Percutaneous transluminal therapeutic ultrasound for high-risk thrombus-containing lesions in native coronary arteries

Utility of Thrombectomy in Primary Percutaneous Coronary Intervention

Thrombectomy in the setting of primary percutaneous coronary intervention allows for improved macrovascular and microvascular perfusion, possible limitation of infarct size, and the preservation of left ventricular function and myocardial viability. The beneficial tissue level effects of thrombectomy have translated into an improvement in cardiovascular mortality. A variety of thrombectomy devices are currently available, including aspiration thrombectomy catheters and rheolytic catheters. A review of the various types of thrombectomy devices available, clinical evidence for their use, clinical pearls for use, and device troubleshooting are presented.

Sonophoresis: recent advancements and future trends

OBJECTIVES

Use of ultrasound in therapeutics and drug delivery has gained importance in recent years, evident by the increase in patents filed and new commercial devices launched. The present review discusses new advancements in sonophoretic drug delivery in the last two decades, and highlights important challenges still to be met to make this technology of more use in the alleviation of diseases.

KEY FINDINGS

Phonophoretic research often suffers from poor calibration in terms of the amount of ultrasound energy emitted, and therefore current research must focus on safety of exposure to ultrasound and miniaturization of devices in order to make this technology a commercial reality. More research is needed to identify the role of various parameters influencing sonophoresis so that the process can be optimized. Establishment of long-term safety issues, broadening the range of drugs that can be delivered through this system, and reduction in the cost of delivery are issues still to be addressed.

SUMMARY

Sonophoresis (phonophoresis) has been shown to increase skin permeability to various low and high molecular weight drugs, including insulin and heparin. However, its therapeutic value is still being evaluated. Some obstacles in transdermal sonophoresis can be overcome by combination with other physical and chemical enhancement techniques. This review describes recent advancements in equipment and devices for phonophoresis, new formulations tried in sonophoresis, synergistic effects with techniques such as chemical enhancers, iontophoresis and electroporation, as well as the growing use of ultrasound in areas such as cancer therapy, cardiovascular disorders, temporary modification of the blood-brain barrier for delivery of imaging and therapeutic agents, hormone replacement therapy, sports medicine, gene therapy and nanotechnology. This review also lists patents pertaining to the formulations and techniques used in sonophoretic drug delivery.

Ultrasonic gene and drug delivery to the cardiovascular system

Ultrasound targeted microbubble destruction has evolved as a promising tool for organ specific gene and drug delivery. This technique has initially been developed as a method in myocardial contrast echocardiography, destroying intramyocardial microbubbles to characterize refill kinetics. When loading similar microbubbles with a bioactive substance, ultrasonic destruction of microbubbles may release the transported substance in the targeted organ. Furthermore, high amplitude oscillations of microbubbles lead to increased capillary and cell membrane permeability, thus facilitating tissue and cell penetration of the released substance. While this technique has been successfully used in many organs, its application in the cardiovascular system has dominated so far. Drug delivery using microbubbles has played a minor role in the cardiovascular system. In contrast, gene transfer has been successfully achieved in many studies. Both viral and non-viral vectors were used for loading on microbubbles. This review article will give an overview on studies that have applied ultrasound targeted microbubble destruction to deliver substances in the heart and blood vessels. It will show potential therapeutic targets, especially for gene therapy, describe feasible substances that can be loaded on microbubbles, and critically discuss prospects and limitations of this technique.

Robust intravascular optical coherence elastography by line correlations

We present a new method for intravascular optical coherence elastography, which is robust against motion artefacts. It employs the correlation between adjacent lines, instead of subsequent frames. Pressure to deform the tissue is applied synchronously with the line scan rate of the optical coherence tomography (OCT) instrument. The viability of the method is demonstrated with a simulation study. We find that the root mean square (rms) error of the displacement estimate is 0.55 microm, and the rms error of the strain is 0.6%. It is shown that high-strain spots in the vessel wall, such as observed at the sites of vulnerable atherosclerotic lesions, can be detected with the technique.

Adjunctive techniques in percutaneous mechanical thrombectomy

Percutaneous mechanical thrombectomy is an established method in interventional radiology and refers to the removal of acute embolic or thrombotic occlusive material in arteries, veins, or vascular grafts using percutaneous transluminal methods. However, initial complete removal of occlusive material can be achieved only in a minority of patients. The amount of removed material varies with the age and composition of the occlusive material. To achieve sufficient revascularization, adjunctive use of a variety of percutaneous endovascular recanalization techniques is necessitated. Additional treatment with local intra-arterial fibrinolysis, balloon angioplasty, stent implantation, endoluminal atherectomy, and other measures results in primary technical success rates of 70% to 100% for revascularization of acutely occluded vessels. The above-mentioned different techniques should not be viewed as competitive treatment modalities, rather a synergistic approach should be offered. The aim of this report is to review different adjunctive techniques in percutaneous mechanical thrombectomy with emphasis on techniques, mechanisms of action, experimental and clinical results, potential complications, and their potential role in view of clinical pathways to treat acute limb ischemia.

Towards safer thrombolytic therapy

Plasminogen activators (PA) are unique agents that are currently applied as thrombolytic therapy to achieve rapid vascular reperfusion. Regimens of PA plus anticoagulants and antiplatelet drugs have attained a high degree of sophistication and predictable rates of positive clinical outcomes for acute myocardial infarction (MI), ischemic stroke, pulmonary embolism (PE), deep vein thrombosis (DVT), and thrombosed catheters. Included in the repertoire are newly approved mutants of tissue plasminogen activator (TPA), which have biochemical advantages that allow for bolus administration. Yet, despite tremendous effort devoted to enormous trials to establish the clinical efficacy of these agents in acute MI, mortality results are not superior to those with native TPA or streptokinase (SK). Furthermore, all PAs have the potential for hemorrhagic complication, most critically intracranial hemorrhage (ICH), occurring in 0.9% of patients treated with native or mutant TPA. It is possible that a limit of clinical effectiveness has been reached, beyond which more potent PAs do not achieve greater benefit without a serious increase in risk of bleeding. A breakthrough is possible, however, if the risk of ICH could be avoided. One solution is the application of the direct-acting thrombolytic enzyme, plasmin. While intravenous plasmin is not effective when administered systemically, regional infusion to a thrombus induces local thrombolysis. Unlike the PAs, plasmin treatment should not cause hemorrhage from vascular trauma sites, as it is neutralized by antiplasmin in the blood. Animal studies are fully consistent with this approach, which offers potential for achieving a truly regional thrombolytic treatment.