American journal of cardiac imaging最新文献

In vitro data have shown that the myocardium exhibits nonlinear passive stress-strain relationship and a non-linear pressure-volume relationship. A finite element (FE) analysis and optimization algorithm was used on three-dimensional reconstructed left ventricular (LV) geometry using echocardiographic images, along with hemodynamic measurements, in seven closed-chest dogs to show a nonlinear stress-strain relationship in vivo. Our analysis included the computation of Poisson's ratio from the measured volumetric strain of the myocardium and a simulated pericardial pressure load ("equivalent pericardial pressure") applied to the epicardial surface of the reconstructed LV. LV geometry was reconstructed in three or four incremental time steps in diastasis and the myocardium was assumed to be homogeneous, isotropic, and linearly elastic during these short intervals in this initial study. Simultaneous LV chamber pressure and equivalent pericardial pressure were incorporated into the algorithm to predict actual LV expansion. Computations were performed iteratively at each interval to compute the optimized elastic modulus. By performing the FE analysis and optimization at each interval (a step-wise linear analysis approach), a linear relationship between the myocardial elastic modulus and LV chamber pressure was derived (r = .87 to .98). Such a linear relationship is equivalent to an exponential myocardial stress-strain relationship in vivo. Detailed measurement of nonhomogeneous regional deformation are becoming possible with the advent of sophisticated imaging techniques. The methodology described in this study, with appropriate modifications in the FE analysis and optimization algorithms, can be applied to assess the complex three-dimensional pressure-deformation characteristics in vivo.

This review summarizes coronary artery calcification as a marker of coronary atherosclerosis as historically noted and detected with radiographic imaging modalities. This review concentrates on the use of ultrafast computed tomography (CT) for coronary artery calcification imaging. Ultrafast CT is uniquely qualified for imaging of the coronary arteries and calcific deposits in particular because of the x-ray attenuation characteristics of calcium. Current validation studies are summarized. In particular, the sensitivity of ultrafast CT coronary calcification in angiographically proven obstructive disease has been shown by many investigators to be above 90%, but with specificity on the order of 40% to 50%. These numbers may be different for younger men and women, where the detection of smaller calcific deposits is more difficult. The positive predictive value has been calculated as between 72% by angiographic validation and 40% in a population with a lower pretest bias.

The prediction of perioperative cardiac events remains a challenging issue in clinical cardiology. The most important cause of perioperative cardiac morbidity and death continues to be myocardial infarction, which is associated with a high prevalence of occult coronary artery disease. A large amount of data substantiates the validity of scintigraphic perfusion imaging for accurate diagnosis of coronary artery disease, as well as the prediction of prognosis in stable coronary disease, post-myocardial infarction, and in the preoperative setting. A normal stress perfusion scan predicts an extremely low rate of future cardiac events. The best predictor of future adverse cardiac events is the quantitative extent, severity, and reversibility of jeopardized myocardium, parameters that are easily assessed with perfusion scintigraphy. Although the sensitivity of scintigraphy for detecting coronary disease is high, the reported specificity of abnormal perfusion scans for predicting cardiac events is variable. Indiscriminant use of this technique with subsequent referral for angiography based on the presence of any perfusion abnormality will result in excessive, costly, and potentially dangerous screening procedures. However, thoughtful consideration of both the extent and severity of perfusion abnormality can appropriately stratify the majority of patients into low-, intermediate-, and high-risk groups. Further efforts should be directed at prospectively evaluating the use of quantitative perfusion defect and reversibility scores in various subgroups of patients to optimize the specificity of these techniques and determine the optimal degree of defect extent and severity that warrants invasive evaluation.

The echocardiographic characteristics of vegetation used by precordial echocardiography (PE) have been transferred unchanged to transesophageal echocardiography (TEE), which has different image definition and structural resolution. Twelve diagnostic criteria of vegetation were tested for their accuracy in 52 patients evaluated by PE and TEE for suspected endocarditis (36 men, 16 women; mean age, 62 +/- 18 years; 42 with proven endocarditis). Results of PE and TEE were validated against gross anatomic and histologic findings. Significant differences (P < .05) included the fact that TEE disclosed more vegetations not prolapsing in the subvalvular region and in absence of valvular regurgitation. At TEE vegetations presented motion distinct from the endocardial surface, irregular conformation, and uneven margins. Only chaotic motion was significantly associated with vegetations at PE; size < 0.5 cm and increased echogenicity characterized pseudovegetations at PE. Other features such as shaggy echoes or location out of the annular zone (previously indicated as typical of vegetations) were not significantly associated with infective lesions. Discriminant analysis of TEE characteristics of vegetations disclosed that chaotic motion was the variable most significantly (P = .008) associated with vegetation. Coexistence of this sign with size < 0.5 cm and uneven margins was associated with 93.3% sensitivity and 83.7% specificity. In conclusion, the echocardiographic aspect of vegetations is rather different when examined from the precordial and the transesophageal approach. Learning about pitfalls and normal variants should improve TEE specificity in the assessment of infective lesions.

The aim of this protocol was to test the feasibility and safety of a prototype steerable intravascular ultrasound (IVUS) catheter (Boston Scientific, Waterton, MA) in comparison with standard IVUS catheters. A 3.5F, 20-MHz mechanical echo transducer was incorporated into a bendable sheath with a blunt tip. The flexible IVUS catheter was compared with a standard IVUS catheter in 13 patients. Seven patients underwent catheterization of the left side of the heart, and six patients had catheterization of the right side of the heart for suspected recurrent pulmonary embolism. In the aorta, three lumen area measurements were made: (1) midway between the aortic arch and the aortic root, (2) at the most cranial part of the aorta, and (3) in the descending aorta at the level of the diaphragm. Evaluation of the accuracy of luminal dimension measurements by both types of catheters in perpendicular positions to the vessel wall was evaluated in a hollow rubber cast of an human aorta and its side branches, representing luminal diameters from 3 to 26 mm. We performed 20 measurements with each type of catheter. The results were compared with ruler measurements, after the cast had been cut in slices. The equation for the standard 3.5F IVUS catheter was: y = 0.89x + 0.15; SE = 0.17; r = .97; for the 4.8F 20-MHz standard IVUS catheter: y = 0.97x + 0.05; SE = 0.18; r = .98; and for the steerable catheter, y = 0.94x + 0.09; SE = 0.12; r = 0.97.(ABSTRACT TRUNCATED AT 250 WORDS)

Ischemic papillary muscle rupture is a potentially lethal complication of myocardial infarction. Acute mitral regurgitation, shock with pulmonary edema, may ensue as its result. Transthoracic echocardiography is the initial noninvasive tool used to confirm the diagnosis. Transesophageal echocardiography has overcome some of the limitations of transthoracic imaging, permitting timely surgical management of these critically ill patients.

Rest technetium 99m-sestamibi uptake may underestimate myocardial viability in asynergic territories. Because nitrate administration was reported to improve thallium 201 uptake in perfusion defects, this study aimed to test the influence of nitrates on 99mTc-sestamibi uptake and on the tracer capability to recognize viable tissue in asynergic segments. In 23 patients with prior infarction and left ventricular dysfunction, regional wall motion was assessed by echocardiography before and after revascularization (13 segments/patient). Group 1 included 97 normokinetic; group 2, 97 hypokinetic; and group 3, 105 akynetic or dyskinetic segments; group 3 was divided into group 3A (72 segments unchanged after revascularization) and group 3B (33 segments with functional recovery). 99mTc-sestamibi uptake was graded using a scoring scheme in the same 13 segments both at rest and, on a separate day, injecting the tracer during isosorbide dinitrate infusion (ISDN). At rest, the mean 99mTc-sestamibi uptake decreased significantly from group 1 through group 3. With ISDN, the mean 99mTc-sestamibi uptake increased in all groups compared with rest, but the increase was significant only in groups 2 and 3, and within the latter, only in group 3B. Thus, with ISDN group 3B was no longer different from group 2. Only 6% of group 3A segments showed an improved uptake with ISDN, versus 33% of group 3B (P < .00005). At rest only 14 of 33 segments of group 3B showed a normal or slightly reduced uptake, whereas these were 25 of 33 with ISDN (P < .02). In conclusion, the acute administration of ISDN increases the uptake of 99mTc-sestamibi mainly in those asynergic territories that show postrevascularization functional recovery. Therefore, ISDN 99mTc-sestamibi imaging might improve the tracer capability to detect viable hibernating myocardium.