Intracardiac Transducer Research Articles

Quantitative evaluation of atrial radio frequency ablation using intracardiac shear-wave elastography.

Radio frequency catheter ablation (RFCA) is a well-established clinical procedure for the treatment of atrial fibrillation (AF) but suffers from a low single-procedure success rate. Recurrence of AF is most likely attributable to discontinuous or nontransmural ablation lesions. Yet, despite this urgent clinical need, there is no clinically available imaging modality that can reliably map the lesion transmural extent in real time. In this study, the authors demonstrated the feasibility of shear-wave elastography (SWE) to map quantitatively the stiffness of RFCA-induced thermal lesions in cardiac tissues in vitro and in vivo using an intracardiac transducer array. SWE was first validated in ex vivo porcine ventricular samples (N = 5). Both B-mode imaging and SWE were performed on normal cardiac tissue before and after RFCA. Areas of the lesions were determined by tissue color change with gross pathology and compared against the SWE stiffness maps. SWE was then performed in vivo in three sheep (N = 3). First, the stiffness of normal atrial tissues was assessed quantitatively as well as its variation during the cardiac cycle. SWE was then performed in atrial tissue after RFCA. A large increase in stiffness was observed in ablated ex vivo regions (average shear modulus across samples in normal tissue: 22 ± 5 kPa, average shear-wave speed (ct): 4.5 ± 0.4 m s(-1) and in determined ablated zones: 99 ± 17 kPa, average ct: 9.0 ± 0.5 m s(-1) for a mean shear modulus increase ratio of 4.5 ± 0.9). In vivo, a threefold increase of the shear modulus was measured in the ablated regions, and the lesion extension was clearly visible on the stiffness maps. By its quantitative and real-time capabilities, Intracardiac SWE is a promising intraoperative imaging technique for the evaluation of thermal ablation during RFCA.

Feasibility of noncontact intracardiac ultrasound ablation and imaging catheter for treatment of atrial fibrillation

Atrial fibrillation (AF) affects 1% of the population and results in a cost of 2.8 billion dollars from hospitalizations alone. Treatments that electrically isolate portions of the atria are clinically effective in curing AF. However, such minimally invasive catheter treatments face difficulties in mechanically positioning the catheter tip and visualizing the anatomy of the region. We propose a noncontact, intracardiac transducer that can ablate tissue and provide rudimentary imaging to guide therapy. Our design consists of a high-power, 20 mm by 2 mm, 128-element, transducer array placed on the side of 7-French catheter. The transducer will be used in imaging mode to locate the atrial wall; then, by focusing at that location, a lesion can be formed. Imaging of previously formed lesions could potentially guide placement of subsequent lesions. Successive rotations of the catheter will potentially enable a contiguous circular lesion to be created around the pulmonary vein. The challenge of intracardiac-sized transducers is achieving high intensities (300-5000 W/cm2) needed to raise the temperature of the tissue above 43 degrees C. In this paper, we demonstrate the feasibility of an intracardiac-sized transducer for treatment of atrial fibrillation. In simulations and proof-of-concept experiments, we show a 37 degrees C temperature rise in the lesion location and demonstrate the possibility of lesion imaging.

Tissue motion analysis medical diagnostic ultrasound system and method

Accurate tissue motion systems and methods are provided. Motion of the ultrasound transducer is accounted for in estimates at tissue motion. Correcting for transducer motion better isolates localized tissue contractions or expansions, such as motion of the myocardial muscle or fibers. Accurate motion estimation is also provided by determining an angle of motion from the ultrasound data. The angle of motion is used to adjust velocity estimates, providing two-dimensional velocity vectors (i.e. motion estimates comprising motion in at least two dimensions). Movement of tissue is determined by correlating speckle or a feature represented by two different sets of ultrasound data obtained at different times. Additional aspects include tracking the location of a tissue of interest. A characteristic of strain, such as the strain rate or strain, is calculated for the tracked tissue of interest. Ultrasound data associated with different positions relative to the transducer are selected as a function of the tracking and used to determine the characteristic of strain. Motion estimates corrected for transducer motion may also be used to determine a strain or strain rate. In yet another aspect, motion estimates are generated with data from an intra-cardiac transducer array. The characteristic of strain is determined from the motion estimates. Other aspects discussed above may be used with an intra-cardiac transducer array, providing accurate motion analysis based on imaging from within the heart.

Protective effect of a novel, potent inhibitor of poly(adenosine 5'-diphosphate-ribose) synthetase in a porcine model of severe bacterial sepsis.

To determine whether activation of the nuclear enzyme poly(adenosine 5'-diphosphate [ADP]-ribose) synthetase (PARS) contributes to mortality rate, myocardial dysfunction, and cardiovascular collapse in a porcine model of sepsis induced by implantation of an infected clot. Prospective, random animal study. Research laboratory at Rush Presbyterian St. Luke's Medical Center. Twenty pigs were chronically instrumented with intracardiac transducers to measure left ventricular pressure, sonomicrometer crystals in the left ventricle to measure short axis diameter, an ultrasonic flow meter to measure cardiac output, and catheters in the pulmonary artery and aorta to measure blood pressures and collect samples. By using a randomized study design, we administered either the novel potent PARS inhibitor PJ34 (10 mg/kg for 1 hr, 2 mg x kg(-1) x hr(-1) for 96 hrs) or vehicle to pigs immediately before intraperitoneal implantation of Escherichia coli 0111.B4 (2.3 +/- 0.1 x 10(10) colony-forming units/kg)-laden fibrin clots to produce peritonitis and bacteremia. In vehicle-treated pigs, 12% survival was recorded at 24 hrs, whereas 83% and 66% survival was recorded in the PJ34-treated animals at 24 and 96 hrs, respectively (p <.05). PJ34 treatment attenuated bacteremia-induced increases in systemic and pulmonary vascular resistances. In controls, peritonitis induced rapid increase in plasma tumor necrosis factor-alpha. PJ34 treatment significantly attenuated this cytokine response. The formation of peroxynitrite and the activation of PARS were confirmed in hearts and lungs of the septic pigs by the immunohistochemical detection of nitrotyrosine and poly(ADP-ribose), respectively. Inhibition of PARS with PJ34 abolished poly(ADP-ribose) formation in septic animals. Treatment with a potent PARS inhibitor improved survival and cardiovascular status and attenuated an important mediator component of the inflammatory response in a lethal porcine model of sepsis.

Randomized, blinded, placebo-controlled trial of tissue factor pathway inhibitor in porcine septic shock.

This study tested the hypothesis that tissue factor pathway inhibitor (TFPI) would improve mortality and morbidity evoked by peritonitis-induced bacteremia in pigs. Secondarily, it sought to determine if TFPI treatment would attenuate cardiodynamic abnormalities produced by this septic model. 32 pigs were chronically instrumented with intracardiac transducers to measure left ventricular pressure and diameter, pulmonary and aortic pressures, and cardiac output. At least 5 days after surgery to implant transducers, basal cardiovascular readings and blood samples were obtained. Using a randomized, blinded study design, either purified, reconstituted TFPI (1 mg/kg bolus, 10 mg/kg/min for 48 h), placebo (arginine buffer), or saline was administered to pigs immediately after Escherichia coli 0111.B4 (3.0-11 x 10(9) colony-forming U/kg)-laden fibrin clots were implanted intraperitoneally, producing peritonitis and bacteremia. Pigs did not receive antibiotics or supportive therapy. No significant differences in primary or secondary endpoints were noted between the arginine and saline groups, so these data were combined into a control group (N = 20). 5 of 12 TFPI pigs survived (42%), while 5 of 20 control pigs survived (25%); this difference was not significant (p = .714, Fisher's exact test). TFPI treatment augmented cardiac output in surviving pigs, but did not affect any other cardiovascular performance variable (heart rate, % diameter shortening, or systemic and pulmonary vascular resistance). In controls, peritonitis induced rapid increase in plasma tumor necrosis factor-alpha (428 +/- 771 to 5,933 +/- 559 pg/mL at 2 h) and interleukin-8 (180 +/- 153 to 1,393 +/- 145 pg/mL at 2 h). TFPI treatment significantly attenuated cytokine responses to sepsis, reducing peak tumor necrosis factor-alpha to 2,103 +/- 813 pg/mL and reducing peak interleukin-8 levels to 534 +/- 211 pg/mL at 2 h (p < .05, Tukey test, two-way ANOVA). In conclusion, TFPI treatment attenuated important mediator components of the inflammatory response but did not provide significant survival benefit.

Usefulness of Intracardiac Echocardiography in Complex Transseptal Catheterization During Percutaneous Transvenous Mitral Commissurotomy

To examine the utility of intracardiac echocardiography in guiding complex transseptal catheterization of patients undergoing percutaneous transvenous mitral commissurotomy. We assessed this procedure in high-risk patients in whom transseptal catheterization is technically complex and more demanding. Fifteen patients with mitral stenosis were studied. Twelve patients had giant left atria (70 mm or more), two had atrial septal aneurysms, and one had severe kyphoscoliosis. A newly developed 8-F 10-MHz intracardiac transducer catheter was placed in the right atrium through an 8-F Mullins sheath inserted from the left femoral vein. Echocardiographic images were used to confirm the septal position of the Brockenbrough needle tip before septal punctures. Transseptal puncture was successful and uncomplicated in all 15 patients. Use of intracardiac echocardiography eliminated the need for atrial angiography. Before transseptal puncture, the needle tip was identified to be in contact with the atrial septum, as an echogenic point with its acoustic shadow and septal indentation. In addition, in the two patients with aneurysms, puncture of the thin-walled aneurysms was avoided. Intracardiac echocardiography facilitates safe complex transseptal catheterization in patients with mitral stenosis and giant left atria, atrial septal aneurysms, or severe kyphoscoliosis.

Sound and pressure signals obtained from a single intracardiac transducer.

Sound and pressure signals obtained from a single intracardiac transducer.