Intracardiac ultrasound measurement of volumes and ejection fraction in normal, infarcted, and aneurysmal left ventricles using a 10-MHz ultrasound catheter

Synthesis of fluorine-18 radio-labeled serum albumins for PET blood pool imaging

We sought to develop a practical, reproducible and clinically translatable method of radiolabeling serum albumins with fluorine-18 for use as a PET blood pool imaging agent in animals and man. Fluorine-18 radiolabeled fluoronicotinic acid-2,3,5,6-tetrafluorophenyl ester, [(18)F]F-Py-TFP was prepared first by the reaction of its quaternary ammonium triflate precursor with [(18)F]tetrabutylammonium fluoride ([(18)F]TBAF) according to a previously published method for peptides, with minor modifications. The incubation of [(18)F]F-Py-TFP with rat serum albumin (RSA) in phosphate buffer (pH9) for 15 min at 37-40 °C produced fluorine-18-radiolabeled RSA and the product was purified using a mini-PD MiniTrap G-25 column. The overall radiochemical yield of the reaction was 18-35% (n=30, uncorrected) in a 90-min synthesis. This procedure, repeated with human serum albumin (HSA), yielded similar results. Fluorine-18-radiolabeled RSA demonstrated prolonged blood retention (biological half-life of 4.8 hours) in healthy awake rats. The distribution of major organ radioactivity remained relatively unchanged during the 4 hour observation periods either by direct tissue counting or by dynamic PET whole-body imaging except for a gradual accumulation of labeled metabolic products in the bladder. This manual method for synthesizing radiolabeled serum albumins uses fluorine-18, a widely available PET radionuclide, and natural protein available in both pure and recombinant forms which could be scaled up for widespread clinical applications. These preclinical biodistribution and PET imaging results indicate that [(18)F]RSA is an effective blood pool imaging agent in rats and might, as [(18)F]HSA, prove similarly useful as a clinical imaging agent.

The use of intracardiac echocardiography during percutaneous pulmonary valve replacement

High-quality live imaging assessment of cardiac valves and cardiac anatomy is crucial for the success of catheter-based procedures. We present our experience using Intracardiac echocardiography (ICE) during transcatheter Percutaneous Pulmonary Valve replacement (tPVR).This is a retrospective study that included 35 patients who underwent tPVR between April 2008 and June 2012. Thirty-one of these patients had the procedure performed under continuous ICE guidance. Pre-procedure transthoracic echocardiography (TTE) was obtained in all patients. ICE was performed at baseline, during the procedure, and at the conclusion of the procedure. Comparisons between the pre-procedure TTE and baseline ICE data and between post-procedure ICE data and the following day TTE were performed. Total of 35 patients had tPVR during the above-mentioned time period. Twenty-one patients received the Edwards Sapien valve and 14 patients had the Melody valve. Thirty-one patients had the procedure performed under continuous ICE guidance. The mean Pre-TTE peak gradient (PG) and Pre-ICE-PG were 45.5 ± 20 vs 33 ± 13 mmHg (p < 0.001) and the mean Pre-TTE mean gradient (MG) and Pre-ICE-MG were 27.7 ± 13 vs 21 ± 18 mmHg (p < 0.001). The mean Post-TTE- PG and Post-ICE-PG were 24.3 ± 11 vs 15.3 ± 7 mmHg (p < 0.001) and the mean of the Post-TTE-MG and Post-ICE-MG were 14.2 ± 7 vs 8.4 ± 4 mmHg (p < 0.001). There was a good correlation between peak ICE and TTE gradient at baseline and after valve placement. For the degree of pulmonary regurgitation, there was no significant difference between TTE and ICE. ICE is an important modality to guide tPVR in patients with dysfunctional homograft valve between the right ventricle and pulmonary artery and should be used to assess valve function before, during and immediately after the procedure.

Intracardiac echocardiographic measurement of left ventricular volume

We tested the utility of intracardiac echocardiography (ICE) in measuring left ventricular (LV) volume. In 4 normal dogs, a 10-F percutaneous sheath was placed inside the LV along its major axis. An ICE catheter (9 F, 9 MHz) was then inserted through the sheath into the LV. The ICE catheter was pulled back in 1-mm intervals starting from the apex, and 2-D tomographic images were continuously acquired. Subsequently, the ICE catheter was replaced in the LV by a conductance catheter to measure single-beat volume signals. Stroke volume was determined by thermodilution for validation. All measurements were made in each dog while pacing the atrium at two different cycle lengths (range=300-500 ms). The endocardium was segmented in the ICE images throughout the cardiac cycle, and LV volume was computed by integrating multiple segments (range=55-70 mm). We found that ICE accurately reconstructed LV 3-D anatomy. Stroke volume by ICE was in excellent agreement with thermodilution (error = 3.8+/-3.0%, r = 0.99, n = 8). Morphology of LV volume signals correlated well with instantaneous volume signals derived by conductance (r=0.93, n=8). In conclusion, ICE accurately reconstructs LV anatomy and volume throughout the cardiac cycle in the normal heart. This approach could facilitate interventional diagnostic and therapeutic procedures.

Dynamic three-dimensional visualization of the left ventricle by intracardiac echocardiography

Cardiac function and hemodynamics are routinely evaluated during catheterization in patients with heart disease. Although intracardiac echocardiography (ICE) has been employed in guiding electrophysiology procedures, it has not been effectively used in assessing hemodynamics. We tested the utility of ICE in measuring left ventricular (LV) volume throughout the cardiac cycle. In four normal dogs (weight = 26 to 37 kg), a 10-F sheath was inserted through the femoral artery and placed inside the LV along its major axis. An ICE catheter (9 F, 9 MHz) was then inserted through the sheath into the LV. The ICE catheter was pulled back inside the sheath in 1-mm intervals starting from the apex, and 2-D tomographic images were continuously acquired while gating to respiration. Subsequently, the ICE catheter was replaced by a conductance catheter to measure single-beat volume signals. Stroke volume was determined by thermodilution for validation. All measurements were made in each dog while pacing the atrium at two different cycle lengths (range = 300 to 500 ms). The endocardial boundary was digitized from the ICE images throughout the cardiac cycle and LV volume was computed by integrating multiple segments along the major axis (range = 55 to 70 mm). We found that ICE accurately reconstructed LV 3-D anatomy. Stroke volume by ICE was in excellent agreement with thermodilution (error = 3.8 +/- 3.0%, r = 0.99, n = 8) and was highly reproducible. Morphology of LV volume signals correlated well with corresponding instantaneous volume signals derived by conductance (r = 0.93, n = 8). In conclusion, ICE accurately reconstructs LV anatomy and volume throughout the cardiac cycle in the normal heart. This approach could facilitate interventional diagnostic and therapeutic procedures.

On-line intracardiac echocardiography alone for Amplatzer Septal Occluder selection and device deployment in adult patients with atrial septal defect

BACKGROUND

During the last few years, several different devices have been proposed for atrial septal defect (ASD) percutaneous closure. For the Amplatzer Septal Occluder (ASO) device, accurate balloon sizing is considered of paramount importance because the prosthesis waist has to be exactly adjusted to the defect diameter (+/-1 mm). In this study, we aimed to demonstrate the possibility of marked misinterpreting of the actual defect size using the balloon technique in patients with secundum ASD and to evaluate the accuracy of intracardiac echocardiography (ICE) measurements as a new method for selecting the size of ASO device.

METHODS

Between February 1999 and December 2000, 166 consecutive adult patients underwent percutaneous transvenous secundum ASD occlusion using the ASO device. In 124 patients (control group), ASD were closed by conventional methods. In 13 patients (pilot group), balloon pulling technique was used in size selection, whereas ICE was used on-line to monitor device placement and off-line to assess its possibilities for accurate quantitative measurements and qualitative evaluation. In 31 patients (study group), ICE was used as the sole imaging tool both for guiding device selection and monitoring the procedure. All patients underwent complete transthoracic echocardiographic study before discharge and during follow-up visits at 3 and 12 months.

RESULTS

Successful device implantation was accomplished in 163 of the 166 patients (98.2%). Short-term follow-up results were available in all eligible patients at least 3 months. Complete occlusion was demonstrated in 91.4% and 92.2% of patients in the control and pilot groups, respectively, increasing to 97.3% in the study group (p<0.01 vs. both control and pilot groups). There were no significant differences in mean ASO diameters in the control and pilot groups (20+/-7.7 and 22+/-5.4 mm, respectively), whereas the mean size of the devices used in the study group was significantly larger (27.4+/-6.2 mm, p<0.01 vs. both control and pilot groups). In the pilot group, the underestimation effect of the balloon strategy was evident, with a mean 12.3% larger diameter required on ICE measurements. Moreover, a misalignment between the ASO and the atrial septum was seen on ICE in 9 of 13 patients of the pilot group, whereas good apposition of the ASO on the septum secundum was seen in all patients of the study group.

CONCLUSION

ICE is a safe and effective method for selecting ASO size and continuous monitoring of the procedure. In contrast to the previously reported implantation procedure (device-to-defect ratio 1:1), a device 10-20% larger than invasively measured stretched defect diameter should be chosen and implanted on the basis of the ICE data.

Use of Intracardiac Echocardiography to Guide Catheter Closure of Atrial Communications

Intracardiac echocardiography (ICE) is slowly replacing transesophageal echocardiography as the preferred imaging tool to guide device closure of atrial septal defects and patent foramen ovale. This article is a brief review of the literature related to ICE, the technical aspects ICE imaging, techniques for obtaining the standard views, and the future directions of this methodology.

Intracardiac echocardiography-guided transcatheter closure of secundum atrial septal defect

OBJECTIVES

We assessed the use of intracardiac echocardiography (ICE) as the primary means for both selection of the Amplatzer Septal Occluder (ASO) and the guidance of transcatheter closure of secundum atrial septal defects (ASDs).

BACKGROUND

The standard method for transcatheter closure of ASDs requires balloon-sizing maneuver and transesophageal echocardiographic (TEE) monitoring. The role of ICE during transcatheter closure of ASDs has not yet been established.

METHODS

In 91 patients with ASDs, two standardized orthogonal sections were used to obtain ICE-derived measurements of the fossa ovalis and to assess optimal device deployment: the transverse section on the aortic valve plane, and the longitudinal section on the four-chamber plane.

RESULTS

In all patients, ICE planes were identified with excellent resolution, providing proper measurements of the fossa ovalis, from which to derive geometric assumptions for the selection of an appropriately sized device. The ASO waist diameter was chosen on the basis of the r value (r = [square root c(2) + p(2)], where r is the radius of an ideal circle that intersects the elliptical fossa ovalis in its semi-latus rectum, c is the foci half-distance of the fossa ovalis, and p is its semi-latus rectum). During the procedure, the four-chamber plane allowed us to obtain easily interpretable images of all stages of device deployment. Midterm complete occlusion rate was 97.8%. No ICE-related complications occurred.

CONCLUSIONS

The ICE evaluation of ASDs allows quantitative and qualitative information for both proper ASO selection and optimal device placement, thus eliminating the cumbersome balloon-sizing maneuver and the need for general anesthesia during TEE monitoring.

Phased-array intracardiac echocardiographic imaging of acute cardiovascular emergencies: Experimental studies in dogs

BACKGROUND

We evaluated a newly developed phased-array intracardiac echocardiographic catheter.

OBJECTIVE

Our aim was to evaluate the imaging capability of this new ICE catheter in an animal model simulating acute cardiovascular abnormalities.

METHODS

ICE images were obtained from the right atrium during (1) acute left ventricular dysfunction; (2) acute coronary occlusion; (3) pericardial effusion and tamponade; and (4) pulmonary embolism.

RESULTS

Left ventricular dysfunction, induced experimentally by halothane inhalation, resulted in a fall in echocardiography-calculated ejection fraction from 47% +/- 11% to 25% +/- 10%, P <.01. Regional contraction abnormalities after acute coronary occlusion were identified without and with the ultrasound contrast agent Optison. Pericardial effusion produced by saline infusion into the pericardium was detected in amounts as small as 15 mL. Right ventricular and atrial compression and respiratory variation in right ventricular inflow during tamponade were demonstrated. After injection of intravenous thrombin to create venous thromboembolism, we demonstrated right ventricular dilatation and dysfunction and thrombi attached to the tricuspid and pulmonary valves and in the pulmonary artery.

CONCLUSION

This new phased-array ICE catheter may be a useful clinical tool for the diagnosis of heart failure, ischemia, tamponade, and pulmonary embolism.

New applications of intracardiac echocardiography: assessment of coronary blood flow by colour and pulsed Doppler imaging in dogs

OBJECTIVE

To explore the application of a new 10 French intracardiac echocardiography (ICE) catheter with phased array and Doppler capable transducer for the assessment of epicardial and intramyocardial coronary blood flow.

METHODS

The coronary arteries were detected by cross sectional imaging in seven closed chest dogs, and coronary blood flow visualised by colour Doppler. Blood flow velocities were recorded by pulsed Doppler at baseline for reproducibility of repeated measurements, and during hyperaemia for coronary flow reserve measurements. Comparisons were made with Doppler guide wire data obtained simultaneously. Intramyocardial coronary artery blood flow was assessed by colour flow mapping, and the blood flow velocities recorded using pulsed Doppler at baseline and during hyperaemia.

RESULTS

Seven left main, six left anterior descending, seven left circumflex, and five right coronary arteries were visualised in the seven animals by cross sectional or colour Doppler imaging. Repeated measurements of coronary flow velocity showed a good correlation (mean diastolic velocity, r = 0.93, n = 22, p < 0.0001; peak diastolic velocity, r = 0.96, n = 22, p < 0.0001, respectively). Intraobserver/interobserver variability was satisfactorily low. Coronary flow reserve from ICE correlated highly with the value obtained from the Doppler guide wire (r = 0.90, n = 26, p < 0.0001). Intramyocardial coronary blood flow was identified in all seven dogs, and flow velocities were recorded at baseline and during hyperaemia in four animals.

CONCLUSIONS

This new ICE catheter provides high quality diagnostic resolution. It is useful for coronary blood flow assessment.

Transvascular Imaging: Feasibility Study Using a Vector Phased Array Ultrasound Catheter

BACKGROUND: Transvascular imaging is defined as the acquisition of anatomic and functional information of structures lying beyond the confines of a vascular conduit within which the imaging device resides. Interrogating structures surrounding the vascular conduit is the subject of this feasibility study using a novel underblood, phased array ultrasound-tipped catheter. METHODS: An intravascular catheter (10-F, 3.2-mm-diameter, four-way articulation) tipped with a 5.5- to 10-MHz frequency agile, vector phased array transducer with full Doppler capability (Sequoia, Acuson) was used. The imaging transducer has a wide range of tissue penetration (2 mm to >10 cm from the lens). The catheter was introduced via an 11-Fr femoral venous sheath into the inferior and superior vena cavae and right heart chambers. As the catheter was advanced, attention was directed to visualization of structures surrounding the vessel in which the catheter resided. RESULTS: From the cavae and femoral vein the thoracic, abdominal and femoral arteries could be easily imaged. Anatomy that was visualized included the liver, hepatic veins, gallbladder, and mesenteric vessels. Normal and pathological anatomy and Doppler physiology could be readily appreciated. Doppler (i.e., pulsed- and continuous-wave, color flow, and tissue Doppler) fostered unique transvascular physiological hemodynamic and flow assessment. CONCLUSION: Transvascular imaging is feasible in human subjects using this 10-Fr catheter tipped with a 5.5- to 10-MHz vector phased array transducer. Intravascular navigation to a desired location within the body and the performance of diagnostic or therapeutic procedures at a remote site under direct ultrasound visualization are possible. Full Doppler capability extends the concept of transvascular hemodynamic and physiological assessment.

Potential applications of intracardiac echocardiography in the assessment of the aortic valve from the right ventricular outflow tract

Intracardiac echocardiography (ICE) is a developing technology and a promising method for visualizing intracardiac structures. However, its applications are currently limited to guidance during mitral valvuloplasty, catheter ablation, or electrophysiologic examination. The goal of this study was to observe the aortic valve, measure the annular diameter of the valve by ICE through a right-sided approach, and compare the results by ICE with those by transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE). We studied 18 patients (9 men, 9 women, aged 19 to 72 years) with various heart diseases, including 15 patients with mitral or aortic valvular disease. An imaging catheter was advanced through a long sheath into the outflow tract of the right ventricle. We obtained good longitudinal views of the aortic valve in all patients. Two of the 18 patients had poor image quality by TTE. The annular diameter by ICE correlated more closely with TEE than with TTE. In conclusion, right-sided ICE is a safe, simple, and useful procedure for observing the aortic valve during cardiac catheterization without additional discomfort in the patients. Right-sided ICE is superior to TTE in observing the aortic valve and measuring the annular diameter of the valve. The annular diameter can be measured by ICE as precisely as by TEE.

Intracardiac echocardiography: computerized detection of left ventricular borders

A semi-automated method for two- and three-dimensional analysis of intracardiac echocardiography (ICE) images and image sequences is reported based on detection of epicardial and endocardial borders using graph searching. The border detection method was applied to 50 ICE images acquired in vivo in five dogs and to 108 images in 16 volumetric ICE image sequences from eight cadaveric pig hearts. The ICE images from the in vivo study showed good correlation between computer-detected and observer-defined left ventricular (LV) cavity areas and epicardial areas (r = 0.99, y = 0.98x + 0.43 [cm2]; r = 0.99, y = 0.98x + 1.11 [cm2]; respectively). In the cadaveric hearts, the LV volumes were determined with the volume measurement error of 7.6 +/- 7.7% and 11.3 +/- 11.2% for the aortic valve and mitral valve image sequences, respectively. Our method facilitates an accurate and computationally efficient approach for the quantitative assessment of ICE image data in 2D and 3D.

Automated tracking of left ventricular wall thickening with intracardiac echocardiography

OBJECTIVE

We developed and evaluated a new method to automatically measure regional left ventricular wall thickening by analyzing the radiofrequency backscatter signal from an intracardiac echocardiographic catheter.

METHODS

We inserted 10-MHz echocardiographic catheters in 11 dogs. Wall thickness was perturbed by altering loading conditions and inotropic state. The backscatter signal from a single selected radial scan line was digitized. An automated algorithm identified the digitized endocardial and epicardial signals, tracked them throughout the cardiac cycle, and plotted the spatial difference over time. Pressure-thickness loops were generated.

RESULTS

End-systolic and end-diastolic thickness and percent wall thickening from the unedited, unsmoothed signals compared favorably with independent manual analysis of transthoracic echocardiographic images of the same region: r = 0.89 for wall thickness and 0.81 for systolic thickening.

CONCLUSION

The backscatter signal from an intracardiac echocardiographic device can be analyzed automatically to continuously assess regional left ventricular wall thickening and generate pressure-thickness loops.

Intracardiac versus transthoracic echocardiographic imaging of translation and rotation of left ventricular center of cavity area in dogs

Motion of the left ventricular cavity center during the cardiac cycle was compared using transthoracic and intracardiac echocardiography. Rotation was comparable for the 2 methods, however, translation of the left ventricular cavity area center was greater with intracardiac echocardiography.

Percutaneous transvenous intracardiac ultrasound imaging in dogs: a new approach to monitor left ventricular function

OBJECTIVE

To evaluate the feasibility and ability of percutaneous transvenous intracardiac echocardiography (ICE) to image the left ventricle (LV) and monitor its function from the right ventricular (RV) cavity.

METHODS

A 10 MHz catheter was advanced into the RV from the jugular vein and positioned along the septum at the LV papillary muscle level in five dogs. The catheter was manipulated until a stable catheter position along the septum, which provided on-axis images of LV, was obtained. Different states of LV size and systolic function (n = 80) were created with dobutamine or esmolol, both in the presence and absence of coronary stenoses. LV stroke area (cm2) obtained by ICE was measured at the mid-ventricular level and compared with stroke volume (cm3) obtained simultaneously with a transaortic flow probe. LV end diastolic, end systolic, and stroke areas obtained by ICE were also compared with those obtained by short-axis epicardial echocardiography.

RESULTS

In 96% of the stages, short axis images of the LV could be obtained and measured by ICE. LV end diastolic, end systolic, and stroke areas measured by ICE were not significantly different from epicardial echocardiographic values. Stroke area correlated with stroke volume in each dog (mean correlation coefficient 0.79 (SEE 0.19) cm2) (P < 0.001).

CONCLUSIONS

Percutaneous intracardiac ultrasound imaging allows monitoring of LV function from the RV with an accuracy comparable to a short-axis epicardial echocardiogram. The present device can be used in closed chest experimental studies. With the development of lower frequency devices, this technique may be valuable for continuous monitoring of LV function in patients in the intensive care unit or operating room.

Quantitative assessment of stenotic aortic valve area by using intracardiac echocardiography: in vitro validation and initial in vivo illustration

Quantitative assessment of aortic stenosis (AS) is subject to the limitations of all current noninvasive and invasive methods. The ability to obtain a direct measure of aortic valve area with high resolution by intracardiac echocardiography (ICE) could be of great benefit to catheterized patients. To provide a fixed AS area as an ideal standard for comparison, we performed ICE in 12 sheep hearts with experimentally created AS and five human AS hearts from autopsies. ICE catheters were passed retrograde across the aortic valve, and the minimal orifice area on pullback was planimetered and compared with calibrated video imaging. The entire orifice circumference could be successfully recorded in 16 (94%) hearts. Orifice area from ICE correlated well with actual values (r=0.98; standard error of the estimate [SEE] = 0.06 cm2). To illustrate the applicability in vivo, two canine models and 10 patients with AS were studied. The limiting orifice could be imaged in both animals and in 8 of 10 patients, in whom values agreed well with invasive data (r= 0.95; SEE = 0.04 cm2). ICE can therefore accurately measure AS orifice area in vitro; it can be applied in vivo as well. These validation studies laid the foundation for subsequent clinical studies and applications.

Intravascular and intracardiac ultrasound: a tool of the future

Intravascular ultrasonography has the capability to visualize the vessel wall and perivascular structures, to identify the spatial distribution and composition of atherosclerotic plaque, and to measure accurately vessel and wall dimensions. This article discusses relevant principles of instrumentation, issues pertaining to the validation and interpretation of intravascular ultrasound images, and the current and potential applications of intravascular (and intracardiac) imaging. Emphasis is placed on uses that are likely to be of interest to the critical care physician.

Intracardiac echocardiography: in vitro and in vivo validation for right ventricular volume and function

To determine the feasibility and accuracy of intracardiac ultrasonography (ICUS) for the measurement of right ventricular (RV) volumes and function, a 10 MHz ICUS catheter was used in an in vitro and in vivo model. In the in vitro study, 16 sheep hearts were imaged. Sequential cross-sectional images from RV apex to base were recorded during a calibrated pullback. Volumes were calculated by applying Simpson's algorithm. ICUS-obtained volumes correlated well with actual volumes (standard error of estimate [SEE] = 2.3 ml, r = 0.98). For the in vivo study, a beating-heart canine model was used (31 hemodynamic stages in six dogs). Actual volumes were measured by an intracavitary balloon connected to an external column. Sequential cross-sectional images were recorded during the ICUS catheter pullback from apex to base of the RV, and volumes calculated by Simpson's algorithm. Good correlations were observed between ICUS and actual values for diastolic (SEE = 4.1 ml, r = 0.97), systolic (SEE = 3.4 ml, r = 0.96), and ejection fraction (SEE = 3.1%, r = 0.87) values. This new technique can accurately quantitate RV volumes, can function both in vitro and in vivo, and has the potential for increasing applications to questions of clinical and research interest.