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Intraluminal management of acute massive pulmonary thromboembolism
Intraluminal management of acute massive pulmonary thromboembolism Clinical experience with acute massive thromboembolism from 1975 to 1977 has been reviewed. The series consists of 15 patients treated by transvenous intraluminal catheter embolectomy and insertion of a vena caval jilter. Twelve patients were in shock and receiving vasopressor therapy (Class IV), and the remainder had acute thromboembolism superimposed on chronic pulmonary hypertension (Class V). Emboli were extracted from 13 patients (87 percent) but could not be removed from two patients, one of whom had cardiac arrest at the time of pulmonary angiography. One additional death occurred after angiography and one patient died after embolectomy because the Swan-Ganz catheter balloon caused rupture of the pulmonary artery (27 percent mortality rate). The number of emboli removed had little effect on pulmonary vascular resistance, and both cardiac output and Pao, increased in all but one of the surviving patients. Complications included postoperative myocardial infarction in two patients, heparin-induced thrombocytopenia in two patients, and groin wound hematomas in two patients. Nine vena cavograms have been obtained in six patients at intervals in excess of I year after operation, and all show patency of the vena caval jilter. No recurrent pulmonary embolism has been seen, and only one late death has occurred from pancreatic carcinoma. Intraluminal management of acute massive thromboembolism can be performed without general anesthesia or cardiopulmonary bypass and achieves satisfactory survival rates (73 percent) and control of recurrent thromboembolism.
Lazar 1. Greenfield, M.D., and J. James Zocco, M.D., Richmond, Va.
Patients who survive acute massive pulmonary embolism long enough for the diagnosis to be confirmed by pulmonary angiography can be expected to live if systemic perfusion can be maintained, anticoagulation can be tolerated, and embolism does not recur. It is much more difficult to predict the outcome in patients who have severe hypoxemia and inadequate systemic perfusion while receiving vasopressor therapy (Class IV). I The mortality rate in these patients has been high enough for them to be considered candidates for pulmonary embolectomy with cardiopulmonary bypass. However, since this procedure carries a high mortality rate," a general trend toward a more conservative approach relying on anticoagulation and supportive therapy alone has been advocated recently. 3 Since each of these alternatives has disadvantages in the management of a critically ill patient after thromboembolism," a more suitable surgical option which avoids general From the Department of Surgery Medical College of Virginia, Virginia Commonwealth University, Richmond, Va. Received for publication July 14, 1978. Accepted for publication Oct. 2, 1978. Address for reprints: Lazar J. Greenfield. M.D., Department of Surgery, P. O. Box 786, MCV Station, Richmond, Va. 23298.
402
anesthesia, thoracotomy, and cardiopulmonary bypass has been investigated." This approach employs a steerable catheter device which is inserted into the femoral vein with the aid of local anesthesia. The initial results with a nonsteerable catheter have been reported previously," and the more recent experience after modification of the technique by catheter tip control will be reviewed. Further improvement in management also has included insertion of a conical vena caval filter? immediately following catheter embolectomy.
Patients and methods Fifteen patients, nine men and six women, have been treated for acute massive thromboembolism over a period of 20 months from May, 1975, to December, 1977. Eight of them were transferred to the Medical College of Virginia Hospital from community hospitals, generally within 2 to 4 hours of the embolic event. Their ages ranged from 17 to 83 years with a mean age of 58 years. The underlying circumstances favoring development of deep venous thrombosis in this group were as follows: Five patients had been operated upon within 10 days of the embolic event, four patients had chronic venous disease, three patients were recovering from trauma involving major fractures, two patients
0022-5223/79/030402+09$00.90/0 © 1979 The C. V. Mosby Co.
Volume 77 Number 3 March, 1979
Management of thromboembolism
40 3
Table I. Classification of pulmonary thromboembolism Class
Symptoms
Gases
PA occlusion (%)
I II
Normal Tachycardia
30-50
CVP elevated, PA > 20 mm. Hg
IV
Shock, dyspnea
>50
V
Dyspnea, syncope
Normal Pao, < 80 mm. Hg PlIco, < 35 mm. Hg Pao, < 65 mm. Hg PlIco, < 30 mm. Hg Pao, < 50 mm. Hg P3(:o, < 30 mm. Hg Pao, < 50 mm. Hg P3(·o, 30-40 mm. Hg
<20 20-30
III
None Anxiety, hyperventilation Dyspnea, collapse
CVP elevated, PA > 25 mm. Hg, BP < 100 mm. Hg PA > 40 mm. Hg, CVP elevated, CO low, no shock
> 50
Hemodynamics
Legend: PA, Pulmonary artery. CVP, Central venous pressure. PA, Mean pulmonary artery. BP, Blood pressure. CO, Cardiac output.
had heart disease, and one patient had been hospitalized for management of diabetic ketoacidosis. Patients were classified physiologically on the basis of the effects of the thromboembolism on the pulmonary and systemic circulations." Twelve of them were in shock and receiving vasopressors (Class IV), and the remaining three patients were categorized in Class Von the basis of signs of long-standing severe pulmonary hypertension (Table I). One of the latter group also required vasopressor support. Four of the patients had been resuscitated from cardiac arrest, and all of them underwent either selective or main pulmonary arteriograms and measurement of pulmonary arterial pressures. Following angiographic confirmation of the diagnosis, and while the patient remained on the radiology table, the right common femoral vein was exposed through a vertical groin incision made with the use of local anesthesia. The steerable cup-catheter then was introduced and contrast medium injected to verify absence of projecting thrombi in the iliac system. The catheter was advanced under fluoroscopic control through the right side of the heart and into the pulmonary artery. The pulmonary arteriogram served as a guide to the most recent embolus, which was indicated by the outline of contrast medium around it; by contrast, complete interruption of dye suggested fixed emboli (Fig. 1). The catheter was advanced into the involved main or lobar pulmonary artery, and hand injections of small amounts of dye were used to confirm proximity of the cup to the embolus. Syringe suction applied to the catheter usually aspirated the embolus into the cup, where it was held by sustained syringe vacuum. With suction being maintained, the catheter then was withdrawn slowly through the right side of the heart, down the inferior vena cava, and removed, bringing with it the attached embolus.! Pulmonary and systemic pressures were monitored as pulmonary emboli were being removed. After restoration of adequate cardiac output as demonstrated by cessation of need for
vasopressors, reduction in pulmonary arterial pressure, and improvement in systemic arterial oxygenation, a repeat pulmonary arteriogram was obtained to verify restoration of perfusion. Following this, a vena caval filter was inserted through the same femoral venotomy by a carrier-catheter which allowed positioning of the filter below the renal vein at the level of the third lumbar vertebra. The entire procedure could usually be completed in 2 hours. Anticoagulation was resumed in those patients who had no contraindication to the treatment approximately 12 hours postoperatively. Follow-up studies included repeated pulmonary arterial and cardiac output measurements and combined venogram and lung perfusion scans done with peripheral injections of isotope of labeled albumin macroaggregates.
Results Twelve of the 15 patients required vasopressor support of systemic blood pressure at the time of pulmonary arteriography, and the systolic blood pressure did not exceed 100 mm. Hg in 14 of them (Table II). The only patient with a normal blood pressure had pulmonary hypertension and had sustained a paradoxical embolus to the femoral artery. There were four deaths in the group, for a mortality rate of 27 percent. One of the deaths occurred in a 59-year-old man who had severe pulmonary hypertension (50/26 mm. Hg, mean 36 mm. Hg), tricuspid insufficiency, and desquamative interstitial pneumonitis. The pulmonary emboli were in the periphery of the lung and none could be extracted. The remaining three deaths were to some extent preventable, since two of them followed cardiac arrest after injection into the main pulmonary artery rather than a more selective study with a smaller volume of contrast media. The final death occurred in a 76-yearold man who was recovering from a myocardial infarction at the time of massive thromboembolism. He had successful removal of five large emboli, which restored
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404 Greenfield and Zocco
Table II. Hemodynamic and blood gas measurements in 15 patients undergoing catheter embolectomy. 1975 to 1977 Systemic pressure (mm, Hg)
I
PAP (mm. Hg)
Post.
Pre.
60/0*
110/80
68. F
126/70
130/80
T. P.
17, F
70/0*
130/80
1/76
O. G.
26, M
90/50
125/70
3/76
H. S.
37, M
100/60
160/90
7/76
R. C.
63, M
55/40 (45) 51125 (30) 50/20 (30) 40/15 (25) 55/30 (45) 45125 (27) 50126 (36) 42/14 (21) 40/10 (21)
Date
Pt.
Age/sex
Pre.
5/75
W.G.
51, M
6/75
N.W.
8/75
90/60*
100/70* 100/60*
7/76
J. W.
59, M
7/76
G. G.
76, M
65/0*
110/70
10/76
E. B.
69, M
90/60*
110/75
10/76
E. P.
63, F
70/0*
6/77
R. H.
44, F
70/0*
100/65
7/77
M. S.
74, F
75/40*
110/60
9/77
R. H.
83, M
65/0*
12/77
G.M.
57, M
1001180*
135/95*
12/77
C. A.
79, F
63/50*
160/90*
100/75*
82/60*
38/20 (24) 35/10 (21) 45125 (37) 74/35 (40) 30/18 (22) 50/15 (36)
I
CO (L./min.)
Post.
Pre.
40/30 (33) 38/18 (20) 28/11 (15) 25/14 (20) 50126 (40) 42/15
2.25
(27) 50122
(30) 36/9 (15) 37/6 (16)
I
Post.
Pre.
4.95
20.
I
Post.
Class
6.6
IV
No. of emboli out
2
V Arrest
1.03
7.83
24.3
2.6
IV IV
4.07
4.99
11.1
8.0
V
1.14
3.10
23.7
8.7
IV
2.28
2.72
15.8
11.0
V
0
IV
>5
IV
2
3.00
4.05
1.89 35/8 (20) 40/19 (30) 45120 (30) 10/4 (8) 21/12 ( 16)
PVR
7.0
3.9
>5
IV
12.7
1.90
3.70
11.0
5.4
IV
>5
4.29
6.57
8.6
4.6
IV
2
2.88
4.15
13.9
7.2
Arrest
>5
3.57
2.45
6.2
3.3
Arrest
2
2.75
4.70
13.1
3.4
Arrest
IV IV
IV
2
Legend: PAP, Pulmonary artery pressure. CO, Cardiac output. PVR, Pulmonary vascular resistance. VGI, Vpper gastrointestinal tract. CA, Carcinoma. *00 vasopressors at embolectomy.
the cardiac output, only to sustain a massive pulmonary hemorrhage when the balloon of the Swan-Ganz catheter was inflated in the periphery of the pulmonary artery from which an embolus had been removed. Emboli were removed from 13 patients, for an extraction rate of 87 percent. Emboli could not be removed from one of the patients who had cardiac arrest following angiography before the catheter could be positioned or from the patient with chronic pulmonary hypertension. The number of emboli removed varied from patient to patient, and it was difficult to gauge the effect of this variable owing to variations in size of the emboli. When the patients were separated into groups depending on whether less than or more than two emboli were extracted, there was no apparent major difference in the reduction in total pulmonary vascular
resistance (pulmonary artery mean pressure/cardiac output). However, the group with more emboli removed had a lower average value (4.6 units) than those having fewer than two emboli removed (9.2 units) (Fig. 2). The average initial pulmonary vascular resistance value was 14.0 units, and the average value at the end of the procedure was 5.9 units. A more accurate assessment of pulmonary vascular resistance was not possible since the presence of bilateral emboli prevented measurement of the pulmonary capillary wedge pressure. Five of the 12 patients receiving vasopressors at the beginning of the procedure required them postoperatively for periods of 3 to 72 hours. Two of these patients had cardiac arrest and then died a short time later. One of the remaining three requiring dopamine
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Pao, (mm . Hg) Pre.
I
Post .
Pa co, (mm. Hg) Pre .
I
Post.
pH Pre.
I
Post .
Outcome
48
90
7 .03
7 .32
Living and well
56
64
7.42
7 .44
Living and well
49
118
7.35
7.39
Living and well
50
138
36
52
7 .38
7 .33
Living and well
55
63
31
30
7.48
7.46
28
73
28
24
7.39
7 .51
Living and well
69
85
38
33
7.42
7.46
Died 7/17
46 54
36 107
23
Died
23
24
53
7.41
7.45
Late death, 8/27/77, from pancreatic CA, two UGI hemorrhages Died Living and well
7 .44
Fig. 1. Selective left pulmon ary arteriogram in a 79-year-old woman (Patient C . A.) in shock despite receiving vasopressors (Class IV). The contrast medium outlines the embolus as a favorable sign of nonattachment to the wall of the pulmonary artery .
70
82
21
26
7 .38
7.45
39
65
31
38
7.49
7.46
50
180
23
33
7.48
7 .35
Died
34
170
37
28
7 .15
7 .52
Living and well
TVR 26
36
69
30
33
7.49
7 .50
Living and well
22
infusion had electrocardiographic changes of an acute myocardial infarction and one was in a septic condition from an infected appendectomy wound. The initial mean pulmonary artery pressure exceeded 21 mm. Hg in all patients and averaged 31 mm . Hg. For all 14 patients who survived the procedure, the postoperative average pulmonary artery mean pressure was 23 mm. Hg. Cardiac output was measured in 12 patients preoperatively and averaged 2.59 L. per minute . Postoperatively, it increased in 10 of II surviving patients to an average value of 4.47 L. per minute . The preoperative blood gases were obtained under varying levels of Flo., and in four patients ventilation was via endotracheal tube using a compressible bag ventilator. Following embolectomy, Pa02 increased in all surviving patients from an initial average value of 49 mm. Hg to 101 mm. Hg. Similarly, pH and Paco. values were restored to more normal levels (Table II).
18 14 10
6
2
PRE
<2
POST PRE EMBOLI
POST
2>
Fig. 2. Comparison of reductions in total pulmonary vascular resistance (TVRj following extraction of less than (left) or more than (right) two pulmonary embol i. Although a more satisfactory fall in resistance appeared to occur after removal of more emboli , there was no significant difference between the two groups .
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Surgery
Fig . 3. Second pulmonary angiogram in Patient C . A., shown in Fig. I. following removal of the embolus on the left side. Nearly complete occlusion of the right main pulmonary artery by massive embolism is demonstrated .
Table III. Complications followin g catheter embolectomy, 1975 to 1977 Complication
No.
Postoperative hemorrhage (anticoagulation) Angiography (nonselective) arrest Myocardial infarction Pulmonary infarction Swan-Ganz catheter rupture of pulmonary artery Wound infection
4
2 2 2 I I
Postoperative anticoagulation with heparin was used in 10 of the II surviving patients, the one exception being a patient who had had neurosurgery. All 13 patients who initially survived the procedure had a vena caval filter inserted under fluoroscopic control at the end of the embolectomy procedure, II of them via the same femoral venotomy and two of them via a separate jugular approach owing to technical problems of insertion of the catheter-carrier from the femoral approach. Anticoagulation was maintained usually for I week with heparin while oral coumarin derivatives were administered. Repeated measurements of cardiac output and pulmonary arterial pre ssures in four patients showed further decreases in total pulmonary vascular re sistance as cardiac output increased . Complications in this group included two instances of cardiac arrest during diagnostic studies and one arrest after unsuccessful attempted embolectomy (Table III) . Transient rhythm d isturbances were seen in most patients while the catheter was being manipulated through the right side of the heart, but none required
treatment. Only one death could be attributed to the procedure, and that was related to inflation of the balloon of the Swan-Ganz catheter, as mentioned previously, not from the embolectomy catheter. Two patients had myocardial infarction po stoperatively, two had thrombocytopenia and hemorrhage controlled by ce ssation of heparin, and two had groin wound hematomas , one of which became infected . A third patient who had an appendectomy at another ho spital developed an infection in the abdominal wound . All surviving patients have been followed for periods ranging from 3 to 34 months (average 19 months). Nine vena cavograms have been obtained in six patients for assessment of patency at intervals in excess of I year, and all have been patent. This is comparable to the experience reported in a larger se ries of patients who required filter insertion but who did not qualify for catheter embolectomy . 7 No episodes of recurrent pulmonary embolism , recurrent thrombophlebitis. or mi gration of the filter were seen . There has been one late death from pancreatic carcinoma , but the remaining patients are alive and well.
Case reports C. A. (No. 8037100) , a 79-year-old woman, underwent emergenc y appendectomy for perforative appendicitis at another hospital 10 days prior to her transfer to the Medical College of Virginia. On the day of admission , she had been resuscitated from cardiac arrest after co llapsing in the bathroom . Dopamine infusion at a rapid rate was required to maintain systemic blood pressure at 90/50 mm. Hg. At the time of admission she had a Pao , of 40 mm. Hg on 10 L. of nasal oxygen and a P
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Fig. 4. Intact emboli removed from the left (top) and right (bottom) pulmonary arteries of Patient C. A.• shown in Figs. I and 3. Each embolus exceeds 15 em. in length and was removed in a single passage of the embolectomy catheter. was obtained (Fig. 8). The contrast study confirmed the capture of another large embolus within the filter. completely filling it. Despite the size of the embolus. vena caval blood flow was preserved around the trapped embolus. A repeat isotope venogram-lung scan I week later confirmed continued patency of the vena cava and normal pulmonary perfusion. She has remained asymptomatic at home receiving oral anticoagulation to control underlying deep venous thrombosis.
Discussion Pulmonary thromboembolism covers such a wide spectrum of physiological effects that comparisons of treatments and outcomes is difficult without some classification of the disorder. We have found the described hemodynamic classification useful in preliminary staging of the condition of a given patient. At that point a rational comparison of the risks of proposed treatment as opposed to the gravity of the situation can be made . Extremes of management are to be avoided . There are adequate data to refute a surgical approach to every patient. and the ultraconservative approach of anticoagulation therapy alone under all circumstances ignores continuing deaths from massive pulmonary embolism and the complications associated with that form of treatment. In the first series of patients who underwent attempted intraluminal catheter embolectomy, there were two early deaths from recurrent embolism before surgical interruption of the inferior vena cava could be accomplished ." Consequently, a filter device was developed which could be inserted through the same femoral venotomy at the conclusion of the embolectomy procedure to provide immediate protection from recurrent embolism ." In addition, the initial nonsteerable catheter provided only limited access to the pulmonary vascular
Fig. 5. Final pulmonary arteriogram of Patient C. A. showing clearing of both main pulmonary arteries and nearly complete restoration of pulmonary perfusion. tree . Therefore, a steerable handle was added for directional control of the cup. This modification increased both the ease of passage through the right side of the heart and the maneuverability within the pulmonary artery for access to more pulmonary emboli . The results in the present series of patients reflect the advantages of these changes. The criteria for selection of patients for pulmonary embolectomy have varied widely from an aggressive approach advocating prophylactic embolectomy" to the statement that there are no indications for open embolectomy.!? These judgments are obviously affected by the high morbidity and mortality rates associated with open pulmonary embolectomy on cardiopulmonary bypass . Since it is now possible to extract massive
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Fig. 6. The KMA-Greenfield filter, inserted through a femoral venotomy, shown after discharge from the catheter-carrier (left) . This carrier differs from the more commonly used jugular vein inserter.
.,
;
~ ..
.
;. ~.
.. .
~:
:~ . "
~ .
Fig. 7. Patient C. A. routine postoperative isotope venogram. No clear concentration of isotope can be seen in the lower inferior vena cava (upper left) , suggesting impairment of vena caval flow through the filter (see Fig. 8). pulmonary emboli without general anesthesia, thoracotomy , and cardiopulmonary bypass, the problem can be placed in more appropriate perspective. The chances for survival of a severely hypoxemic patient in shock despite vasopressor support seem sufficiently precarious to warrant intervention for mechanical relief provided that the procedure itself does not contribute further risk . The passage of the embolectomy catheter through the right side of the heart has been remarkably free of complications, an unusual fact considering the increased risks usually associated with catheter manipulation in a patient with pulmonary hypertension. The explanation may be the short period of time that the catheter stays in the right ventricle en route to the pul-
monary artery . In addition, the cup device is made of relatively soft radiopaque plastic which has not caused any mechanical damage during passage . The presence of a Swan-Ganz catheter in the pulmonary artery during the embolectomy usually poses no problem, although it rarely can impair extraction of a large embolus and was associated in this series with one fatal complication consisting of balloon rupture of the pulmonary artery. The deaths which occurred in this series reflect not only the seriousness of the underlying disorders, but also the potentially lethal effects of injecting a large volume of contrast material. This resulted in cardiac arrest in two patients, from which they could not be resuscitated despite adequate embolectomy in one of
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them. The remaining death represented poor selection for the procedure, since the patient had peripheral, occlusive , chronic pulmonary embolism, established pulmonary hypertension (Class V), and tricuspid insufficiency. Currently, we would treat such a patient by placement of a vena caval filter and anticoagulation alone. The number of emboli removed did not significantly affect the outcome, since a satisfactory reduction in vascular resistance occurred when as little as one embolus was removed. Obviously, the volume and orientation of the embolus dictate the effects on the pulmonary circulation, but the net effects on pulmonary pressure and cardiac output can be determined serially as emboli are removed while the Swan-Ganz catheter remains in position. Usually there is a threshold for critical reduction of flow which produces inadequate cardiac output , and when that threshold is restored by disimpaction of a critical embolus, the effects are dramatic, with a sudden increase in both systemic and pulmonary blood pressures. II This is usually the point at which the vasopressor agents can be discontinued. If further emboli can be extracted easily, they are removed, with the aim of reaching a mean pulmonary arterial pressure of 20 mm. Hg or less at completion . The postoperative arteriogram usually shows persistent pruning of small pulmonary arterioles suggesting the possibility of residual vasospastic as well as fragmentary embolic occlusion . Occasionally , a patient will demonstrate reinforcement of a hormonal or neural vasospastic component. 12 One such patient was a 17year-old girl in this series who had cardiac arrest after a single embolus to the right lower lobar pulmonary artery . In this patient, who should have been able to tolerate much more vascular occlusion, the postoperative angiogram showed poor perfusion in the segment from which an intact embolus had been removed. 1 Vasodilating agents have not been employed but perhaps could be beneficial under these circumstances. Similarly, fibrinolytic agents have not been used since a recent operative wound is a contraindication to their use because of bleeding complications. If intraluminal catheter embolectomy can be performed with low morbidity and mortality rates, then the indications for its application should expand to include Class III patients, who have large volume embolism in the absence of shock . Since the time course and adequacy of spontaneous lysis of these major thrombi remains speculative, their removal in association with placement of a vena caval filter should hasten recovery of the patient and avoid the consequences of delayed resolution of impacted emboli. Wider application of the
CA Fig. 8. Patient C. A. contrast inferior vena cavogram obtained because of an abnormal isotope venogram (Fig. 7). A large embolus is seen coiled up and trapped in the filter but with preservation of blood flow around it. vena caval filter device alone in patients who do not require embolectomy has been associated with very favorable results, including lysis of entrapped emboli within the filter over a period of several weeks. 7 The option of venoarterial partial bypass through the opposite femoral artery and vein has been used only for resuscitation of patients having cardiac arrest, and usually without survival. In these patients who are actively being resuscitated, transfer to the operating room is advisable . If cardiac output cannot be restored, then open embolectomy on cardiopulmonary bypass should be performed. The requirement for closed chest cardiac massage obviously excludes fluoroscopy and represents a contraindication to attempted catheter embolectomy. Similarly, patients who have not responded to attempted removal by catheter technique should undergo open embolectomy. However, for institutions where cardiopulmonary bypass is not available, the catheter technique represents an alternative method for emergency management and potential salvage of patients following acute massive pulmonary embolism.
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REFERENCES
2
3
4
5
Greenfield U: Pulmonary embolism. Diagnosis and management. Current Problems in Surgery, Chicago, 1976, Year Book Medical Publishers, Inc., Vol 13, No.4, pp I-52 DeWeese JA: The role of pulmonary embolectomy in venous thromboembolism. J Cardiovas Surg 17:348-353, 1976 Alpert JS, Smith RE, Ockene IS, Askenazi J, Dexter L, Dalen JE: Treatment of massive pulmonary embolism. The role of pulmonary embolectomy. Am Heart J 89:413-418, 1975 Miller GAH, Hall RJC, Paneth M: Pulmonary embolectomy, heparin, and streptokinase. Their place in the treatment of acute massive pulmonary embolism. Am Heart J 93:568-574, 1977 Greenfield LJ, Bruce TA, Nichols NB: Transvenous pulmonary embolectomy by catheter device. Ann Surg 174:881-886, 1971
6 Greenfield U, Peyton MD, Brown PP, Elkins RC: Transvenous management of pulmonary embolic disease. Ann Surg 180:461-468, 1974 7 Greenfield LJ, Zocco J, Wilk JD, Schroeder MD, Elkins RC: Clinical experience with the Kim-Ray Greenfield vena caval filter. Ann Surg 185:692-698, 1977 8 Brown PP, Elkins RC, Greenfield U: Comparison of a new intracaval filter with the Mobin-Uddin device and clinical experience. Circulation 48:Suppl 4:5, 1973 9 Berger RL: Pulmonary embolectomy with preoperative circulatory support. Ann Thorac Surg 16:217-227, 1973 10 Sautter RD, Myers WO, Ray JF III, Wenzel FJ: Pulmonary embolectomy. Review and current status. Progr Cardiovasc Dis 17:371-389, 1975 II Greenfield LJ: Surgery for pulmonary embolism. Venous Problems, Chicago, 1978, Year Book Medical Publishers, Inc., Vol 22, pp 355-366
Information for authors Most of the provisions of the Copyright Act of 1976 became effective on January I, 1978. Therefore, all manuscripts must be accompanied by the following written statement, signed by one author: "The undersigned author transfers all copyright ownership of the manuscript (title of article) to The C. V. Mosby Company in the event the work is published. The undersigned author warrants that the article is original, is not under consideration by another journal, and has not been previously published. I sign for and accept responsibility for releasing this material on behalf of any and all co-authors." Authors will be consulted, when possible, regarding republication of their material.
Lazar 1. Greenfield, M.D., and J. James Zocco, M.D., Richmond, Va.
Patients who survive acute massive pulmonary embolism long enough for the diagnosis to be confirmed by pulmonary angiography can be expected to live if systemic perfusion can be maintained, anticoagulation can be tolerated, and embolism does not recur. It is much more difficult to predict the outcome in patients who have severe hypoxemia and inadequate systemic perfusion while receiving vasopressor therapy (Class IV). I The mortality rate in these patients has been high enough for them to be considered candidates for pulmonary embolectomy with cardiopulmonary bypass. However, since this procedure carries a high mortality rate," a general trend toward a more conservative approach relying on anticoagulation and supportive therapy alone has been advocated recently. 3 Since each of these alternatives has disadvantages in the management of a critically ill patient after thromboembolism," a more suitable surgical option which avoids general From the Department of Surgery Medical College of Virginia, Virginia Commonwealth University, Richmond, Va. Received for publication July 14, 1978. Accepted for publication Oct. 2, 1978. Address for reprints: Lazar J. Greenfield. M.D., Department of Surgery, P. O. Box 786, MCV Station, Richmond, Va. 23298.
402
anesthesia, thoracotomy, and cardiopulmonary bypass has been investigated." This approach employs a steerable catheter device which is inserted into the femoral vein with the aid of local anesthesia. The initial results with a nonsteerable catheter have been reported previously," and the more recent experience after modification of the technique by catheter tip control will be reviewed. Further improvement in management also has included insertion of a conical vena caval filter? immediately following catheter embolectomy.
Patients and methods Fifteen patients, nine men and six women, have been treated for acute massive thromboembolism over a period of 20 months from May, 1975, to December, 1977. Eight of them were transferred to the Medical College of Virginia Hospital from community hospitals, generally within 2 to 4 hours of the embolic event. Their ages ranged from 17 to 83 years with a mean age of 58 years. The underlying circumstances favoring development of deep venous thrombosis in this group were as follows: Five patients had been operated upon within 10 days of the embolic event, four patients had chronic venous disease, three patients were recovering from trauma involving major fractures, two patients
0022-5223/79/030402+09$00.90/0 © 1979 The C. V. Mosby Co.
Volume 77 Number 3 March, 1979
Management of thromboembolism
40 3
Table I. Classification of pulmonary thromboembolism Class
Symptoms
Gases
PA occlusion (%)
I II
Normal Tachycardia
30-50
CVP elevated, PA > 20 mm. Hg
IV
Shock, dyspnea
>50
V
Dyspnea, syncope
Normal Pao, < 80 mm. Hg PlIco, < 35 mm. Hg Pao, < 65 mm. Hg PlIco, < 30 mm. Hg Pao, < 50 mm. Hg P3(:o, < 30 mm. Hg Pao, < 50 mm. Hg P3(·o, 30-40 mm. Hg
<20 20-30
III
None Anxiety, hyperventilation Dyspnea, collapse
CVP elevated, PA > 25 mm. Hg, BP < 100 mm. Hg PA > 40 mm. Hg, CVP elevated, CO low, no shock
> 50
Hemodynamics
Legend: PA, Pulmonary artery. CVP, Central venous pressure. PA, Mean pulmonary artery. BP, Blood pressure. CO, Cardiac output.
had heart disease, and one patient had been hospitalized for management of diabetic ketoacidosis. Patients were classified physiologically on the basis of the effects of the thromboembolism on the pulmonary and systemic circulations." Twelve of them were in shock and receiving vasopressors (Class IV), and the remaining three patients were categorized in Class Von the basis of signs of long-standing severe pulmonary hypertension (Table I). One of the latter group also required vasopressor support. Four of the patients had been resuscitated from cardiac arrest, and all of them underwent either selective or main pulmonary arteriograms and measurement of pulmonary arterial pressures. Following angiographic confirmation of the diagnosis, and while the patient remained on the radiology table, the right common femoral vein was exposed through a vertical groin incision made with the use of local anesthesia. The steerable cup-catheter then was introduced and contrast medium injected to verify absence of projecting thrombi in the iliac system. The catheter was advanced under fluoroscopic control through the right side of the heart and into the pulmonary artery. The pulmonary arteriogram served as a guide to the most recent embolus, which was indicated by the outline of contrast medium around it; by contrast, complete interruption of dye suggested fixed emboli (Fig. 1). The catheter was advanced into the involved main or lobar pulmonary artery, and hand injections of small amounts of dye were used to confirm proximity of the cup to the embolus. Syringe suction applied to the catheter usually aspirated the embolus into the cup, where it was held by sustained syringe vacuum. With suction being maintained, the catheter then was withdrawn slowly through the right side of the heart, down the inferior vena cava, and removed, bringing with it the attached embolus.! Pulmonary and systemic pressures were monitored as pulmonary emboli were being removed. After restoration of adequate cardiac output as demonstrated by cessation of need for
vasopressors, reduction in pulmonary arterial pressure, and improvement in systemic arterial oxygenation, a repeat pulmonary arteriogram was obtained to verify restoration of perfusion. Following this, a vena caval filter was inserted through the same femoral venotomy by a carrier-catheter which allowed positioning of the filter below the renal vein at the level of the third lumbar vertebra. The entire procedure could usually be completed in 2 hours. Anticoagulation was resumed in those patients who had no contraindication to the treatment approximately 12 hours postoperatively. Follow-up studies included repeated pulmonary arterial and cardiac output measurements and combined venogram and lung perfusion scans done with peripheral injections of isotope of labeled albumin macroaggregates.
Results Twelve of the 15 patients required vasopressor support of systemic blood pressure at the time of pulmonary arteriography, and the systolic blood pressure did not exceed 100 mm. Hg in 14 of them (Table II). The only patient with a normal blood pressure had pulmonary hypertension and had sustained a paradoxical embolus to the femoral artery. There were four deaths in the group, for a mortality rate of 27 percent. One of the deaths occurred in a 59-year-old man who had severe pulmonary hypertension (50/26 mm. Hg, mean 36 mm. Hg), tricuspid insufficiency, and desquamative interstitial pneumonitis. The pulmonary emboli were in the periphery of the lung and none could be extracted. The remaining three deaths were to some extent preventable, since two of them followed cardiac arrest after injection into the main pulmonary artery rather than a more selective study with a smaller volume of contrast media. The final death occurred in a 76-yearold man who was recovering from a myocardial infarction at the time of massive thromboembolism. He had successful removal of five large emboli, which restored
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404 Greenfield and Zocco
Table II. Hemodynamic and blood gas measurements in 15 patients undergoing catheter embolectomy. 1975 to 1977 Systemic pressure (mm, Hg)
I
PAP (mm. Hg)
Post.
Pre.
60/0*
110/80
68. F
126/70
130/80
T. P.
17, F
70/0*
130/80
1/76
O. G.
26, M
90/50
125/70
3/76
H. S.
37, M
100/60
160/90
7/76
R. C.
63, M
55/40 (45) 51125 (30) 50/20 (30) 40/15 (25) 55/30 (45) 45125 (27) 50126 (36) 42/14 (21) 40/10 (21)
Date
Pt.
Age/sex
Pre.
5/75
W.G.
51, M
6/75
N.W.
8/75
90/60*
100/70* 100/60*
7/76
J. W.
59, M
7/76
G. G.
76, M
65/0*
110/70
10/76
E. B.
69, M
90/60*
110/75
10/76
E. P.
63, F
70/0*
6/77
R. H.
44, F
70/0*
100/65
7/77
M. S.
74, F
75/40*
110/60
9/77
R. H.
83, M
65/0*
12/77
G.M.
57, M
1001180*
135/95*
12/77
C. A.
79, F
63/50*
160/90*
100/75*
82/60*
38/20 (24) 35/10 (21) 45125 (37) 74/35 (40) 30/18 (22) 50/15 (36)
I
CO (L./min.)
Post.
Pre.
40/30 (33) 38/18 (20) 28/11 (15) 25/14 (20) 50126 (40) 42/15
2.25
(27) 50122
(30) 36/9 (15) 37/6 (16)
I
Post.
Pre.
4.95
20.
I
Post.
Class
6.6
IV
No. of emboli out
2
V Arrest
1.03
7.83
24.3
2.6
IV IV
4.07
4.99
11.1
8.0
V
1.14
3.10
23.7
8.7
IV
2.28
2.72
15.8
11.0
V
0
IV
>5
IV
2
3.00
4.05
1.89 35/8 (20) 40/19 (30) 45120 (30) 10/4 (8) 21/12 ( 16)
PVR
7.0
3.9
>5
IV
12.7
1.90
3.70
11.0
5.4
IV
>5
4.29
6.57
8.6
4.6
IV
2
2.88
4.15
13.9
7.2
Arrest
>5
3.57
2.45
6.2
3.3
Arrest
2
2.75
4.70
13.1
3.4
Arrest
IV IV
IV
2
Legend: PAP, Pulmonary artery pressure. CO, Cardiac output. PVR, Pulmonary vascular resistance. VGI, Vpper gastrointestinal tract. CA, Carcinoma. *00 vasopressors at embolectomy.
the cardiac output, only to sustain a massive pulmonary hemorrhage when the balloon of the Swan-Ganz catheter was inflated in the periphery of the pulmonary artery from which an embolus had been removed. Emboli were removed from 13 patients, for an extraction rate of 87 percent. Emboli could not be removed from one of the patients who had cardiac arrest following angiography before the catheter could be positioned or from the patient with chronic pulmonary hypertension. The number of emboli removed varied from patient to patient, and it was difficult to gauge the effect of this variable owing to variations in size of the emboli. When the patients were separated into groups depending on whether less than or more than two emboli were extracted, there was no apparent major difference in the reduction in total pulmonary vascular
resistance (pulmonary artery mean pressure/cardiac output). However, the group with more emboli removed had a lower average value (4.6 units) than those having fewer than two emboli removed (9.2 units) (Fig. 2). The average initial pulmonary vascular resistance value was 14.0 units, and the average value at the end of the procedure was 5.9 units. A more accurate assessment of pulmonary vascular resistance was not possible since the presence of bilateral emboli prevented measurement of the pulmonary capillary wedge pressure. Five of the 12 patients receiving vasopressors at the beginning of the procedure required them postoperatively for periods of 3 to 72 hours. Two of these patients had cardiac arrest and then died a short time later. One of the remaining three requiring dopamine
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Pao, (mm . Hg) Pre.
I
Post .
Pa co, (mm. Hg) Pre .
I
Post.
pH Pre.
I
Post .
Outcome
48
90
7 .03
7 .32
Living and well
56
64
7.42
7 .44
Living and well
49
118
7.35
7.39
Living and well
50
138
36
52
7 .38
7 .33
Living and well
55
63
31
30
7.48
7.46
28
73
28
24
7.39
7 .51
Living and well
69
85
38
33
7.42
7.46
Died 7/17
46 54
36 107
23
Died
23
24
53
7.41
7.45
Late death, 8/27/77, from pancreatic CA, two UGI hemorrhages Died Living and well
7 .44
Fig. 1. Selective left pulmon ary arteriogram in a 79-year-old woman (Patient C . A.) in shock despite receiving vasopressors (Class IV). The contrast medium outlines the embolus as a favorable sign of nonattachment to the wall of the pulmonary artery .
70
82
21
26
7 .38
7.45
39
65
31
38
7.49
7.46
50
180
23
33
7.48
7 .35
Died
34
170
37
28
7 .15
7 .52
Living and well
TVR 26
36
69
30
33
7.49
7 .50
Living and well
22
infusion had electrocardiographic changes of an acute myocardial infarction and one was in a septic condition from an infected appendectomy wound. The initial mean pulmonary artery pressure exceeded 21 mm. Hg in all patients and averaged 31 mm . Hg. For all 14 patients who survived the procedure, the postoperative average pulmonary artery mean pressure was 23 mm. Hg. Cardiac output was measured in 12 patients preoperatively and averaged 2.59 L. per minute . Postoperatively, it increased in 10 of II surviving patients to an average value of 4.47 L. per minute . The preoperative blood gases were obtained under varying levels of Flo., and in four patients ventilation was via endotracheal tube using a compressible bag ventilator. Following embolectomy, Pa02 increased in all surviving patients from an initial average value of 49 mm. Hg to 101 mm. Hg. Similarly, pH and Paco. values were restored to more normal levels (Table II).
18 14 10
6
2
PRE
<2
POST PRE EMBOLI
POST
2>
Fig. 2. Comparison of reductions in total pulmonary vascular resistance (TVRj following extraction of less than (left) or more than (right) two pulmonary embol i. Although a more satisfactory fall in resistance appeared to occur after removal of more emboli , there was no significant difference between the two groups .
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Surgery
Fig . 3. Second pulmonary angiogram in Patient C . A., shown in Fig. I. following removal of the embolus on the left side. Nearly complete occlusion of the right main pulmonary artery by massive embolism is demonstrated .
Table III. Complications followin g catheter embolectomy, 1975 to 1977 Complication
No.
Postoperative hemorrhage (anticoagulation) Angiography (nonselective) arrest Myocardial infarction Pulmonary infarction Swan-Ganz catheter rupture of pulmonary artery Wound infection
4
2 2 2 I I
Postoperative anticoagulation with heparin was used in 10 of the II surviving patients, the one exception being a patient who had had neurosurgery. All 13 patients who initially survived the procedure had a vena caval filter inserted under fluoroscopic control at the end of the embolectomy procedure, II of them via the same femoral venotomy and two of them via a separate jugular approach owing to technical problems of insertion of the catheter-carrier from the femoral approach. Anticoagulation was maintained usually for I week with heparin while oral coumarin derivatives were administered. Repeated measurements of cardiac output and pulmonary arterial pre ssures in four patients showed further decreases in total pulmonary vascular re sistance as cardiac output increased . Complications in this group included two instances of cardiac arrest during diagnostic studies and one arrest after unsuccessful attempted embolectomy (Table III) . Transient rhythm d isturbances were seen in most patients while the catheter was being manipulated through the right side of the heart, but none required
treatment. Only one death could be attributed to the procedure, and that was related to inflation of the balloon of the Swan-Ganz catheter, as mentioned previously, not from the embolectomy catheter. Two patients had myocardial infarction po stoperatively, two had thrombocytopenia and hemorrhage controlled by ce ssation of heparin, and two had groin wound hematomas , one of which became infected . A third patient who had an appendectomy at another ho spital developed an infection in the abdominal wound . All surviving patients have been followed for periods ranging from 3 to 34 months (average 19 months). Nine vena cavograms have been obtained in six patients for assessment of patency at intervals in excess of I year, and all have been patent. This is comparable to the experience reported in a larger se ries of patients who required filter insertion but who did not qualify for catheter embolectomy . 7 No episodes of recurrent pulmonary embolism , recurrent thrombophlebitis. or mi gration of the filter were seen . There has been one late death from pancreatic carcinoma , but the remaining patients are alive and well.
Case reports C. A. (No. 8037100) , a 79-year-old woman, underwent emergenc y appendectomy for perforative appendicitis at another hospital 10 days prior to her transfer to the Medical College of Virginia. On the day of admission , she had been resuscitated from cardiac arrest after co llapsing in the bathroom . Dopamine infusion at a rapid rate was required to maintain systemic blood pressure at 90/50 mm. Hg. At the time of admission she had a Pao , of 40 mm. Hg on 10 L. of nasal oxygen and a P
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Management of thromboembolism
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Fig. 4. Intact emboli removed from the left (top) and right (bottom) pulmonary arteries of Patient C. A.• shown in Figs. I and 3. Each embolus exceeds 15 em. in length and was removed in a single passage of the embolectomy catheter. was obtained (Fig. 8). The contrast study confirmed the capture of another large embolus within the filter. completely filling it. Despite the size of the embolus. vena caval blood flow was preserved around the trapped embolus. A repeat isotope venogram-lung scan I week later confirmed continued patency of the vena cava and normal pulmonary perfusion. She has remained asymptomatic at home receiving oral anticoagulation to control underlying deep venous thrombosis.
Discussion Pulmonary thromboembolism covers such a wide spectrum of physiological effects that comparisons of treatments and outcomes is difficult without some classification of the disorder. We have found the described hemodynamic classification useful in preliminary staging of the condition of a given patient. At that point a rational comparison of the risks of proposed treatment as opposed to the gravity of the situation can be made . Extremes of management are to be avoided . There are adequate data to refute a surgical approach to every patient. and the ultraconservative approach of anticoagulation therapy alone under all circumstances ignores continuing deaths from massive pulmonary embolism and the complications associated with that form of treatment. In the first series of patients who underwent attempted intraluminal catheter embolectomy, there were two early deaths from recurrent embolism before surgical interruption of the inferior vena cava could be accomplished ." Consequently, a filter device was developed which could be inserted through the same femoral venotomy at the conclusion of the embolectomy procedure to provide immediate protection from recurrent embolism ." In addition, the initial nonsteerable catheter provided only limited access to the pulmonary vascular
Fig. 5. Final pulmonary arteriogram of Patient C. A. showing clearing of both main pulmonary arteries and nearly complete restoration of pulmonary perfusion. tree . Therefore, a steerable handle was added for directional control of the cup. This modification increased both the ease of passage through the right side of the heart and the maneuverability within the pulmonary artery for access to more pulmonary emboli . The results in the present series of patients reflect the advantages of these changes. The criteria for selection of patients for pulmonary embolectomy have varied widely from an aggressive approach advocating prophylactic embolectomy" to the statement that there are no indications for open embolectomy.!? These judgments are obviously affected by the high morbidity and mortality rates associated with open pulmonary embolectomy on cardiopulmonary bypass . Since it is now possible to extract massive
408
The Joumal 01 Thoracic and Cardiovascular Surgery
Greenfield and Zocco
Fig. 6. The KMA-Greenfield filter, inserted through a femoral venotomy, shown after discharge from the catheter-carrier (left) . This carrier differs from the more commonly used jugular vein inserter.
.,
;
~ ..
.
;. ~.
.. .
~:
:~ . "
~ .
Fig. 7. Patient C. A. routine postoperative isotope venogram. No clear concentration of isotope can be seen in the lower inferior vena cava (upper left) , suggesting impairment of vena caval flow through the filter (see Fig. 8). pulmonary emboli without general anesthesia, thoracotomy , and cardiopulmonary bypass, the problem can be placed in more appropriate perspective. The chances for survival of a severely hypoxemic patient in shock despite vasopressor support seem sufficiently precarious to warrant intervention for mechanical relief provided that the procedure itself does not contribute further risk . The passage of the embolectomy catheter through the right side of the heart has been remarkably free of complications, an unusual fact considering the increased risks usually associated with catheter manipulation in a patient with pulmonary hypertension. The explanation may be the short period of time that the catheter stays in the right ventricle en route to the pul-
monary artery . In addition, the cup device is made of relatively soft radiopaque plastic which has not caused any mechanical damage during passage . The presence of a Swan-Ganz catheter in the pulmonary artery during the embolectomy usually poses no problem, although it rarely can impair extraction of a large embolus and was associated in this series with one fatal complication consisting of balloon rupture of the pulmonary artery. The deaths which occurred in this series reflect not only the seriousness of the underlying disorders, but also the potentially lethal effects of injecting a large volume of contrast material. This resulted in cardiac arrest in two patients, from which they could not be resuscitated despite adequate embolectomy in one of
Volume T7 Number 3
Management of thromboembolism
409
March, 1979
them. The remaining death represented poor selection for the procedure, since the patient had peripheral, occlusive , chronic pulmonary embolism, established pulmonary hypertension (Class V), and tricuspid insufficiency. Currently, we would treat such a patient by placement of a vena caval filter and anticoagulation alone. The number of emboli removed did not significantly affect the outcome, since a satisfactory reduction in vascular resistance occurred when as little as one embolus was removed. Obviously, the volume and orientation of the embolus dictate the effects on the pulmonary circulation, but the net effects on pulmonary pressure and cardiac output can be determined serially as emboli are removed while the Swan-Ganz catheter remains in position. Usually there is a threshold for critical reduction of flow which produces inadequate cardiac output , and when that threshold is restored by disimpaction of a critical embolus, the effects are dramatic, with a sudden increase in both systemic and pulmonary blood pressures. II This is usually the point at which the vasopressor agents can be discontinued. If further emboli can be extracted easily, they are removed, with the aim of reaching a mean pulmonary arterial pressure of 20 mm. Hg or less at completion . The postoperative arteriogram usually shows persistent pruning of small pulmonary arterioles suggesting the possibility of residual vasospastic as well as fragmentary embolic occlusion . Occasionally , a patient will demonstrate reinforcement of a hormonal or neural vasospastic component. 12 One such patient was a 17year-old girl in this series who had cardiac arrest after a single embolus to the right lower lobar pulmonary artery . In this patient, who should have been able to tolerate much more vascular occlusion, the postoperative angiogram showed poor perfusion in the segment from which an intact embolus had been removed. 1 Vasodilating agents have not been employed but perhaps could be beneficial under these circumstances. Similarly, fibrinolytic agents have not been used since a recent operative wound is a contraindication to their use because of bleeding complications. If intraluminal catheter embolectomy can be performed with low morbidity and mortality rates, then the indications for its application should expand to include Class III patients, who have large volume embolism in the absence of shock . Since the time course and adequacy of spontaneous lysis of these major thrombi remains speculative, their removal in association with placement of a vena caval filter should hasten recovery of the patient and avoid the consequences of delayed resolution of impacted emboli. Wider application of the
CA Fig. 8. Patient C. A. contrast inferior vena cavogram obtained because of an abnormal isotope venogram (Fig. 7). A large embolus is seen coiled up and trapped in the filter but with preservation of blood flow around it. vena caval filter device alone in patients who do not require embolectomy has been associated with very favorable results, including lysis of entrapped emboli within the filter over a period of several weeks. 7 The option of venoarterial partial bypass through the opposite femoral artery and vein has been used only for resuscitation of patients having cardiac arrest, and usually without survival. In these patients who are actively being resuscitated, transfer to the operating room is advisable . If cardiac output cannot be restored, then open embolectomy on cardiopulmonary bypass should be performed. The requirement for closed chest cardiac massage obviously excludes fluoroscopy and represents a contraindication to attempted catheter embolectomy. Similarly, patients who have not responded to attempted removal by catheter technique should undergo open embolectomy. However, for institutions where cardiopulmonary bypass is not available, the catheter technique represents an alternative method for emergency management and potential salvage of patients following acute massive pulmonary embolism.
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REFERENCES
2
3
4
5
Greenfield U: Pulmonary embolism. Diagnosis and management. Current Problems in Surgery, Chicago, 1976, Year Book Medical Publishers, Inc., Vol 13, No.4, pp I-52 DeWeese JA: The role of pulmonary embolectomy in venous thromboembolism. J Cardiovas Surg 17:348-353, 1976 Alpert JS, Smith RE, Ockene IS, Askenazi J, Dexter L, Dalen JE: Treatment of massive pulmonary embolism. The role of pulmonary embolectomy. Am Heart J 89:413-418, 1975 Miller GAH, Hall RJC, Paneth M: Pulmonary embolectomy, heparin, and streptokinase. Their place in the treatment of acute massive pulmonary embolism. Am Heart J 93:568-574, 1977 Greenfield LJ, Bruce TA, Nichols NB: Transvenous pulmonary embolectomy by catheter device. Ann Surg 174:881-886, 1971
6 Greenfield U, Peyton MD, Brown PP, Elkins RC: Transvenous management of pulmonary embolic disease. Ann Surg 180:461-468, 1974 7 Greenfield LJ, Zocco J, Wilk JD, Schroeder MD, Elkins RC: Clinical experience with the Kim-Ray Greenfield vena caval filter. Ann Surg 185:692-698, 1977 8 Brown PP, Elkins RC, Greenfield U: Comparison of a new intracaval filter with the Mobin-Uddin device and clinical experience. Circulation 48:Suppl 4:5, 1973 9 Berger RL: Pulmonary embolectomy with preoperative circulatory support. Ann Thorac Surg 16:217-227, 1973 10 Sautter RD, Myers WO, Ray JF III, Wenzel FJ: Pulmonary embolectomy. Review and current status. Progr Cardiovasc Dis 17:371-389, 1975 II Greenfield LJ: Surgery for pulmonary embolism. Venous Problems, Chicago, 1978, Year Book Medical Publishers, Inc., Vol 22, pp 355-366
Information for authors Most of the provisions of the Copyright Act of 1976 became effective on January I, 1978. Therefore, all manuscripts must be accompanied by the following written statement, signed by one author: "The undersigned author transfers all copyright ownership of the manuscript (title of article) to The C. V. Mosby Company in the event the work is published. The undersigned author warrants that the article is original, is not under consideration by another journal, and has not been previously published. I sign for and accept responsibility for releasing this material on behalf of any and all co-authors." Authors will be consulted, when possible, regarding republication of their material.