Left ventricular and biventricular pacing in congestive heart failure

Dual-chamber pacing improved hemodynamics acutely in a subset of patients with left ventricular (LV) dysfunction but conveyed no long-term symptomatic benefit in most. More recently, LV pacing and biventricular (multisite) pacing have been used to improve systolic contractility by altering the electrical and mechanical ventricular activation sequence in patients with severe congestive heart failure (CHF) and intraventricular conduction delay or left bundle branch block (LBBB). Intraventricular conduction delay and LBBB cause dyssynchronous right ventricular and LV contraction and worsen LV dysfunction in cardiomyopathies. Both LV and biventricular cardiac pacing are thought to improve cardiac function in this situation by effecting a more coordinated and efficient ventricular contraction. Short-term hemodynamic studies have shown improvement in LV systolic function, which seems more pronounced with monoventricular LV pacing than with biventricular pacing. Recent clinical studies in limited numbers of patients suggest long-term clinical benefit of biventricular pacing in patients with severe CHF symptoms. Continuing and future studies will demonstrate whether and in which patients LV and biventricular pacing are permanently effective and equivalent and which pacing site within the LV produces the most beneficial hemodynamic results.

Use of a new myocardial centroid for measurement of regional myocardial dysfunction by electron beam computed tomography: comparison with technetium-99m sestamibi infarct size quantification

RATIONALE AND OBJECTIVES

The study compared the performance of conventional endocardial and epicardial centroid algorithms with the new "myocardial" centroid algorithm in patients with anterior myocardial infarction. "Floating" endocardial or epicardial centroid algorithms, commonly used in tomographic imaging methods to assess regional motion, may misrepresent left ventricular regional myocardial function in the presence of markedly asymmetric left ventricular contraction.

METHODS

A new centroid algorithm based on regional myocardial mass distribution was tested in 29 patients with a first anterior myocardial infarction and was compared with conventional centroid algorithms. Direct comparisons in 60 equal sectors at one midventricular level per patient were performed between electron beam computed tomography and technetium-99m sestamibi single-photon emission computed tomography. The thresholds of regional myocardial function used to define infarction were varied for regional ejection fraction from 20% to 40% and for regional wall thickening from 0 to 4 mm. Regression and Bland-Altman analysis were used to compare infarct size by regional myocardial function with infarct size by sestamibi single-photon emission computed tomography.

RESULTS

The new myocardial centroid showed the least shift toward infarcted myocardium from diastole to systole and had the highest amplitudes of the measurement curves for regional ejection fraction and regional wall thickening. The optimal regional myocardial function thresholds for each centroid algorithm for regional ejection fraction were endocardial, 30% (R = 0.62; mean difference to sestamibi, -0.5% +/- 22.1% tomographic infarct size points); epicardial, 30% (R = 0.79; mean difference, 2.2% +/- 13.1% tomographic infarct size points); and new myocardial, 25% (R = 0.88; mean difference, -0.6% +/- 9.5% tomographic infarct size points). The optimal thresholds for regional wall thickening were endocardial, 1 mm (R = 0.70; mean difference, -2.2% +/- 14.3% tomographic infarct size points); epicardial, 1 mm (R = 0.78; mean difference, -4.6% +/- 12.7% tomographic infarct size points); and new myocardial, 2 mm (R = 0.71; mean difference, 2.1% +/- 14.1% tomographic infarct size points). The best agreement (R = 0.88) between electron beam computed tomography infarct size and sestamibi single-photon emission computed tomography infarct size was achieved with regional ejection fraction and the new myocardial centroid algorithm.

CONCLUSIONS

In asymmetrically contracting left ventricles, the new myocardial centroid algorithm is superior to conventional methods for tomographic analysis of regional myocardial function.

Evaluation of the coronary venous system using electron beam computed tomography

New therapeutic strategies in interventional cardiology and electrophysiology involve the coronary veins. This study examines the potential usefulness of electron beam computed tomography to obtain detailed noninvasive definition of the coronary venous anatomy and of arteriovenous relationships. Electron beam computed tomography allows acquisition and three-dimensional reconstruction of tomographic images of the beating heart with high spatial and temporal resolution. Contrast-enhanced, thin-section electron beam computed tomographic coronary arteriographic images of 34 patients (21 men and 13 women, age 60+/-10 years) were analyzed. The visibility of the coronary veins and their spatial relationship to the coronary arteries were assessed qualitatively on two- and three-dimensional displays. The coronary sinus was visible in 91%, the great cardiac vein in 100%, the middle cardiac vein in 88%, at least one vein overlying the lateral surface of the left ventricle in 97%, the anterior interventricular vein in 97%, and the small cardiac vein in 68%. A left marginal and a left posterior vein were seen in 44%, one of the two in 38%, and neither in 3%. The course of the anterior interventricular vein was parallel to the left anterior coronary artery in 79% and a crossover between the two vessels at an obtuse angle occurred in 12%. Contrast-enhanced electron beam computed tomography imaging of the heart noninvasively provides information on the coronary venous system and arteriovenous relationships that may help guide new interventional procedures.

[Economic aspects of using electron beam computerized tomography]

Electron beam computed tomography (EBCT) allows visualization and quantification of calcium in the coronary arteries. This has been demonstrated to correlate well with the overall plaque burden in the coronary arteries. EBCT is, therefore, well suited for the detection of early stages of coronary atherosclerosis. Especially in asymptomatic patients with several risk factors, staging coronary artery disease by coronary calcium, scanning may allow prognostic assessment and guide preventive and therapeutic interventions. To date, only scant data are available regarding the cost effectiveness and the economic impact of this imaging technique. In this manuscript we compare various methods for the diagnosis of coronary artery disease using a theoretical model and review the results of a prospective trial in our emergency room of coronary calcium scanning in patients with acute chest pain. Using Framingham data and prognostic data from long-term follow-up, we discuss the impact of coronary calcification scanning on primary preventive measures and its economical consequences. EBCT is a promising technique which has created a lot of attention due to its ease of application. It is currently undergoing critical appraisal in the medical literature. Further randomized prospective trials are needed (and underway, i.e., MESA, EDIC, CARDIA II) to better define its value and limitations in the clinical arena.

Differentiation of intracardiac tumors and thrombi by echocardiographic tissue characterization: comparison of an artificial neural network and human observers

The feasibility of classifying ultrasound images of intracardiac tumors and thrombi with a neural network-based algorithm was compared with the performance of experienced echocardiographers. The neural network used statistical descriptors of the apparent echocardiographic texture of the masses, and the blinded echocardiographers were given photographic prints of enlarged regions of interest without clinical data. The network classified 66% of the images correctly and the echocardiographers, 83%. The network and echocardiographers agreed in 88% of the images. Human observers usually base their classification of intracardiac masses on clinical data. The echocardiographic texture of tumors is quantitatively different from that of thrombi. This difference can be recognized by a neural network and potentially be useful in assisting with the diagnosis when clinical clues are insufficient.

Digoxin, hypercalcaemia, and cardiac conduction

The cardiac effects of hypercalcaemia are usually manifest as a shortening of the QT-interval. Hypercalcaemia is infrequently associated with a clinically manifest arrhythmia. However, concomitant therapy with digoxin or underlying cardiac disease can potentiate the arrhythmogenic effects of hypercalcaemia, leading to a symptomatic rhythm disorder. We describe a symptomatic arrhythmia, which developed in a patient with hypercalcaemia secondary to squamous cell carcinoma of the bronchus. The patient was on digoxin therapy at the time. The arrhythmia did not recur after discontinuation of digoxin therapy and correction of the hypercalcaemia. Because of its effect on cardiac conduction, hypercalcaemia should be considered in the evaluation of any patient with an unexplained bradyarrhythmia. Conversely, patients with hypercalcaemia should discontinue digoxin therapy and be evaluated for the presence of rhythm disorders while receiving appropriate treatment for hypercalcaemia.

Comparison of measurement of left ventricular ejection fraction by Tc-99m sestamibi first-pass angiography with electron beam computed tomography in patients with anterior wall acute myocardial infarction

The goal of this study was to compare measurements of left ventricular (LV) ejection fraction (EF) by first-pass radionuclide angiography ("first-pass angiography") using technetium-99m (Tc-99m) sestamibi with those by contrast-enhanced electron beam computed tomography ("electron beam tomography") as a reference technique in patients with an anterior wall acute myocardial infarction (AMI). Twenty-five patients with first Q-wave anterior wall AMI underwent paired electron beam tomographic and first-pass angiographic studies (mean, 1 day apart). Fourteen patients had 2 sets of measurements of the LVEF obtained by both methods (separated by at least 6 weeks), for a total of 39 paired measurements. LVEF by electron beam tomography was calculated from absolute systolic and diastolic LV chamber volumes. LV volumes by electron beam tomography were 199 +/- 51 ml at end-diastole and 111 +/- 42 ml at end-systole. Mean LVEF was 45 +/- 11% by first-pass tomography and 46 +/- 9% by electron beam tomography. The linear correlation coefficient between both methods was 0.82 (p <0.0001), with slope = 1.0, y-intercept = -1.1, and SEE = 6.1. The mean difference between the 2 methods was -0.7 +/- 6.0 EF units (p = 0.75). The correlation between the differences and means of both methods was 0.34 (p = 0.04), indicating a trend for first-pass angiography to overestimate LVEF in the higher range. LVEFs measured by first-pass angiography in patients with abnormal LV geometry and contraction patterns caused by anterior wall AMI agree well with those measured by electron beam tomography in the clinically relevant range.

[Electron beam tomography in cost effective diagnosis of coronary heart disease]

BACKGROUND

Electron beam CT (EBCT) can acquire rapid, multiple thin-section tomograms of the beating heart in synchrony with the electrocardiogram and quantity coronary calcification without intravenous contrast. Coronary calcification is an active process exclusively associated with atherosclerotic plaque formation and regulated in a manner similar to the calcification of bone. Clinical studies have demonstrated that EBCT coronary calcification (1) follows a pattern similar to the epidemiology of coronary artery disease (CAD), (2) has a high sensitivity (90-95%) for coronary plaque and significant angiographic coronary stenoses, and (3) has the potential to assess the prognosis of patients with coronary atherosclerotic disease. Coronary calcium area or "score" correlates best with overall plaque burden within the coronary system. However, coronary calcium is of limited value in distinguishing coronary stenosis on a segment-by-segment basis.

EBCT AND CAD

Due to spiraling health care costs, there is a need for cost-efficient strategies in the diagnosis and stratification of patients with known or suspected CAD. There are two major patient groups in which EBCT calcium scanning has a potential for cost-efficient application: (1) in asymptomatic, high-risk patients, identification of significant plaque burden may direct judicious use of long-term drug therapy or further investigation to those individuals most likely to benefit from an aggressive risk factor modification and medical program; (2) in patients with chest pain syndromes but no prior CAD, EBCT calcium scanning compares favorably with conventional diagnostic methods. In particular, using receiver operating characteristic analysis, the sensitivity and specificity of an EBCT calcium score of 80 in detecting obstructive CAD are both about 85%. Using a theoretical model, EBCT calcium scanning was found to be the most cost-effective approach to diagnosis in populations with a low-to-moderate likelihood of obstructive CAD when compared with treadmill exercise, stress thallium, and stress echocardiography.

CONCLUSIONS

EBCT calcium scanning is not a substitute for coronary angiography, but it has clear advantages over other more traditional diagnostic methods for CAD. In particular, it can be performed conveniently and inexpensively in most patients. Additionally, the site and extent of calcification are intimately related to the atherosclerotic plaque burden. The analyses presented suggest that it may also provide a cost-effective clinical alternative in specific subsets of the population.

Three-dimensional reconstruction of color Doppler jets in the human heart

A computer algorithm has been developed for segmentation and three-dimensional (3D) reconstruction of Doppler color-flow images. The algorithm enables the user to select a range of velocities, represented by colors, for segmentation and subsequent 3D reconstruction. The reconstructed flows are assigned a color palette and merged with the volume-rendered gray-scale image to produce a 3D image containing both flow and anatomic information. The results demonstrate the application of the algorithm to regurgitant and shunt jets with complex spatial and velocity patterns. We conclude that 3D reconstruction of selected color spectra (e.g., velocities) of Doppler color flows and surrounding anatomy is feasible in the clinical setting.

Extent of atherosclerosis and remodeling of the left main coronary artery determined by intravascular ultrasound

This study used intravascular ultrasound (IU) to assess the incidence and extent of left main coronary artery (LMCA) disease and the effects of arterial remodeling. Sixty-nine patients undergoing cardiac catheterization were imaged with a 20 MHz rotational-tip IU device. Nine of the 69 studies (13%) could not be analyzed because of technical (n = 2) or anatomic (n = 7) reasons. Of the remaining 60 patients, 38 (63%) had at least 1 lesion in the left coronary artery perfusion territory by angiography; significant LMCA stenosis was present in 2 patients (3%). Intravascular ultrasonography demonstrated plaques in 27 of 60 LMCAs (45%), 6 of them in patients with normal angiograms. Twenty-four plaques (89%) were eccentric and calcium was present in 4 (15%). The mean minimal lumen diameter was 4.9 +/- 0.8 mm, the maximal lumen diameter was 5.6 +/- 0.8 mm, the planimetered lumen area was 22.6 +/- 6.0 mm2, the plaque area was 3.9 +/- 5.8 mm2, the vessel area was 26.5 +/- 5.9 mm2, and the area stenosis was 13 +/- 19%. In the 27 patients with plaque, plaque area was 8.7 +/- 5.7 mm2 and the area stenosis was 30 +/- 17%. The vessel area was significantly larger in diseased LMCAs (p < 0.001) and correlated with plaque area (r = 0.46). IU examination of the LMCA was feasible in 87% of patients and was more reliable for delineating plaques than angiography.

Three-dimensional ultrasound imaging of the atrial septum: normal and pathologic anatomy

OBJECTIVES

This study investigated the feasibility of producing three-dimensional gray scale ultrasound images of the atrial septum to demonstrate normal and pathologic anatomy.

BACKGROUND

Two-dimensional echocardiography is the principal technique used for imaging the atrial septum. Although the diagnostic accuracy of two-dimensional echocardiography is high, its capability for displaying complex three-dimensional relations is limited.

METHODS

Three-dimensional ultrasound images were reconstructed from tomographic images obtained during routine transesophageal echocardiographic examinations. Custom-made semi-automatic algorithms for image enhancement, interpolation and segmentation were used to produce volumetric gray scale images. Volume-rendered displays of the atrial septum were generated for analysis. Sequential three-dimensional images were generated through the cardiac cycle and displayed cinematographically to permit assessment of motion.

RESULTS

The three-dimensional images obtained from six patients clearly demonstrated normal and pathologic anatomy of the atrial septum, including atrial septal defects, atrial septal aneurysm and aortic valve ring abscess. The images could be manipulated electronically to demonstrate spatial relations and internal structural details.

CONCLUSIONS

Three-dimensional gray scale reconstruction of ultrasound images obtained by transesophageal echocardiography is feasible. These images clearly demonstrate anatomic details and spatial relations. The gray scale images may be interactively manipulated to optimize the clinician's visualization of the atrial septum and its associated pathologic conditions.

Three- and four-dimensional cardiovascular ultrasound imaging: a new era for echocardiography

Three-dimensional and four-dimensional ultrasonography were pioneered in the 1960s yet have been used little clinically. Only recently have advances in cardiovascular ultrasound equipment and in digital image storage, manipulation, and display techniques made three- and four-dimensional imaging clinically feasible. In this report, we review the historical development of these technologies during 3 decades to their culmination in current state-of-the-art technology. Examples of such multidimensional images are presented, with special emphasis on clinical applications. Although several limitations persist, three-dimensional cardiovascular ultrasonography seems likely to enhance imaging of the heart and vessels in a manner similar to the advent of two-dimensional echocardiography in the M-mode era. Clinician-scientists will soon be able to extract an object, such as the heart, from the body electronically for the purpose of anatomic, functional, and histologic analysis without adverse effect on the patient.

Multidimensional visualization in echocardiography: an introduction

X-ray films depict three-dimensional objects as shadows in a two-dimensional plane; thus, objects become superimposed. Computed tomography and other types of tomographic imaging, such as ultrasonography, acquire two-dimensional images of a material property within a thin slice. Sequential adjacent two-dimensional tomograms can be used to construct three-dimensional displays of objects. Visualization, a field of computer science, enables scientists to measure image attributes (extraction of features), identify features (classification), separate objects from one another (segmentation), and produce comprehensible, information-dense images from three-dimensional data sets (rendering). A three-dimensional rendering of the heart can be used to represent only one component of the heart, such as the atrial septum or the ventricular chamber, and can be shaded or colored to enhance comprehension. Three-dimensional images rendered sequentially over time result in a dynamic four-dimensional display. This report describes multidimensional visualization of objects and tissues and specifically discusses examples from echocardiography.

Classification of morphologic effects of percutaneous transluminal coronary angioplasty assessed by intravascular ultrasound

The aim of this study was the assessment and classification of the morphologic effects of percutaneous transluminal angioplasty (PTCA) by intravascular ultrasound (IU). Fifty-eight patients were examined immediately after PTCA with a 4.8Fr, 20 MHz rotational tip IU system. In 10 patients (17%), IU images could not be analyzed due to failure of the imaging system or poor image quality. In 48 patients (83%; 40 men and 8 women, aged 55 +/- 9 years), IU images of 48 PTCA segments, as well as 41 distal and 44 proximal sites, were analyzed. The left anterior descending artery was studied in 30 patients, the right coronary artery in 17 and the left main coronary artery in 1. Calcium was present in 32 of 48 PTCA segments (67%). Plaque morphology was concentric in 18 patients (38%) and eccentric in 30 (62%). Seven distinct morphologic patterns were observed. In concentric plaques, plaque compression without significant wall alterations (type 1) was found in 2 patients (4%), superficial tears within the plaque (type 2) in 1 (2%) and deep tears (type 3) in 8 (17%). Deep tearing associated with submedial or subintimal dissection (type 4) was found in 2 patients (4%). Dissection between plaque and vessel wall without noticeable intimal tearing (type 5) was the most common morphology (n = 15; 31%) and occurred in concentric and eccentric plaques. In eccentric plaques, no significant tearing of the plaque (type 6) was found in 6 patients (13%), and tearing of the plaque close to its base with dissection (type 7) in 14 (29%).(ABSTRACT TRUNCATED AT 250 WORDS)