Nuclear and echocardiographic imaging for prediction of reversible left ventricular ischemic dysfunction after coronary revascularization: current status and future directions

Three-dimensional canine heart model for cardiac elastography

PURPOSE

A three-dimensional finite element analysis based canine heart model is introduced that would enable the assessment of cardiac function.

METHODS

The three-dimensional canine heart model is based on the cardiac deformation and motion model obtained from the Cardiac Mechanics Research Group at UCSD. The canine heart model is incorporated into ultrasound simulation programs previously developed in the laboratory, enabling the generation of simulated ultrasound radiofrequency data to evaluate algorithms for cardiac elastography. The authors utilize a two-dimensional multilevel hybrid method to estimate local displacements and strain from the simulated cardiac radiofrequency data.

RESULTS

Tissue displacements and strains estimated along both the axial and lateral directions (with respect to the ultrasound scan plane) are compared to the actual scatterer movement obtained using the canine heart model. Simulation and strain estimation algorithms combined with the three-dimensional canine heart model provide high resolution displacement and strain curves for improved analysis of cardiac function. The use of principal component analysis along parasternal cardiac short axis views is also presented.

CONCLUSIONS

A 3D cardiac deformation model is proposed for evaluating displacement tracking and strain estimation algorithms for cardiac strain imaging. Validation of the model is shown using ultrasound simulations to generate axial and lateral displacement and strain curves that are similar to the actual axial and lateral displacement and strain curves.

Current role of contrast echocardiography in the diagnosis of cardiovascular diseases

The use of contrast echocardiography (CE) in cardiovascular medicine has grown significantly over the last 15 years. Depending on the site of injection, contrast enhancement of the right- or left-sided cardiac chambers or myocardium now can be achieved. Contrast echocardiography can improve the evaluation of patients with valvular heart disease by enhancing the Doppler signal; CE also improves detection of intracardiac or intrapulmonary shunts. In patients with coronary artery disease, enhancement of the endocardial blood-tissue boundary allows for improved visualization of endocardial wall motion, assessment of wall thickening, and calculation of ejection fraction. Contrast echocardiography promises to delineate myocardial perfusion and has the potential for quantitating coronary flow and assessing myocardial viability. These applications may add important physiologic information to the anatomic information readily available from noncontrast echocardiography. Because it can be rapidly performed at the bedside, CE may be a valuable tool for use with inpatients with acute myocardial ischemia. When CE has been used after recanalization of occluded coronary arteries, the assessment of myocardial salvage conveys information concerning reflow, stunning, and prognosis, and in the case of an angioplasty it provides immediate information regarding the success of the procedure. Contrast echocardiography can also assess myocardial areas at risk of irreversible damage and the presence or absence of collateral flow. When performed with transesophageal or epicardial echocardiography in the operating room, CE is emerging as a valuable tool in the assessment of cardioplegia distribution and graft patency as well as in the delineation of the regional supply of each graft. With the continued development of newer contrast agents and refinement of ultrasound imaging equipment, the applications of CE will continue to grow.

Concordance between dobutamine Doppler tissue imaging echocardiography and rest reinjection thallium-201 tomography in dysfunctional hypoperfused myocardium

OBJECTIVE

To evaluate the efficiency of the new technique colour Doppler tissue imaging (DTI) by studying the concordance between dobutamine DTI, standard grey scale echocardiography (SE), and rest-reinjection TI-201 tomography (TI) in dysfunctional myocardium.

PATIENTS

23 patients with chronic wall motion abnormalities and proven coronary artery disease (> 70% diameter stenosis of at least one major coronary artery at angiogram).

METHODS

The contractile reserve and the resting perfusion characteristics of dysfunctional myocardial segments were assessed with low dose dobutamine SE and/or DTI (2.5 up to 20 gamma/kg/min) and TI on a semiquantitative basis. The DTI or SE data were separately compared with TI, on the basis of a 13 segment ventricular model. The resulting score of combined DTI and SE was also compared with TI. Finally the results obtained from DTI were compared with SE.

RESULTS

A total of 142 severely hypokinetic or akinetic segments were visualised. The viability study was feasible in 127 (89%) and 121 (85%) segments with DTI and SE, respectively. TI detected viability more frequently than DTI (84 v 61, p < 0.001) and SE (80 v 50, p < 0.001). However, as many viable segments were detected with combined DTI and SE as with TI (78 v 84, NS). The kappa values between TI and SE, DTI or combined SE and DTI were 0.38, 0.45, and 0.57, respectively, and increased to 0.52 and 0.76, respectively, for SE and DTI versus TI when mid-anterior and mid-inferior segments only were considered. The kappa value between SE and DTI was 0.34.

CONCLUSIONS

DTI is a helpful adjunct to SE, when using low dose dobutamine. This combination revealed as many viable segments as TI and showed a better agreement than DTI or SE alone for the assessment of myocardial viable segments evidenced by TI.

Ultrasonic tissue characterization in patients with dilated cardiomyopathy: comparison with findings from right ventricular endomyocardial biopsy

AIM

The clinical usefulness of integrated backscatter (IB) imaging was compared with right ventricular endomyocardial biopsy for assessing myocardial damage in patients with dilated cardiomyopathy (DCM).

METHODS

We examined 15 patients with DCM and 20 healthy controls. In addition to the conventional M-mode echocardiographic parameters, we determined the cyclic variation in IB values (CV-IB) obtained from parasternal short axis views of the left ventricle just under the transducer for both the interventricular septum (IVS) and the left ventricular posterior wall (PW). The per cent fibrosis area (%) and the transverse diameter of myocytes (microm) were measured in right ventricular endomyocardial biopsy specimens by computer image analysis. To analyze the relationship between pathological findings and CV-IB, we divided patients into four subgroups on the basis of the pathological characteristics of endomyocardial biopsy specimens as follows: degeneration dominant group (n = 5), fibrosis dominant group (n = 5), dilated phase hypertrophic cardiomyopathy (n = 2), and mixed type (n = 3).

RESULTS

CV-IB in the IVS and the PW was lower in patients with DCM (8.8 +/- 2.9, 8.3 +/- 2.7 dB, respectively) than in normal subjects (14.4 +/- 2.9, 13.6 +/- 2.6 dB, respectively). Biopsy findings showed a mean per cent fibrosis area of 24.0 +/- 12.3%, and a mean myocyte diameter of 14.3 +/- 2.9 microm in patients with DCM. CV-IB was correlated with both of these findings: per cent fibrosis area (r = -0.56 in IVS, r = -0.56 in PW) and myocyte diameter (r = 0.67 in IVS, r = 0.71 in PW). CV-IB was decreased in all DCM subgroups compared with normal subjects, but there was no significant difference between subgroups.

CONCLUSIONS

CV-IB was correlated with both the extent of fibrosis in myocardial tissue and the myocyte diameter. These findings suggest that ultrasonic tissue characterization is a good indicator of the severity of fibrosis and myocyte atrophy in patients with DCM.