Changes in blood flow, vessel walls, and characteristics of blood flow, trauma, and stasis (reduction or stoppage of blood flow) all are possible causes of SVT. In addition, a much-overlooked cause is a hypercoagulable state (blood clotting disorder). Findings in one study did suggest that an SVT event indicates an increased risk of a having a hypercoagulable state, especially low levels of antithrombin III. A significant percentage of deep venous thromboses occur in association with SVT and may be an extension of thrombosis (clot) from the superficial veins in some cases.

The most common trauma associated with SVT is an intravenous cannula (commonly known as an IV and is essentially a plastic tube inserted into a vein). Redness, warmth, and tenderness may follow the course of the cannula. After removal of the cannula, warm compresses are placed on the site to arrest the clotting process and to provide some pain relief. A lump may persist for months.

Occasionally, a catheter causes SVT in the arm. Treatment is the same as for the leg-catheter removal, warm compresses, and nonsteroidal anti-inflammatory drugs (e.g., aspirin, ibuprofen).