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Biomedical subjects

Mani A Vannan

Publications and source records attributed to Mani A Vannan.

At least 19 recordsLinked to original sources
PubMed2006

Left ventricular structure and function: basic science for cardiac imaging.

The myofiber geometry of the left ventricle (LV) changes gradually from a right-handed helix in the subendocardium to a left-handed helix in the subepicardium. In this review, we associate the LV myofiber architecture with emerging concepts of the electromechanical sequence in a beating heart. We discuss: 1) the morphogenesis and anatomical arrangement of muscle fibers in the adult LV; 2) the sequence of depolarization and repolarization; 3) the physiological inhomogeneity of transmural myocardial mechanics and the apex-to-base sequence of longitudinal and circumferential deformation; 4) the sequence of LV rotation; and 5) the link between LV deformation and the intracavitary flow direction observed during each phase of the cardiac cycle. Integrating the LV structure with electrical activation and motion sequences observed in vivo provides an understanding about the spatiotemporal sequence of regional myocardial performance that is essential for noninvasive cardiac imaging.

Aging↗
PubMed2005

Myocardial contrast echocardiography for the detection of coronary artery stenosis: a prospective multicenter study in comparison with single-photon emission computed tomography.

OBJECTIVES: The purpose of this study was to compare myocardial contrast echocardiography (MCE) with single-photon emission computed tomography (SPECT) for the detection of significant coronary artery disease (CAD) in patients with symptoms suggestive of CAD. BACKGROUND: Single-photon emission computed tomography is a well-established method of assessing patients with CAD. Myocardial contrast echocardiography is a new technique allowing bedside assessment of myocardial perfusion. We hypothesized that MCE was comparable to SPECT in the assessment of patients with known or suspected CAD. METHODS: A total of 123 patients scheduled for coronary angiography underwent intermediate (mechanical index 0.5) triggered replenishment MCE and SPECT imaging at rest and after vasodilator stress. Coronary angiography was performed within four weeks of stress imaging. RESULTS: In total, 96 of 123 (78%) patients demonstrated CAD (stenosis >/=50%). There was no difference in the sensitivity of MCE compared with SPECT in the detection of CAD (84% vs. 82%; p = NS), and both demonstrated similar specificity (56% vs. 52%, respectively). In patients with multivessel disease, MCE and SPECT also demonstrated similar sensitivity (91% and 88%, respectively) for the detection of CAD. Agreement between MCE and SPECT for the presence or absence of CAD was 73%. CONCLUSIONS: Myocardial contrast echocardiography is comparable to SPECT in the detection of CAD not only on a patient basis but also in the localization of disease by vascular territory in a relatively high-risk population.

Contrast Media↗
PubMed2005

Effect of cardiac resynchronization therapy on longitudinal and circumferential left ventricular mechanics by velocity vector imaging: description and initial clinical application of a novel method using high-frame rate B-mode echocardiographic images.

Cardiac resynchronization therapy (CRT) has emerged as an important method to treat patient with symptomatic heart failure with evidence of intraventricular dyssynchrony. Tissue Doppler imaging by echocardiography has been shown to be an excellent tool for the assessment of mechanical left ventricular dyssynchrony and the selection of patients for CRT. However, there are some patients who do not show symptomatic improvement following CRT. One possible explanation for this is the need to optimize not only longitudinal synchrony, but also improve the circumferential and radial dynamics of the left ventricle. Doppler imaging does not allow reliable assessment of the latter because of the angle-dependency of the technique. Velocity Vector Imaging (VVI) is a newer technique which is angle-independent and thus provides an avenue to evaluate short-axis mechanics of the left ventricle. We describe a case in which VVI was used to assess the left ventricular dynamics in a patient with heart failure who did not respond to CRT.

Algorithms↗
PubMed2004

Catheter-based intracardiac echocardiography in the interventional cardiac laboratory.

Recent advances in technology have engendered a renewed enthusiasm in the use of intracardiac echocardiography (ICE) to guide and assess cardiac interventions. AcuNav is a phased-array sector imaging probe equipped with color and spectral Doppler capabilities. Previous-generation imaging catheters yielded unfamiliar limited-depth radial images with no flow information. Current imaging technology such as the AcuNav has not only consolidated the role of ICE but opened newer applications in the interventional laboratory. ICE has clear advantages over transesophageal echocardiography as the imaging modality of choice in the cardiac catheterization and electrophysiological laboratories. We review the technical evolution of ICE and describe the expanded utility of the AcuNav imaging catheter during cardiac interventions.

Cardiac Catheterization↗
PubMed2004

Microbubble contrast agents for echocardiography: rationale, composition, ultrasound interactions, and safety.

Imaging the small blood vessels within the myocardium, which contains only a small fraction of the total coronary blood volume, is a significant challenge for ultrasound imaging. Recent advances in microbubble design and ultrasound technology have improved our ability to image the microcirculation. It is essential to understand the fundamentals of microbubble behavior in an ultrasound field and how it impacts technology and safety.

Coronary Vessels↗
PubMed2004

Imaging technologies and techniques.

Equipment manufacturers provide contrast-specific detection techniques that have excellent sensitivity and excellent agent-to-tissue specificity along with helpful tools that improve workflow efficiency dramatically. Excellent contrast agents have been approved for LV opacification and are available worldwide. Techniques designed for low-MI imaging offer real-time acquisition capabilities and lead to faster examinations. Techniques designed for medium-MI imaging offer better sensitivity than low-MI techniques while maintaining the benefit of rapid image acquisition. Techniques designed for high-MI imaging offer the best sensitivity with longer acquisition times. These techniques are viable means for imaging contrast agents tailored to clinical needs. Progress by contrast agent manufacturers, equipment manufacturers, and physicians will continue to drive improvements in the areas of detection and clinical workflow for improved patient care.

Coronary Circulation↗
PubMed2004

Myocardial contrast echocardiography in acute coronary syndromes.

MCE is a reliable, bedside technique for assessment of a patient with acute coronary syndrome. It can be used to estimate the myocardial risk-area and infarct size and to establish peri-infarct viability. This information is critical in both management decision-making and in assigning prognosis in the setting of acute coronary syndromes.

Echocardiography↗
PubMed2004

Targeted ultrasound imaging using microbubbles.

Targeted ultrasound imaging uses acoustically active contrast agents bearing a ligand on the surface that binds to a function-specific molecule. These ultrasound contrast agents are typically gas-filled microbubbles, nongaseous liposomes, or lipid-encapsulated perfluorocarbon emulsions. Binding of the contrast agent to the target results in persistent contrast enhancement during ultrasound imaging. This approach has been applied to the ultrasound imaging of pathophysiologic processes such as inflammation associated with ischemia reperfusion, heart transplant rejection, atherosclerotic plaque, thrombus, and apoptosis.

Animals↗
PubMed2004

Myocardial contrast echocardiography in chronic ischemic and nonischemic cardiomyopathies.

The coronary microcirculation is integral in the pathophysiology of both ischemic and non-ischemic cardiomyopathies. MCE is a unique tool for studying microcirculatory integrity, not only to aid diagnosis and determination of prognosis but also to guide interventions and management. The expanding paradigm of microcirculatory disturbances may in the future also include hypertensive and diabetic heart disease.

Cardiomyopathies↗
PubMed2003

Targeting of apoptotic macrophages and experimental atheroma with radiolabeled annexin V: a technique with potential for noninvasive imaging of vulnerable plaque.

BACKGROUND: Apoptosis is common in advanced human atheroma and contributes to plaque instability. Because annexin V has a high affinity for exposed phosphatidylserine on apoptotic cells, radiolabeled annexin V may be used for noninvasive detection of apoptosis in atherosclerotic lesions. METHODS AND RESULTS: Atherosclerotic plaques were produced in 5 rabbits by deendothelialization of the infradiaphragmatic aorta followed by 12 weeks of cholesterol diet; 5 controls were studied without manipulation. Animals were injected with human recombinant annexin V labeled with technetium-99m before imaging. Aortas were explanted for ex vivo imaging, macroautoradiography, and histological characterization of plaque. Radiolabeled annexin V cleared rapidly from the circulation (T1/2, alpha 9 and beta 46 minutes). There was intense uptake of radiolabel within lesions by 2 hours; no uptake was seen in controls. The results were confirmed in the ex vivo imaging of the explanted aorta. Quantitative annexin uptake was 9.3-fold higher in lesion versus nonlesion areas; the lesion-to-blood ratio was 3.0+/-0.37. Annexin uptake paralleled lesion severity and macrophage burden; no correlation was observed with smooth muscle cells. DNA fragmentation staining of apoptotic nuclei was increased in advanced lesions with evolving necrotic cores, predominantly in macrophages; the uptake of radiolabel correlated with the apoptotic index. CONCLUSIONS: Because annexin V clears rapidly from blood and targets apoptotic macrophage population, it should constitute an attractive imaging agent for the noninvasive detection of unstable atherosclerotic plaques.

Animals↗
PubMed2003

Delineation of intracardiac shunts using contrast echocardiography.

Contrast echocardiography is useful to visualize the endocardial borders of the left ventricle and improve the signal intensity of spectral Doppler signals. It can also help to define intracardiac flow dynamics in complex situations. We report 2 cases where contrast echocardiography improved the delineation of complex shunts and also provided new information not available by conventional echocardiography.

Adult↗
PubMed2003

Detection of resting myocardial perfusion defects by SonoVue myocardial contrast echocardiography.

BACKGROUND: SonoVue is a new microbubble contrast agent containing sulfur hexafluoride. We assessed the efficacy of SonoVue myocardial contrast echocardiography (MCE) to detect resting perfusion abnormalities. METHODS: Nineteen adult patients with a wall motion abnormality in a screening echocardiogram were studied. Each patient received up to four bolus injections of 2.0 mL SonoVue (Bracco Diagnostics, Inc.) during echocardiographic examination using either B-mode(n = 12)or power Doppler(n = 7)imaging. Each patient also had SPECT nuclear perfusion imaging performed. Segmental assessment of myocardial perfusion from SonoVue MCE images were compared with corresponding SPECT nuclear images. RESULTS: Using B-mode imaging, the mean number of views obtained with a single SonoVue injection ranged from 1.4 to 1.9, with 2 or 3 injections required for a complete examination. Ninety-four percent of segments were scored as diagnostic. Agreement between B-mode and SPECT images was 72% for segments with a perfusion defect, 86% for normal perfusion, and 80% for segments with either perfusion defect or normal perfusion (all views combined). Using power Doppler imaging, the mean number of views obtained with a single SonoVue injection ranged from 1.0 to 1.3, with 2 to 4 injections required for a complete examination. Sixty-eight percent of segments were scored as diagnostic. Agreement between power Doppler and SPECT images was 67% for perfusion defects, 53% for segments with normal perfusion, and 59% for segments with either perfusion defect or normal perfusion (all views combined). CONCLUSIONS: SonoVue MCE has the potential to assess myocardial perfusion at rest. B-mode imaging was more accurate than power Doppler imaging when compared with SPECT nuclear imaging.

Aged↗
PubMed2003

Myocardial contrast echocardiography in acute myocardial infarction.

PURPOSE OF REVIEW: Myocardial contrast echocardiography (MCE) has evolved into an important clinical tool for imaging coronary microcirculation. It can be used to delineate the spectrum of perfusion derangements that characterize acute myocardial infarction. RECENT FINDINGS: Presently, MCE uses microcirculatory perfusion as the basis to distinguish myocardial necrosis and viability in the post-infarct stage. Its future role may expand to image cellular integrity, inflammation, and angiogenesis, all of which contribute to the pathophysiology of the myocardial infarction. SUMMARY: This review provides an update of the current role and future clinical applications of MCE in acute myocardial infarction.

Acute Disease↗
PubMed2002

Methods of contrast administration for myocardial perfusion imaging: continuous infusion versus bolus injection.

The debate over the optimal contrast administration method involves many issues. This article discusses bolus versus infusion administration pertaining to myocardial perfusion imaging. Continuous infusion ensures efficient and optimal data capture during contrast studies and is preferred over bolus injection for both theoretical and practical reasons. Although bolus administration is easier, its relative disadvantages outweigh its usefulness in myocardial perfusion imaging.

Contrast Media↗
PubMed2002

Catheter-based interventions guided solely by a new phased-array intracardiac imaging catheter: in vivo experimental studies.

BACKGROUND: Intracardiac echocardiography (ICE) has had useful but limited use during interventional procedures because of technologic limitations. We used a novel phased-array ICE device (AcuNav) with 2-dimensional sector imaging and full Doppler capability to see whether it could guide cardiac interventions without fluoroscopy. METHODS: Twelve dogs were studied, and we performed atrial septostomy, tricuspid, and pulmonary valve disruption using only ICE. Preinterventional and postinterventional anatomic and hemodynamic data were noted. RESULTS: All attempts were successful in the placement of the ICE catheter (100%). We attempted septostomy on 11 dogs and were successful 8 times (73%). Tricuspid valve disruption and balloon dilatation were performed successfully on 5 dogs (100%). We attempted pulmonary valve disruption on 4 dogs and could always correctly place the guidewire (100%). We performed pulmonary valve balloon dilatation on one dog (25%). A comprehensive echocardiographic examination was always possible. CONCLUSION: This new ICE device can guide interventions without fluoroscopy. However, further studies are needed to evaluate whether it can replace fluoroscopy.

Animals↗