by Assaf Graif, MD; Christoperh J. Grilli, DO; and Mark J. Garcia, MD, FSIR

Vascular and Interventional Radiology, Christina Care Health System, Newark, DE

Deep venous thrombosis (DVT) is part of the spectrum of diseases termed venous thromboembolism (VTE), which includes both asymptomatic and symptomatic DVT, as well as pulmonary embolus (PE).¹ The U.S. Department of Health and Human Services estimates that between 500,000 and 600,000 Americans develop DVT/ PE each year, and at least 100,000 individuals die as a direct or indirect result of VTE ^.2

The economic impact DVT and its complications have on the United States alone is in the billions of dollars every year.³ A study of six European countries has estimated the incidence of first lifetime and recurrent DVT at 148 per 100,000 person-years.4 The incidence of VTE exceeds the total number of myocardial infarctions and strokes in the United States annually,⁵ and the number of VTE -related deaths exceeds that of myocardial infarction- or stroke-related deaths.⁵

Lower extremity DVT can be separated into proximal or distal, depending on its location. Proximal DVT is defined as the presence of venous thrombus within the popliteal, femoral or iliac veins, or inferior vena cava (IVC).¹ Approximately 50% of patients with untreated proximal DVT above the knee will develop symptomatic PE within three months,⁶ as well as a nearly doubled mortality rate when compared with distal lower extremity DVT below the knee.⁷

Post-thrombotic syndrome (PTS) is the most common complication of DVT, which develops in 25% to 60% of patients who suffer a first episode of proximal DVT.8 PTS can be highly debilitating and can manifest itself as chronic, daily limb pain, aching, fatigue, swelling, and in severe cases, venous claudication and skin ulceration—all considerably reduce the patients’ quality of life.9 Compression stockings have been used for acute control of edema at time of presentation, and is continued for at least two years to prevent post-thrombotic syndrome,¹⁰ although this is disputed given the results of the SOX trial.¹¹

At a macroscopic level, the continued presence of thrombus, and incomplete clearance of the original clot burden during the initial weeks after an acute DVT, leads to PTS.¹² Thus, complete removal of the clot burden, at the initial presentation, is considered key to preserving valve function and reducing the likelihood of PTS.

DVT Treatment

For nearly 50 years, the mainstay of acute DVT treatment has been systemic anticoagulation,¹³ which is initiated at the time of presentation and continued for at least 3-6 months. “Thinning” the blood prevents propagation of the clot, but does not promote lysis, does not reduce the thrombus load, does not contribute to the restoration of venous valve function, and therefore does not protect the limb from PTS.¹⁴

Thrombolysis is enhanced by the direct delivery of the thrombolytic agent to the thrombus, where it activates plasminogen and enhances its effectiveness. There are three main approaches to the endovascular treatment of acute DVT: Catheter-directed thrombolysis (CDT), percutaneous mechanical thrombectomy (PMT), and pharmacomechanical catheter-directed thrombolysis (PCDT).

CDT includes placing a multi-side-hole catheter in the thrombus and directly infusing the fibrinolytic agent, most commonly tissue-plasminogen activator, or r-tPA (Genentech, San Francisco, CA). The infusion may last up to 72 hours, with the patient under close surveillance in a stepdown or intensive care unit. New methods of CDT employ using ultrasound-equipped infusion catheters that accelerate the lytic effect by loosening the fibrin lattice and enhancing the drug penetration into the clot. CDT has been found to reduce the late occurrence of PTS and improve quality of life when compared to anticoagulation alone.¹⁵

PMT involves a myriad of different devices that physically macerate the thrombus, while others (e.g. the AngioJet Rheolytic Catheter System [MEDRAD Interventional, Minneapolis, MN]) also aspirate the macerated clot. As a stand-alone therapy, this method is rarely used, due to longer procedure times and residual clot burden adherent to the vessel walls, which necessitates adjunct CDT. PCDT involves the use of a PMT device, combined with a fibrinolytic agent.

PCDT can be subdivided into two main categories: (1) “First-generation” PCDT methods involve the use of a mechanical thrombectomy device, along with traditional infusion CDT. The use of PMT prior to or following CDT, aims at reducing the infusion time and the amount of drug delivered; and (2) “Single-session” PCDT methods enable rapid intrathrombus dispersion of a thrombolytic drug to enhance the complete on-table removal of thrombus in a single session.1 Any residual clot after employment of a “single session” PCDT method will require further treatment with balloon maceration of the thrombus, or adjunct CDT.¹⁶

RAPID lysis

In an attempt to safely and effectively remove thrombus in a rapid fashion, in 1997, we developed a PCDT technique termed “RAPID lysis,” or rheolytic accelerated pharmacomechanical directional thrombectomy. While PMT devices are very adept at creating a channel through the thrombus, the clot adherent to the wall often remains. In order to reach the peripherally adherent clot, and effectively remove it, a coaxial system was devised. This system includes a 6F AngioJet rheolytic thrombectomy catheter, which is placed through an angled directional 8F guiding catheter. The lytic agent is placed into the saline infusate, instead of heparin. While treating the thrombus, the system is retracted through the clot in a “spiraling” fashion by rotating the outer guide catheter along the entire length of the thrombus, allowing for effective circumferential wall-to-wall thrombectomy.

The angle of the guiding catheter allows for a larger effective rheolytic zone by increasing the AngioJet catheter’s active radius from the center of the vessel. Furthermore, the angle allows greater proximity and radial force in regards to the vessel wall, as seen in Figure 1. Following the RAPID thrombectomy, venography is performed. If the operator sees fit, he or she will perform adjunct CDT and/or percutaneous transluminal balloon angioplasty (PTA), either with or without stenting.

Our single center data was reviewed in over 300 patients. The data showed 47% of the limbs treated were completed in a single session, while 53% needed adjunctive CDT with an average infusion time of 17.7 hours, the majority of which included overnight infusion. Eighty-six percent of the cases were completed in less than 24 hours. Following the initial RAPID thrombectomy, 89% were seen as having complete or substantial thrombus removal with restoration of flow. In our institution, the RAPID Lysis technique has become the standard treatment option for patients with acute DVT.

Summary

In summary, our spiraling “wall-to-wall” RAPID thrombectomy method has been safe and effective in restoring venous blood flow, reducing residual circumferential clot burden, and subsequently, the need for adjunctive CDT. We believe the ability to effectively remove thrombus will correlate with a lower incidence of PTS, as has been previously reported.¹⁷ It may also reduce hospital length of stay and costs.

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