Fig. 2.2–2 Flow model for flow-physiological explanation of incomplete systolic thrombolysis. Turbulence proximal to the occlusion (B) and diversion of the blood flow into the unoccluded left pulmonary artery. The turbulence in front of the thrombus leads to poor contact between the thrombolytic agent and the thrombus (Uflacker 2004). RUL, right upper pulmonary arteries; RI, right inferior pulmonary arteries; B, thrombus; T, main pulmonary artery trunk; LUL, left upper pulmonary arteries; LLL, left lower pulmonary arteries.
Endovascular therapy
Indications for endovascular therapy
The same indications apply as for systemic lysis treatment—massive pulmonary embolism in which more than 50% of the pulmonary circulation is obstructed, with the patient showing hemodynamic instability.
Contraindications against endovascular therapy
In contrast to systemic lysis, there are no real contraindications here. Any patient, including those in resuscitation conditions, can receive percutaneous endovascular treatment.
In principle, the general contraindications against the use of iodine-containing radiographic contrast media apply (e.g., hyperthyroidosis, previous severe reaction to contrast medium, advanced renal insufficiency), with no option available for using an alternative contrast agent (e.g., gadolinium in DSA-capable x-ray equipment).
Patient preparation
As this is usually an emergency procedure, patients must have the basic aspects of the planned procedure explained to them if they are conscious, and the legally prescribed waiting period of 1 day does not need to be observed.
Medication
With unstable hemodynamic indices, all patients have already received therapeutic heparinization. Administration of platelet aggregation inhibitors has not been confirmed in controlled studies, but is recommended (with an intravenous bolus dose of 50 mg acetylsalicylic acid). After placement of the femoral sheath, a heparin bolus of 2500– 5000 IU is administered, depending on the patient’s body weight and the expected length of the procedure.
Access route
The most frequently used access route is transvenous femoral access, or less frequently brachial access via the basilic vein or cephalic vein. Jugular access is reserved for special large-lumen catheter systems.
Femoral access
Femoral access is the standard route. The femoral artery pulse can serve for guidance; the femoral vein lies approximately 1.0–1.5 cm medial to the artery. Due to the potential need for local lysis, detailed attention should be given to ensure that the artery is not punctured. It may be helpful to carry out the puncture with fluoroscopy, as the artery can be identified radiographically if there is calcification of the arterial walls. The size and length of the sheath depend on the selected interventional technique and can vary from 5F to 11F and from 11–90 cm, respectively. Reaching the right ventricle or pulmonary arteries is easiest using a flow-directed balloon-tipped catheter that has a guidewire lumen. After the flow-directed balloon-tipped catheter has been positioned in the right ventricle, the guidewire (0.035-inch Glidewire®, Terumo) is introduced, and the flow-directed catheter is exchanged over the guidewire for a pigtail catheter (5F or 6F) for diagnostic angiography.
Brachial access
A 5F or 6F sheath is placed in the basilic vein or alternatively in the cephalic vein, and a pigtail catheter is advanced into the right ventricle or main pulmonary arterial trunk for diagnosis, as in femoral access.
Preinterventional angiography
Either conventional angiography or DSA (15 mL/s contrast injection at 600 psi, total amount 30 mL) is carried out via the pigtail catheter. It is possible to distinguish between submassive and massive pulmonary embolism using the Miller score. With a maximum score of 34 (central obstruction of the right pulmonary artery, 9 points; left pulmonary artery, 7 points; peripheral obstruction of the upper, middle, and lower lobe of the lung, each with no flow, 3 points; severely reduced flow, 2 points; moderately reduced perfusion, 1 point), a score > 10 signifies a massive pulmonary embolism.
Fig. 2.2–3a, b Angiographic image of an embolism (arrow) in the pulmonary artery supplying the left lower lobe, (a) 15 min after 8-mm PTA and 15 mg rt-PA locally as a bolus (b).
Fig. 2.2–4a, b (a) Embolism in the left main pulmonary artery trunk (MRI). (b) Image 6 months after local lysis treatment.
Interventional techniques
Various catheter-based interventional techniques are available, although none of these except local thrombolysis can be regarded as generally valid.
Local thrombolysis
Only some 60–70% of patients with massive pulmonary embolism are able to undergo lysis treatment; the remaining 30–40% have contraindications such as a recent history of surgery, trauma, or carcinoma. In local catheter thrombolysis, a 5F Cragg-McNamara lysis catheter with side holes over a length of 5–10 cm (ev3 and Boston Scientific, etc.) is placed in the thrombus over a hydrophilic-coated 0.035-inch guidewire. As a lytic agent, either urokinase (4500 IU/kg body weight as a bolus, followed by 2000 IU/kg body weight/h) or rt-PA (25–50 mg as a bolus, followed by 25–50 mg/h) is used. When rt-PA is used, heparin with PTT guidance needs to be infused to reduce reocclusion rates. The patient either remains in the catheter laboratory so that the success of the lysis treatment can be documented with serial angiography or, if there is adequate circulatory stability, can be returned to the intensive care unit, where lysis can be continued until hemodynamic improvement is seen.
According to the International Cooperative Embolism Registry (ICOPER), relevant bleeding complications occur with lysis treatment in up to 21% of cases, and intracranial hemorrhage in up to 3% of cases.
Ultrasound-enhanced local thrombolysis. For this procedure, a catheter with several ultrasound-emitting probes attached to its sides (EkoSonic™; Ekos Corporation, Bothell, Washington, USA) is placed in the pulmonary artery and the thrombolytic agent is infused via the catheter during the application of ultrasound waves. The ultrasound waves are intended to separate the fibrin bridges and thus allow better penetration of the drug into the thrombus, shortening the time required for thrombolysis. Controlled studies on the technique are in progress.
Mechanical catheter thrombus fragmentation and local catheter lysis
In central obstruction of the major pulmonary artery trunk, simple mechanical thrombus fragmentation with the guidewire or by rotating the pigtail catheter used for diagnostic angiography in the thrombus can already lead to significant hemodynamic improvement. Mechanical thrombus fragmentation can also be achieved using balloon dilation. However, the contrary effect of further hemodynamic deterioration can occur due to shifting of the thrombi into the peripheral vascular region (Fig. 2.2-5). Mechanical thrombus fragmentation should therefore always be combined with subsequent local lysis over a 5–10-cm sidehole catheter.
Thrombus aspiration
Pulmonary thrombus aspiration was first reported by Greenfield et al. in 1971 using a 10F aspiration catheter. This system is currently the only aspiration catheter approved by the U.S. Food and Drug Administration (FDA). It is now possible