Improved 3-D-echocardiographic endocardial border delineation using the contrast agent FS069 (Optison) transesophageal studies in a porcine model

Impact of myocardial contrast echocardiography on vascular permeability: comparison of three different contrast agents

Microvascular permeabilization, petechial hemorrhage and premature ventricular contractions (PVCs) have been demonstrated in an in vivo rat model of myocardial contrast echocardiography (MCE). The purpose of this study was to compare these effects for three US Food and Drug Administration (FDA)-approved ultrasound (US) contrast agents (US CA): Optison, Definity and Imagent. Evans blue dye, an indicator of microvascular permeability, and a contrast agent were injected IV in anesthetized rats suspended in a water bath to mimic scanning depths seen in clinical echocardiology. Diagnostic US B-mode scans with 1:4 end-systolic triggering were performed at 1.7 MHz using a cardiac phased-array scanhead to provide a short axis view of the left ventricle. To elicit readily measurable effects for comparisons, relatively high doses of the agent were used (50 to 500 microL kg(-1) for Optison, 25 to 200 microL kg(-1) for Imagent, 10 to 100 microL kg(-1) for Definity). Microvascular leakage was characterized by the area of Evans blue dye coloration on the hearts and by extraction of the dye from tissue samples. The number of petechia were counted on the epicardial surface of excised hearts. PVCs were counted from ECG traces recorded with the MCE images. Neither evidence of capillary leakage nor PVCs were seen in sham animals. Based on volume dose, Definity MCE produced more microvascular leakage, but there was no apparent difference between the three agents' microvascular damage potential, which increased linearly with dose at low doses, when expressed in terms of the number of stabilized microbubbles. Definity MCE resulted in fewer PVCs than the other agents. The effects increased strongly with peak rarefactional pressure amplitude, with apparent thresholds for petechiae at 0.4 MPa and for PVCs at about 1.0 MPa. These results should be of value for minimizing adverse potential in diagnosis and optimizing efficacy in therapeutic applications.

In vivo analysis of aortic valve dynamics by transesophageal 3-dimensional echocardiography with high temporal resolution

OBJECTIVES

Knowledge of aortic valve function has been obtained from experimental studies. The aim of the present study was to investigate characteristics of aortic valve motion in humans.

METHODS

Fifty-six patients were studied: 19 with normal valve and good systolic left ventricular function (Group NL), 12 with normal valve and reduced left ventricular function (Group CMP), and 25 with aortic stenosis and good left ventricular function (Group AS). The frame rate was doubled (50 Hz) compared with previous 3-dimensional systems. A mean of 38 +/- 9 images were acquired per cardiac cycle, with 14 +/- 4 images during the systole. The changes in shape and orifice area were analyzed over time.

RESULTS

With normal valves, valve movement proceeded in 3 phases: rapid opening, slow closing, rapid closing. Stenotic valves showed a slower opening and closing movement. The times to maximum opening in Groups NL, CMP, AS were 76 +/- 30, 88 +/- 18 (P =.06), and 130 +/- 29 (P <.01) ms, respectively. It was inversely correlated to the maximum orifice area (r = -0.59, P <.001). The opening velocities in Groups NL, CMP, AS were 42 +/- 23, 28 +/- 9 (P <.05), and 5 +/- 2 (P <.001) cm(2)/s, respectively. There was a close correlation between the opening velocity and the maximum orifice area (r = 0.87, P <.001). Slow valve closings occurred at a velocity of 8.0 +/- 5.2, 5.3 +/- 2.0 (P =.21), 2.8 +/- 1.1 (P <.01) cm(2)/s, respectively, and rapid closings in Groups NL and CMP at 50 +/- 23, 29 +/- 8 (P <.01) cm(2)/s. The results show good agreement with experimental data.

CONCLUSION

Rapid aortic valve movement can be recorded by 3-dimensional echocardiography and analyzed quantitatively. Time and velocity indices of valve dynamics are influenced by valvular and myocardial factors. A comparable in vivo analysis is not possible with any other imaging procedure.

Three-dimensional echocardiographic determination of cardiac output at rest and under dobutamine stress: comparison with thermodilution measurements in the ischemic pig model

Determination of cardiac output is a potentially important clinical application of three-dimensional (3-D) echocardiography since it could replace invasive measurements with the Swan-Ganz-catheter. To date, there are no studies available to determine whether cardiac output measured by thermodilution can be predicted reliably under changing hemodynamic conditions. Fifteen pigs with ischemic myocardium were examined under four hemodynamic conditions at rest and under pharmacological stress with 5, 10, and 20 microg/kg/min dobutamine. The 3-D datasets were recorded by means of transesophageal echocardiography. The endocardial definition was enhanced by administering the contrast agent FS069 (Optison). Cardiac output was calculated as the product of stroke volume (end-diastolic - end-systolic volume) and heart rate. The invasive measurements were performed with a continuous thermodilution system. In general, there was moderate correlation between 3-D echocardiography and thermodilution(r = 0.72, P < 0.001). At rest, the 3-D echocardiographic measurements were slightly but significantly lower than the invasive measurements (mean difference 0.6 +/- 0.5L/min,P < 0.001). Under stress with 5, 10, and 20 microg/kg/min dobutamine, there was a marked increase in the deviation (1.3 +/- 0.5L/min,P < 0.001; 1.6 +/- 0.7 L/min,P < 0.001; and 2.1 +/- 1.1L/min,P < 0.001, respectively). The deviation was based on two factors: (1). Under stress, the decreasing number of frames per cardiac cycle acquired with 3-D echocardiography led to imprecise recording of end-diastolic and end-systolic volumes, and thus to an underestimation of cardiac output. At least 30 frames per cardiac cycle are needed to eliminate this effect. (2). There is a systematic difference between 3-D echocardiographic and invasive measurements, which is independent of the imaging rate. This is based on an overestimation of the true values by thermodilution. In conclusion, cardiac output can be determined correctly by 3-D echocardiography for normal heart rates at rest. At elevated heart rates, the temporal resolution of 3-D systems currently available is not adequate for reliable determination. In performing and evaluating future clinical comparative studies, the systematic difference between 3-D echocardiography and thermodilution, based on overestimation by thermodilution, must be taken into account.

Missed diagnosis of unruptured, huge left ventricular pseudoaneurysm

We report a case of a huge left ventricular pseudoaneurysm following myocardial infarction. Early after myocardial infarction, the pseudoaneurysm was missed during the cardiac examination. The patient underwent coronary bypass surgery with endoaneurysmorraphy of the pseudoaneurysm, and made a satisfactory recovery.

3-D freehand echocardiography for automatic left ventricle reconstruction and analysis based on multiple acoustic windows

A new method is proposed to reconstruct and analyze the left ventricle (LV) from multiple acoustic window three-dimensional (3-D) ultrasound acquired using a transthoracic 3-D rotational probe. Prior research in this area has been based on one acoustic window acquisition. However, the data suffers from several limitations that degrade the reconstruction and reduce the clinical value of interpretation, such as the presence of shadow due to bone (ribs) and air (in the lungs) and motion of the probe during the acquisition. In this paper, we show how to overcome these limitations by automatically fusing information from multiple acoustic window sparse-view acquisitions and using a position sensor to track the probe in real time. Geometric constraints of the object shape, and spatiotemporal information relating to the image acquisition process, are used in new algorithms for 1) grouping endocardial edge cues from an initial image segmentation and 2) defining a novel reconstruction method that utilizes information from multiple acoustic windows. The new method has been validated on a phantom and three real heart data sets. In the phantom study, one finger of a latex glove was scanned from two acoustic windows and reconstructed using the new method. The volume error was measured to be less than 4%. In the clinical case study, 3-D ultrasound and magnetic resonance imaging (MRI) scanning were performed on the same healthy volunteers. Quantitative ejection fractions (EFs) and volume-time curves over a cardiac cycle were estimated using the new method and compared to cardiac MRI measurements. This showed that the new method agrees better with MRI measurements than the previous approach we have developed based on a single acoustic window. The EF errors of the new method with respect to MRI measurements were less than 6%. A more extensive clinical validation is required to establish whether these promising first results translate to a method suitable for routine clinical use.