patency of the infarct-related artery. Echocardiography is a low-cost, safe, bedside, repeatable tool, particularly useful for prognostic stratification after myocardial injury. Two-dimensional echocardiography analyzes left ventricular function, the most powerful predictor of survival immediately after acute myocardial infarction. Myocardial contrast echocardiography measures the infarct size and detects viable myocardium. Stress echocardiography stratifies patients with viable myocardium and/or multivessel coronary artery disease who need further diagnostic and therapeutic interventions. Transthoracic coronary Doppler ultrasonography assesses effective recanalization and coronary flow reserve of the left anterior descending coronary artery. Further technologic advances are needed to allow direct noninvasive measurement of flow by transthoracic Doppler ultrasonography in other coronary arteries.

Transthoracic Doppler echocardiography - noninvasive diagnostic window for coronary flow reserve assessment

This review focuses on transthoracic Doppler echocardiography as noninvasive method used to assess coronary flow reserve (CFR) in a wide spectrum of clinical settings. Transthoracic Doppler echocardiography is rapidly gaining appreciation as popular tool to measure CFR both in stenosed and normal epicardial coronary arteries (predominantly in left anterior descending coronary artery). Post-stenotic CFR measurement is helpful in: functional assessment of moderate stenosis, detection of significant or critical stenosis, monitoring of restenosis after revascularization. In the absence of stenosis in the epicardial coronary artery, decreased CFR enable to detect impaired microvascular vasodilatation in: reperfused myocardial infarct, arterial hypertension with or without left ventricular hypertrophy, diabetes mellitus, hypercholesterolemia, syndrome X, hypertrophic cardiomyopathy. In these diseases, noninvasive transthoracic Doppler echocardiography allows for serial CFR evaluations to explore the effect of various pharmacological therapies.