Chronic venous insufficiency (CVI) is a prevalent condition associated with significant morbidity and economic burden [1, 2]. The most common pathophysiological mechanism in CVI is axial reflux, defined as retrograde flow in the major superficial veins (great saphenous vein (GSV), small saphenous vein (SSV), or anterior accessory saphenous vein (AASV)), leading to venous hypertension and the clinical manifestations of the disease [3, 4]. Endovenous thermal ablation (EVTA) techniques have largely replaced high ligation and stripping as the standard first-line treatment for insufficient superficial truncal veins due to their high success rates, faster recovery, and low complication rates [5–7]. This is reflected in the most recent European Society for Vascular Surgery (ESVS) guidelines, which assign EVTA the highest level of recommendation (Class IA) [7].

Endovenous thermal ablation techniques use intraluminal thermal energy to induce a controlled vein wall injury, ultimately leading to thermal destruction of the venous wall and permanent vein closure [8, 9]. The two principal modalities are radiofrequency ablation (RFA) and endovenous laser ablation (EVLA), both of which are ultrasound-guided, minimally invasive procedures that can be performed in an outpatient setting under local tumescent anesthesia, allowing for rapid recovery and return to normal activities [6, 7, 9].

The procedure involves percutaneous venous access at the distal segment of the target vein, followed by catheter or fiber advancement to the planned treatment endpoint, which is often located just distal to the saphenofemoral or saphenopopliteal junction. The activated catheter or fiber is then withdrawn in a controlled manner while thermal energy is delivered to the vein wall, causing controlled injury that leads to collagen denaturation, endothelial destruction, fibrosis, and permanent vein closure. Continuous ultrasound guidance allows for accurate puncture site selection, precise catheter positioning, and continuous monitoring throughout the procedure [6, 10] (Fig. 1).

The treatment modalities differ in the type of energy delivered and the thermal profile achieved. RFA delivers radiofrequency energy via a segmental or continuous catheter system, heating the vein wall to a controlled temperature of approximately 120 °C for 20 seconds per segment, resulting in a steady, plateau-shaped thermal curve. The device is withdrawn in a controlled stepwise manner until the entire refluxing segment is treated [8, 10]. EVLA, on the other hand, employs intraluminal laser energy, delivered continuously during controlled fiber pullback to achieve uniform energy distribution along the vein. The laser light is absorbed by the vein tissue and converted into heat. This process produces brief, high-peak temperatures that rapidly coagulate the endothelium and vein wall [10, 11]. Evidence on optimal energy dosing remains limited, though one study suggested a threshold of ~6.3 J/cm per millimeter of vein diameter for durable closure [12].

A critical step in both procedures is the administration of tumescent anesthesia. Under ultrasound guidance, a dilute local anesthetic solution, typically consisting of lidocaine or prilocaine, sodium bicarbonate, epinephrine, and saline, is injected around the vein. Multiple perivenous injections are administered along the course of the target vein to ensure complete coverage before energy application. Tumescent anesthesia serves three essential purposes. First, it provides effective local analgesia during the procedure. Second, it insulates surrounding tissues, particularly skin and nerves, from heat-related injury. Third, it compresses the vein, thereby improving contact between the catheter or fiber and the vein wall and optimizing energy transmission [7, 9, 10]. Additionally, the applied pressure and vasoconstrictive effect of epinephrine reduce the risk of bleeding [13].

Endovenous thermal ablation techniques, including RFA and EVLA, are indicated as first-line therapy for patients with CVI and insufficient superficial truncal veins, particularly those with symptomatic reflux of the GSV, SSV, or AASV confirmed by duplex ultrasound. The European Society for Vascular Surgery, the American Venous Forum (AVF), the American Vein and Lymphatic Society, and the NICE guidelines recommend endovenous thermal ablation (EVTA) over surgical ligation and stripping, citing comparable technical success rates with fewer complications and faster recovery [5, 7, 14]. The AWMF guidelines recommend an individualized treatment approach based on the underlying pathological alterations and patient preference [15].

EVTA is appropriate for patients with CEAP C2s (varicose veins with symptoms or complications) or higher disease, and may be considered even if axial reflux is incomplete or the saphenofemoral junction is competent, provided symptoms are present [5, 7]. A broad body of evidence demonstrates that interventional treatment of saphenous vein reflux provides significant benefits not only in advanced chronic venous disease (CEAP C4–C6) but also in patients with varicose veins (C2). Interventions improve symptoms and quality of life and reduce the risk of disease progression [16, 17]. Consequently, European and American guidelines recommend interventional treatment from CEAP stage C2s onwards [5, 7].

Also in large (>10 mm), nonaneurysmal saphenous veins, thermal ablation is preferred over nonthermal techniques. In cases of below-knee GSV reflux, ablation should extend to the lowest point of reflux. However, nonthermal methods may be considered for distal calf segments to minimize nerve injury risk. Concomitant phlebectomy and/or ultrasound-guided foam sclerotherapy (UGFS) may be performed when tributary veins require treatment. Shared decision-making is recommended, especially for isolated segmental reflux or when anatomical factors may influence modality selection [7, 18].

A comprehensive pre-operative diagnostic evaluation is essential. This typically includes a detailed medical history and physical examination, focusing on venous symptoms and signs. Duplex ultrasound (DU) scanning is the gold standard for evaluating venous anatomy, reflux patterns, aneurysmal changes, and obstructions, thereby enabling accurate vein mapping and treatment planning. A complete DU study should evaluate deep, superficial, and perforating veins in both transverse and longitudinal planes. Spectral Doppler assessment with caliper measurements in dependent position is recommended to document reflux at baseline and in response to Valsalva or distal augmentation in the common femoral vein, saphenofemoral junction (SFJ), mid-femoral and popliteal veins, GSV at the proximal thigh and knee, and SSV at the saphenopopliteal junction (SPJ) or proximal calf. Additionally, diameter measurements with the leg in the dependent position should be obtained at the SFJ, GSV (proximal thigh and knee), and SSV (SPJ or proximal calf). In complex cases, additional imaging such as venography or CT venography may be necessary [5, 6].

Complications of EVTA procedures are generally infrequent and—particularly in comparison to open surgical approaches—have been reported by many authors to be associated with lower severity [19–21]. The most clinically relevant adverse events are thrombotic complications, particularly Ablation-Related Thrombus Extension (ARTE), deep vein thrombosis (DVT), and pulmonary embolism (PE). These occur in fewer than 1% of cases, with studies reporting DVT rates of 0.3–0.7% and PE rates of 0.1% for both EVLA and RFA [22, 23]. The risk of venous thromboembolism (VTE) increases when EVTA is combined with open procedures such as phlebectomy or HLS [24]. In case of VTE, anticoagulation should be initiated [5].

Endothermal heat-induced thrombosis (EHIT) or post-ablation thrombus extension (PATE) represents a specific form of ARTE following endovenous thermal ablation and is defined as thrombus propagation from an ablated superficial vein into a contiguous deep vein. The AWMF guidelines distinguish five grades, ranging from no protrusion (PATE 0) to complete deep vein occlusion (PATE IV, Fig. 2) [25]. Therapeutic anticoagulation is recommended from PATE II onwards until resolution of the thrombus to level 0 [25]. Risk mitigation strategies include meticulous ultrasound-guided catheter placement, ensuring ablation is performed distal from deep vein junctions [26], and early post-procedural duplex scanning in high-risk or symptomatic patients [7]. Postoperative management should emphasize early mobilization and short-term compression therapy. Selective pharmacologic thromboprophylaxis may be considered in patients with elevated VTE risk, but routine use is controversially discussed [5].

Other complications include thermal injury (skin burns or paresthesia from nerve damage), superficial vein thrombosis, ecchymosis, hyperpigmentation, hematoma, and infection, most being minor and transient [9]. Proper use of tumescent anesthesia is the key measure to prevent thermal damage [5]. EVTA of the SSV carries a risk of sural nerve injury due to the close anatomical relationship between the two structures. To minimize this risk, ablation should be initiated above the mid-calf level [27]. In trials using older 980-nm bare-tip laser fibers, patients reported more early postoperative pain after EVLA, whereas RFA was associated with fewer heat-related adverse events such as paresthesia and ecchymoses [28, 29]. Contemporary EVLA practice favors long-wave (1470-nm or 1940 nm) lasers with radial fibers over earlier 810-nm bare-tip systems, as they are associated with lower rates of postoperative pain and bruising [30–32]. Hyperpigmentation and bruising are generally self-limiting. Both techniques have a lower rate of wound infections and bruising compared with HLS [19].

At 1 year, both EVLA and RFA achieve high GSV occlusion rates (>90%), accompanied by significant improvements in the Venous Clinical Severity Score (VCSS) and the Aberdeen Varicose Vein Questionnaire (AVVQ) [28]. Both modalities demonstrate durable long-term efficacy, maintaining occlusion rates of approximately 90–95% at 3–5 years, with no clinically meaningful differences in recurrence rates or quality-of-life outcomes [33, 34]. Current EVLA practice predominantly employs 1470 nm lasers with radial fibers, which deliver circumferential energy to the vein wall. This approach is associated with reduced postoperative pain and bruising compared to older lower-wavelength 980 nm lasers [31, 35]. The 1940 nm laser, which also uses radial or circumferential fiber designs, achieves similar or lower pain scores and ecchymosis rates compared to the 1470 nm system, with studies suggesting a further reduction in patient discomfort [36, 37]. Fiber configuration (radial vs. bare-tip) does not significantly influence treatment success [38].

In the early years of EVTA, a safety margin to the terminal valve of the saphenofemoral junction was routinely maintained [26]. More recently, however, ablation of the truncal vein up to the terminal valve—known as flush ablation—has become the standard approach to reduce recurrences originating from proximal tributaries near the junction [39, 40]. In particular, recurrence via the AASV has been highlighted as a notable concern in long-term follow-up studies [41].

The multicenter SYNCHRONOUS study is currently evaluating whether simultaneous ablation of the AASV during EVLA of the GSV can help prevent varicose vein recurrence. Six-month follow-up data suggest that prophylactic AASV closure alongside GSV treatment is safe, showing comparable complication rates to GSV-only EVLA. Whether this approach reduces recurrence remains to be determined [42].