Noncritical Coronary Stenosis Research Articles

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

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. 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. 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. 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.

Morphological Characteristics of Eroded Plaques with Noncritical Coronary Stenosis: An Optical Coherence Tomography Study.

Aims: Recent studies suggested plaque erosion with noncritical stenosis could be treated distinctly from that with critical stenosis, but their morphological features remained largely unknown. The present study aimed to investigate morphological features of eroded plaques with different lumen stenosis using optical coherence tomography (OCT). Methods: A total of 348 ST-segment elevated myocardial infarction patients with culprit OCT-defined plaque erosion (OCT-erosion) were analyzed. Based on the severity of lumen area stenosis, all patients with OCT-erosions were divided into the following three groups: Group A (area stenosis ＜50%, n =50); Group B (50% ≤ area stenosis ＜75%, n =146); Group C (area stenosis ≥ 75%, n =152). Results: Compared with patients in Groups A and B, patients in Group C were older ( p =0.008) and had higher prevalence of hypertension ( p =0.029). Angiographic analysis showed that 72.0% of the eroded plaques in Group A were located in the left anterior descending artery, followed by 67.8% in Group B, and 53.9% in Group C ( p =0.039). OCT analysis showed that Group A had the highest prevalence of fibrous plaques ( p ＜0.001) and nearby bifurcation ( p =0.036), but the lowest prevalence of lipid-rich plaques ( p ＜0.001), macrophage accumulation ( p ＜0.001), microvessels ( p =0.009), cholesterol crystals ( p ＜0.001), and calcification ( p =0.023). Multivariable regression analysis showed fibrous plaque (odds ratio [OR]: 3.014, 95% confidence interval [CI]: 1.932–4.702, p ＜0.001) and nearby bifurcation (OR: 1.750, 95% CI: 1.109–2.761, p =0.016) were independently associated with OCT-erosion with an area stenosis of ＜75%. Conclusions: More than half of OCT-erosions presented with ＜75% area stenosis, having distinct morphological features from those of OCT-erosions with critical stenosis. Fibrous plaque and nearby bifurcation were independently associated with noncritically stenotic OCT-erosion, suggesting that eroded plaques might need individualized treatment.

Morphological characteristics of plaque erosion with noncritical coronary stenosis: an optical coherence tomography study

Abstract Background Plaque erosion is a frequent and important mechanism of acute coronary thrombosis only secondary to plaque rupture. Recent studies suggested plaque erosion with noncritical stenosis could be treated conservatively that distinct from those with critical stenosis. However, characteristics of plaque erosions with different coronary stenosis remain unknown. Purpose The present study aimed to investigate morphological features of plaque erosions with different coronary stenosis using optical coherence tomography (OCT). Methods Consecutive ST-segment elevated myocardial infarction (STEMI) patients with OCT images of culprit lesion between August 2014 and December 2017 were enrolled and 348 cases presented with plaque erosion identified by OCT. Based on the severity of lumen area stenosis [calculated by (1-minimal lumen area/reference lumen area) * 100%], all culprit plaque erosions were divided into three groups: Group A (area stenosis&amp;lt;50%, n=50, 14.4%); Group B (50%≤area stenosis&amp;lt;75%, n=146, 42.0%); Group C (area stenosis≥75%, n=152, 43.7%). Clinical characteristics, lesion features detected by coronary angiography and OCT were compared among three groups. Results Of all 348 STEMI patients with plaque erosions, patients in Group A were youngest (p=0.008) and had the lowest frequency of hypertension (p=0.029) as compared with those in Group B and C. Angiographic analysis showed 72.0% of plaque erosions in Group A located in LAD, while 67.8% in Group B and 53.9% in Group C (p=0.039). OCT findings (Figure 1-A) showed the prevalence of fibrous plaque was significantly highest in Group A than those in Group B and C (82.0% vs. 54.8% vs. 34.9%, p&amp;lt;0.001), whereas lipid rich plaque was most frequent in Group C (16.0% vs. 43.8% vs. 62.5%, p&amp;lt;0.001). The prevalence of macrophage (p&amp;lt;0.001), microvessel (p=0.009) and cholesterol crystals (p&amp;lt;0.001) increased gradually from plaque erosion with lumen area stenosis &amp;lt;50% to 50–75% to ≥75%. Notably, compared with Group B and C, nearby bifurcation was most common in Group A (72.0% vs. 67.1% vs. 55.3%, p=0.036). Multivariable regression analyses (Figure 1-B) showed fibrous plaque and nearby bifurcation were independently associated with plaque erosion with noncritical stenosis (area stenosis&amp;lt;75%). Conclusion 56.3% plaque erosion in STEMI patients presented with noncritical stenosis, having distinct morphological features from erosion with critical stenosis. Fibrous plaque and nearby bifurcation were independently associated with the presence of noncritically stenotic plaque erosion, remaining a desire to tailor treatment therapy to individual patients. Figure 1 Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): National Key R&amp;D Program of China

Role of cardiac nuclear stress perfusion exam after computed tomographic coronary angiogram for evaluation of obstructive coronary artery disease in patients with chest pain.

BackgroundClinical workup for chest pain varies among institutions. Acute coronary syndrome (ACS) is the primary diagnosis to rule out in the differential diagnosis, due to its associated mortality and morbidity. Although studies have demonstrated efficacy of coronary computed tomographic angiography (CCTA) in diagnosis obstructive coronary artery disease (CAD), there is limited evidence in the clinical value of performing cardiac nuclear stress perfusion imaging [myocardial perfusion imaging (MPI)] exam in patients with chest pain after undergoing CCTA. We aim to evaluate clinical value of follow-up nuclear cardiac MPI in patients with chest pain who have undergone recent CCTA.MethodsA total of 1,000 patients were evaluated in this IRB approved retrospective study who presented with symptoms of ACS. Patients who had elevated troponin or abnormal electrocardiogram (ECG) findings at initial presentation or prior to cardiac nuclear MPI were excluded from the study. All patients who underwent 64- or 320-detector row ECG-gated CCTA as well as a follow-up nuclear MPI. Patients who had diagnostics studies limited by artifact [e.g., suboptimal intravenous (IV) contrast bolus in CCTA, motion artifact on CCTA or MPI, etc.] were excluded.ResultsOne hundred patients met the inclusion criteria. Patient demographics include average age 64.3 [32–89] years, 59 male, 41 females. Ninety-five/100 patients had at least one vessel with 50–70% coronary artery diameter stenosis measured on CCTA. There were no focal perfusion abnormalities identified on cardiac nuclear MPI in patients with less than 70% stenosis diagnosed on CCTA. Five percent of patients were identified with coronary arterial narrowing greater than 70% on CCTA and all 5 of these patients have evidence of abnormal cardiac nuclear stress test (perfusion abnormalities, chest pain, abnormal ECG).ConclusionsIn low-to-intermediate risk patients with chest pain and evidence of non-critical coronary artery stenosis (i.e., less than 70% stenosis) diagnosed on CCTA, a follow-up cardiac nuclear perfusion imaging is of limited value.

Association of plaque calcification pattern and attenuation with instability features and coronary stenosis and calcification grade

Background and aimsCoronary computed tomography (CT) allows calculating coronary artery calcium score (CACS). However, other CT features might be more strongly related to plaque vulnerability and risk of future coronary events. This study investigated the association of plaque calcification pattern and attenuation with plaque instability features, coronary artery disease (CAD) grade and CACS. MethodsOne-hundred patients with coronary stenosis associated with calcified plaques were considered for this analysis. CACS, CAD grade, calcification pattern and attenuation, features of plaque instability, and epicardial adipose tissue (EAT) thickness and attenuation were assessed with non-contrast and contrast-enhanced CT angiography. ResultsOf 373 calcified plaques, 131 were responsible for the highest degree of coronary stenosis (1.31 ± 0.53 per patient). Participants were stratified according to the features of the highest-grade lesion(s) into patients with large (35%), spotty (52%) or mixed (13%) calcification pattern and tertiles of plaque calcification attenuation (using the mean value for multiple lesions). Patients with large calcification pattern or higher plaque calcification attenuation had higher stenosis and CACS grade (and EAT attenuation), but lower plaque instability score, whereas those with spotty calcification pattern or lower plaque calcification attenuation had lower stenosis and CACS grade (and EAT attenuation), but higher plaque instability score. Among the instability features, low attenuation and napkin-ring sign, but not positive remodeling, were associated with a spotty pattern and a lower calcification attenuation. ConclusionsBoth the pattern and attenuation of calcification should be considered, in addition to CACS, for risk stratification of heavily calcified high-risk patients with non-critical coronary stenosis.

Ranolazine may exert its beneficial effects by increasing myocardial adenosine levels.

We hypothesized that ranolazine-induced adenosine release is responsible for its beneficial effects in ischemic heart disease. Sixteen open-chest anesthetized dogs with noncritical coronary stenosis were studied at rest, during dobutamine stress, and during dobutamine stress with ranolazine. Six additional dogs without stenosis were studied only at rest. Regional myocardial function and perfusion were assessed. Coronary venous blood was drawn. Murine endothelial cells and cardiomyocytes were incubated with ranolazine and adenosine metabolic enzyme inhibitors, and adenosine levels were measured. Cardiomyocytes were also exposed to dobutamine and dobutamine with ranolazine. Modeling was employed to determine whether ranolazine can bind to an enzyme that alters adenosine stores. Ranolazine was associated with increased adenosine levels in the absence (21.7 ± 3.0 vs. 9.4 ± 2.1 ng/mL, P < 0.05) and presence of ischemia (43.1 ± 13.2 vs. 23.4 ± 5.3 ng/mL, P < 0.05). Left ventricular end-systolic wall stress decreased (49.85 ± 4.68 vs. 57.42 ± 3.73 dyn/cm2, P < 0.05) and endocardial-to-epicardial myocardial blood flow ratio tended to normalize (0.89 ± 0.08 vs. 0.76 ± 0.10, P = nonsignificant). Adenosine levels increased in cardiac endothelial cells and cardiomyocytes when incubated with ranolazine that was reversed when cytosolic-5'-nucleotidase (cN-II) was inhibited. Point mutation of cN-II aborted an increase in its specific activity by ranolazine. Similarly, adenosine levels did not increase when cardiomyocytes were incubated with dobutamine. Modeling demonstrated plausible binding of ranolazine to cN-II with a docking energy of -11.7 kcal/mol. We conclude that the anti-adrenergic and cardioprotective effects of ranolazine-induced increase in tissue adenosine levels, likely mediated by increasing cN-II activity, may contribute to its beneficial effects in ischemic heart disease.NEW & NOTEWORTHY Ranolazine is a drug used for treatment of angina pectoris in patients with ischemic heart disease. We discovered a novel mechanism by which this drug may exhibit its beneficial effects. It increases coronary venous levels of adenosine both at rest and during dobutamine-induced myocardial ischemia. Ranolazine also increases adenosine levels in endothelial cells and cardiomyocytes in vitro, by principally increasing activity of the enzyme cytosolic-5'-nucleotidase. Adenosine has well-known myocardial protective and anti-adrenergic properties that may explain, in part, ranolazine's beneficial effect in ischemic heart disease.

Myocardial perfusion echocardiography and coronary microvascular dysfunction.

Our understanding of coronary syndromes has evolved in the last two decades out of the obstructive atherosclerosis of epicardial coronary arteries paradigm to include anatomo-functional abnormalities of coronary microcirculation. No current diagnostic technique allows direct visualization of coronary microcirculation, but functional assessments of this circulation are possible. This represents a challenge in cardiology. Myocardial contrast echocardiography (MCE) was a breakthrough in echocardiography several years ago that claimed the capability to detect myocardial perfusion abnormalities and quantify coronary blood flow. Research demonstrated that the integration of quantitative MCE and fractional flow reserve improved the definition of ischemic burden and the relative contribution of collaterals in non-critical coronary stenosis. MCE identified no-reflow and low-flow within and around myocardial infarction, respectively, and predicted the potential functional recovery of stunned myocardium using appropriate interventions. MCE exhibited diagnostic performances that were comparable to positron emission tomography in microvascular reserve and microvascular dysfunction in angina patients. Overall, MCE improved echocardiographic evaluations of ischemic heart disease in daily clinical practice, but the approval of regulatory authorities is lacking.

Prinzmetal angina: ECG changes and clinical considerations: a consensus paper.

We will focus our attention in this article in the ECG changes of classical Prinzmetal angina that occur during occlusive proximal coronary spasm usually in patients with normal or noncritical coronary stenosis. The most important ECG change during a focal proximal coronary spasm is in around 50% of cases the appearance of peaked and symmetrical T wave that is followed, if the spasm persist, by progressive ST-segment elevation that last for a few minutes, and later progressively resolve. The most frequent ECG changes associated with ST-segment elevation are: (a) increased height of the R wave, (b) coincident S-wave diminution, (c) upsloping TQ in many cases, and (d) alternans of the elevated ST-segment and negative T wave deepness in 20% of cases. The presence of arrhythmias is very frequent during Prinzmetal angina crises, especially ventricular arrhythmias. The prevalence and importance of ventricular arrhythmias were related to: (a) duration of episodes, (b) degree of ST-segment elevation, (c) presence of ST-T wave alternans, and (d) the presence of >25% increase of the R wave. The incidence of Prinzmetal angina is much lower then 50 years ago for many reasons including treatment with calcium channel blocks to treat hypertension and ischemia heart disease and the decrease of smoking habits.

Carotid intima–media thickness is a useful screening tool to detect coronary artery plaque in type 2 diabetic patients with zero calcium score

Coronary artery disease (CAD) is the leading cause of death for individuals with type 2 diabetes mellitus (DM) [1,2], and acute coronary syndrome is believed to result from plaque rupture at the site of a noncritical coronary stenosis (<50%) [3]. Because the association between coronary artery calcium score (CACS) and the presence of coronary atherosclerosis or future cardiovascular event is widely recognized [4], the screening for occult CAD using CACS is a popular method. Especially, diabetic patients tend to have higher CACS, which is related more closely to a greater increase in prevalence of CAD and mortality [5,6].

Myocardial Perfusion Imaging After Coronary Artery Bypass Surgery Using Cardiovascular Magnetic Resonance

Background— Absolute quantification of perfusion with cardiovascular magnetic resonance has not previously been applied in patients with coronary artery bypass grafting (CABG). Owing to increased contrast bolus dispersion due to the greater distance of travel through a bypass graft, this approach may result in systematic underestimation of myocardial blood flow (MBF). As resting MBF remains normal in segments supplied by noncritical coronary stenosis (&lt;85%), measurement of perfusion in such territories may be utilized to reveal systematic error in the quantification of MBF. The objective of this study was to test whether absolute quantification of perfusion with cardiovascular magnetic resonance systematically underestimates MBF in segments subtended by bypass grafts. Methods and Results— The study population comprised 28 patients undergoing elective CABG for treatment of multivessel coronary artery disease. Eligible patients had angiographic evidence of at least 1 myocardial segment subtended by a noncritically stenosed coronary artery (&lt;85%). Subjects were studied at 1.5 T, with evaluation of resting MBF using model-independent deconvolution. Analyses were confined to myocardial segments subtended by native coronary arteries with &lt;85% stenosis at baseline, and MBF was compared in grafted and ungrafted segments before and after revascularization. A total of 249 segments were subtended by coronary arteries with &lt;85% stenosis at baseline. After revascularization, there was no significant difference in MBF in ungrafted (0.82±0.19 mL/min/g) versus grafted segments (0.82±0.15 mL/min/g, P =0.57). In the latter, MBF after revascularization did not change significantly from baseline (0.86±0.20 mL/min/g, P =0.82). Conclusions— Model-independent deconvolution analysis does not systematically underestimate blood flow in graft-subtended territories, justifying the use of this methodology to evaluate myocardial perfusion in patients with CABG.

Evaluation of non-critical coronary stenosis by coherent contrast imaging

Objective To investigate whether non-critical coronary stenosis can be detected by coherent contrast imaging(CCI) at rest without stress.Methods Three degrees of stenosis were made in left anterior descending of 12 dogs.Myocardial contrast echocardiography(MCE) was performed with CCI and the correlation among the variables of MCE curve and the degrees of stenosis were analyzed by cubic regression.Results The time to peak was significantly prolonged with progressive coronary stenosis (P＜0.01) and related to the degree of stenosis (R~2=0.991,P＜0.001).Conclusions CCI could be used to detected non-critical coronary stenosis at rest without stress. Key words: Echocardiography; Microbubbles; Coronary stenosis

Myocardial perfusion is preserved in patients with psoriasis without clinically evident cardiovascular disease

Psoriasis is associated with a premature atherosclerosis due to the chronic inflammatory process. To evaluate the effect of disease process on myocardial perfusion, we planned to perform 99mTc-MIBI myocardial perfusion single photon emission computed tomography (SPECT) in patients with psoriasis. The study group consisted of 28 psoriasis patients (17 men, 11 women), aged 18-76 years, and mean age 41.2 +/- 14.1 years. The patients were selected among those who were older than 18 years and longer than 10 years of disease duration with more than two times of systemic treatment. All patients underwent 99mTc-MIBI myocardial perfusion SPECT with the same day protocol. We detected various risk factors including smoking habits in 7, family history of cardiovascular disease in 4, hypertension in 1, hyperlipidemia in 9 patients. We completed myocardial perfusion SPECT for each patient and found normal perfusion pattern in SPECT images. We detected that myocardial perfusion is preserved in the patients with psoriasis. The majority of acute heart attacks are caused by noncritical coronary stenosis and this may be an explanation for increased cardiovascular risk in these patients despite normal coronary perfusion.

Abstract 2688: Can Stress Echocardiography With Tissue Characterization Evaluate Noncritical Coronary Stenosis? A Validation Study Against Simultaneous Measurement of Fractional Flow Reserve

Aim of this study was to evaluate the ability of different echocardiographic modalities to detect myocardial ischemia due to non-critical coronary stenosis, compared to the fractional flow reserve (FFR) as gold standard. Material and Methods: We investigated 22 consecutive patients presenting with stable angina, negative exercise tests and coronary 1-vessel disease with 50–75% diameter stenosis. TDE/SRI was performed at baseline and at peak hyperemia during 0.14 mg/kg/min adenosine infusion simultaneously with intracoronary FFR measurements. Angioplasty was carried out if FFR &lt; 0.75, repeating TDE/SRI during first balloon inflation. Visual wall motion score, peak systolic values for myocardial velocity (Vs), strain rate (SRs), strain (Ss) and peak overall strain (Smax) were determined in the region of interest. Postsystolic shortening (PSS), accepted as typical marker of acute myocardial ischemia, was defined as (Smax-Ss)/Smax &gt; 0.3, with reduced Ss &lt; 15%. Results: Pathologic FFR &lt; 0.75 was found in 11 patients (Table 1 ), who underwent angioplasty. Myocardial contractility reflected by SRs increased during hyperemia only in the patient group with FFR &gt; 0.75 and decreased markedly during balloon inflation. Hyperemic SRs variation correlated with FFR (r = 0.5, p = 0.018) and predicted significantly pathologic FFR with an area under ROC curve of 0.86 (p &lt;0.01). PSS was identified in 10 of 11 patients during vessel occlusion, but had a low sensitivity (2 of 11 patients with FFR &lt; 0.75) for the more subtle changes during hyperemia. Conclusion: Functional assessment of moderate-to-severe coronary stenosis remains a diagnostic challenge. PSS occurrence cannot serve as a reliable noninvasive alternative to FFR. However, the blunted hyperemic variation of systolic strain rate was able to predict a pathologic FFR, even in this small group of patients. Therefore, TDE/SRI emerges as a promising tool to enhance the diagnostic accuracy of adenosine stress echocardiography. Table 1

214 Can stress echocardiography with tissue characterization evaluate non-critical coronary stenosis? A validation study against simultaneous measurement of fractional flow reserve

Background: Fractional flow reserve (FFR) is accepted as gold standard for the functional assessment of coronary stenosis. The typical marker of acute myocardial ischemia by tissue Doppler echocardiography with strain rate imaging (TDE/SRI) is postsystolic shortening (PSS). The study evaluated different echocardiographic modalities for detection of myocardial ischemia due to non-critical coronary stenosis. Material and methods: We investigated 22 consecutive patients presenting with stable angina, negative exercise tests and coronary 1-vessel disease with 50-75% diameter stenosis. TDE/SRI was performed at baseline and at peak hyperemia during 0.14 mg/kg/min adenosine infusion simultaneously with intracoronary FFR measurements. Angioplasty was carried out if FFR 0.3, with reduced Ss <15%. Results: Pathologic FFR <0.75 was found in 11 patients, who underwent angioplasty. Myocardial contractility reflected by SRs increased during hyperemia only in the patient group with FFR ≥0.75 and decreased markedly during balloon inflation, but its variation was not robust enough to predict pathologic FFR (Fig. 1). PSS was identified in 10 of 11 patients during vessel occlusion, but had a low sensitivity (2 of 11 patients with FFR <0.75) for the more subtle changes during hyperemia. Conclusion: Although TDE/SRI enhances the diagnostic accuracy of adenosine stress echocardiography, it still cannot serve as a reliable noninvasive alternative to FFR for the functional assessment of moderate-to-severe coronary stenosis.

Cyclic Variation in Ultrasonic Myocardial Integrated Backscatter Is Due to Phasic Changes in the Number of Patent Myocardial Microvessels

We tested the hypothesis that the cyclic variation in ultrasonic myocardial integrated backscatter (IBS) is due to cardiac contraction-induced changes in the number of patent myocardial microvessels. We performed experiments in open-chest dogs in which we increased the number of patent myocardial microvessels without changing cardiac contraction. We achieved this either by direct intracoronary administration of adenosine (group 1; n = 10) or by producing a noncritical coronary stenosis (group 2; n = 7). At baseline, IBS was lowest in systole and highest in diastole. This cyclic variation in IBS was closely associated with the phasic changes in myocardial blood volume that were measured with myocardial contrast echocardiography. During adenosine administration, the diastolic IBS increased from -18.8 +/- 6.5 to -17.5 +/- 6.1 dB (P = .002), with an associated increase in the difference between the systolic and diastolic IBS from 3.8 +/- 1.1 to 4.6 +/- 1.0 dB (P = .009). After a noncritical stenosis was produced, diastolic IBS also increased from -26.6 +/- 8.3 to -25.2 +/- 7.3 dB (P = .001), with an associated increase in the difference between the systolic and diastolic IBS from 3.7 +/- 1.2 to 5.0 +/- 1.0 dB (P = .02). No change in IBS was noted in the bed that did not receive adenosine or the bed that had a stenosis. The variation in IBS during the cardiac cycle is closely associated with the phasic changes in myocardial blood volume seen during cardiac contraction. When the number of patent myocardial arterioles is increased via adenosine or placement of a noncritical stenosis, diastolic IBS increases with a concomitant increase in IBS cyclic variation. These results may have important clinical applications for the noninvasive diagnosis of noncritical coronary stenosis at rest.

1001-32 Detection of noncritical coronary stenosis at rest with myocardial contrast echocardiography

1001-32 Detection of noncritical coronary stenosis at rest with myocardial contrast echocardiography

Direct effects of dobutamine on the coronary microcirculation: comparison with adenosine using myocardial contrast echocardiography

The direct effects of dobutamine on capillary blood volume (VOL) and blood flow velocity (VEL) are not known. We hypothesized that these would be more similar to that of adenosine because of its effects on the β 2 receptors on the coronary circulation. A total of 9 open-chest anesthetized dogs were studied after placement of 2 noncritical stenoses at rest and during separate intracoronary administrations of 5 μg/kg −1/min −1 of adenosine and 2 μg/kg −1/min −1 of dobutamine. VOL and VEL were measured using myocardial contrast echocardiography, wall thickening with 2-dimensional echocardiography, and myocardial blood flow (MBF) with radiolabeled microspheres. Dobutamine increased the rate-pressure product significantly, whereas adenosine had no effect on the rate-pressure product. In the normal myocardium, adenosine had no effect on VOL and increases in MBF were all a result of increases in VEL. Dobutamine also caused mostly an increase in VEL and only a 30% increase in VOL indicating modest capillary recruitment. In the bed with stenosis both drugs attenuated increase in MBF by the same amount, which was associated with an attenuation in the increase in VEL secondary to a 15% increase in capillary resistance because of capillary derecruitment. The MBF-wall thickening relation was described for both drugs by the same function: y = 1 − exp(x) with wall thickening being significantly higher for dobutamine compared with adenosine for each level of MBF. We conclude that the increase in MBF in the normal myocardium with intracoronary dobutamine occurs mostly from an increase in VEL rather than from an increase in VOL. In the bed with a noncritical stenosis, the increases in MBF and VEL are similar for both drugs. Similar to intracoronary adenosine, intracoronary dobutamine also caused capillary derecruitment distal to a noncritical coronary stenosis.

Mechanism of reversible (99m)Tc-sestamibi perfusion defects during pharmacologically induced vasodilatation.

Reversible perfusion defects on (99m)Tc-sestamibi imaging during hyperemia are thought to occur due to myocardial blood flow (MBF) "mismatch" between regions with and without stenosis. We have recently shown that myocardial blood volume (MBV) distal to a stenosis decreases during hyperemia, resulting in a reversible perfusion defect on myocardial contrast echocardiography (MCE). In this study, we hypothesized that a reversible perfusion defect on (99m)Tc-sestamibi imaging during hyperemia results from the same mechanism. We tested our hypothesis under the following conditions: 1) increases in MBF in the absence of changes in MBV by using direct intracoronary infusion of adenosine (group I, n = 10 dogs); 2) decrease in MBV despite an increase in MBF by left main infusion of adenosine proximal to a noncritical coronary stenosis placed on either coronary artery (group II, n = 13 dogs); and 3) reduction in both resting MBF and MBV by placement of a severe stenosis (group III, n = 7 dogs). In group I dogs, no difference in MBV or (99m)Tc-sestamibi uptake was found between the two coronary beds despite an up to fourfold increase in MBF in one bed with adenosine. In group II dogs, MBV distal to the stenosis decreased during hyperemia despite a twofold increase in mean MBF. A good correlation was found between (99m)Tc-sestamibi uptake and MBV ratios from the stenosed versus normal bed (r = 0.91, P < 0.001). In group III dogs, both MBF and MBV were decreased in the stenosed bed at rest with a good correlation noted between (99m)Tc-sestamibi uptake and MBV ratios from the stenosed versus normal bed (r = 0.92, P = 0.004). We conclude that reversible defects on (99m)Tc-sestamibi during vasodilator stress imaging are related to decreases in MBV distal to a stenosis and not to "flow mismatch" between beds. The decrease in MBV results in reduced (99m)Tc-sestamibi uptake during hyperemia.

Variant Angina Culminating in Coronary Thrombosis and Myocardial Infarction

A patient with variant angina is described who developed inferior wall myocardial infarction in the midst of recurrent episodes of rest angina associated with inferior lead ST elevations. Coronary arteriography within six hours of onset of persistent chest pain demonstrated right coronary thrombotic occlusion which was lysed by intracoronary streptokinase and revealed an underlying non-critical coronary stenosis.