Comparison of pharmacologic stress agents

Medication and ECG Patterns That May Hinder SPECT Myocardial Perfusion Scans

Coronary artery disease (CAD) is the leading cause of death followed by cancer, in men and women. With risk factors being endemic and the increasing costs of healthcare for management and treatment, myocardial perfusion imaging (MPI) finds a central role in risk stratification and prognosis for CAD patients, but it comes with its limitations in that the referring clinician and managing team must be aware of and use at their advantage. This narrative review examines the utility of myocardial perfusion scans in the diagnosis and management of patients with ECG alterations such as atrioventricular block (AVB), and medications including calcium channel blockers (CCB), beta blockers (BB), and nitroglycerin which may impact the interpretation of the exam. The review analyzes the current evidence and provides insights into the limitations, delving into the reasons behind some of the contraindications to MPI.

Qualitative and Quantitative Stress Perfusion Cardiac Magnetic Resonance in Clinical Practice: A Comprehensive Review

Stress cardiovascular magnetic resonance (CMR) imaging is a well-validated non-invasive stress test to diagnose significant coronary artery disease (CAD), with higher diagnostic accuracy than other common functional imaging modalities. One-stop assessment of myocardial ischemia, cardiac function, and myocardial viability qualitatively and quantitatively has been proven to be a cost-effective method in clinical practice for CAD evaluation. Beyond diagnosis, stress CMR also provides prognostic information and guides coronary revascularisation. In addition to CAD, there is a large body of literature demonstrating CMR's diagnostic performance and prognostic value in other common cardiovascular diseases (CVDs), especially coronary microvascular dysfunction (CMD). This review focuses on the clinical applications of stress CMR, including stress CMR scanning methods, practical interpretation of stress CMR images, and clinical utility of stress CMR in a setting of CVDs with possible myocardial ischemia.

Impact of Intravascular Ultrasound-Derived Lesion-Specific Virtual Fractional Flow Reserve Predicts 3-Year Outcomes of Untreated Nonculprit Lesions: The PROSPECT Study

BACKGROUND

Hemodynamic assessment of untreated nonculprit lesions was not studied in the PROSPECT study (Providing Regional Observations to Study Predictors of Events in the Coronary Tree). We developed a virtual intravascular ultrasound-derived lesion-specific fractional flow reserve (lesion-specific IVUS-FFR) algorithm to assess individual lesion-level FFR. We sought to investigate the relation between lesion-specific IVUS-FFR and major adverse cardiovascular events (MACE) arising from untreated nonculprit lesions in the PROSPECT study.

METHODS

In PROSPECT, 697 patients with acute coronary syndromes underwent 3-vessel grayscale and virtual histology-IVUS to correlate untreated nonculprit plaque morphology with 3-year nonculprit related MACE (composite of cardiac death, cardiac arrest, myocardial infarction, or rehospitalization due to unstable or progressive angina). Lesion-specific IVUS-FFR was calculated from volumetric IVUS lumen area measurements at 0.4 mm intervals by applying a mathematical circulation model using basic fluid dynamics equations.

RESULTS

Lesion-specific IVUS-FFR was analyzable in 3227 nonculprit lesions in 660 patients among whom 54 nonculprit MACE events (3 myocardial infarctions) occurred at median 3.4-year follow-up. By receiver-operating characteristic analysis, the best cutoff value of lesion-specific IVUS-FFR to predict nonculprit MACE was ≤0.95. After adjusting for patient and lesion characteristics, lesion-specific IVUS-FFR (hazard ratio, 4.83 [95% CI, 2.20-10.61]; P<0.001) was an independent predictor of 3-year nonculprit MACE, in addition to minimum lumen area≤4.0 mm², plaque burden ≥70%, and virtual histology thin-cap fibroatheroma.

CONCLUSIONS

Minor reductions in lesion-specific IVUS-FFR were independently associated with future nonculprit MACE arising from untreated angiographically mild stenoses along with previously established high-risk lesion morphological characteristics.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT00180466.

Pharmacologic stress cardiovascular magnetic resonance in the pediatric population: A review of the literature, proposed protocol, and two examples in patients with Kawasaki disease

Pharmacologic stress cardiovascular magnetic resonance (PSCMR) is a well-established and reliable diagnostic tool for evaluation of coronary artery disease in the adult population. Stress imaging overall and PSCMR in particular is less utilized in the pediatric population with limited reported data. In this review, we highlight the potential use of PSCMR in specific pediatric cohorts with congenital and acquired heart disease, and we review the reported experience. A suggested protocol is presented in addition to two case examples of patients with Kawasaki disease where PSCMR aided decision making.

Is coronary calcium scoring too late? Total body arterial calcium burden in patients without known CAD and normal MPI

BACKGROUND

Patients with normal myocardial perfusion imaging (MPI) have a good prognosis. However, pre-clinical coronary and extracoronary atherosclerosis may exist in the absence of myocardial ischemia.

METHODS

154 Egyptian patients (mean age 53 years) underwent whole-body non-contrast CT following normal MPI.

RESULTS

Atherosclerosis in the form of calcification was observed in ≥1 vascular bed in 115 of 154 (75%) patients. This included the iliofemoral (62%), abdominal aorta (53%), thoracic aorta (47%), coronary (47%), and carotid (25%) vascular beds. Mean total body calcium score was 3172 ± 530 AU. Extracoronary atherosclerosis in patients with a zero coronary artery calcium (CAC) score was common, occurring in the above-listed beds 42%, 36%, 29%, and 7% of the time, respectively. CAC was rarely present without iliofemoral or abdominal aortic calcification.

CONCLUSION

Quantitative assessment of calcification in different vascular beds demonstrates that extracoronary atherosclerosis is common in patients who have normal MPI. Atherosclerotic calcifications are most common in the iliofemoral arteries and abdominal aorta, which typically predate coronary calcifications. An imaging strategy to detect extracoronary atherosclerosis could lead to greater understanding of the natural history of atherosclerosis in its long pre-clinical phase and possibly to earlier preventive strategies.

Intracoronary Optical Coherence Tomography-Derived Virtual Fractional Flow Reserve for the Assessment of Coronary Artery Disease

Fractional flow reserve (FFR) is widely used for the assessment of myocardial ischemia. Optical coherence tomography (OCT) provides accurate visualization of coronary artery morphology. The aim of this study was to investigate the relation between FFR and OCT-derived FFR. We retrospectively analyzed 31 lesions (25 left anterior descending arteries, 2 left circumflex arteries, and 4 right coronary arteries) in 31 patients with moderate-to-severe coronary stenosis, who underwent OCT and FFR measurements simultaneously. OCT-derived FFR was calculated by the original algorithm, which was calculated using the following equation based on fluid dynamics: ΔP = FV + SV², where V is the flow velocity, F is the coefficient of pressure loss because of viscous friction (Poiseuille resistance), and S is the coefficient of local pressure loss because of abrupt enhancement (flow separation). Mean values of % diameter stenosis by quantitative coronary angiography and FFR were 55.2 ± 14.0% and 0.70 ± 0.14, respectively. OCT-derived FFR showed a stronger linear correlation with FFR measurements (r = 0.89, p <0.001; root mean square error = 0.062 FFR units) than quantitative coronary angiography % diameter stenosis (r = -0.65, p <0.001), OCT measurements of minimum lumen area (r = 0.68, p <0.001), and % area stenosis (r = -0.70, p <0.001). OCT-derived FFR has the potential to become an alternative method for the assessment of functional myocardial ischemia, and may elucidate the relation between coronary morphology and FFR.

Myocardial perfusion imaging is an effective screening test for coronary artery disease in liver transplant candidates

A reliable screening test for coronary artery disease (CAD) in liver transplant (LT) candidates with end-stage liver disease is essential because a high percentage of perioperative mortality and morbidity is CAD-related. In this study, the effectiveness of myocardial perfusion imaging (MPI) for identification of significant CAD in LT candidates was evaluated. Records of 244 patients meeting criteria for MPI were evaluated: 74 met inclusion criteria; 40 had a positive MPI and cardiology follow-up; 27 had a negative MPI and underwent LT; and seven had a negative MPI and then had coronary angiography or a significant cardiac event. A selective MPI interpretation strategy was established where MPI-positive patients were divided into high, intermediate, and low CAD risk groups. The overall incidence of CAD in this study population was 5.1% and our strategy resulted in PPV 20%, NPV 94%, sensitivity 80%, and specificity 50% for categorizing CAD risk. When applied only to the subset of patients categorized as high CAD risk, the strategy was more effective, with PPV 67%, NPV 97%, sensitivity 80%, and specificity 94%. We determined that renal dysfunction was an independent predictive factor for CAD (p < 0.0001, odds ratio = 8.1), and grades of coronary occlusion correlated significantly with chronic renal dysfunction (p = 0.0079).

Myocardial blood flow quantification for evaluation of coronary artery disease by positron emission tomography, cardiac magnetic resonance imaging, and computed tomography

The noninvasive detection of the presence and functional significance of coronary artery stenosis is important in the diagnosis, risk assessment, and management of patients with known or suspected coronary artery disease. Quantitative assessment of myocardial perfusion can provide an objective and reproducible estimate of myocardial ischemia and risk prediction. Positron emission tomography, cardiac magnetic resonance, and cardiac computed tomography perfusion are modalities capable of measuring myocardial blood flow and coronary flow reserve. In this review, we will discuss the technical aspects of quantitative myocardial perfusion imaging with positron emission tomography, cardiac magnetic resonance imaging, and computed tomography, and its emerging clinical applications.

Myocardial perfusion scintigraphy in asymptomatic diabetic patients: a critical review

The increasing prevalence of diabetes mellitus and the associated high cardiovascular risk has made the non-invasive identification of silent coronary heart disease in diabetic individuals an important issue. This strategy could identify higher risk asymptomatic patients with diabetes mellitus in whom coronary revascularization may improve the outcome beyond that achieved by currently recommended medical management. Stress myocardial perfusion imaging has been shown to be effective in detecting coronary heart disease and predicting adverse cardiac events in asymptomatic diabetic patients. However, the clinical utility of myocardial perfusion scintigraphy is debated intensively due to the paucity of prospective and outcome based evidence. The controversy stems from several observational studies, epidemiologic data and cost-effectiveness analyses. Thus, although several authors and professional organizations advocate the use of stress imaging for screening higher risk asymptomatic diabetic patients, others are cautious in recommending any kind of stress testing in that population. This review is based on a broad survey of the literature and discusses the potential role of stress myocardial perfusion scintigraphy in screening asymptomatic diabetic subjects for coronary heart disease in the current era and in relation with other non-invasive screening tools.

Nonacute coronary syndrome anginal chest pain

Anginal chest pain is one of the most common complaints in the outpatient setting. While much of the focus has been on identifying obstructive atherosclerotic coronary artery disease (CAD) as the cause of anginal chest pain, it is clear that microvascular coronary dysfunction (MCD) can also cause anginal chest pain as a manifestation of ischemic heart disease, and carries an increased cardiovascular risk. Epicardial coronary vasospasm, aortic stenosis, left ventricular hypertrophy, congenital coronary anomalies, mitral valve prolapse, and abnormal cardiac nociception can also present as angina of cardiac origin. For nonacute coronary syndrome (ACS) stable chest pain, exercise treadmill testing (ETT) remains the primary tool for diagnosis of ischemia and cardiac risk stratification; however, in certain subsets of patients, such as women, ETT has a lower sensitivity and specificity for identifying obstructive CAD. When combined with an imaging modality, such as nuclear perfusion or echocardiography testing, the sensitivity and specificity of stress testing for detection of obstructive CAD improves significantly. Advancements in stress cardiac magnetic resonance imaging enables detection of perfusion abnormalities in a specific coronary artery territory, as well as subendocardial ischemia associated with MCD. Coronary computed tomography angiography enables visual assessment of obstructive CAD, albeit with a higher radiation dose. Invasive coronary angiography remains the gold standard for diagnosis and treatment of obstructive lesions that cause medically refractory stable angina. Furthermore, in patients with normal coronary angiograms, the addition of coronary reactivity testing can help diagnose endothelial-dependent and -independent microvascular dysfunction. Lifestyle modification and pharmacologic intervention remains the cornerstone of therapy to reduce morbidity and mortality in patients with stable angina. This review focuses on the pathophysiology, diagnosis, and treatment of stable, non-ACS anginal chest pain.

Respiratory resistance of patients during cardiac stress testing with adenosine: is dyspnea a sign of bronchospasm?

BACKGROUND

Adenosine is widely used for stress-testing in myocardial perfusion imaging. During adenosine infusion, dyspnea is one of the main complaints of patients. The aim of this study was to determine whether dyspnea during adenosine infusion is caused by bronchospasm.

METHODS

Fifty-four patients were enrolled in the study. Seven of these 54 suffered from mild chronic obstructive pulmonary disease (COPD). We continuously measured respiratory resistance (Rrs), using impulse oscillometry. Respiratory resistance was measured before, during, and after a continuous infusion of 140 microg/kg/min adenosine.

RESULTS

Sixty-seven percent of patients suffered from dyspnea during adenosine infusion. In patients with mild COPD, Rrs was higher compared with other patients (0.48 vs 0.27 kPa/L/s, P < .05). Neither patients with COPD nor those without COPD exhibited a significant increase in Rrs during adenosine infusion. The Rrs of patients with dyspnea was insignificantly lower compared with patients without dyspnea (P = .469).

CONCLUSIONS

Dyspnea as a side effect of adenosine infusion is not correlated with impaired respiratory resistance in nonasthmatic patients and in patients with mild COPD. Thus bronchospasm is ruled out as cause of this clinical symptom. Despite the small number of COPD patients enrolled in the study, adenosine infusion might be possible in patients with mild COPD.

Caffeine Attenuates the Duration of Coronary Vasodilation and Changes in Hemodynamics Induced by Regadenoson (CVT-3146), a Novel Adenosine A2A Receptor Agonist

Effects of caffeine on regadenoson-induced coronary vasodilation and changes in hemodynamics were examined in conscious dogs. Sixteen dogs were chronically instrumented for measurements of coronary blood flow (CBF), mean arterial pressure (MAP), and heart rate (HR). Regadenoson (5 microg/kg, IV) increased CBF from 34 +/- 2 to 191 +/- 7 mL/min. The duration of the 2-fold increase in CBF was 515 +/- 71 seconds. Regadenoson decreased MAP by 15 +/- 2% and increased HR by 114 +/- 14%. Regadenoson-induced maximum increases in CBF were not significantly lower in the presence of caffeine at 1, 2, 4, and 10 mg/kg (2 +/- 3, 0.7 +/- 3, 16 +/- 5, and 13 +/- 8%, respectively; all P > 0.05). Caffeine at 1, 2, 4, and 10 mg/kg significantly decreased the duration of the 2-fold increase in CBF induced by regadenoson by 17% +/- 4%, 48% +/- 8%, 62% +/- 5%, and 82% +/- 5%, respectively (all P < 0.05). Caffeine at 4 and 10 mg/kg significantly attenuated the effects of regadenoson on MAP and HR. The results indicate that 1 to 10 mg/kg caffeine dose-dependently reduced the duration, but not the peak increase of CBF caused by 5 microg/kg regadenoson.

Detection of moderate regional ischemia in pig hearts in vivo by near-infrared and thermal imaging: effects of dipyridamole

Effects of coronary vasodilator, dipyridamole, on epicardial oxygenation and flow were investigated under conditions of moderate coronary occlusion using near-infrared spectroscopic (NIRS) and thermal imaging. In anesthetized open chest pigs an inflatable occluder and flow probe were placed around the left anterior descending artery (LAD). In the ischemic group (n = 11) LAD occlusion (50% flow, 80 min) was followed by complete occlusion (10 min, n = 4), and reflow. Dipyridamole was infused (0.14 mg/min/kg/4 min) intravenously during 50% occlusion. In the control group (n = 6) LAD flow was temporarily increased (hyperemic response) by two 2-min periods of complete LAD occlusion applied 120 min apart, with a 4-min period of dipyridamole infusion between the two occlusions. NIRS and thermal images were acquired throughout the protocol. Maps of subepicardial oxygen saturation parameter (OSP), and epicardial temperature (T) were obtained. Partial occlusion reduced OSP and the temperature by 0.23 +/- 0.08 and 0.88 +/- 0.39 degrees C versus remote region, respectively. Dipyridamole decreased systolic blood pressure by 36%, which caused further decline in the LAD flow to 18% and OSP and T by 0.37 +/- 0.01 and 2.46 +/- 0.32 degrees C, respectively. Reflow restored OSP and T to their baseline levels. In control group dipyridamole and hyperemia increased LAD flow 2-4-fold associated with moderate increase in OSP and T. OSP and T showed linear dependence on the flow below 100%, which is leveled-off at flows above normal. Dipyridamole increases differences in the epicardial oxygenation and T between normal and moderately ischemic areas due to enhancement of disparity in perfusion of these areas.

Visualization and grading of regional ischemia in pigs in vivo using near-infrared and thermal imagingThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute

Reductions in regional coronary flow result in tissue deoxygenation and decrease in surface temperature, changes detectable by near-infrared spectroscopic (NIRS) and thermal imaging, respectively. In anesthetized open-chest pigs, an inflatable occluder and flow probe were placed around the left anterior descending artery. Gated NIRS and nongated thermal images were acquired at baseline, partial (17% and 50%), and complete occlusion and reflow. At each step, dobutamine was infused (10 μg·min–1·kg–1) for 7–9 min to increase blood pressure and flow. Changes in the oxygen saturation parameter, rate of indocyanine green flow tracer passage, and the surface temperature were correlated with the measured left anterior descending artery flow. Location and sizes of the areas of reduced oxygenation, indocyanine green uptake, and temperature were similar. Decrease in the coronary flow to 50% and 17% of baseline resulted in progressive decrease in the above parameters, whereas increase in flow from 75% to ~250% achieved by dobutamine and reactive hyperemia did not significantly change them. Dobutamine increased total and epicardial flow in ischemic areas and increased subepicardial oxygenation. NIRS and thermal imaging provide epicardial maps of oxygen saturation and perfusion that reveal ischemic areas. Combination of these techniques may be useful in the coronary artery bypass graft (CABG) surgery setting.

Impaired myocardial perfusion reserve in experimental hypercholesterolemia is independent of myocardial neovascularization

Our objective was to investigate the functional role of hypercholesterolemia-associated myocardial neovascularization in early atherosclerosis using the antiangiogenic thalidomide. Experimental atherosclerosis is characterized by myocardial neovascularization, associated with a decrease in myocardial perfusion response to challenge, coronary endothelial dysfunction, and high oxidative stress. However, the functional significance of these neovessels is not known. Three groups of pigs (n = 6 each) were studied after 12 wk of normal or hypercholesterolemic diet without (HC) or with thalidomide (HC + Thal). Myocardial perfusion and permeability were assessed at baseline and in response to cardiac challenge, using electron beam computed tomography, and coronary endothelial function was assessed using organ chambers. Myocardial samples were scanned ex vivo with a three-dimensional microscopic computed tomography scanner, and the spatial density of the myocardial microvessels was quantified. Growth factors and oxidative stress were measured in the myocardial tissue. As a results of these procedures, myocardial perfusion response to adenosine and dobutamine was blunted in both HC and HC + Thal pigs compared with normal pigs (P < 0.05, HC and HC + Thal vs. normal) as was the coronary endothelial function. Myocardial permeability response to adenosine was increased in both HC and HC + Thal pigs compared with normal pigs (P < 0.05, HC and HC + Thal vs. normal, and HC + Thal vs. HC). The microvascular density was increased in HC pigs compared with normal pigs but normalized in HC + Thal pigs (P < 0.001 HC vs. normal and HC + Thal). HC + Thal pigs showed decreased expression of Flk-1 and basic FGF but increased expression of VEGF compared with normal and HC pigs. Oxidative stress was increased in both HC and HC + Thal pigs compared with normal pigs. In conclusion, chronic administration of thalidomide attenuates myocardial neovascularization in experimental HC pigs without affecting myocardial perfusion response to stimulation. This suggests that the myocardial neovascularization may not contribute to the attenuated myocardial perfusion response in hypercholesterolemia.

Noninvasive monitoring of medical therapy

An extensive literature base documents the substantial incremental prognostic value of nuclear cardiology compared with information provided by risk factors, clinical history, electrocardiographic stress testing results, and coronary arteriography. A smaller, well-established and growing literature addresses the unique potential of nuclear cardiology to assess therapeutic response of ischemic heart disease to lifestyle and medical therapies in individual patients. General guidelines focus on management of individual risk factors based on large studies, but may not reflect the optimum treatment strategy for an individual patient. The central rationale for noninvasive serial monitoring is to optimize the effectiveness and timing of lifestyle, medical, and revascularization therapies to minimize coronary event risk. Ideally, this monitoring of therapy should be early in the management of coronary artery disease (CAD) and guide the need for more intensive therapeutics. The application of technical advances in serial monitoring has the potential to revolutionize the way we diagnose and prevent CAD, even in asymptomatic patients. The potential long-term cost effectiveness of positron emission tomography and single-photon emission CT myocardial perfusion scintigraphy in detecting and monitoring treatment of CAD offers great promise for reducing coronary events in known or suspected ischemic heart disease.

Evaluation of the patient with diabetes mellitus and suspected coronary artery disease

Coronary artery disease (CAD) is the leading cause of morbidity and mortality in patients with diabetes mellitus. In fact, patients with diabetes have the same risk of myocardial infarction as do nondiabetic subjects with a history of infarction. For this reason, diabetes has been designated by the American College of Cardiology (ACC) and the American Heart Association (AHA) as a CAD equivalent. For women, data indicate a substantially elevated risk of cardiovascular disease (CVD) even before a clinical diagnosis of type 2 diabetes has been made. Identifying patients with diabetes who have CAD and who will benefit from medical and/or invasive intervention to prevent cardiovascular events is a challenge in both symptomatic and asymptomatic patients. The decision to evaluate patients with diabetes who are asymptomatic for CAD presents the greatest challenge; investigation will reveal 10% to 15% of these patients to have CAD. Current diagnostic tools include exercise tolerance testing, stress echocardiography, stress myocardial perfusion imaging (MPI), and cardiac catheterization. Few guidelines are available to aid in the choice of testing modalities for a given patient. Although cardiac catheterization is useful, it is generally reserved for patients in whom invasive intervention is suitable. The American Diabetes Association (ADA) recommends exercise tolerance testing alone in symptomatic patients with > or = 2 CAD risk factors or an abnormal resting electrocardiogram (ECG). However, that recommendation is not based on data; it is the consensus of an expert panel. Stress echocardiography is a useful, noninvasive procedure; however, there is limited experience with this technology in the diabetic population. Recently accumulated data support both diagnostic and prognostic roles for stress MPI, particularly with ECG-gated single-photon emission computed tomographic imaging. In symptomatic patients with diabetes, the presence and extent of abnormal stress MPI findings have been found to be highly accurate independent predictors of subsequent cardiac events: 18% to 26% of asymptomatic patients with diabetes have perfusion defects consistent with CAD. However, CVD risk factors are not predictive of abnormal MPI findings even though duration of diabetes and abnormal ECGs are. The results of future studies may be helpful in guiding the selection of asymptomatic patients to undergo myocardial perfusion and function studies. In conclusion, MPI provides clinicians with an important diagnostic tool, because it offers perfusion as well as functional information for diagnosis and risk stratification in patients with diabetes. These capabilities facilitate decision making regarding the appropriateness of medical therapy or surgical intervention in these individuals.

Comparative profile of vasodilation by CVT-3146, a novel A2A receptor agonist, and adenosine in conscious dogs

The purpose of this study was to determine the magnitude of vasodilation by CVT-3146 in different vascular beds and to compare it with that by adenosine in conscious dogs. Intravenous bolus injections of CVT-3146 (0.1-2.5 microg/kg) or adenosine (10-250 microg/kg) caused a dose-dependent increase in the coronary blood flow (CBF) and a dose-dependent decrease in the late diastolic coronary resistance. Although the maximal increase in CBF response to the two drugs was not significantly different, the ED50 of CVT-3146 and adenosine were 0.45 +/- 0.07 microg/kg and 47 +/- 7.77 microg/kg, respectively. The highest dose of CVT-3146 caused a much longer coronary vasodilation than the highest dose of adenosine. There were no significant differences in increases in cardiac output induced by higher doses of CVT-3146 or adenosine. Most importantly, CVT-3146 resulted in a smaller decrease in total peripheral resistance (TPR) compared to that seen with adenosine. In addition, CVT-3146 yielded a smaller increase in the lower body flow (LBF) than adenosine. Adenosine also caused dose-dependent renal vasoconstriction, whereas CVT-3146 did not affect the renal blood flow. The administration of CVT-3146 or adenosine caused a dose-dependent vasodilation in the mesentery, which was not significantly different from each other. In summary, CVT-3146 is a 100-fold more potent coronary vasodilator than adenosine. CVT-3146 causes smaller decreases in TPR and smaller increases in LBF than those induced by adenosine, indicating that it is more selective for coronary than peripheral vasodilation. Furthermore, CVT-3146 did not cause renal vasoconstriction. These features make CVT-3146 a better candidate for pharmacologic stress testing.

Simvastatin preserves myocardial perfusion and coronary microvascular permeability in experimental hypercholesterolemia independent of lipid lowering

OBJECTIVES; This study was designed to assess the lipid-independent effects of simvastatin on myocardial perfusion (MP) and coronary microvascular permeability index (PI) at baseline and during episodes of increased cardiac demand in experimental hypercholesterolemia.

BACKGROUND

Simvastatin preserves coronary endothelial function in experimental hypercholesterolemia independent of its lipid-lowering effect. However, the functional significance of this observation is unknown.

METHODS

Pigs were randomized to three groups: normal diet (N), high-cholesterol diet (HC) and HC diet plus simvastatin (HC+S) for 12 weeks. Subsequently, cardiac electron beam computed tomography was performed before and during intravenous infusion of adenosine and dobutamine, and MP and PI were calculated.

RESULTS

Total and low density lipoprotein cholesterol levels were similarly and significantly increased in HC and HC+S animals compared with N. Basal MP was similar in all groups. Myocardial perfusion significantly increased in response to either adenosine or dobutamine in N and HC+S animals. Dobutamine also significantly increased MP in HC animals. However, the changes of MP in response to either drug were significantly lower in the HC group compared with the other two groups (p < 0.01 for adenosine and p < 0.05 for dobutamine vs. N and HC+S). Basal PI was similar in all groups and was not altered by either drug in N and HC+S animals. In contrast, PI significantly increased in HC pigs during infusion of either adenosine (p < 0.001) or dobutamine (p < 0.05).

CONCLUSIONS

These findings demonstrate that chronic administration of simvastatin preserves myocardial perfusion response and coronary microvascular integrity during cardiac stress in experimental hypercholesterolemia independent of lipid lowering.

Effect of adrenergic stimulation on Rb(+) uptake in normal and ischemic areas of isolated pig hearts: (87)Rb MRI study

The role of adrenergic stimulation in Rb(+) uptake in normal and ischemic areas of pig hearts was investigated using an agonist (dobutamine) and an antagonist (S-propranolol). The left anterior descending artery (LAD) in isolated pig hearts was cannulated to maintain adequate perfusion of the LAD bed (2.2-2.8 ml/min/g). Rb(+) loading was initiated by switching perfusion to Rb(+)-containing Krebs-Henseleit (KH) buffer in the presence of 0.1 microM dobutamine, 0.5 microM propranolol, or no drug (control), and the LAD flow was reduced to 10% of the baseline for 120 min. The flow through the LAD was then restored to normal and the drugs were removed. In all groups the rate of Rb(+) uptake obtained from serial (87)Rb images was severely depressed in the ischemic anterior wall relative to that in the normal posterior wall. Dobutamine increased the rate of Rb(+) uptake in the posterior wall (6.3% +/- 1.4% vs. 2.5% +/- 0.25% per minute in control) and did not affect the rate in the anterior wall (0.86% +/- 0.40% vs. 1.14% +/- 0.19% per minute in control). Propranolol did not affect Rb(+) uptake in either of these areas. We conclude that the stimulation of Rb(+) uptake by dobutamine is related to activation of Na(+)/K(+) ATPase and passive Na(+) influx in normal tissue. The lack of any effect of propranolol implies a low level of endogenous norepinephrine during low-flow (LF) ischemia.

Inotropic stress with arbutamine is superior to vasodilator stress with dipyridamole for the detection of reversible ischemia with Tc-99m sestamibi single-photon emission computed tomography

BACKGROUND

There is a paucity of data comparing the relative merits of inotropic and vasodilator stress Tc-99m sestamibi single-photon emission computed tomography (SPECT) for the detection of coronary artery disease and reversible ischemia.

METHODS AND RESULTS

Twenty-seven patients referred for diagnostic coronary arteriography underwent separate day dipyridamole and arbutamine Tc-99m sestamibi SPECT imaging with simultaneous two-dimensional echocardiography. The sensitivity of arbutamine and dipyridamole Tc-99m sestamibi for the detection of coronary artery disease was 100% (21 of 21) and 90% (19 of 21), respectively, with a specificity of 66% (4 of 6) for both. Coronary artery disease was detected in all six patients with single vessel disease by both stress modalities. The sensitivity for prediction of multivessel disease was 66% (10 of 15) for arbutamine and 46% (7 of 15) for dipyridamole stress. Arbutamine stress induced a greater extent and severity of perfusion abnormality at peak stress (peak perfusion score 25 +/- 6.2 and 21 +/- 5.9 for arbutamine and dipyridamole, respectively, p = 0.001) and reversible perfusion defects (difference between peak stress and rest scores 8.8 +/- 5.5 and 5.2 +/- 4.4 for arbutamine and dipyridamole, respectively, p = 0.001). Furthermore a significantly higher percentage of reversible defects induced by arbutamine stress was associated with wall thickening abnormality on simultaneous echocardiography, which is a more specific marker of myocardial ischemia (88% and 24% for arbutamine and dipyridamole, respectively, p = 0.002).

CONCLUSION

Inotropic stress may be superior to vasodilators for the determination of the extent and severity of myocardial involvement and reversible ischemia by Tc-99m sestamibi SPECT.