New noninvasive method for coronary flow reserve assessment: contrast-enhanced transthoracic second harmonic echo Doppler

Coronary microvascular dysfunction in autoimmune rheumatic diseases: beyond coronary flow velocity reserve

Autoimmune rheumatic diseases (ARDs) are a heterogeneous group of disorders characterized by an inappropriate immune reactivity against different body tissues. Patients affected by ARDs present increased cardiovascular morbidity and mortality, which significantly impacts long-term prognosis. Endothelial dysfunction, inflammation, oxidative stress, and autoimmunity are strictly involved in atherosclerosis progression and coronary microvascular dysfunction (CMD), both of which contribute to increased cardiovascular risk. CMD represents the inability of the coronary microvasculature to respond with vasodilation to increased cardiac metabolic demands and can be assessed by non-invasive and invasive imaging tests. Coronary flow velocity reserve assessed by echocardiography has been demonstrated to accurately identify ARDs patients with CMD. However, stress cardiac magnetic resonance (CMR) accurately assesses myocardial ischemia, perfusion, and viability in ARDs patients. The myocardial perfusion reserve index (MPRI) is a robust semiquantitative imaging marker that represents the vasodilatory capacity of the coronary microcirculation in response to a vasodilator stress. In the absence of significant coronary stenosis, ARDs patients revealed a reduced MPRI in comparison with the general population, regardless of the presence of myocardial fibrosis. Identification of CMD in asymptomatic patients could be crucial to precociously start targeted medical therapy, avoiding major adverse cardiac events in this clinical setting. This review aims to summarize the current evidence regarding CMD in ARDs patients, focusing on the role of stress CMR and the promising myocardial perfusion analysis.

Accelerated stenotic flow in the left anterior descending coronary artery explains the causes of impaired coronary flow reserve: an integrated transthoracic enhanced Doppler study

BACKGROUND

Accelerated stenotic flow (AsF) in the entire left anterior descending coronary artery (LAD), assessed by transthoracic enhanced color Doppler (E-Doppler TTE), can reveal coronary stenosis (CS) and its severity, enabling a distinction between the microcirculatory and epicardial causes of coronary flow reserve (CFR) impairment.

METHODS

Eighty-four consecutive patients with a CFR <2.0 (1.5 ± 0.4), as assessed by E-Doppler TTE, scheduled for coronary angiography (CA) and eventually intracoronary ultrasounds (IVUS), were studied. CFR was calculated by the ratio of peak diastolic flow velocities: during i.v. adenosine (140 mcg/Kg/m) over resting; AsF was calculated as the percentage increase of localized maximal velocity in relation to a reference velocity.

RESULTS

CA showed ≥50% lumen diameter narrowing of the LAD (critical CS) in 68% of patients (57/84) vs. non-critical CS in 32% (27/84). Based on the established CA/IVUS criteria, the non-critical CS subgroup was further subdivided into 2 groups: subcritical/diffuse [16/27 pts (57%)] and no atherosclerosis [11/27 pts (43%)]. CFR was similar in the three groups: 1.4 ± 0.3 in critical CS, 1.5 ± 0.4 in subcritical/diffuse CS, and 1.6 ± 0.4 in no atherosclerosis (p = ns). Overall, at least one segment of accelerated stenotic flow in the LAD was found in 73 patients (87%), while in 11 (13%) it was not. The AsF was very predictive of coronary segmental narrowing in both angio subgroups of atherosclerosis but as expected with the usage of different cutoffs. On the basis of the ROC curve, the optimal cutoff was 109% and 16% AsF % increment to successfully distinguish critical from non-critical CS (area under the curve [AUC] = 0.99, p < 0.001) and diffuse/subcritical from no CS (AUC = 0.91%, p < 0.001). Sensitivity and specificity were 96% and 100% and 82% and 100%, respectively.

CONCLUSION

E-Doppler TTE is highly feasible and reliable in detecting the CS of any grade of severity, distinguishing epicardial athero from microvascular causes of a severe CFR reduction.

Sympathetic control of the coronary circulation during trigeminal nerve stimulation in humans

PURPOSE

We sought to investigate the sympathetic mechanism controlling coronary circulation during trigeminal nerve stimulation in healthy women.

METHODS

The protocol consisted of 3 min of trigeminal nerve stimulation (TGS) with cold stimuli to the face, in two conditions: (1) control and β-blockade (oral propranolol), and (2) control and α-blockade (oral prazosin).

RESULTS

Thirty-one healthy young subjects (women: n = 13; men: n = 18) participated in the study. By design, TGS decreased heart rate (HR), and increased blood pressure (BP) and cardiac output (CO). Before the β-blockade coronary blood velocity (CBV-Δ1.4 ± 1.3 cm s-1) increased along with the decrease of coronary vascular conductance index (CVCi-Δ-0.04 ± 0.04 cm s-1 mmHg-1) during TGS and the β-blockade abolished the CBV increase and a further decrease of CVCi was observed with TGS (Δ-0.06 ± 0.07 cm s-1 mmHg-1). During the α-blockade condition before the blockade, the CBV increased (Δ0.93 ± 1.48 cm s-1) along with the decrease of CVCi (Δ-0.05 ± 1.12 cm s-1 mmHg-1) during TGS, after the α-blockade CBV (Δ0.98 ± cm s-1) and CVCi (Δ-0.03 ± 0.06 cm s-1 mmHg-1) response to TGS did not change.

CONCLUSION

Coronary circulation increases during sympathetic stimulation even with a decrease in heart rate.

Echocardiographic assessment of primary microvascular angina and primary coronary microvascular dysfunction

There is an increasing interest in the role of echocardiography in the evaluation of primary microvascular angina, which is attributed to primary coronary microvascular dysfunction. Valid echocardiographic techniques are expected to facilitate the diagnosis and follow-up of these patients and would be valuable for research purposes and therapy evaluation. However, adequate echocardiographic data are lacking, and the interpretation of the limited available literature is hindered by the previous addition of microvascular angina under more inclusive entities, such as cardiac syndrome X. In experienced hands, the assessment of primary coronary microvascular dysfunction in patients with suspected primary microvascular angina, using multiple echocardiographic techniques is feasible, relatively inexpensive, and safe. Exclusion of obstructive epicardial coronary artery disease is, however, a prerequisite for diagnosis. Two-dimensional transthoracic echocardiography, routine stress echocardiography, and speckle-tracking echocardiography indirectly assess primary coronary microvascular dysfunction by evaluating potential impairment in myocardial function and lack diagnostic sensitivity and specificity. Conversely, certain echocardiographic techniques, including Doppler-derived coronary flow velocity reserve and myocardial contrast echocardiography, assess some coronary microvascular dysfunction parameters and have exhibited diagnostic and prognostic potentials. Doppler-derived coronary flow velocity reserve is the best studied and only guideline-approved echocardiographic technique for documenting coronary microvascular dysfunction in patients with suspected microvascular angina. Myocardial contrast echocardiography, by comparison, can detect heterogeneous and patchy myocardial involvement by coronary microvascular dysfunction, which is an advantage over the common practice of coronary flow velocity reserve assessment in a single vessel (commonly the left anterior descending artery) which only reflects regional microvascular function. However, there is no consensus regarding the diagnostic criteria, and expertise performing this technique is limited. Echocardiography remains underexplored and inadequately utilized in the setting of microvascular angina and coronary microvascular dysfunction. Appraisal of the current echocardiographic literature regarding coronary microvascular dysfunction and microvascular angina is important to stay current with the progress in its clinical recognition and create a basis for future research and technological advancements.

Assessment of the Severity of Left Anterior Descending Coronary Artery Stenoses by Enhanced Transthoracic Doppler Echocardiography: Validation of a Method Based on the Continuity Equation

BACKGROUND

To verify whether the severity of coronary stenosis could be non-invasively assessed by enhanced transthoracic coronary echo Doppler in convergent color Doppler mode (E-Doppler TTE) over a wide range of values (from mild to severe).

METHODS

Color-guided pulsed wave Doppler sampling in the left anterior descending coronary artery (LAD) was performed in 103 diseased LAD segments (corresponding to 94 patients examined) as assessed by quantitative coronary angiography (QCA) or intracoronary ultrasound (IVUS). The E-Doppler TTE examinations consisted of measuring the velocity (vel) at the stenosis site and a reference adjacent segment. Then the continuity equation (C-Eq) was applied to calculate the percent cross-sectional area reduction (%CSA) at the stenosis site. The applied formula was: %CSA = 100 × (1 - [TVIref × 0.5]/TVIs). TVI = the time velocity integral at the stenosis [s] and the reference site [ref], respectively); 0.5 = the correcting factor for a parabolic profile was used only when the % accelerated stenotic flow was >122% (AsF = diastolic peak vel at first site - diastolic peak vel at second site/diastolic peak vel at second site × 100).

RESULTS

E-Doppler TTE feasibility was 100%. Doppler and QCA/IVUS-derived %CSA stenosis showed very good agreement over a large range of values (from mild to severe), with no significant bias; the maximum difference between QCA/IVUS and transthoracic Doppler %CSA was mostly around 20% with a few patients exceeding this limit (limits of agreement = -27.53 to 23.5%). The scattering was slightly larger for the non-significant stenoses. The correlation was strong (r = 0.89, p < 0.001).

CONCLUSION

E-Doppler TTE is a feasible and reliable method for assessing the severity of LAD stenosis by applying the C-Eq.

Heart Rate Lowering Significantly Increases Feasibility in Doppler Recording Blood Flow Velocity in Coronaries during Transthoracic Doppler Echocardiography

Background: Coronary blood flow Doppler recording by Transthoracic Doppler in convergent mode (E-Doppler TTE) might be further improved by lowering heart rate (HRL) down to <60 bpm, since low HR < 60 b/m causes a disproportional lengthening of the diastole, so the coronaries are still for a longer time, very much improving the Doppler signal/noise ratio. Methods: A group of 26 patients underwent E-Doppler TTE before and after HR lowering in four branches of the coronary tree, namely, the left main (LMCA); left anterior descending (LAD), subdivided into three segments: proximal, mid and distal; proximal left circumflex (LCx); and obtuse marginal (OM). Color and PW coronary Doppler signal was judged by two expert observers as undetectable (SCORE 1), weak or with clutter artifacts (SCORE 2), or well delineated (SCORE 3). In addition, local accelerated stenotic flow (AsF) was measured in the LAD before and after HRL. Results: Beta-blockers significantly decreased the mean HR from 76 ± 5 to 57 ± 6 bpm (p < 0.001). Before HRL, the Doppler quality was very poor in the proximal and mid-LAD segments (median score value = 1 in both), while in the distal LAD, it was significantly better but still suboptimal (median score value = 1.5, p = 0.009 vs. proximal and mid-LAD score). After HRL, blood flow Doppler recording in the three LAD segments was strikingly improved (median score value = 3, 3 and 3, p = ns), so the effect of HRL was more efficacious in the two more proximal LAD segments. In 10 patients undergoing coronary angiography (CA), no AsF as expression of transtenotic velocity was detected at baseline. After HRL, thanks to the better quality and length of color flow, ASF was detected in five patients while in five others, it was not in perfect agreement with CA (Spearman correlation coefficient = 1, p < 0.01). The color flow in the proximal LCx and OM was extremely poor at baseline (color flow length 0 and 0, median (interquartile range) mm, respectively) and improved considerably after HRL (color flow length 23 [13.5] and 25 [12.0] mm, respectively, p < 0.001). Conclusions: HRL greatly improved the success rate of blood flow Doppler recording in coronaries, not only in the LAD, but also in the LCx. Therefore, AsF for stenosis detection and coronary flow reserve assessment can have wider clinical applications. However, further studies with larger samples are needed to confirm these results.

Coronary Flow Velocity Reserve by Echocardiography: Beyond Atherosclerotic Disease

Coronary flow velocity reserve (CFVR) is defined as the ratio between coronary flow velocity during maximal hyperemia and coronary flow at rest. Gold-standard techniques to measure CFVR are either invasive or require radiation and are therefore inappropriate for large-scale adoption. More than 30 years ago, echocardiography was demonstrated to be a reliable tool to assess CFVR, and its field of application rapidly expanded. Although initially validated to assess the hemodynamic relevance of a coronary stenosis, CFVR by echocardiography was later used to investigate coronary microcirculation. Microvascular dysfunction was detected in many different conditions, ranging from organ transplantation to inflammatory disorders and from metabolic diseases to cardiomyopathies. Moreover, it has been proven that CFVR by echocardiography not only detects coronary microvascular involvement but is also an effective prognostic factor that allows a precise risk stratification of the patients. In this review, we will summarize the many applications of CFVR by echocardiography, focusing on the coronary involvement of systemic diseases.

Hidden Coronary Atherosclerosis Assessment but Not Coronary Flow Reserve Helps to Explain the Slow Coronary Flow Phenomenon in Patients with Angiographically Normal Coronary Arteries

The significance of the slow coronary flow phenomenon (SCFph), as visualized in patients (pts) with angiographically normal coronary arteries, is controversial. Absolute coronary flow reserve (CFR) in the left anterior descending coronary artery (LAD), non-invasively assessed by a transthoracic color-guided pulsed-wave Doppler (E-Doppler TTE), is a reliable parameter to assess coronary microcirculatory dysfunction (CMD). Mild and angiographically hidden epicardial atherosclerosis (Hath), as visualized by intracoronary ultrasound (IVUS), which could be the clue to atherosclerotic coronary microvascular involvement, has never been investigated together with CFR in patients. This study was aimed at assessing the value of CFR and HA in explaining the SCFph. Methods. Both non-invasive assessment of CFR in the LAD and corrected TIMI frame count assessment of the coronary contrast runoff were performed in 124 pts with angiographically normal coronary arteries. Among the whole group, 32 patients also underwent intracoronary ultrasounds in the LMCA and LAD, and the maximal plaque burden was assessed (Lesion external elastic (EEM) cross sectional area (CSA)—Lesion Lumen CSA/Lesion EEM CSA * 100). We found that 24 of the 124 pts (group 1) had the SCFph and the remaining 100 had a normal runoff (group 2). CFR, evaluated in both groups, was not significantly different, being 2.79 ± 0.79 (Mean ± SD) in group 1 and 2.90 ± 0.8 in group 2 (p = ns); in the pts also examined by IVUS (32 pts), the SCFph was always associated with hidden atherosclerosis, and a plaque burden of ≥33%. On the contrary, in the normal runoff group, any grade of PB was observed (from no athero to a PB > 70%) and remarkably, 10 pts had no signs of athero or just a minimal plaque burden. This resulted in a ROC curve analysis in which PB < 33% had a high negative predictive value (100%) in ruling out the SCFph. In addition, considering a CFR value < 2.21 as an index of coronary microcirculatory dysfunction, we found CMD in 15 pts (15%) in group 1 and in 7 pts (29%) in group 2 (p = ns). In conclusion, the SCFph is strongly connected to epicardial athero to the extent that the absence of hidden coronary athero has a very high negative predictive power in ruling out SCFph. CFR that is based on an endothelium-independent mechanism remains fairly normal in this condition. An endothelium-dependent microcirculatory constriction at rest due to atherosclerotic involvement of the coronary microvascular network is a possible explanation of the SCFph.

Coronary Flow Evaluation in Heart Transplant Patients Compared to Healthy Controls Documents the Superiority of Coronary Flow Velocity Reserve Companion as Diagnostic and Prognostic Tool

Background

Distinct contributions by functional or structural alterations of coronary microcirculation in heart transplantation (HT) and their prognostic role have not been fully elucidated. We aimed to identify the mechanisms of coronary microvascular dysfunction (CMD) in HT and their prognostic implications.

Methods

134 patients, surviving at least 5 years after HT, without evidence of angiographic vasculopathy or symptoms/signs of rejection were included. 50 healthy volunteers served as controls. All underwent the assessment of rest and hyperemic coronary diastolic peak flow velocity (DPVr and DPVh) and coronary flow velocity reserve (CFVR) and its inherent companion that is based on the adjusted quadratic mean: CCFVR = √{(DPVr)2 + (DPVh)2}. Additionally, basal and hyperemic coronary microvascular resistance (BMR and HMR) were estimated.

Results

Based on CFVR and DPVh, HT patients can be assigned to four endotypes: endotype 1, discordant with preserved CFVR (3.1 ± 0.4); endotype 2, concordant with preserved CFVR (3.4 ± 0.5); endotype 3, concordant with impaired CFVR (1.8 ± 0.3) and endotype 4, discordant with impaired CFVR (2.0 ± 0.2). Intriguingly, endotype 1 showed lower DPVr (p &lt; 0.0001) and lower DPVh (p &lt; 0.0001) than controls with lower CFVR (p &lt; 0.0001) and lower CCFVR (p &lt; 0.0001) than controls. Moreover, both BMR and HMR were higher in endotype 1 than in controls (p = 0.001 and p &lt; 0.0001, respectively), suggesting structural microvascular remodeling. Conversely, endotype 2 was comparable to controls. A 13/32 (41%) patients in endotype 1 died in a follow up of 28 years and mortality rate was comparable to endotype 3 (14/31, 45%). However, CCFVR was &lt; 80 cm/s in all 13 deaths of endotype 1 (characterized by preserved CFVR). At multivariable analysis, CMD, DPVh &lt; 75 cm/s and CCFVR &lt; 80 cm/s were independent predictors of mortality. The inclusion of CCFVR &lt; 80 cm/s to models with clinical indicators of mortality better predicted survival, compared to only adding CMD or DPVh &lt; 75 cm/s (p &lt; 0.0001 and p = 0.03, respectively).

Conclusion

A normal CFVR could hide detection of microvasculopathy with high flow resistance and low flow velocities at rest. This microvasculopathy seems to be secondary to factors unrelated to HT (less rejections and more often diabetes). The combined use of CFVR and CCFVR provides more complete clinical and prognostic information on coronary microvasculopathy in HT.

Coronary microvascular disease: The "Meeting Point" of Cardiology, Rheumatology and Endocrinology

BACKGROUND

Exertional chest pain/dyspnea or chest pain at rest are the main symptoms of coronary artery disease (CAD), which are traditionally attributed to insufficiency of the epicardial coronary arteries. However, 2/3 of women and 1/3 of men with angina and 10% of patients with acute myocardial infarction have no evidence of epicardial coronary artery stenosis in X-ray coronary angiography. In these cases, coronary microvascular disease (CMD) is the main causative factor.

AIMS

To present the pathophysiology of CMD in Cardiology, Rheumatology and Endocrinology.

MATERIALS-METHODS

The pathophysiology of CMD in Cardiology, Rheumatology and Endocrinology was evaluated. It includes impaired microvascular vasodilatation, which leads to inability of the organism to deal with myocardial oxygen needs and, hence, development of ischemic pain. CMD, observed in inflammatory autoimmune rheumatic and endocrine/metabolic disorders, brings together Cardiology, Rheumatology and Endocrinology. Causative factors include persistent systemic inflammation and endocrine/metabolic abnormalities influencing directly the coronary microvasculature. In the past, the evaluation of microcirculation was feasible only with the use of invasive techniques, such as coronary flow reserve assessment. Currently, the application of advanced imaging modalities, such as cardiovascular magnetic resonance (CMR), can evaluate CMD non-invasively and without ionizing radiation.

RESULTS

CMD may present with a variety of symptoms with 1/3 to 2/3 of them expressed as typical chest pain in effort, more commonly found in women during menopause than in men. Atypical presentation includes chest pain at rest or exertional dyspnea,but post exercise symptoms are not uncommon. The treatment with nitrates is less effective in CMD, because their vasodilator action in coronary micro-circulation is less pronounced than in the epicardial coronary arteries.

DISCUSSION

Although both classic and new medications have been used in the treatment of CMD, there are still many questions regarding both the pathophysiology and the treatment of this disorder. The potential effects of anti-rheumatic and endocrine medications on the evolution of CMD need further evaluation.

CONCLUSION

CMD is a multifactorial disease leading to myocardial ischemia/fibrosis alone or in combination with epicardial coronary artery disease. Endothelial dysfunction/vasospasm, systemic inflammation, and/or neuroendocrine activation may act as causative factors and bring Cardiology, Rheumatology and Endocrinology together. Currently, the application of advanced imaging modalities, and specifically CMR, allows reliable assessment of the extent and severity of CMD. These measurements should not be limited to "pure cardiac patients", as it is known that CMD affects the majority of patients with autoimmune rheumatic and endocrine/metabolic disorders.

Wellens' Syndrome from COVID-19 Infection Assessed by Enhanced Transthoracic Coronary Echo Doppler: A Case Report

Wellens' syndrome (WS) is a preinfarction state caused by a sub-occlusion of the proximal left anterior descending coronary artery (LAD). In this case report, for the first time, we describe how this syndrome can be caused by COVID-19 infection and, most importantly, that it can be assessed bedside by enhanced transthoracic coronary echo Doppler (E-Doppler TTE). This seasoned technique allows blood flow Doppler to be recorded in the coronaries and at the stenosis site but has never been tested in an acute setting. Two weeks after clinical recovery from bronchitis allegedly caused by COVID-19 infection on the basis of epidemiologic criteria (no swab performed during the acute phase but only during recovery, at which time it was negative), our patient developed typical angina for the first time, mainly during effort but also at rest. He was admitted to our tertiary center, where pharyngeal swabs tested positive for COVID-19. A typical EKG finding supporting WS prompted an assessment of the left main coronary artery (LMCA) and the whole LAD blood flow velocity by E-Doppler TTE. Localized high velocity (transtenotic velocity) (100 cm/s) was recorded in the proximal LAD, with the reference velocity being 20 cm/s. This indicated severe stenosis with 90% area narrowing according to the continuity equation, as confirmed by coronary angiography. During follow-up after successful stenting, E-Doppler TTE showed a decrease in the transtenotic acceleration, confirming stent patency and a normal coronary flow reserve (3.2) and illustrating a normal microcirculatory function. Conclusion: COVID infection can trigger a coronary syndrome like WS. E-Doppler TTE, an ionizing radiation-free method, allows safe and rapid bedside management of the syndrome. This new strategy can be pivotal in distinguishing true WS from pseudo-WS. In cases of pseudo-WS, coronary angiography can be avoided. If E-Doppler TTE confirms the stenosis and PCI (percutaneous coronary intervention) is performed, the same method can allow assessment over time of the precise residual stenosis after stenting and verify the microvasculature status by evaluating coronary flow reserve.

Coronary Flow Velocity Reserve Using Dobutamine Test for Noninvasive Functional Assessment of Myocardial Bridging

Background: It has been shown that coronary flow velocity reserve (CFVR) measurement by transthoracic Doppler echocardiography (TTDE) during dobutamine (DOB) provocation provides a more accurate functional evaluation of myocardial bridging (MB) compared to adenosine. However; the cut-off value of CFVR during DOB for identification of MB associated with myocardial ischemia has not been fully clarified. Purpose: This prospective study aimed to determine the cut-off value of TTDE-CFVR during DOB in patients with isolated-MB, as compared with stress-induced wall motion abnormalities (VMA) during exercise stress-echocardiography (SE) as reference. Methods: Eighty-one symptomatic patients (55 males [68%], mean age 56 ± 10 years; range: 27–74 years) with the existence of isolated-MB on the left anterior descending artery (LAD) and systolic MB-compression ≥50% diameter stenosis (DS) were eligible to participate in the study. Each patient underwent treadmill exercise-SE, invasive coronary angiography, and TTDE-CFVR measurements in the distal segment of LAD during DOB infusion (DOB: 10–40 μg/kg/min). Using quantitative coronary angiography, both minimal luminal diameter (MLD) and percent DS at MB-site at end-systole and end-diastole were determined. Results: Stress-induced myocardial ischemia with the occurrence of WMA was found in 23 patients (28%). CFVR during peak DOB was significantly lower in the SE-positive group compared with the SE-negative group (1.94 ± 0.16 vs. 2.78 ± 0.53; p < 0.001). ROC analyses identified the optimal CFVR cut-off value ≤ 2.1 obtained during high-dose dobutamine (>20 µg/kg/min) for the identification of MB associated with stress-induced WMA, with a sensitivity, specificity, positive and negative predictive value of 96%, 95%, 88%, and 98%, respectively (AUC 0.986; 95% CI: 0.967–1.000; p < 0.001). Multivariate logistic regression analysis revealed that MLD and percent DS, both at end-diastole, were the only independent predictors of ischemic CFVR values ≤2.1 (OR: 0.023; 95% CI: 0.001–0.534; p = 0.019; OR: 1.147; 95% CI: 1.042–1.263; p = 0.005; respectively). Conclusions: Noninvasive CFVR during dobutamine provocation appears to be an additional and important noninvasive tool to determine the functional severity of isolated-MB. A transthoracic CFVR cut-off ≤2.1 measured at a high-dobutamine dose may be adequate for detecting myocardial ischemia in patients with isolated-MB.

Sympathetic regulation of coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in men

NEW FINDINGS

What is the central question of this study? What is the role of β- and α-adrenergic receptors in the control of the coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in humans? What is the main finding and its importance? β-Adrenergic receptor, but not α-adrenergic receptor, blockade significantly blunted the increases in coronary blood velocity observed during handgrip. Coronary blood velocity was unchanged from baseline during isolated muscle metaboreflex activation. This highlights the important role of β-adrenergic receptors in the coronary circulation during handgrip in humans, and the more limited involvement of the α-adrenergic receptors.

ABSTRACT

We sought to investigate the role of β- and α-adrenergic receptors in coronary circulation during static handgrip exercise and isolated muscle metaboreflex activation in humans. Seventeen healthy young men underwent two experimental sessions, consisting of 3 min of static handgrip exercise at a target force of 40% maximum voluntary force (not achieved for the full 3 min), and 3 min of metaboreflex activation (post-exercise ischaemia) in two conditions: (1) control and β-blockade (oral propranolol), and (2) control and α-blockade (oral prazosin). In both sessions, coronary blood velocity (CBV, echocardiography) was increased during handgrip (Δ8.0 ± 7.4 cm s^-1 ) but unchanged with metaboreflex activation (Δ2.5 ± 3.2 cm s^-1 ) under control conditions. β-Blockade abolished the increase in CBV during handgrip, while CBV was unchanged from control with α-blockade. Cardiac work, estimated from rate pressure product (RPP; systolic blood pressure multiplied by heart rate), increased during handgrip and metaboreflex in control conditions in both sessions. β-Blockade reduced RPP responses to handgrip and metaboreflex, whereas α-blockade increased RPP, but the responses to handgrip and metaboreflex were unchanged. CBV and RPP were only significantly correlated during handgrip under control (r = 0.71, P < 0.01) and β-blockade (r = 0.54, P = 0.03) conditions, and the slope of this relationship was unaltered with β-blockade. Collectively, these findings indicate that β-adrenergic receptors play the primary role to the increase of coronary circulation during handgrip exercise, but CBV is unchanged with metaboreflex activation, while α-adrenergic receptor stimulation seems to exert no effect in the control of the coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in humans.

A new noninvasive method for assessing mild coronary atherosclerosis: transthoracic convergent color Doppler after heart rate reduction. Validation vs. intracoronary ultrasound

BACKGROUND

A more sensitive transthoracic color Doppler technology (convergent color Doppler), along with a heart rate (HR) reduction and new tomographic planes, can greatly improve coronary blood flow velocity (BFV) recordings in the left main (LMCA) and left anterior descending (LAD) coronary arteries, allowing the detection of even a slight acceleration of BFV due to mild coronary stenosis.

METHODS

A group of 26 patients underwent convergent color Doppler transthoracic echocardiography (CC-Doppler TTE) in the LMCA and in the LAD coronary arteries before and after HR lowering. A second group of 71 patients scheduled for intravascular ultrasound, expanded to 96 with 25 more patients with normal LAD (by angiography/low likelihood of disease), underwent BFV Doppler recordings by CC-Doppler TTE of the whole LAD (specifically the proximal, mid and distal segments) to detect a localized increase in BFV, after attaining maximal and reference BFV in each segment.

RESULTS

In the first group, HR reduction dramatically improved the detection of optimal flow in the LMCA and LAD, from 4 to 54% and from 6 to 94% of the segments, respectively (P < 0.001). In the second group intravascular ultrasonography (IVUS) showed mild stenoses in 60 patients. The maximum velocity was higher in the diseased segment than normal segments (49 ± 24 vs. 33 ± 11 cm/s; P < 0.001) and as the reference velocity was similar (32 ± 9 vs. 33 ± 11 cm/s; P = ns), the % increase was also higher (52 ± 52 vs. 0.7 ± 3%; P < 0.001). Using a >21% increase in velocity as a cutoff value, the sensitivity and specificity of CC-Doppler TTE in detecting at least one LAD plaque were 87% (52/60 patients [pts]) and 100% (36/36 pts), respectively.

CONCLUSION

CC-Doppler TTE evaluation of LAD BFV is greatly improved after reducing HR, allowing accurate noninvasive assessment of mild LAD stenosis with no radiation exposure.

Effect of Rosuvastatin on Coronary Flow Reserve in Hypertensive Patients at Cardiovascular Risk

BACKGROUND

It has been unclear whether statin therapy directly improves coronary flow reserve (CFR) in hypertensive patients at cardiovascular risk, independent of lifestyle modification and antihypertensive medications.

METHODS

In this double-blind, randomized controlled trial, we randomly assigned 95 hypertensive patients at cardiovascular risk to receive either rosuvastatin 10 mg or placebo for 12 months, in addition to antihypertensive therapy and lifestyle modification for hypercholesterolemia. Using Doppler echocardiography, coronary flow velocity in the distal left anterior descending artery was measured and CFR was calculated as the ratio of hyperemic to basal averaged peak diastolic flow velocity. The primary end point was change in CFR from baseline to 12 months follow-up.

RESULTS

Low-density lipoprotein-cholesterol was changed from 157 ± 23 to 84 ± 16 mg/dL in the rosuvastatin group (p < 0.001) and from 152 ± 19 to 144 ± 22 mg/dL in the control group (p = 0.041, but there were no significant differences between the treatment groups in the changes in C-reactive protein, high-density lipoprotein cholesterol, and blood pressures. CFR was changed from 3.03 ± 0.44 to 3.25 ± 0.49 in the rosuvastatin group (p < 0.001) and from 3.15 ± 0.54 to 3.17 ± 0.56 in the control group (p = 0.65). The primary end point of change in CFR was significantly different between the rosuvastatin group and the control group (0.216 ± 0.279 vs. 0.015 ± 0.217; p < 0.001).

CONCLUSIONS

Compared with lifestyle modification alone, addition of rosuvastatin significantly improved CFR in hypertensive patients at cardiovascular risk.

Human coronary inflammation by computed tomography: Relationship with coronary microvascular dysfunction

Background A new imaging metric using coronary computed tomography angiography (CCTA), addressing the peri-coronary adipose tissue (PCAT) computed tomography (CT) attenuation, has been clinically validated. This method provides information regarding coronary inflammation. It is unclear how coronary inflammation affects microvascular function. The non-invasive evaluation of coronary flow velocity reserve is widely used in clinical practice using Doppler measurement on the left anterior descending coronary artery (CFVR-lad) during stress-echocardiography (SE). We hypothesize that coronary inflammation affects CFVR-lad and, in the absence of overt CAD, they are significantly correlated. Methods We evaluated the relationship between coronary inflammation (by PCAT CT attenuation) and coronary microvascular function (by CFVR-lad) in subjects with no or non-obstructive (diameter stenosis <70%) coronary artery disease (CAD). Results Two-hundred and two subjects were enrolled in the study. The relationship between PCAT CT attenuation and CFVR-lad show a significant inverse relationship in the entire group of subjects enrolled in the study (r = -0.32, p < 0.001). Correlation between PCAT CT attenuation and CFVR-lad was significant in subjects with no or mild CAD-lad, while this was not the case in subjects with intermediate CAD-lad. The R and R² were respectively -0.40, -0.16 in subjects without CAD (p < 0.001) and - 0.35 and - 0.12 in subjects with mild CAD-lad (p = 0.001). Conclusions The main finding of the current study is the independent relationship between coronary microvascular function, by Doppler CFVR-lad during SE, in subjects without severely obstructive CAD in the left anterior descending coronary artery, and the level of local coronary inflammation, by PCAT attenuation measurement on CCTA.

Feasibility and Utility of Adenosine Stress Echocardiography in Children Following Post-Arterial Switch Operation: A Comparison with Technetium 99m-Sestamibi Myocardial Perfusion SPECT (MPS)

There is a need for a sensitive, safe, and cost-effective tool for coronary assessment among asymptomatic post-operative children who have undergone arterial switch operation (ASO) for transposition of great arteries (TGA). Adenosine stress echocardiography may be useful in assessing major structures as well for coronary functional assessment. Twenty-six children [median age 6.0 years; IQR 4.9-7.1 years, (22 boys)], who had undergone ASO at a median age of 40 days (IQR 30-75 days), were prospectively included. Left ventricular ejection fraction (LVEF) was calculated in both rest and stress studies (140 µg/kg/min of adenosine IV over 4 min), along with assessment of regional myocardial wall motion. Coronary flow reserve (CFR) was also measured in the left anterior descending artery (LAD). Technetium 99m-MIBI [0.2mCi/kg] was injected after 2 min of adenosine infusion. Adenosine infusion had to be stopped in two children, due to transient atrioventricular (AV) block. The LVEF increased from 55.87 ± 7.27 to 61.20 ± 7.70% (p  < 0.001) with adenosine stress. No significant regional wall motion abnormality was seen in rest or stress. Distal LAD could not be visualized in four patients. Basal and peak coronary flow velocities were 41.51 ± 14.12 and 74.18 ± 6.01 cm/s. Mean CFR was 1.91 ± 0.51. Myocardial perfusion scintigraphy (MPS) was normal in all the patients. Four patients were lost to follow-up and remaining children did not develop any adverse events in the follow-up period of 64.5 ± 7.19 months. Adenosine stress echocardiography is feasible as the initial screening test in the assessment of asymptomatic post-operative children with ASO, at minimal to no inconvenience to the patient. The findings concurred with stress MPS.

Coronary Flow and Reserve by Enhanced Transthoracic Doppler Trumps Coronary Anatomy by Computed Tomography in Assessing Coronary Artery Stenosis

We report the case of a 71-year-old patient with many risk factors for coronary atherosclerosis, who underwent computed coronary angiography (CTA), in accordance with the guidelines, for recent onset atypical chest pain. CTA revealed critical (>50% lumen diameter narrowing) stenosis of the proximal anterior descending coronary, and the patient was scheduled for invasive coronary angiography (ICA). Before ICA he underwent enhanced transthoracic echo-Doppler (E-Doppler TTE) for coronary flow detection by color-guided pulsed-wave Doppler recording of the left main (LMCA) and whole left anterior descending coronary artery (LAD,) along with coronary flow reserve (CFR) in the distal LAD calculated as the ratio, of peak flow velocity during i.v. adenosine (140 mcg/Kg/m) to resting flow velocity. E-Doppler TTE mapping revealed only mild stenosis (28% area narrowing) of the mid LAD and a CFR of 3.20, in perfect agreement with the color mapping showing no flow limiting stenosis in the LMCA and LAD. ICA revealed only a very mild stenosis in the mid LAD and mild atherosclerosis in the other coronaries (intimal irregularities). Thus, coronary stenosis was better predicted by E-Doppler TTE than by CTA. Coronary flow and reserve as assessed by E-Doppler TTE trumps coronary anatomy as assessed by CTA, without exposing the patient to harmful radiation and iodinated contrast medium.

Inflammation and Coronary Microvascular Dysfunction in Autoimmune Rheumatic Diseases

Autoimmune rheumatic diseases (ARDs) form a heterogeneous group of disorders that include systemic lupus erythematosus (SLE), systemic sclerosis (SSc), rheumatoid arthritis (RA), idiopathic inflammatory myopathies (IIMs), and systemic vasculitis. Coronary microvascular dysfunction (CMD) is quite common in patients with ARDs and is linked to increased cardiovascular morbidity and mortality. Inflammation plays a crucial role in the pathogenesis of both accelerated atherosclerosis and CMD in ARDs, especially in patients affected by SLE and RA. In this regard, some studies have highlighted the efficacy of immunosuppressants and/or biologics in restoring CMD in these patients. By contrast, the role of inflammation in the pathogenesis of CMD-SSc appears to be much less relevant compared to endothelial dysfunction and microvascular ischemia, with calcium-channel blockers providing some benefits. Few studies have endeavored to assess the occurrence of CMD in IIMs and systemic vasculitis, thus warranting further investigations. The present review summarizes the current evidence on the occurrence of CMD in ARDs, focusing on the role of inflammation and possible therapeutic approaches.

Assessing Coronary Microvascular Dysfunction in Ischaemic Heart Disease: Little Things Can Make a Big Difference

The role of coronary microvascular dysfunction (CMD) in the pathogenesis of ischaemic heart disease and in determining long-term prognosis is increasingly recognised. In selected patients, a comprehensive coronary assessment including an assessment of microvascular function may help refine risk stratification and improve patient outcomes. Various non-invasive and invasive techniques have been developed to assess the coronary microcirculation. Many of these tests utilise the indicator-dilution principle to determine coronary or myocardial blood flow. However, these techniques are often limited by their variability and lack of specificity for the coronary microvasculature. Consequently, there is still paucity of data on targeted therapies for CMD and their implications on long-term clinical outcomes, particularly in the setting of non-ST elevation acute coronary syndromes. Recent technical advancements, such as the index of microcirculatory resistance, have largely overcome these limitations and are able to provide novel insights into the assessment and treatment of CMD. This review summarises the currently available techniques for the assessment of CMD and provides an overview of its clinical implications.

Association of coronary artery Doppler-echocardiography diastolic-systolic velocity ratio at rest with obstructive coronary artery stenosis on the left main or left anterior descending coronary artery

BACKGROUND

We assessed whether the non-invasive measure of peak diastolic-systolic velocity ratio (rDSVR) at rest on the left anterior descending artery (LAD) using Doppler transthoracic echocardiography is associated with obstructive coronary artery disease (CAD) on the LAD and left main (LM) arteries. We compared rDSVR diagnostic accuracy with stress wall motion (WM) and coronary flow reserve (CFR-LAD), in a group of subjects who underwent contrast stress-echocardiography (cSE) and coronary angiography within 3 months.

METHODS

286 patients selected with a clinical indication to cSE, in which CFR-LAD was measured during the test who also underwent coronary angiography within 3 months were selected and diagnostic performance compared.

RESULTS

Demographics and clinical variables were univariate predictors of LAD or LM >50% stenosis, but rDSVR < 1.7 outperformed other variables (OR 11.18, 95% CI 5.82-21.49, p < 0.001), comprising cSE variables such as reversible WM abnormalities (OR 1.53, 95% CI 0.94-2.49, p = 0.087) or CFR-LAD < 2 (OR 2.88, 95% CI 21.74-4.77, p < 0.001). The addition of rDSVR to multivariate logistic regression models (clinical or clinical + cSE variables) led to a marked increase in C-index (0.82, 95%CI 0.78-0.87) with significant improvement compared to all prior models (p < 0.001).

CONCLUSIONS

Our data suggest a strict association of reduced rDSVR with >50% coronary artery stenosis on the LM/LAD, superior to other standard clinical or cSE related indexes, such as WM assessment or CFR-LAD, and builds incrementally to them and clinical variables in multivariable logistic models for the prediction of CAD on LM and LAD coronaries.

Nailfold avascular score and coronary microvascular dysfunction in systemic sclerosis: A newsworthy association

BACKGROUND AND AIMS

We aimed to assess the relationship between nailfold videocapillaroscopy (NVC) abnormalities and coronary flow reserve (CFR), a marker of coronary microvascular dysfunction (CMD) in patients with systemic sclerosis (SSc).

METHODS

We studied 39 SSc patients (33 females, mean ± SD age 54 ± 12 years, median disease duration 11 years, range 6-22) and 22 controls (matched for age and sex) without any evidence of cardiovascular disease. Clinical assessment was performed by modified Rodnan skin score (mRss) and EUSTAR score. Coronary flow velocities in the left anterior descending coronary artery were measured by transthoracic echocardiography. Average peak flow velocities, CFR and microvascular resistance at baseline (BMR) and in hyperaemic (HMR) condition were assessed. CFR ≤2.5 was considered marker of CMD. Six NVC-abnormalities were evaluated by a semi quantitative scoring system: enlarged and giant capillaries (diameter > 20 μm and >50 μm, respectively), hemorrhages, disarray, capillary ramifications and loss of capillaries (avascular score). Statistic was performed using SPSS.

RESULTS

CFR was lower in SSc patients than in controls (2.6 ± 0.5 vs 3.3 ± 0.5). CMD was detected in 24 patients (61.5%) vs 0 controls (p < .0001). CFR was inversely correlated with NVC-avascular score (rho =-0.750, p < .0001). Avascular and capillary ramifications scores (p = .001 and p = .03, respectively), mRss (p = .003) and EUSTAR score (p = .01) were higher in patients with CMD than in those without. At multivariable analysis, avascular score was independently associated with CMD (p = .01). HMR was directly correlated with avascular score (rho = 0.416, p = .008).

CONCLUSIONS

In our SSc patients NVC-avascular score was associated with CMD which seems to be the result of a structural microvascular remodeling.

Prognostic value of proximal left coronary artery flow velocity detected by transthoracic Doppler echocardiography

BACKGROUND

Lesions in the proximal left coronary artery (LCA) are associated with a poor prognosis compared with other lesional sites. Transthoracic Doppler echocardiography (TTDE) can help to detect proximal LCA flow, and an accelerated coronary flow velocity (CFV) indicates the presence of proximal LCA lesions. This study aimed to investigate the prognostic value of CFV in the proximal LCA measured by TTDE.

METHODS

We enrolled 1472 consecutive hemodynamically stable patients with known or suspected heart disease whose CFV was successfully detected using TTDE accompanied by routine echocardiography between 2008 and 2011. The primary outcome was cardiac death (acute myocardial infarction, heart failure, or sudden cardiac death) and patients were followed up over a median of 6.3 years.

RESULTS

Overall, 42 cardiac deaths (3%) were observed. An increased CFV was significantly associated with the outcome in several models based on potential confounders (age, rate pressure product, Framingham Risk Score, diabetes, coronary artery disease, hemoglobin, brain natriuretic peptide, estimated glomerular filtration rate, left ventricular mass, left ventricular ejection fraction, and E/e'). Using a receiver operating characteristic curve analysis, the optimal cut-off value for the CFV to the association of the outcome was 37 cm/s (area under the curve, 0.70; sensitivity, 82%; specificity, 62%). In sequential Cox proportional hazards models, the CFV added incremental prognostic information to the clinical and basic echocardiographic parameters (chi-squared: 110.7 to 146.6, P < 0.01).

CONCLUSIONS

An increased CFV in the proximal LCA was associated with cardiac death, incremental to the clinical and basic echocardiographic parameters.

Impaired Endothelial Function in Hereditary Angioedema During the Symptom-Free Period

Introduction: The presence of coronary endothelial dysfunction was previously shown in Hereditary Angioedema (HAE) patients. The aim of our study was to evaluate the effect of HAE on systemic endothelial function and whether there was a relationship among endothelial function, asymmetric dimethylarginine (ADMA) -which is a strong inhibitor of nitric oxide synthesis-, and disease severity scores. Methods: Twenty-four HAE patients (18 females, aged 47.9 ± 2 years) without factors known to interfere with endothelial function were studied and compared with 24 healthy peers age- and gender-matched. Endothelial function was assessed by means of non-invasive finger plethysmography (reactive hyperaemia index: RHI) and ADMA levels by high-performance liquid chromatography. HAE severity scores have been calculated according to published literature. Results: In HAE patients RHI was lower (2.03 ± 0.46 vs. 2.82 ± 0.34, p < 0.0001) and ADMA higher (0.636 ± 7 vs. 585 ± 5 micromol/L, p < 0.01) than in controls. A statistically significant inverse correlation was revealed between RHI and patients' ADMA levels (r = -0.516, p = 0.009) as well as between RHI and patients' chronological age (r = -0.49, p = 0.015). A statistically significant correlation between RHI and ADMA was confirmed even when excluding the possible influence of cholesterol (r = -0.408, p = 0.048). No other significant correlations were found with the examined laboratory and clinical parameters (chronological age, age at disease onset, disease duration, severity scores, and gender). Conclusion: The dysfunction previously shown in HAE patients at the coronary arteries seems to involve the peripheral vessels as well, without a correlation with disease severity.

Detection of angiographically significant coronary obstruction using resting transthoracic coronary Doppler echocardiography

BACKGROUND

Transesophageal Doppler echocardiography has shown that significant stenosis can be detected based on the presence of aliasing with color Doppler in the stenotic area. The study aimed to assess the detection of angiographically significant coronary stenosis (ASCS) by analyzing the characteristics and velocities of resting coronary artery flow (RCF) using transthoracic coronary Doppler echocardiography (TCDE).

METHODS

TCDE was performed before diagnostic coronary angiography (CA). The following velocities were measured: peak systolic velocity (PSV), peak diastolic velocity (PDV), mean diastolic velocity (MDV), end-diastolic velocity (EDV), and distal to proximal velocity ratios.

RESULTS

Twenty-five patients were included, and CA revealed ASCS in 14 patients. With TCDE, the proximal and distal portions of the left anterior descending artery (LAD) could be measured in 84% of cases. Among 12 patients with ASCS in the distal left main coronary artery (LMCA) or proximal or mid LAD, proximal and distal flow could be measured in ten patients. Proximal diastolic velocities were higher in patients with ASCS in the LAD, and a distal MDV/proximal MDV ratio < 0.5 had a 60% sensitivity and a 92% specificity for the detection of ASCS (AUC 0.77, 95% CI 0.56-0.92). For the detection of ASCS limited to the LMCA and/or proximal LAD, the distal MDV/proximal MDV ratio had a sensitivity of 100% and a specificity of 89% (AUC 0.98, 95% CI 0.81-0.99).

CONCLUSIONS

Resting TCDE can detect ASCS in the LAD, particularly at the proximal level, analyzing the ratio between distal and proximal flow velocities. These results could not be demonstrated in the RCA and CX arteries.

Feasibility, symptoms, adverse effects, and complications associated with noninvasive assessment of coronary flow velocity reserve in women with suspected or known coronary artery disease

BACKGROUND

Microvascular coronary impairment, defined as reduced coronary flow reserve, represents the predominant etiologic mechanism of ischemia in women with chest pain and no obstructive coronary artery disease. Transthoracic echocardiography (TTE) is a noninvasive method for assessing coronary flow velocity reserve (CFVR) in the left anterior descending coronary artery (LAD). The purpose of this investigation was to define the safety profile, feasibility, adverse events, and rate of complications of the test in women with suspected CAD.

METHODS

We evaluated CFVR in LAD with TTE during adenosine infusion in 1455 women aged 66.4±11.9 years.

RESULTS

A complete CFVR study was achieved in 1429 pts (feasibility 98.2%), the test being performed also in the early phase of acute coronary syndrome and on obese patients. Minor symptoms or adverse effects occurred in 43.7% of patients not requiring test termination: hyperpnea (16.7%), flushing (9.4%), atypical chest pain (9.9%), headache (6.6%), minor arrhythmias (2.9%), chest pain with EKG changes (1.5%) were the symptoms reported. No major complications were observed.

CONCLUSIONS

Noninvasive assessment of CFVR in LAD by TTE is a very feasible method with very low incidence of adverse events and complications in women with suspected or known CAD. It is safe and can be used when evaluating female patients with atherosclerotic LAD disease or with coronary microvascular impairment.

The use of echocardiography for the non-invasive evaluation of coronary artery disease

In the Western world, there are now millions of patients who undergo clinical procedures that evaluate coronary artery status each year. Methods span from direct imaging using angiography, computerized tomography, to nuclear magnetic imaging as well as to functional studies, such as positron emission tomography. These techniques have provided significant information to physicians, but there is still need for an improved accessibility. Angiographic methods are expensive and expose the patient to significant amounts of radiation, undesirable in younger patients. Among the novel technologies for coronary diagnostics, transthoracic echocardiography (TTE) of coronary arteries has provided an important alternative, particularly in everyday practice. Diagnostic arterial TTE can allow determination of the coronary wall lumen in at least three major coronary segments (left main [LM], left arterial descending [LAD] and right coronary artery [RCA]). Coronary wall thickness using the LAD has been preliminarily shown to be related to the risk of coronary events. Since it is well ascertained that coronary lesions found in any location indicate that at least 80% of the coronary tree is affected, this is very important clinical information. Evaluation of coronary status by TTE is a novel technology providing important information in ischemic syndromes, in cases of coronary malformations and other coronary diseases. KEY MESSAGES Coronary evaluation can be carried out by a variety of both invasive and non-invasive methods, many requiring radiation exposure or patient immobility. Transthoracic echocardiography (TTE) of the coronaries can, in particular, evaluate the coronary wall thickness, and this may be directly related to the coronary disease risk. TTE is a useful method for the monitoring of coronary flow reserve and can allow the detection of coronary malformations.

Concepts and Tradeoffs in Velocity Estimation With Plane-Wave Contrast-Enhanced Doppler

While long Doppler ensembles are, in principle, beneficial for velocity estimates, short acoustic pulses must be used in microbubble contrast-enhanced (CE) Doppler to mitigate microbubble destruction. This introduces inherent tradeoffs in velocity estimates with autocorrelators, which are studied here. A model of the autocorrelation function adapted to the microbubble Doppler signal accounting for transit time, the echo frequency uncertainty, and contrast-agent destruction is derived and validated in vitro. It is further demonstrated that a local measurement of the center frequency of the microbubble echo is essential in order to avoid significant bias in velocity estimates arising from the linear and nonlinear frequency-dependent scattering of microbubbles and compensate for the inherent speckle nature of the received echo frequency. For these reasons, broadband Doppler estimators (2-D autocorrelator and Radon projection) are better suited than simpler narrow-band estimators (1-D autocorrelator and 1-D Fourier transform) for CE flow assessment. A case study of perfusion in a VX-2 carcinoma using CE plane-wave Doppler is also shown. We demonstrate that even when considering all uncertainties associated with microbubble-related decorrelation (destruction, pulse bandwidth, transit time, and flow gradient) and the need for real-time imaging, a coefficient of variation of 4% on the axial velocity is achievable with plane-wave imaging.

Is dipyridamole useful in improving left ventricular systolic and diastolic function in patients with coronary slow flow?

BACKGROUND

Coronary slow flow (CSF) is an angiographic finding characterized by delayed opacification of epicardial coronary arteries without obstructive coronary disease. Previous studies have shown greater impairment of left ventricular (LV) systolic and diastolic function in patients with CSF. We aimed to examine the effect of dipyridamole on these functions.

METHODS

Our study included 40 patients with CSF and 40 subjects with normal coronary arteries. Conventional echocardiography Doppler imaging (CDI) and tissue Doppler echocardiography imaging (TDI) were used to evaluate LV systolic and diastolic function before and 2 months after treatment with dipyridamole.

RESULTS

Using CDI, we observed that early diastolic velocity (E) was significantly lower in patients with CSF, while late diastolic velocity (A), E/A ratio, isovolumic relaxation time, and myocardial performance index (MPI) were significantly higher in CSF patients compared with controls. Similarly, while early myocardial velocity (Em) was significantly lower, late myocardial velocity (Am), Em/Am ratio, isovolumic relaxation time (IRT), and MPI were significantly higher in CSF patients according to TDI measurements. Although there was no significant improvement in conventional Doppler parameters, there was significant normalization in tissue Doppler parameters after treatment with dipyridamole.

CONCLUSION

Left ventricular systolic and diastolic function may be negatively affected by CSF. Dipyridamole may improve these functions, especially at the tissue level.

Coronary flow velocity reserve by echocardiography: feasibility, reproducibility and agreement with PET in overweight and obese patients with stable and revascularized coronary artery disease

Background

Coronary flow velocity reserve (CFVR) measured by transthoracic Doppler echocardiography of the LAD is used to assess microvascular function but validation studies in clinical settings are lacking. We aimed to assess feasibility, reproducibility and agreement with myocardial flow reserve (MFR) measured by PET in overweight and obese patients.

Methods

Participants with revascularized coronary artery disease were examined by CFVR. Subgroups were examined by repeated CFVR (reproducibility) or Rubidium-82-PET (agreement). To account for time variation, results were computed for scans performed within a week (1-week) and for all scans regardless of time gap (total) and to account for scar tissue for patients with and without previous myocardial infarction (MI).

Results

Eighty-six patients with median BMI 30.9 (IQR 29.4–32.9) kg × m⁻² and CFVR 2.29 (1.90–2.63) were included. CFVR was feasible in 83 (97 %) using a contrast agent in 14 %. For reproducibility overall (n = 21) limits of agreement (LOA) were (−0.75;0.71), within-subjects coefficient of variation (CV) 11 %, and reliability 0.84. For reproducibility within 1-week (n = 13) LOA were (−0.33;0.25), within-subjects CV 5 %, and reliability 0.97. Agreement with MFR of the LAD territory (n = 35) was without significant bias and overall LOA were (−1.40;1.46). Agreement was best for examinations performed within 1-week of participants without MI of the LAD-territory (n = 12); LOA = (−0.68;0.88).

Conclusions

CFVR was highly feasible with a good reproducibility on par with other contemporary measures applied in cardiology. Agreement with MFR was acceptable, though discrepancy related to prior MI has to be considered. CFVR of LAD is a valid tool in overweight and obese patients.

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.

Differences in coronary artery blood velocities in the setting of normal coronary angiography and normal stress echocardiography

Background

Normal left anterior descending (LAD) coronary artery as determined by coronary angiography is considered not only to reflect normal angiography but also to correlate with normal anatomy and function. However, subjects who undergo coronary angiography may differ from those who do not need to have invasive evaluation even if their functional noninvasive studies like dobutamine stress echocardiography (DSE) were normal.

Aim

LAD velocities in subjects with normal angiography and those with normal DSE are equal.

Methods

A total of 244 subjects were evaluated, 78 had normal LAD by angiography and 166 had normal LAD by DSE. All had Doppler sampling of LAD velocities by transthoracic echocardiography.

Results

Velocity was higher in the angiographic subgroup in diastole 41 ± 23 vs 33 ± 14 cm/s, p = 0.0078; systole 18 ± 14 vs 13 ± 7 cm/s, p = 0.012; diastolic integral 12.6 ± 5 vs 9.8 ± 3.8 cm, p = 3.15 × 10^-5; systolic velocity integral 4 ± 2.9 vs 2.8 ± 1.9, p = 0.0014. While heart rate was similar in both groups, the product of diastolic velocity integral and heart rate of the LAD in the angiographic group was higher: 902 ± 450 vs 656 ± 394, p = 0.00599. Diastolic velocity deceleration time was similar in both groups. Coronary flow reserve defined as diastolic velocity ratio before and immediately after DSE correlated negatively with baseline velocity, r = -0.4.

Conclusions

Mode of defining normality of coronary artery affects velocity behavior of the vessel, reflecting functional differences possibly related to microvasculature and vasodilatation.

Ivabradine and Bisoprolol on Doppler-derived Coronary Flow Velocity Reserve in Patients with Stable Coronary Artery Disease: Beyond the Heart Rate

Introduction

Coronary flow velocity reserve (CFVR) is an important prognostic marker in patients with stable coronary artery disease (CAD). Beta-blockers and ivabradine have been shown to improve CFVR in patients with stable CAD, but their effects were never compared. The aim of the current study was to compare the effects of bisoprolol and ivabradine on CFVR in patients with stable CAD.

Methods

Patients in sinus rhythm with stable CAD were enrolled in this prospective, randomized, double-blind trial. Patients had to be in a stable condition for at least 15 days before enrollment, on their usual therapy. Patients who were receiving beta-blockers or ivabradine entered a 2-week washout period from these drugs before randomization. Transthoracic Doppler-derived CFVR was assessed in left anterior descending coronary artery, and was calculated as the ratio of hyperemic to baseline diastolic coronary flow velocity (CFV). Hyperemic CFV was obtained using dipyridamole administration using standard protocols. After CFVR assessment, patients were randomized to ivabradine or bisoprolol and entered an up-titration phase, and CFVR was assessed again 1 month after the end of the up-titration phase.

Results

Fifty-nine patients (38 male, 21 female; mean age 69 ± 9 years) were enrolled. Transthoracic Doppler-derived assessment of CFV and CFVR was successfully performed in all patients. Baseline characteristics were similar between the bisoprolol and ivabradine groups. No patient dropped out during the study. At baseline, rest and hyperemic peak CFV as well as CFVR was not significantly different in the ivabradine and bisoprolol groups. After the therapy, resting peak CFV significantly decreased in both the ivabradine and bisoprolol groups, but there was no significant difference between the groups (ivabradine group 20.7 ± 4.6 vs. 22.8 ± 5.2, P < 0.001; bisoprolol group 20.1 ± 4.1 vs. 22.1 ± 4.3, P < 0.001). However, hyperemic peak CFV significantly increased in both groups, but to a greater extent in patients treated with ivabradine (ivabradine: 70.7 ± 9.4 vs. 58.8 ± 9.2, P < 0.001; bisoprolol: 65 ± 8.3 vs. 58.7 ± 8.2, P < 0.001). Accordingly, CFVR significantly increased in both groups (ivabradine 3.52 ± 0.64 vs. 2.67 ± 0.55, P < 0.001; bisoprolol 3.35 ± 0.70 vs. 2.72 ± 0.55, P < 0.001), but it was significantly higher in ivabradine group, despite a similar decrease in heart rate (63 ± 7 vs. 61 ± 6; P not significant).

Conclusion

Ivabradine improves hyperemic peak CFV and CFVR to a greater extent than bisoprolol in patients with stable CAD, despite a similar decrease in heart rate. These data demonstrate that the benefits from ivabradine therapy go beyond the heart rate. This could be due to a different mechanism such as diastolic perfusion time, isovolumic ventricular relaxation, end-diastolic pressure, and collaterals.

Funding

Servier.

Electronic supplementary material

The online version of this article (doi:10.1007/s12325-015-0237-x) contains supplementary material, which is available to authorized users.

Coronary Flow Velocity Reserve Assessment with Transthoracic Doppler Echocardiography

Coronary flow velocity reserve (CFVR) reflects global coronary atherosclerotic burden, endothelial function and state of the microvasculature. It could be measured using transthoracic Doppler echocardiography in a non-invasive, feasible, reliable and reproducible fashion, following a standardised protocol with different vasodilatory stimuli. CFVR measurement is a recommended complement to vasodilator stress echocardiography. It could serve as a diagnostic tool for coronary microvascular dysfunction and in the setting of epicardial coronary artery stenoses could help in identification and assessment of functional significance of coronary lesions and follow-up of patients after coronary interventions. CFVR has also a prognostic significance in different clinical situations.

Ultrasound based assessment of coronary artery flow and coronary flow reserve using the pressure overload model in mice

Transthoracic Doppler echocardiography (TTDE) is a clinically useful, noninvasive tool for studying coronary artery flow velocity and coronary flow reserve (CFR) in humans. Reduced CFR is accompanied by marked intramyocardial and pericoronary fibrosis and is used as an indication of the severity of dysfunction. This study explores, step-by-step, the real-time changes measured in the coronary flow velocity, CFR and systolic to diastolic peak velocity (S/D) ratio in the setting of an aortic banding model in mice. By using a Doppler transthoracic imaging technique that yields reproducible and reliable data, the method assesses changes in flow in the septal coronary artery (SCA), for a period of over two weeks in mice, that previously either underwent aortic banding or thoracotomy. During imaging, hyperemia in all mice was induced by isoflurane, an anesthetic that increased coronary flow velocity when compared with resting flow. All images were acquired by a single imager. Two ratios, (1) CFR, the ratio between hyperemic and baseline flow velocities, and (2) systolic (S) to diastolic (D) flow were determined, using a proprietary software and by two independent observers. Importantly, the observed changes in coronary flow preceded LV dysfunction as evidenced by normal LV mass and fractional shortening (FS). The method was benchmarked against the current gold standard of coronary assessment, histopathology. The latter technique showed clear pathologic changes in the coronary artery in the form of peri-coronary fibrosis that correlated to the flow changes as assessed by echocardiography. The study underscores the value of using a non-invasive technique to monitor coronary circulation in mouse hearts. The method minimizes redundant use of research animals and demonstrates that advanced ultrasound-based indices, such as CFR and S/D ratios, can serve as viable diagnostic tools in a variety of investigational protocols including drug studies and the study of genetically modified strains.

Current Diagnostic and Therapeutic Strategies in Microvascular Angina

Microvascular angina is common among patients with signs and symptoms of acute coronary syndrome and is associated with an increased risk of cardiovascular and cerebrovascular events. Unfortunately, microvascular is often under-recognized in clinical settings. The diagnosis of microvascular angina relies on assessment of the functional status of the coronary microvasculature. Invasive strategies include acetylcholine provocation, intracoronary Doppler ultrasound, and intracoronary thermodilution; noninvasive strategies include cardiac positron emission tomography (PET), cardiac magnetic resonance, and Doppler echocardiography. Once the diagnosis of microvascular angina is established, treatment is focused on improving symptoms and reducing future risk of cardiovascular and cerebrovascular events. Pharmacologic options and lifestyle modifications for patients with microvascular angina are similar to those for patients with coronary artery disease.

Effect of rosuvastatin on coronary flow reserve in patients with systemic hypertension

Although statins reduce cardiac events in hypertensive patients with cardiovascular risk factors, the effect of statins on coronary flow reserve (CFR) has not been examined. We tried to examine the effect of rosuvastatin on CFR in hypertensive patients at cardiovascular risk. CFR was studied in 56 hypertensive patients (40 men, 61 ± 9 years) with cardiovascular risk factors and without coronary artery disease in a prospective clinical trial. Using Doppler echocardiography, coronary flow velocity in the distal left anterior descending artery was recorded at baseline and during intravenous adenosine infusion, and CFR was defined as the ratio of hyperemic to basal average peak diastolic flow velocity. The primary efficacy measure was defined as the change in CFR after rosuvastatin therapy for 12 months. CFR was measured successfully in 55 of 56 enrolled patients (98%). CFR was 3.16 ± 0.44 at baseline and negatively correlated with age (R = -0.30, p = 0.025). All patients continued rosuvastatin 10 mg/day without any serious adverse events. After rosuvastatin therapy, serum total cholesterol, low-density lipoprotein cholesterol, and high-sensitivity C-reactive protein significantly decreased from 222 ± 18 to 142 ± 20 mg/dl, 148 ± 21 to 85 ± 18 mg/dl, and 1.7 ± 2.9 to 1.2 ± 3.1 mg/L, respectively (all p <0.01). CFR significantly increased from 3.16 ± 0.44 to 3.31 ± 0.42 (p <0.001). The change in CFR correlated with the change in low-density lipoprotein cholesterol (R = -0.28, p = 0.040) but not with the change in high-sensitivity C-reactive protein. In conclusion, CFR was significantly improved after 12 months of rosuvastatin therapy in hypertensive patients at cardiovascular risk and average levels of serum cholesterol.

Remote ischemic conditioning improves coronary microcirculation in healthy subjects and patients with heart failure

BACKGROUND

Remote ischemic conditioning (RIC) is a treatment modality that suppresses inflammation and improves endothelial function, which are factors involved in the pathogenesis of heart failure (HF) with reduced left ventricular ejection fraction. Coronary flow reserve (CFR) is a physiological index of coronary microcirculation and is noninvasively measured by transthoracic Doppler echocardiography (TTDE). This study aimed to investigate the effects of RIC on CFR in healthy subjects and patients with HF, through the assessment by TTDE.

METHODS

Ten patients with HF with left ventricular ejection fraction of less than 40%, and ten healthy volunteers were enrolled in this study. RIC treatment was performed twice a day for 1 week. Our custom-made RIC device was programmed to automatically conduct 4 cycles of 5 minutes inflation and 5 minutes deflation of a blood pressure cuff to create intermittent arm ischemia. CFR measurements and laboratory tests were examined before, and after 1 week of RIC treatment.

RESULTS

One week of RIC treatment was well tolerated in both groups. RIC treatment increased CFR from 4.0 ± 0.9 to 4.6 ± 1.3 (mean ± standard deviation) in healthy subjects (P=0.02), and from 1.9 ± 0.4 to 2.3 ± 0.7 in patients with HF (P = 0.03), respectively. Systolic blood pressure in healthy subjects, and heart rate in HF patients decreased after RIC treatment (both P<0.01).

CONCLUSION

This study demonstrated that a 1 week course of RIC treatment improved coronary microcirculation in healthy subjects and patients with HF associated with reduced left ventricular ejection fraction.

Coronary microvasculopathy in heart transplantation: Consequences and therapeutic implications

Despite the progress made in the prevention and treatment of rejection of the transplanted heart, cardiac allograft vasculopathy (CAV) remains the main cause of death in late survival transplanted patients. CAV consists of a progressive diffuse intimal hyperplasia and the proliferation of vascular smooth muscle cells, ending in wall thickening of epicardial vessels, intramyocardial arteries (50-20 μm), arterioles (20-10 μm), and capillaries (< 10 μm). The etiology of CAV remains unclear; both immunologic and non-immunologic mechanisms contribute to endothelial damage with a sustained inflammatory response. The immunological factors involved are Human Leukocyte Antigen compatibility between donor and recipient, alloreactive T cells and the humoral immune system. The non-immunological factors are older donor age, ischemia-reperfusion time, hyperlipidemia and CMV infections. Diagnostic techniques that are able to assess microvascular function are lacking. Intravascular ultrasound and fractional flow reserve, when performed during coronary angiography, are able to detect epicardial coronary artery disease but are not sensitive enough to assess microvascular changes. Some authors have proposed an index of microcirculatory resistance during maximal hyperemia, which is calculated by dividing pressure by flow (distal pressure multiplied by the hyperemic mean transit time). Non-invasive methods to assess coronary physiology are stress echocardiography, coronary flow reserve by transthoracic Doppler echocardiography, single photon emission computed tomography, and perfusion cardiac magnetic resonance. In this review, we intend to analyze the mechanisms, consequences and therapeutic implications of microvascular dysfunction, including an extended citation of relevant literature data.

Systemic inflammation is related to coronary microvascular dysfunction in obese patients without obstructive coronary disease

BACKGROUND AND AIMS

Obesity, systemic inflammation and changes in the heart functions are associated with increased cardiovascular risk. This study aimed to investigate coronary microvascular dysfunction as an early marker of atherosclerosis in obese patients without any evidence of cardiovascular disease.

METHODS AND RESULTS

86 obese subjects (aged 44 ± 12 years, body mass index (BMI) 41 ± 8 kg m(-2)), without evidence of heart disease, and 48 lean controls were studied using transthoracic Doppler echocardiography for detecting coronary flow reserve (CFR). A value of CFR ≤ 2.5 was considered abnormal. We measured interleukin-6 (IL-6), tumour necrosis factor-α (TNF-α) and adiponectin in all patients. Patients with abnormal CFR underwent coronary multislice computed tomography (MSCT) in order to exclude an epicardial stenosis. CFR in obese subjects was lower than in lean subjects (3.2 ± 0.8 vs. 3.7 ± 0.7, p = 0.02) and was abnormal in 27 (31%) obese patients and in one (2%) control (p < 0.0001). All subjects with abnormal CFR showed no coronary stenosis at MSCT. At multivariable analysis, IL-6 and TNF-α were the only determinants of CFR (p < 0.02 and p < 0.02, respectively). At multivariable logistic regression analysis, IL-6 and TNF-α were the only determinants of CFR ≤ 2.5 (p < 0.03 and p < 0.03, respectively).

CONCLUSIONS

CFR is often reduced in obese subjects without clinical evidence of heart disease, suggesting a coronary microvascular impairment. This microvascular dysfunction seems to be related to a chronic inflammation mediated by adipocytokines. Our findings may explain the increased cardiovascular risk in obesity, independently of BMI.

Acceleration time of systolic coronary flow velocity to diagnose coronary stenosis in patients with microvascular dysfunction

BACKGROUND

The aim of this study was to test whether acceleration time of systolic coronary flow velocity could contribute to the diagnosis of coronary stenosis in patients with microvascular dysfunction, on the basis of the hypothesis that systolic coronary flow is less influenced by microvascular function because of compressed myocardium.

METHODS

Coronary flow velocity was assessed in the left anterior descending coronary artery during hyperemia with intravenous adenosine by echocardiography in 502 patients who were scheduled for coronary angiography because of coronary artery disease and significant valvular disease. Coronary flow velocity reserve (CFVR) and the percentage acceleration time (%AT), as the percentage of the time from the beginning to the peak of systolic coronary flow over systolic time during hyperemia, were calculated. The diagnostic ability of CFVR and %AT for angiographic coronary artery stenosis was then analyzed. As invasive substudies, fractional flow reserve and %AT by a dual-sensor (pressure and Doppler velocity) guidewire were measured simultaneously with %AT on transthoracic echocardiography (n = 14).

RESULTS

Patients with coronary stenosis had significantly lower CFVR (1.7 ± 0.4) and greater %AT (65 ± 9%) compared with those without stenosis (2.6 ± 0.6 and 50 ± 13%, respectively). Percentage acceleration time by Doppler echocardiography was in good agreement with %AT (r = 0.98) and fractional flow reserve (r = 0.74) invasively measured by dual-sensor guidewire. Cutoff values of CFVR and %AT were determined as 2.0 and 60% in receiver operating characteristic curve analysis. The sensitivity, specificity, and accuracy of CFVR to detect coronary stenosis were 71.1%, 77.3%, and 75.4%, while those of %AT were 83.4%, 71.8%, and 75.4%, respectively. In addition, %AT provided high accuracy to detect coronary stenosis, especially in patients with previous myocardial infarctions, valvular disease, and left ventricular hypertrophy (81.1%, 84.1%, and 73.4%, respectively).

CONCLUSIONS

The %AT of systolic coronary flow velocity is a promising marker to diagnose coronary stenosis in patients with microvascular dysfunction.