The Society of Interventional Radiology defines acute proximal pulmonary embolism (PE) as a new main or lobar embolism identified on radiographic imaging within 14 days of PE symptoms (1). Acute PE is currently classified as low-risk, sub-massive (i.e., intermediate-risk), and massive (i.e., high-risk). Massive or high-risk PE is characterized by the presence of sustained systemic arterial hypotension defined by a systolic blood pressure <90 mmHg for at least 15 minutes or requiring inotropic support (2).

According to data published in the International Coo-perative Pulmonary Embolism Registry, 17.4% of patients suffering from acute PE died within 90 days. This registry included 2452 patients from 52 centers in 7 countries (3). Kasper et al. reported that these patients carried a mortality risk of 25%∼65% (4).

Treatment options for pulmonary embolism include oral anticoagulation, systemic thrombolysis, catheter-directed the-rapy (CDT), and surgical pulmonary embolectomy with or without extra-corporeal life support. In a recent study that included 58974 patients with acute PE, 33553 patients were treated with systemic thrombolysis, 22336 with CDT, and 3085 with surgical embolectomy from 2010 to 2014 (5). Although rates of major bleeding and intracranial hemor-rhage were the highest in the systemic thrombolysis group, thrombolysis was the most common option.

Several reports have indicated favorable surgical out-comes in high-risk (massive) PE and/or intermediate-risk (sub-massive) PE (6-11).

The indications for surgical embolectomy in patients with massive PE might include contraindications to thrombolysis, right ventricle (RV) dysfunction, failed medical treatment, and large intracardiac thrombi (12).

In a single-center, 25 patients (17 men, mean age 60 years) underwent emergency open embolectomy for acute PE (6). The most frequent indication for surgical embolec-tomy was RV hemodynamic dysfunction (n=19; 76%). Wood (13) suggested that RV dysfunction without shock is a reasonable indication for surgical embolectomy because as PA (pulmonary artery)-RV pressures increase, the right ventricle might ultimately fail. The development of shock and multisystem organ failure as a consequence of RV failure is associated with at least 30% mortality, whereas if cardiac arrest occurs, the mortality approaches 70%. RV ischemia caused by interatrial septum displacement might reduce coronary artery perfusion to the right ventricle, which can cause RV ischemic infarction and death (14).

Other investigators also considered hemodynamically stable patients with massive PE and moderate-to-severe RV dysfunction for surgical embolectomy (15,16). In addition, several major centers have expanded the use of surgical embolectomy to include patients with PE associated with moderate-to-severe RV dysfunction without hemodynamic compromise (12,17,18).

In critically ill PE patients, veno-arterial extracorporeal membrane oxygenation (VA ECMO) could be applied for life-saving support. Indeed, ECMO is commonly utilized as an important strategy before surgical embolectomy (19).

Surgical embolectomy in acute PE is performed through a median sternotomy with mild hypothermic cardiopulmo-nary bypass using bicaval cannulation, followed by an incision of the pulmonary artery (20). Surgeons can opt for other strategies: normothermic (37℃) beating heart, tepid hypothermic (27℃) cardioplegia, or deep hypothermic (18℃) ventricular fibrillation with intermittent circulatory arrest (7).

The main pulmonary artery is opened with a longitudinal incision, which is extended into the right or left pulmonary artery branches, if necessary. All branches are inspected, and then the thrombotic material is extracted using forceps and assisting suction. Furthermore, the right atrium and ventricle are explored, and the clot is carefully removed (6).

The clot is extracted using suction catheters, forceps, and/or Fogarty balloon catheters. Fogarty catheter extraction of peripheral clots must be done carefully to avoid injuring the thin-walled pulmonary artery branches (21).

For complete clot removal, bilateral lung manual compressions or massage can be performed (22). Each lung compression can mobilize a clot more proximally, so that more peripheral thrombi can be removed. However, this practice may increase bleeding complications. This maneu-ver should not be used in patients on thrombolytic therapy as intractable endobronchial hemorrhage may occur (23). Therefore, Kadner et al. (6) did not perform this manual lung massage to avoid additional damage to the lung parenchyma.

The distal segmental pulmonary arteries might be more carefully visualized through a flexible videoscope (24). Additionally, the right atrium was explored; the scope was passed through the tricuspid valve into the right ventricle. Careful inspection of the apex of the right ventricle and outflow tract could be easily carried out.

An analysis of peer-reviewed literature suggested that the mortality rates in patients treated with surgical embolectomy have decreased substantially over time (22). The cumulative mortality within periods 1968∼1989, 1990∼1999, and thereafter were calculated to be 35%, 30%, and 19%, res-pectively (p<0.05). This improvement might be associated with rapid diagnosis and prompt surgical intervention (12). Moreover, pulmonary embolectomy was the last treatment option for patients with PE in the past because it was associated with high mortality (25).

The large-cohort analysis of more than 2700 adult patients undergoing surgical embolectomy for acute PE from 1999 to 2008 demonstrated a nationwide inpatient mortality rate of 27.2% (26). Recently, mortality occurred in 19.8% of patients undergoing surgical embolectomy for acute PE in another contemporary, nationwide study (5). This represents a significant improvement compared with previous surgical outcomes and supports the role of surgery in the multidisciplinary treatment of these high-risk patients.

In comparison with the medical treatment of massive PE, surgical embolectomy was found to have lower mortality rates, a lower number of hemorrhagic events, and recurrent thrombosis (6). Surgical embolectomy offers similar early and late survival to thrombolysis, with superior freedom from recurrent PE, early stroke, and reintervention (10).

Significantly higher mortality rates among patients with massive PE were observed in patients who underwent cardiopulmonary resuscitation (CPR) (13). Furthermore, patients brought to the operating room undergoing con-tinuous CPR had higher mortality than those undergoing intermittent CPR with stable hemodynamics on arrival to the operating room (80% vs 40%, respectively) (27). In addition, an analysis of the Society of Thoracic Surgery Database with multicenter data collection, including 214 patients admitted for surgical embolectomy, revealed an in-hospital mortality rate of 12%, with the worst outcome (32%) in the group experiencing pre-operative cardiac arrest (8). Preoperative cardiac arrest requiring cardiopulmonary resuscitation has been identified as an independent risk factor causing mortality in patients with PE (17,28). Re-cently, Goldberg et al. (29) reported that morbidity and mor-tality were highly associated with pre-operative cardiopul-monary resuscitation.

RV dysfunction alone has been implicated as an early and late independent risk factor for RV failure and mortality in numerous studies, and recovery of its function has been identified as an early predictor of a favorable in-hospital course (3,12,18,30-32).

Additionally, age greater than 60 years, presence of atrial fibrillation, congestive heart failure, and non-saddle PE were associated with an increase in in-hospital mortality among patients who underwent surgical embolectomy (5).

Early surgical intervention might be an important prog-nostic factor. Ahmed et al. suggested that patients who have undergone a surgical intervention in the first 24 hour of the event experienced a 40% relative reduction in mortality rates (18).

The indications for surgical embolectomy in patients with massive PE might include contraindications to thrombolysis, right ventricle (RV) dysfunction, failed medical treatment, and large intracardiac thrombi (12).

In a single-center, 25 patients (17 men, mean age 60 years) underwent emergency open embolectomy for acute PE (6). The most frequent indication for surgical embolec-tomy was RV hemodynamic dysfunction (n=19; 76%). Wood (13) suggested that RV dysfunction without shock is a reasonable indication for surgical embolectomy because as PA (pulmonary artery)-RV pressures increase, the right ventricle might ultimately fail. The development of shock and multisystem organ failure as a consequence of RV failure is associated with at least 30% mortality, whereas if cardiac arrest occurs, the mortality approaches 70%. RV ischemia caused by interatrial septum displacement might reduce coronary artery perfusion to the right ventricle, which can cause RV ischemic infarction and death (14).

Other investigators also considered hemodynamically stable patients with massive PE and moderate-to-severe RV dysfunction for surgical embolectomy (15,16). In addition, several major centers have expanded the use of surgical embolectomy to include patients with PE associated with moderate-to-severe RV dysfunction without hemodynamic compromise (12,17,18).

In critically ill PE patients, veno-arterial extracorporeal membrane oxygenation (VA ECMO) could be applied for life-saving support. Indeed, ECMO is commonly utilized as an important strategy before surgical embolectomy (19).

The author declares no potential conflict of interest.