New modalities of regional and global left ventricular function analysis: state of the art

Validation of cadmium-zinc-telluride camera for measurement of left ventricular systolic performance

BACKGROUND

There are paucity of data comparing measurements of left ventricular systolic performance using cadmium-zinc-telluride (CZT) semiconductor cameras with other imaging modalities. This study compared the new system with echocardiography (echo) and cardiac magnetic resonance (CMR) imaging.

METHODS

60 Patients presenting with ST-elevated myocardial infarction (MI) were included. Each patient underwent echo, myocardial perfusion imaging using Spectrum Dynamics D-SPECT(r) (CZT-SPECT), and CMR 6 weeks after MI. The primary endpoint was the agreement between CZT-SPECT and CMR for left ventricular ejection fraction (LVEF) measurement.

RESULTS

48 of the 60 patients underwent all 3 studies (echo, CMR, and CZT-SPECT) 40 days after admission. CZT-SPECT and CMR LVEF were well correlated (r = .79, P < .0001), as well as CZT-SPECT vs echo and CMR vs echo (r = .79 and .84, respectively, P < .0001). The segmental LV wall thickening and wall motion also showed good concordance between three techniques.

CONCLUSIONS

CZT-SPECT is reliable for LVEF measurement.

Tracking of regions-of-interest in myocardial contrast echocardiography

Analysis of intramyocardial perfusion by contrast echocardiography provides quantitative parameters for the assessment of ischemic disease. This analysis can be achieved by applying an ultrasound (US) burst of high mechanical index to destroy contrast bubbles, measuring various myocardial refilling parameters from the time curves obtained from regions-of-interest (ROIs) within the myocardial wall. To obtain reliable intensity curves, the position of the ROIs must be tracked to compensate for the heart motion along the sequence. In this work, we studied the use of optical flow techniques for ROI repositioning. Two block-matching and one differential technique were evaluated for this purpose. Performance was measured by comparing the result of automatic tracking with results of ROI repositioning by a human expert. This evaluation was carried out on experimental data from animals as well as on sequences from clinical studies. Results are considered to be accurate enough for clinical purposes, and computation times may allow for a real-time processing if incorporated into a US scanner.

Alternative Echocardiographic Methods to Assess Left Ventricular Diastolic Function

The standard noninvasive method to assess left ventricular diastolic function has been pulsed Doppler echocardiographic recordings of mitral inflow early diastolic (E) and atrial (A) filling velocities and the ratio of E to A, in combination with isovolumic relaxation and deceleration times. Pulmonary venous inflow velocities (systolic, diastolic, and atrial reversal) are used to assess left atrial and left ventricular end-diastolic pressures. These measurements are influenced by changes in preload, including left ventricular end-diastolic pressure, left atrial or pulmonary capillary wedge pressure, and left ventricular volumes. Newer methods such as tissue Doppler imaging (TDI) of the mitral annulus and color M-mode recording of left ventricular diastolic flow propagation (FP) have now evolved as additional techniques for detecting abnormalities in left ventricular diastolic function that can complement the standard pulsed Doppler echocardiography methods. Both TDI and color M-mode flow FP appear to offer distinct advantages as relatively load-independent measures of diastolic function. TDI can be used for measurement of regional diastolic myocardial velocities at the mitral annulus, and it is particularly useful in identifying abnormalities of left ventricular diastolic relaxation or estimation of left ventricular filling pressures. Color M-mode FP can be used for quantification of abnormalities of left ventricular relaxation and diastolic filling characteristics of the left ventricle.

Four-dimensional reconstruction of the left ventricle using a fast rotating classical phased array scan head: preliminary results

The evaluation of left ventricular function by noninvasive methods is still a major problem in cardiology. Two-dimensional echocardiography requires mental reconstruction of the heart by the physician and is always based on approximation of heart shapes and volumes. Three-dimensional echocardiography is promising but has rhythmic and function constraints because of the acquisition during many cardiac cycles. This article reports a study carried out to validate a new 4-dimensional echocardiography method. With the use of a classical phased-array sensor with a fast rotating motorized motion and a standard ultrasound system, many slices at different angulations are obtained in a single cardiac cycle. After manual endocardial delineation and computation, a representation of the left ventricle (beating heart) and a volume quantification are obtained at each instant of the cardiac cycle. This method has been tested on 11 healthy volunteers and the results are in agreement with those obtained with standard 2-dimensional echocardiography. Because of its simplicity of operation and short time acquisition, this new imaging modality is highly valuable in left ventricle evaluation, even if further studies on pathologic hearts need to be performed.

Imaging three-dimensional cardiac function

The three-dimensional (3-D) nature of myocardial deformations is dependent on ventricular geometry, muscle fiber architecture, wall stresses, and myocardial-material properties. The imaging modalities of X-ray angiography, echocardiography, computed tomography, and magnetic resonance (MR) imaging (MRI) are described in the context of visualizing and quantifying cardiac mechanical function. The quantification of ventricular anatomy and cavity volumes is then reviewed, and surface reconstructions in three dimensions are demonstrated. The imaging of myocardial wall motion is discussed, with an emphasis on current MRI and tissue Doppler imaging techniques and their potential clinical applications. Calculation of 3-D regional strains from motion maps is reviewed and illustrated with clinical MRI tagging results. We conclude by presenting a promising technique to assess myocardial-fiber architecture, and we outline its potential applications, in conjunction with quantification of anatomy and regional strains, for the determination of myocardial stress and work distributions. The quantification of multiple components of 3-D cardiac function has potential for both fundamental-science and clinical applications.

Tissue Doppler imaging: a useful echocardiographic method for the cardiac sonographer to assess systolic and diastolic ventricular function

Tissue Doppler imaging (TDI) has evolved to become a useful noninvasive method that can complement other echocardiographic techniques in the assessment of left ventricular myocardial velocities in a variety of clinical conditions. Color 2-dimensional and color M-mode TDI are used for quantification of systolic myocardial velocities during myocardial ischemia at rest and with pharmacologic stress testing. Spectral pulsed TDI can provide measurements of regional systolic and diastolic myocardial velocities, and it is particularly useful in the identification of abnormalities of left ventricular diastolic relaxation. This review summarizes the clinical applications of TDI to promote understanding of its utility in the evaluation of left ventricular myocardial function.

Cardiovascular structure and function in baboons with Type 1 diabetes -- a transvenous ultrasound study

Diabetes mellitus is an important risk factor for both macrovascular and cardiac disease in humans. The availability of a novel intravenous ultrasound probe allows detailed interrogation of a large proportion of the vasculature, as well as the heart, during the same examination. Six male baboons (Papio hamadryas) with Type 1 diabetes and known microangiopathy, and six control animals were studied. Vascular structure in the major large arteries and cardiac function were studied using transvenous ultrasound introduced via the right femoral vein and positioned under fluoroscopy. All arteries were examined for atherosclerotic plaque and for presence of increased intima-media thickness (IMT). Left ventricular function was assessed at rest and following infusions of dobutamine (positive inotrope) and esmolol (negative inotrope). The procedure was performed safely and successfully in all cases. No atherosclerotic plaque was seen in either diabetic or normal baboons. There was no difference in the aortic IMT (0.38+/-0.04 vs. 0.37+/-0.05 mm, normal vs. diabetic, P=NS) or in doppler flow in the renal or iliac arteries between diabetic and normal baboons. Left ventricular wall thickness and systolic tissue velocity were similar in the two groups at rest (6.9+/-2.5 vs. 6.2+/-1.4 cm/s, normal vs. diabetic, P=NS), after dobutamine (15.5+/-2.2 vs. 12.7+/-3.9 cm/s, normal vs. diabetic, P=NS), and after esmolol (4.3+/-1.0 vs. 5.6+/-1.0 cm/s, normal vs. diabetic, P=NS). In a high primate model of diabetes with microangiopathy, the presence of hyperglycemia for 7 years per se does not produce abnormalities of macrovascular or cardiac structure.

New insights into regional systolic and diastolic left ventricular function with tissue Doppler echocardiography: from qualitative analysis to a quantitative approach

Tissue Doppler echocardiography is a variation of conventional Doppler flow imaging. This modality allows quantification of the Doppler shift within the range of myocardial tissue motion. The velocity at a variety of myocardial sites can be determined and distinguished very rapidly by using Doppler techniques. The velocity of moving tissue can be studied with pulsed wave tissue Doppler sampling, which displays the velocity of a selected myocardial region against time, with high temporal resolution. In addition, the velocities can be calculated with time-velocity maps and displayed as color-encoded velocity maps in either an M-mode or 2-dimensional format. This review will focus on the technical aspects and the different methods of tissue Doppler echocardiography for the analysis of regional systolic and diastolic left ventricular function. Whereas pulsed wave tissue Doppler echocardiography allows measurements of velocities of a selected myocardial region, color tissue Doppler gives the best overview of cardiac dynamics because the entire scanned color data are displayed simultaneously. However, there is an increasing need for objective evaluation of tissue Doppler information. Digital images and postprocessing of the data allow for quantitative off-line analysis, and the different approaches and parameters proposed from different centers are discussed.

Tissue Doppler imaging of the fetal heart

OBJECTIVES

The objectives of this study were: (i) to assess the feasibility of a tissue Doppler imaging (TDI) evaluation in the fetus, (ii) to identify color-TDI patterns consistent with the various phases of the cardiac cycle; and (iii) to assess myocardial velocities and the myocardial velocity gradient.

METHODS

Eighty-nine normal fetuses between the 17th and the 37th week of gestation were studied. Color-TDI was superimposed on an apical four-chamber view of the fetal heart and three cardiac cycles captured in cine-loop format. By reviewing the cine-loop strip, color patterns consistent with the various phases of the cardiac cycle were identified. The procedure was then repeated with a transverse four-chamber view. On each frame corresponding to mid-systole, early and late diastole, myocardial velocities were calculated at the subepicardial and subendocardial layer and regressed against gestational age. Statistics included correlation and regression analysis, calculation of the 95% confidence intervals and of the Cronbach's alpha reliability coefficient for repeated observations.

RESULTS

TDI examination is acceptably reproducible in the fetus. We were able to identify color-TDI patterns depicting the systolic contraction wave, ventricular relaxation and atrial contraction. Statistical evaluation demonstrated that: all variables (systolic right and left subendocardial and subepicardial velocities, early diastolic right and left subendocardial and subepicardial velocities, end diastolic right and left subendocardial velocities, right subepicardial velocities) except end-diastolic right and left subepicardial velocities, showed a positive correlation with advancing gestational age; subendocardial velocities were higher than subepicardial ones throughout the cardiac cycle in both ventricles; systolic myocardial velocities were higher in the left ventricle whereas early diastolic velocities were higher in the right ventricle; and the ratio between early and late diastolic subendocardial velocities (EM/AM) was constantly < 1 and did not change with advancing gestational age.

CONCLUSIONS

TDI evaluation of the fetal heart is feasible and reproducible. Color-TDI is able to identify the various phases of the cardiac cycle. Quantitative evaluation of myocardial velocities has shown also in the fetus the existence of the myocardial velocity gradient found in postnatal life.

Transesophageal echocardiographic (TEE) evaluation of ventricular function

Transesophageal echocardiography (TEE) provides excellent delineation of ventricular function in the ambulatory and critical settings. Major indications include the acutely ill patient with suboptimal images with other techniques and the intraoperative assessment of patients undergoing cardiac surgery and of cardiac patients undergoing noncardiac surgery. The methodology of quantification of ventricular function is quite accurate, though it has inherent limitations. Newer technologies, such as edge enhancement techniques, three-dimensional acquisition, and contrast agents, all have the potential to improve evaluation of ventricular function with TEE. Stress imaging with TEE is possible with dobutamine and with pacing techniques. This is sage and accurate, and it is indicated in patients, such as the morbidly obese, who are impossible to image by other methods.

The echocardiography laboratory in the informatic era

This article overviews the latest progress in echocardiography in this informatic era. We will present new, different techniques available in clinical settings for qualitative and quantitative evaluation of global and regional left ventricular function, showing their helpfulness in clinical work. We will also report our personal experiences with 3-dimensional (3-D) echocardiography in quantification of left ventricular total mass and left-ventricular dysfunctional mass, and in evaluation of left-ventricular parietal stress. Finally, we will show how the organization of a modern echocardiography laboratory is changing after informatic progress: we will report our personal experiences about transmission of echocardiography data between 2 work stations, located in different places; in this way we can realize an informatic web, which can go out from the single echocardiography laboratories and move toward intradepartment and interdepartment services.

Dobutamine stress echocardiography for the diagnosis of myocardial viability: assessment of left ventricular systolic velocities in longitudinal axis by pulsed Doppler tissue imaging

Dobutamine (DOB) stress two-dimensional echocardiography is an established method for the detection of viable myocardium, but conventional assessment of wall motion is subjective. We measured quantitatively the left ventricular systolic velocities along the longitudinal axis by pulsed Doppler tissue imaging (DTI). In 30 patients with previous myocardial infarction, pulsed DTI focused on the infarct area was performed from an apical two- or four-chamber view before and during DOB (10 microg/kg/min) stress one day before coronary angioplasty. We calculated peak systolic velocity (S), regional pre-ejection period (PEP, the time interval from the onset of QRS to the onset of systolic wave) and regional ejection time (ET). Left ventriculography was obtained before and 3 months after coronary angioplasty to assess regional wall motion. Improvement of abnormal wall motion was observed in 19 patients (group P) but not in 11 (group N). Group P had significantly larger S and smaller PEP/ET than group N during DOB stress, although there were no significant differences in these indices between the groups at baseline. As a consequence, group P had a significantly larger percent change in S and a smaller percent change in PEP/ET than group N (164+/-39 vs 117+/-20% and 88+/-17 vs 116+/-29%, respectively, p < 0.01). It is suggested that the quantitative measurement of longitudinal systolic velocities during DOB stress by DTI is useful for the precise assessment of myocardial viability.

Intraoperative Echocardiography for the Patient Undergoing Minimally Invasive Heart Surgery

Minimally invasive heart surgeries are commonly used to avoid large surgical incisions and facilitate early extubation and recovery after cardiac surgeries. Trans esophageal echocardiography (TEE) is especially valu able in minimally invasive cardiac surgery because the inherently limited access to the thorax and mediasti num impairs direct visualization of the heart. TEE influ ences the clinical decision making process in several ways. Changes to the anesthetic management include alteration in volume loading in the presence of diastolic dysfunction or left ventricular outflow tract obstruction, as well as augmenting coronary perfusion pressure and implementing coronary vasodilators for new regional wall motion abnormalities. Changes to the surgical plans include replacement or repair for regurgitant valves, placement of intra-aortic balloon pumps for persistent regional wall motion abnormalities, and changing the surgical approach in the presence of severe aortic disease. Currently, two approaches are commonly used in minimally invasive cardiac surgery. The first approach, port-access minimally invasive car diac surgery, continues to use cardiopulmonary bypass. This approach relies extensively on TEE to correctly place endovascular devices necessary for cardiopulmo nary bypass in addition to routine assessment of car diac function. The second approach, minimally invasive direct coronary artery bypass, involves performing the revascularization on a beating heart. Here, TEE is essen tial for assessment of ventricular function if ischemic preconditioning is used as a strategy for myocardial protection.

Intracoronary shunt prevents left ventricular function impairment during beating heart coronary revascularization

OBJECTIVE

Beating heart coronary revascularization is becoming increasingly popular world-wide. Temporary occlusion of the coronary artery is often required in order to perform the anastomosis. An alternative method to maintain perfusion is to use an intracoronary shunt. In this study, we monitored global left ventricular function and regional wall motion in the presence or absence of a shunt using transesophageal echocardiography (TEE).

METHOD

Left ventricular wall motion score index (WMSI), wall motion score (WMS) in the left anterior descending (LAD) coronary artery territory, and ejection fraction (EF%) were measured by multiplane TEE during construction of the left internal mammary artery (LIMA)-LAD coronary artery anastomosis in 40 patients undergoing revascularization with or without the use of a shunt. WMSI was assessed preoperatively, 1, 3 and 6 min during the construction of the anastomosis and after 5 min of reperfusion. WMS was assessed at 6 min during anastomosis and after 5 min of reperfusion. EF% was calculated preoperatively, 5 min into the construction of the anastomosis, and 5 min after reperfusion.

RESULTS

During construction of the anastomosis, when the shunt was used, there were no changes in WMSI, WMS in the LAD territory or EF%. A significant decline in these parameters was seen in the group in which the shunt was not used, although on reperfusion all the values returned to baseline control.

CONCLUSION

(i) occlusion of the LAD to perform the anastomosis results in temporary impairment in left ventricular function with complete recovery on reperfusion; (ii) the use of an intracoronary shunt presumably by maintaining myocardial perfusion prevents deterioration in ventricular function; (iii) from this data it seems therefore advisable to use an intracoronary shunt in patients with unstable angina, poor left ventricular function, or in cases in which a longer time to perform the anastomosis is anticipated.