Effect of Ambient Conditions on Acoustic Activation of the Perfluoropropane Droplets Within the Infarct Zone.

BACKGROUND: Acoustically activated perfluoropropane droplets (PD) formulated from lipid encapsulated microbubble preparations produce a delayed myocardial contrast enhancement that preferentially highlights the infarct zones (IZ). Since activation of PDs may be temperature sensitive, it is unclear what effect body temperature (BT) has on acoustic activation (AA). OBJECTIVE: We sought to determine whether the microvascular retention and degree of myocardial contrast intensity (MCI) would be affected by BT at the time of intravenous injection. METHODS: We administered intravenous (IV) PD in nine rats following 60 min of ischemia followed by reperfusion. Injections in these rats were given at temperatures above and below 36.5°C, with high MI activation in both groups at 3 or 6 min following IV injection (IVI). In six additional rats (three in each group), IV PDs were given only at one temperature (<36.5°C or ≥36.5°C), permitting a total of 12 comparisons of different BT. Differences in background subtracted MCI at 3-6 min post-injection were compared in the infarct zone (IZ) and remote zone (RZ). Post-mortem lung hematoxylin and eosin (H&E) staining was performed to assess the effect potential thermal activation on lung tissue. RESULTS: Selective MCI within the IZ was observed in 8 of 12 rats who received IVI of PDs at <36.5°C, but none of the 12 rats who had IVI at the higher temperature (p < 0.0001). Absolute MCI following droplet activation was significantly higher in both the IZ and RZ when given at the lower BT. H&E indicated significant red blood extravasation in 5/7 rats who had had IV injections at higher BT, and 0/7 rats who had IV PDs at <36.5°C. CONCLUSIONS: Selective IZ enhancement with AA of intravenous PDs is possible, but temperature sensitive. Thermal activation appears to occur when PDs are given at higher temperatures, preventing AA, and increasing unwanted bioeffects.

Acoustic Activation Imaging With Intravenous Perfluoropropane Nanodroplets Results in Selective Bioactivation of the Risk Area.

BACKGROUND: Acoustically activatable perfluoropropane droplets (PD) can be formulated from commercially available microbubble preparations. Diagnostic transthoracic ultrasound frequencies have resulted in acoustic activation (AA) predominately within myocardial infarct zones (IZ). OBJECTIVE: We hypothesized that the AA area following acute coronary ischemia/reperfusion (I/R) would selectively enhance the developing scar zone, and target bioeffects specifically to this region. METHODS: We administered intravenous PD in 36 rats and 20 pigs at various stages of myocardial scar formation (30 minutes, 1 day, and 7 days post I/R) to determine what effect infarct age had on the AA within the IZ. This was correlated with histology, myeloperoxidase activity, and tissue nitrite activity. RESULTS: The degree of AA within the IZ in rats was not associated with collagen content, neutrophil infiltration, or infarct age. AA within 24 hours of I/R was associated with increased nitric oxide utilization selectively within the IZ (P < .05 compared with remote zone). The spatial extent of AA in pigs correlated with infarct size only when performed before sacrifice at 7 days (r = .74, P < .01). CONCLUSIONS: Acoustic activation of intravenous PD enhances the developing scar zone following I/R, and results in selective tissue nitric oxide utilization.

Acoustic Detection of Retained Perfluoropropane Droplets Within the Developing Myocardial Infarct Zone.

Perfluoropropane droplets (PDs) cross endothelial barriers and can be acoustically activated for selective myocardial extravascular enhancement following intravenous injection (IVI). Our objective was to determine how to optimally activate extravascular PDs for transthoracic ultrasound-enhanced delineation of a developing scar zone (DSZ). Ultrafast-frame-rate microscopy was conducted to determine the effect of pulse sequence on the threshold of bubble formation from PDs. In vitro studies were subsequently performed at different flow rates to determine acoustic activation and inertial cavitation thresholds for a PD infusion using multipulse fundamental non-linear or single-pulse harmonic imaging. IVIs of PDs were given in 9 rats and 10 pigs following prolonged left anterior descending ischemia to detect and quantify PD kinetics within the DSZ. A multipulse sequence had a lower myocardial index threshold for acoustic activation by ultrafast-frame-rate microscopy. Acoustic activation was observed at a myocardial index ≥0.4 below the inertial cavitation threshold for both pulse sequences. In rats, confocal microscopy and serial acoustic activation imaging detected higher droplet presence (relative to remote regions) within the DSZ at 3 min post-IVI. Transthoracic high-mechanical-index impulses with fundamental non-linear imaging in pigs at this time post-IVI resulted in selective contrast enhancement within the DSZ.

Efficacy of Sonothrombolysis Using Acoustically Activated Perflutren Nanodroplets versus Perflutren Microbubbles.

Nanoscale-diameter liquid droplets from commercially available microbubbles may optimize thrombus permeation and subsequent thrombus dissolution (TD). Thrombi were made using fresh porcine arterial whole blood and placed in an in vitro vascular simulation. A diagnostic ultrasound probe in contact with a tissue-mimicking phantom tested intermittent high-mechanical-index (HMI) fundamental multipulse (focused ultrasound [FUS], 1.8 MHz) versus harmonic single-pulse (HUS, 1.3 MHz) modes during a 10-min infusion of Definity nanodroplets (DNDs), Definity microbubbles (DMBs) or saline. The ability of FUS and intravenous DNDs to improve epicardial and microvascular flow was then tested in four pigs with left anterior descending thrombotic occlusion. Sixty in vitro thrombi were tested, 20 in each group. Percentage TD was significantly higher for DND-treated thrombi than DMB-treated thrombi and controls (DNDs: 42.4%, DMBs: 26.7%, saline: 15.0%; p < 0.0001 vs. control). The highest %TD was seen in the HMI FUS-treated DND group (51 ± 17% TD). HMI FUS detected droplet activation within the risk area in three of four pigs with left anterior descending thrombotic occlusion and re-canalized the epicardial vessel in two. DNDs with intermittent diagnostic HMI ultrasound resulted in significantly more intravascular TD than DMBs and have potential for coronary and risk area thrombolysis.

Delayed Echo Enhancement Imaging to Quantify Myocardial Infarct Size.

BACKGROUND: Perfluoropropane droplets formulated from commercial microbubbles exhibit different acoustic characteristics than their parent microbubbles, most likely from enhanced endothelial permeability. This enhanced permeability may permit delayed echo-enhancement imaging (DEEI) similar to delayed enhancement magnetic resonance imaging (DE-MRI). We hypothesized this would allow detection and quantification of myocardial scar. METHODS: In 15 pigs undergoing 90 minutes of left anterior descending ischemia by either balloon (n = 13) or thrombotic occlusion (n = 2), DE-MRI was performed at 2-24 days postocclusion. Delayed echo-enhancement imaging was performed at 2-4 minutes following an intravenous injection of 1 mL of 50% Definity (Lantheus Medical) compressed into 180 nm droplets; DEEI was attempted in all pigs with single-pulse harmonic imaging at 1.7 transmit/3.4 MHz receive. Myocardial defects observed with DEEI were quantified (percentage of infarct area) and compared with DE-MRI as well as postmortem staining. In six pigs, multipulse low-mechanical index (MI) fundamental nonlinear imaging (FNLI) with intermittent high-MI impulses was performed to determine whether droplet activation within the infarct zone was achievable with a longer pulse duration. RESULTS: The range of infarct size area by DE-MRI ranged from 0% to 46% of total left ventricular area. Single-pulse harmonic imaging detected a contrast defect that correlated closely with infarct area by DE-MRI (r = 0.81, P = .0001). The FNLI high-MI impulses resulted in droplet activation in both the infarct and normal zones. Harmonic subtraction of the FNLI images resulted in infarct zone enhancement that also correlated closely with infarct size (r = 0.83; P = .04). Droplets were observed on postmortem transmission electron microscopy within myocytes of the infarct and remote normal zone. CONCLUSION: Intravenously Definity nanodroplets can be utilized to detect and quantify infarct zone at the bedside using DEEI techniques.

Selective infarct zone imaging with intravenous acoustically activated droplets.

BACKGROUND: Microbubbles (MB) can be compressed to nanometer-sized droplets and reactivated with diagnostic ultrasound; these reactivated MB possess unique imaging characteristics. OBJECTIVE: We hypothesized that droplets formed from compressing Definity MB may be used for infarct-enhancement imaging. METHODS: Fourteen rats underwent ligation of their left anterior descending (LAD) artery, and five pigs underwent 90 minute balloon occlusions of their mid LAD. At 48 hours in rats, transthoracic ultrasound was performed at two and four minutes following 200 µL intravenous injections (IVI) of Definity droplets (DD), at which point the MI was increased from 0.5 to 1.5 to assess for a transient contrast enhancement zone (TEZ) within akinetic segments. In pigs, 1.0 mL injections of DD were administered and low frame rate (triggered end systolic or 10 Hz) imaging 2-4 minutes post iVI to selectively activate and image the infarct zone (IZ). Infarct size was defined by delayed enhancement magnetic resonance imaging (DE-MRI) and post-mortem staining (TTC). RESULTS: Increasing MI to 1.5 (at two or four minutes after IVI) resulted in a TEZ in rats, which correlated with infarct size (r = 0.94, p<0.001). A TEZ was not seen at 2-4 minutes in any rat (n = 8) following Definity MB injections. Fluorescent staining confirmed DD presence within the infarct zone 10 minutes after intravenous injection. In pigs, selective enhancement within the IZ was achieved by using a low frame rate single pulse harmonic mode; IZ size matched the location seen with DE-MRI and correlated with TTC defect size (r = 0.90, p<0.05). CONCLUSION: DD formulated from commercially available MB can be acoustically activated for selective infarct enhancement imaging.

Surgical technique of placement of an external jugular tunneled hemodialysis catheter in a large pig model.

BACKGROUND: Currently, there is insufficient knowledge about the surgical anatomy and surgical techniques in large animals that can be used to test medical devices designed for human use. We encountered this problem in our study requiring the placement of jugular vein, tunneled, cuffed hemodialysis catheter in 70 kg pigs. Despite the operator's extensive expertise in placing tunneled hemodialysis catheters in humans, the important differences in anatomy made the procedure and choosing the appropriate catheter length challenging. METHODS: The following article describes the anatomy and our technique for the placement of tunneled hemodialysis catheter in the pig model. RESULTS: We consider our surgical technique to be sound because in all animals the catheters were placed in the desired location, the procedures were well tolerated by the animals, and there were no immediate or late complications. CONCLUSION: We present our experience to help other researchers who might encounter the same problem.

Location and structure of fibrous sheath formed after placing a tunneled hemodialysis catheter in a large pig model.

BACKGROUND AND OBJECTIVES: We evaluated the location and structure of the fibrous sheath formed after the placement of tunneled, cuffed hemodialysis catheters in large animals, 70 kg pigs. We focused on describing the location of the fibrous sheath in relation to the catheter. Its location explains the fibrous sheath's ability to cause catheter dysfunction by covering the catheter exit ports located at the catheter's tip. DESIGN: We used three animals. Each animal had a tunneled, cuffed, 15-French diameter hemodialysis catheter placed in the external jugular vein, with the tip at the junction of the superior vena cava and the right atrium. Two animals were sacrificed at 5 weeks and one animal at 17 weeks after catheter placement. The catheter and surrounding tissues were removed in one block. The fibrous sheath was dissected and longitudinally cut along the catheter to evaluate its extension in relation to the catheter. Relevant portions of the fibrous sheath were sent for pathology examination. RESULTS: The fibrous sheath covered the catheter in its entire length and circumference. It started at the entry site and continued without any interruption along the entire length of the catheter, including the tip. Its average thickness is 1 mm and has an inner cellular/inflammatory layer comprising lymphocytes, plasma cells, neutrophils, macrophages, multinucleated giant cells, and spindled cells and an outer layer comprising a mixture of collagen and fibroblasts. CONCLUSION: Our model showed that the fibrous sheath forms around all catheters and covers them in their entire length and circumference without any gaps.

Sheep Model of Hemodialysis Arteriovenous Fistula Using Superficial Veins.

Current models of animal arteriovenous fistula (AVF) are swine models of femoral vein terminolaterally anastomosed to femoral artery, creating a deep AVF. This feature sets it aside from human AVFs using superficial veins. Our AVF model uses sheep superficial veins to create an AVF almost identical to human model. AVFs were created in six sheep using basilic veins sutured terminolaterally to brachial artery. Presurgery vein and artery diameters were measured. We measured AVFs and feeding arteries blood flows and diameters at 1, 3, and 5 weeks postsurgery. At 5 weeks we performed angiograms, euthanized animals, and harvested AVFs. Four animals completed the study. Three AVFs developed and were patent at 5 weeks; one thrombosed. Animal weight and presurgery vessels diameters predicted AVFs blood flows and diameters. Despite using vessels with diameters smaller than the ones recommended for human AVF, the Fistulas developed. Two animals died before the study conclusion for causes unrelated to surgery. This AVF model is anatomically almost identical to the human AVF and has a good maturation rate. It is a viable model for studying AVF maturation, devices intended to improve AVF maturation, AVF related procedures and can even support hemodialysis needles.