Electrical Foot Stimulation: A Potential New Method of Deep Venous Thrombosis Prophylaxis

James J. Czyrny; Robert E. Kaplan; Gregory E. Wilding; Christopher H. Purdy; Jack Hirsh

Disclosures

Vascular. 2010;18(1):20-27. 

In This Article

Abstract and Introduction

Abstract

The purpose of this study was to compare venous blood flow velocity of intermittent pneumatic compression to electrical stimulation of the foot. A prospective randomized controlled study of 40 healthy volunteers was conducted. Subjects were seated for 4 hours during which they received electrical stimulation of the sole of the foot or knee-high intermittent pneumatic compression. Popliteal and femoral venous blood flow velocities were measured via Doppler ultrasonography. Blood flow velocity in the nonstimulated or noncompressed lower extremity served as a simultaneous control. For both the femoral and popliteal veins, the electrical foot stimulation group exhibited a greater increase in blood flow velocity than the intermittent pneumatic compression group. Electrical foot stimulation was noninferior relative to standard intermittent pneumatic compression. Specifically, this result of a greater increase in blood flow velocity is achieved at time = 120 minutes for the femoral vein (t = 2.70; p = .005) and time = 120 (t = 2.75; p = .004) and 240 (t = 2.27; p = .014) minutes for the popliteal vein. Short-term electrical foot stimulation is at least as effective as knee-high intermittent pneumatic compression in increasing popliteal and femoral blood flow velocity. Electrical foot stimulation has the potential to be an effective method of deep venous thrombosis prophylaxis.

Introduction

Venous thrombosis and pulmonary embolism or venous thromboembolism (VTE) are important complications of medical and surgical conditions that are associated with prolonged immobilization.[1] Immobilization is also a major contributor to the increased risk of VTE associated with prolonged air travel.[2–4]

Despite good evidence that prophylaxis is effective, there is widespread underuse of prophylaxis for VTE following major surgical procedures as well as medical conditions that produce weakness or prolonged bed rest.[1,5] There is also good evidence that the risk of VTE continues for weeks after major orthopedic and other types of surgery. It is now recognized that VTE occurring in the acute hospital setting, during rehabilitation, and after hospital discharge is a single entity[6] and that extended prophylaxis with anticoagulants reduces the risk. A safe and more convenient method for reducing venous stasis would be particularly useful for preventing venous thrombosis in patients who require prolonged prophylaxis or cannot receive anticoagulation therapy.

Anticoagulant prophylaxis after hospital discharge,[7] although indicated in certain high-risk groups, is inconvenient because the recommended methods, low-molecularweight heparin and fondaparinux, must be administered by subcutaneous injection and warfarin requires laboratory monitoring. The oral anticoagulant rivaroxaban shows promise, but the risk of bleeding remains.

Physical methods that increase blood flow in the leg veins are effective for reducing venous thrombosis in high-risk hospitalized medical and surgical patients. These methods include high-intensity electrical calf stimulation during surgery, graduated compression stockings, and intermittent pneumatic compression (IPC) of the leg or foot. Of these, only graduated compression stockings, which are not very effective, can be used after hospital discharge. Graduated compression stockings, however, cannot be adapted to fit all leg shapes, may be improperly applied, have a tendency to slip down the leg, and are found to be uncomfortable by many patients. High-intensity electrical calf muscle stimulation is painful and can be used only during general anesthesia. AC-powered external pneumatic compression can be used only while the patient is fully immobilized. Thus, alternative convenient methods are needed that can be used in both the immobilized and the partly mobile patient, particularly after hospital discharge.

We attempted to overcome the limitations of currently available physical devices by using mild electrical stimulation of the plantar muscles of the feet. The efficacy of IPC foot pumps for deep venous thrombosis (DVT) prophylaxis has been well established.[8–10] In our technique, transcutaneous electrical foot stimulation has been substituted for pneumatic foot compression. Each electrical discharge elicits a small foot twitch only in the plantar intrinsic foot muscles. This contraction compresses the plantar plexus of veins, thereby increasing venous velocity in the popliteal and femoral veins, which is transmitted proximally up the leg veins.

Our compact plantar foot stimulation device is powered by a 9-volt battery and small enough to be inserted into a sock. It has the potential to be worn while a patient is immobile, standing, or walking and therefore is suitable for use both during the initial period of immobilization and throughout rehabilitation. This device allows patients to receive and participate in their rehabilitative therapy in an unencumbered manner. Activities of daily living can be addressed without interference from this technology (Figure 1).

Figure 1.

Electrical foot stimulation prototype device to enhance venous blood flow from the lower extremities (A, side view; B, sole view).

In an earlier study, we reported that mild electrical stimulation of the plantar foot muscles caused an increase in blood flow comparable to that produced by direct calf stimulation.[11] The aim of this new study was to determine if, over a 4-hour period, mild electrical stimulation of the plantar foot muscles increases venous blood flow velocity to the same degree as IPC of the leg in both obese and nonobese subjects.

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