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Frequency of deep venous thrombosis in asymptomatic patients with coronary artery bypass grafts
Frequency of deep venous thrombosis in asymptomatic patients with coronary artery bypass grafts The frequency of deep vein thrombosis (DVT) in patients undergoing coronary artery bypass graft (CABG) surgery has not been established. Therefore to estimate the frequency of clinically silent DVT, we Performed ultrasound examinations of the leg veins In 29 asymptomatk CABG patients before hospital discharge. We used high-resolution B-mode ultrasonography with color Doppler imaging. Fourteen (48.3%, 98% confidence interval 30.1 to 60.4%) had 20 documented leg vein thromboses, and all but one patlent had DVT Mmlted to the calf veins. Of the 20 thrombi 10 (50.0%) were present in the leg Ipsltater& and 10 (BO.O%) In the Ieg contralateral to the saphenous vein harvest site. None of the DVTs were suspected cltnkally. DVT was not associated with any locat sign attributed to saphonous vein harvest such as pitting edema, lncisional drainage, or local tenderness or with any putative risk factor for DVT such as cigarette use, distairt history of malignancy, or varkose veins. Follow-up of these patients 5 to 11 months after CABG surgciry showed no cllnkal evidence of DVT or pulmonary embolism. Our findings indicate that asymptomatk DVT of the calf occurs with surprisingly high frequency, 44.8% after CABG suigery. Future studies in patients undergoing CABG surgery should address the natural history of asymptomatk DVT, determine its clinkal Importance, and develop optimal strategies for prophylaxis and treatment. (AM HEART J 1991;122:478.)
Steven E. Reis, MD, Joseph F. Polak, MD, Denise R. Hirsch, MD, Lawrence H. Cohn, MD, Mark A. Creager, MD, Barbara C. Donovan, Samuel Z. Goldhaber, MD. Boston, Muss.
Although the frequency of deep venous thrombosis (DVT) is well established in postoperative orthopedic and general surgical patients, the rate of DVT and subsequent pulmonary embolism has not been surveyed eitensively in patients undergoing coronary artery bypdss graft (CABG) surgery.’ Clinical recognition of DVT in postoperative CABG patients is difficult because most patients undergo saphenous v&n harvest and have resultant incisional edema, erythema, and tenderness of the lower legs. These normal postoperative findings may mask DVT. The advent of venous ultrasound imaging by means of high-resolution B-mode ultrasonography with color Doppler imaging of the deep leg veins permits an accurate noninvasive approach to the diagnosis of DVT2$ 3 and Can also be used to evaluate the deep leg From the Departments of Medicine, Radiology, and Surgery, Brigham and Women’s Hospital, Harvard Medical School. Supported in’part by the CLINFO system at Brigham and Women’s Hospital (grant 5MOl-RR02635). Received for publication Nov. 16, 1990, accepted Dec. 28, 1990. Reprint requests: Samuel 2. Goldhaber, MD, Brigham and Women’s Hospital, Cardiovascular Division, 75 Francis St., Boston, MA 02115. 4/l/29857
478
RN, and
veins of CABG patients. We used this noninvasive imaging modality to .examine asymptomatic CABG patients before they were discharged and assessed the frequency of clinically silent DVT. METHODS Patient
population. Ultrasound examination of the veins of the lower legs was performed in 30 CABG patients before hospital discharge. Except for one patient who was excluded from further analysis, these patients had no postoperative signs or symptoms suggestive of DVT. They were nonconsecutive and were selected on the basis of the availability of one ultrasonographer (J.F.P.) to examine their leg veins. All patients were mobilized rapidly after surgery and treated routinely with postoperative graded elastic compression stockings. Patients who were maintained on a regimen of anticoagulation therapy or who underwent concomitant valve replacement or implantation of an automatic implantable cardiac defibrillator were not evaluated. Venous ultrasound examination. All patients underwent venous ultrasound examination of each leg, which was performed with 5.0 and 7.0 mHz transducers (Acuson Computed Sonography, Mountain View, Calif.) and color Doppler imaging to evaluate the presence of asymptomatic DVT before hospital discharge. The venous ultrasound ex-
Volume 122 Number 2
Deep vein thrombosis
amination entailed the application of pressure on the skin by the transducer to compress the walls of the vein and not those of the artery. Color Doppler imaging was performed with flow augmentation by squeezing the calf muscles while monitoring for an increase in flow signals in the venous segment being examined. Four patients with DVT underwent follow-up venous ultrasound examination within 2 months after discharge. Patients were imaged initially in the supine position. The common femoral and profunda femoris veins were surveyed by holding the transducer transverse to the vein. Imaging of the superficial femoral vein was done by sequentially moving the transducer down the leg in 1 to 2 cm increments and by applying compression at each increment. To image the popliteal segment the subjects’ liibs were externally rotated into the frog-leg position, and the transducer was placed transverse to the vein to perform imaging from behind the knee. Imaging of the calf veins was conducted with a modification of a previously described method.4 The location of the anterior tibial, posterior tibial, and peroneal veins was confirmed with color-flow accentuation after the lower third of the calf was squeezed. Once located, these veins were imaged both transversely and longitudinally. Imaging of the length of the peroneal vein was performed from the lateral approach with direct visualization of the vein in close apposition to the fibula as it coursed in the distal and proximal third of the calf at the tibioperoneal junction; only flow accentuation with color Doppler imaging was used to exclude the presence of obstructing thrombi, since the vein was not clearly seen on grey-scale imaging. The muscular veins of the calf including the sural veins, the draining veins of the lateral and medial heads of the gastrocnemius muscle, and the soleus muscle veins were imaged with a 7.0 MHz transducer with the subject’s limb in the frog-leg, neutral, slightly bent, and dangling positions. The criteria used to diagnose DVT were lack of apposition of the venous walls during compression ultrasonography and loss of the expected increase in flow signals during color Doppler imaging with flow augmentation. These findings were confirmed by two observers. Data collection and analysis. Descriptive data were collected including patient demographics, type of procedures performed, putative risk factors, and signs and symptoms in the legs related to saphenous vein harvest. DVTs confirmed by venous ultrasound examination were classified as calf or proximal (involving the popliteal vein or above) vein thrombosis. Postoperative follow-up was established by means of telephone contact an average of 244 days (range 153 to 348) after CABG surgery. Patients and families were asked specifically about subsequent episodes of DVT or pulmonary embolism after hospital discharge. The data were entered on a VAX 1 l/750 computer (Digital Equipment Corp., Maynard, Mass.) and analyzed with the CLINFO software package. RESULTS
Twenty-nine
CABG patients
were evaluated
by
means of predischarge venous ultrasound examinations performed on average 6.5 days after surgery.
Table
after CABG
479
1. Clinical characteristics (N = 29) Clinical
characteristics
Sex (M/F) Age (yr) Raw Mean r SD
65.4
Procedure (No. of patients) LIMA + SVG R1M.A SVG Grafts (NoJprocedure) &we MeanzkSD
SVG harvest site (No. of patients) Left leg
Riht leg Bilateral legs No SVG harvested Study day (No. of days after surgery) Range Mean t SD DVT prophylaxis (No. of patients) Graded elastic compression stockings Aspirin therapy (No. of patients) LIMA, Left internal mammary artery graft; SVG, saphenous
40-83 2 10.4 26 1 ‘2
2-s 3.1 “i 0.7 19 6
5-11 6.5 f 1.4
29 29
artery graft; RIMA, right internal mammary vein graft; SD, standard deviation.
There were 23 men and six woman with a mean age of 65.4 r?~10.4 years (Table I). had an internal mamm (65.5 % ), six (20.7 % left, right, and bila for grafts, reap have either saphenous vein harvested. We detected a 49.3% frequeq rate (14 of 29) of clinically silent DVT (95%, ax&dame interval 30.1 to 66.4%). One patient had pr DVT (Fig. l), which required stay (5 days) for initiation of anti
II). Ten clota (50.0 %
edema (34.5%), i tenderness (3.4% ) more than one sign. ation between any of these DVT. The presence of DVT was not suspected clinically in any patient.
480
Reis et al.
August 1991 Heart Journal
American
Fig. 1. Longitudinal vein. Tip of thrombus
sonogram taken at knee level showing large nonobstructing thrombus in popliteal (open arrows) is free floating and partly anchored to more distal portion of vein
(closed arrows).
II. Results of venous ultrasound (N = 29)
examination
Results
N
fable
Table III. Signs present in the lower legs at the saphenous vein harvest site Sign
No. of patients with DVT No. of patients with superficial vein thrombosis Total number with DVT Location of clots Popliteal vein (proximal) Muscular veins (soleus, sural, gastrocnemius) Peroneal vein Posterior tibia1 vein Leg with DVT (compared to SVG harvest site) Ipsilateral Contralateral SVG, Saphenous
14 2 20
Edema (n = 10) Drainage (n = 10) Tenderness (n = 1) None
(n = 8)
D VT present (N = 14)
No DVT present (N = 15)
4 6 0 4
6 4 1 4
1 14 4 1
10 10
vein graft.
Risk factors for DVT, excluding the inherent risk related to the surgical procedure and postoperative rehabilitation, werepresent in 27.6% of the patients (Table IV). These included current cigarette use (17.2%), past history of malignancy (6.9%), and presence of varicose veins (3.4%). None of the patients had more than one putative risk factor or a prior history of DVT. Two patients had a diagnosis of malignancy after CARG surgery. One patient underwent thoracotomy for lung adenocarcinoma within 7 months, and onepatient underwent cystectomy for bladder cancer within 1?4 months. There
was no statistically significant association between any of these factors and formation of DVT. None of the four patients who underwentfollow-up venous ultrasound studies after hospital discharge showedproximal extensionof clot. At follow-up examination 5 to 11 months after CARG surgery, no patients described episodesof clinically suspected DVT or pulmonary embolism. Follow-up findings wereobtained from 28 of 29 patients, including all of those with DVT. The patient with an identified popliteal thrombus took warfarin for less than 4 months after dischargewith no apparentrecurrences. One patient was seenat another hospital 3 weeksafter dischargewith new atrial fibrillation of unknown cause.She had had sural and soleusclots identified postoperatively but denied subsequent lower extremity or pulmonary symptoms. Another patient describedpoor incisional healing at the vein harvesting site in the leg with identified soleusand peroneal thrombi. Results of follow-up ultrasound exami-
volume 122 Numbar 2
Deep vein thrombosis
after C’ABG
481
Fig. 2. Sonogram showing early nonobstructive thrombus measuring 1.5 X 0.5 cm within a muscular vein sinusoid (arrows). This particular sinusoid communicates with posterior tibia1 veins (PTI. This small thrombus has not entered paired tibia1 veins.
nation, however, thrombi.
showed
resolution
of these calf
DISCUSSION
It is important to study the frequency of DVT after CABG surgery because more than 250,000 CABGs are performed annually in the United States. The contribution of DVT to postoperative morbidity has not been defined adequately in this patient population. Our data indicate that postoperatively CABG patients have a surprisingly high frequency (48.3 % ) of clinically silent DVT as documented by results of venous ultrasound examination performed before hospital discharge. The formation of DVT postoperatively in CABG patients may be explained by pathophysiologic mechanisms that are common to other high-risk surgical procedures. These include venous stasis, endothelial damage,5 and a local hypercoagulable state6 resulting from the effects of anesthetic agents and immobilization. Patients who undergo CABG surgery may be at additional risk for DVT because of positioning and immobilization of the lower legs during saphenous vein harvest and immobilization in the intensive care unit during postoperative recuperation. The documented thromboses in this study were not suspected clinically. Although signs suggestive of DVT may have been masked by local edema at the saphenous vein harvest site, the number of clots located in the leg ipsilateral to the harvest site was similar to the number found in the contralateral leg. This suggests that direct trauma related to saphenous vein harvest does not explain the high frequency
Table
IV. Potential risk factors for DVT Risk factor
D VT present (N = 14)
Cigarette use (n = 5) Past malignancy (n = 2) Varicose veins (n = 1) None (n = 21)
3 0 0 11
No DVT present ;n: = 15)
.-
” 2 : IO
of DVT in CABG patients and that physical examination is not a sensitive screening test for DVT in these patients. Calf veins were the source of the majority of thromboses identified in this report, which is similar to the 44% frequency of calf DVT reported by Liu et al7 among asymptomatic patients after totaI hip replacement or repair of hip fracture. Our 44.8% frequency of calf DVT in postoperative CABG patients may also be compared with the 462% frequency of venographically documented calf DVT in 638 patients who underwent knee arthroptasty as reported by Stulberg et aLa Only 6 % of theee patients had clinical findings suggestive of DVT. However, this study of orthopedic surgical patients reported only a 3.2% frequency of DVT in the contralateral calf, which suggests that the predisposition and pathophysiologic mechanisms responsible for formation of DVT differ between orthopedic and CABG patients. Furthermore, orthopedic patients appear to be more susceptible to proximal extension of DVT and to pulmonary embolism. The documented high rate of asymptomatic calf
482
Reis et al.
vein thrombosis in CARG patients is of unknown significance.Lagerstedtet al9 demonstrateda 28.6% recurrencerate of untreated symptomatic calf DVT within 3 months of diagnosis.Although it is difficult to extrapolate these data to our population with asymptomatic calf DVT, the potential sequelaeof calf vein thrombosis-such as proximal propagation to the thigh, pulmonary embolism, and chronic venous insufficiency- justify further investigation.‘O*l1 The subsequent clinical course of patients followed in this study suggeststhat the majority of asymptomatic DVTs in the calf in post-CABG patients may be benign. Although repeat studies were performed in only 4 of 14 patients with documented DVT, there is no evidence of clinically related acute sequelae.One patient described an event (atria1fibrillation) that may havebeen attributable to pulmonary embolism, but many other causesexist. Most patients who undergo CABG surgery are treatedroutinelywith antiplateletagentsin an attempt to prevent graft occlusion.All patients in this report weretreated with aspirin, which (aswith orthopedic patients)appearsto be inadequateprophylaxisagainst calf vein thrombosis. Graded elastic compression stockings were worn by all patients as routine prophylaxisagainstDVT. The frequencyof DVT in postoperative CABG patients who do not wear graded elastic compressionstockings may be even higher. Our report has certain limitations with regard to detection of DVT, the relatively small sample size, and potential selection bias. First, although venous ultrasound examination is highly accuratein the detection of proximal vein DVT, it may underestimate the frequency of DVT in the calfn2Our findings were not confirmed by other techniques such as venography or fibrinogen scanning.Also, ultrasound evaluation of the legthat underwent saphenousvein harvest may have been technically limited becauseof the presence of edema. Therefore the actual rate of asymptomatic DVT in postoperativeCABG patients may be evenhigher than the rate we report. Second, the small sample size resulted in wide confidence limits for detection of DVT, ranging from 30% to 66%. Third, selection bias may have occurred becausepatients were chosenon the basisof the availability of oneinvestigator (J.F.P.) to perform the ultrasound examination.
American
August 1891 Heart Journal
Results of our survey suggestthat asymptomatic DVT is a surprisingly frequent postoperative complication of CABG surgery.However,the ultrasound evaluation that we undertook before dischargedoes not addressthe rate of DVT formation during postdischarge outpatient recuperation. Future studies should follow patients systematically after discharge to determine this frequency. Postdischargestudies should also be performed to addressthe natural history of documentedDVT in this patient population to determine the clinical importance of this finding and the needfor treatment of recognizedthrombus. Additional investigations should assessthe needfor and efficacyof routine mechanicaland/or pharmacologic prophylaxis against DVT in the more than 250,000patients who undergo CABG surgery each year. We thank the technologists of the Noninvasive Vascular Laboratory and the nurses of the Venous Thromboembolism Research Group for their invaluable assistance.
REFERENCES
1. Rao G, Zikria EA, Miller WH, et al. Incidence and prevention of pulmonary embolism after coronary artery surgery. Vast Surg 1975;9:37-45. 2. Lensing AWA, Prandoni P, Brandjes D, et al. Detection of deep-vein thrombosis by real-time B-mode ultrasonography. N Engl J Med 1989;320:342-5. 3. White RH, McGahan JP, Daschbach MM, et al. Diagnosis of deep-vein thrombosis using duplex ultrasound. Ann Intern Med 1989;111:297-304. 4. Polak JF, Cutler SS, O’Leary DH. Deep veins of the calf: assessment with color Doppler flow imaging. Radiology 1989; 171:481-5. 5. Comerota AJ, Stewart GJ, Albungen PD, et al. Operative venodilatation: a previously unsuspected factor in the cause of postoperative deep vein thrombosis. Sureerv 1982:106:301-9. 6. Ham& JD, Malone PC, Silver IA. The PO; in venous valve pockets: its possible bearing on thrombogenesis. Br J Surg 1981;68:166-70. 7. Liu GC, Ferris EJ, Reifsteck JR, et al. Effect of anatomic variations on deep venous thrombosis of the lower extremity. Am J Radio1 1986;146:845-8. 8. Stulberg BN, Insall JN, Williams GW, et al. Deep-vein thrombosis following total knee replacement. J Bone Joint Surg [Am] 1984;66:194-201. 9. Lagerstedt CI, Olsson CG, Fooher BO, et al. Need for long-term anticoagulant treatment in symptomatic calf-vein thrombosis. Lancet 1985;2:515-8. 10. Doyle DJ, Turpie AGG, Hirsh J, et al. Adjusted subcutaneous heparin or continuous intravenous heparin in patients with acute deep vein thrombosis. Ann Intern Med 1987;107:441-5. 11. Huisman MV, Buller HR, ten Cate JW, et al. Unexpected high prevalence of silent pulmonary embolism in patients with deep venous thrombosis. Chest 1989:95:498-502.
Steven E. Reis, MD, Joseph F. Polak, MD, Denise R. Hirsch, MD, Lawrence H. Cohn, MD, Mark A. Creager, MD, Barbara C. Donovan, Samuel Z. Goldhaber, MD. Boston, Muss.
Although the frequency of deep venous thrombosis (DVT) is well established in postoperative orthopedic and general surgical patients, the rate of DVT and subsequent pulmonary embolism has not been surveyed eitensively in patients undergoing coronary artery bypdss graft (CABG) surgery.’ Clinical recognition of DVT in postoperative CABG patients is difficult because most patients undergo saphenous v&n harvest and have resultant incisional edema, erythema, and tenderness of the lower legs. These normal postoperative findings may mask DVT. The advent of venous ultrasound imaging by means of high-resolution B-mode ultrasonography with color Doppler imaging of the deep leg veins permits an accurate noninvasive approach to the diagnosis of DVT2$ 3 and Can also be used to evaluate the deep leg From the Departments of Medicine, Radiology, and Surgery, Brigham and Women’s Hospital, Harvard Medical School. Supported in’part by the CLINFO system at Brigham and Women’s Hospital (grant 5MOl-RR02635). Received for publication Nov. 16, 1990, accepted Dec. 28, 1990. Reprint requests: Samuel 2. Goldhaber, MD, Brigham and Women’s Hospital, Cardiovascular Division, 75 Francis St., Boston, MA 02115. 4/l/29857
478
RN, and
veins of CABG patients. We used this noninvasive imaging modality to .examine asymptomatic CABG patients before they were discharged and assessed the frequency of clinically silent DVT. METHODS Patient
population. Ultrasound examination of the veins of the lower legs was performed in 30 CABG patients before hospital discharge. Except for one patient who was excluded from further analysis, these patients had no postoperative signs or symptoms suggestive of DVT. They were nonconsecutive and were selected on the basis of the availability of one ultrasonographer (J.F.P.) to examine their leg veins. All patients were mobilized rapidly after surgery and treated routinely with postoperative graded elastic compression stockings. Patients who were maintained on a regimen of anticoagulation therapy or who underwent concomitant valve replacement or implantation of an automatic implantable cardiac defibrillator were not evaluated. Venous ultrasound examination. All patients underwent venous ultrasound examination of each leg, which was performed with 5.0 and 7.0 mHz transducers (Acuson Computed Sonography, Mountain View, Calif.) and color Doppler imaging to evaluate the presence of asymptomatic DVT before hospital discharge. The venous ultrasound ex-
Volume 122 Number 2
Deep vein thrombosis
amination entailed the application of pressure on the skin by the transducer to compress the walls of the vein and not those of the artery. Color Doppler imaging was performed with flow augmentation by squeezing the calf muscles while monitoring for an increase in flow signals in the venous segment being examined. Four patients with DVT underwent follow-up venous ultrasound examination within 2 months after discharge. Patients were imaged initially in the supine position. The common femoral and profunda femoris veins were surveyed by holding the transducer transverse to the vein. Imaging of the superficial femoral vein was done by sequentially moving the transducer down the leg in 1 to 2 cm increments and by applying compression at each increment. To image the popliteal segment the subjects’ liibs were externally rotated into the frog-leg position, and the transducer was placed transverse to the vein to perform imaging from behind the knee. Imaging of the calf veins was conducted with a modification of a previously described method.4 The location of the anterior tibial, posterior tibial, and peroneal veins was confirmed with color-flow accentuation after the lower third of the calf was squeezed. Once located, these veins were imaged both transversely and longitudinally. Imaging of the length of the peroneal vein was performed from the lateral approach with direct visualization of the vein in close apposition to the fibula as it coursed in the distal and proximal third of the calf at the tibioperoneal junction; only flow accentuation with color Doppler imaging was used to exclude the presence of obstructing thrombi, since the vein was not clearly seen on grey-scale imaging. The muscular veins of the calf including the sural veins, the draining veins of the lateral and medial heads of the gastrocnemius muscle, and the soleus muscle veins were imaged with a 7.0 MHz transducer with the subject’s limb in the frog-leg, neutral, slightly bent, and dangling positions. The criteria used to diagnose DVT were lack of apposition of the venous walls during compression ultrasonography and loss of the expected increase in flow signals during color Doppler imaging with flow augmentation. These findings were confirmed by two observers. Data collection and analysis. Descriptive data were collected including patient demographics, type of procedures performed, putative risk factors, and signs and symptoms in the legs related to saphenous vein harvest. DVTs confirmed by venous ultrasound examination were classified as calf or proximal (involving the popliteal vein or above) vein thrombosis. Postoperative follow-up was established by means of telephone contact an average of 244 days (range 153 to 348) after CABG surgery. Patients and families were asked specifically about subsequent episodes of DVT or pulmonary embolism after hospital discharge. The data were entered on a VAX 1 l/750 computer (Digital Equipment Corp., Maynard, Mass.) and analyzed with the CLINFO software package. RESULTS
Twenty-nine
CABG patients
were evaluated
by
means of predischarge venous ultrasound examinations performed on average 6.5 days after surgery.
Table
after CABG
479
1. Clinical characteristics (N = 29) Clinical
characteristics
Sex (M/F) Age (yr) Raw Mean r SD
65.4
Procedure (No. of patients) LIMA + SVG R1M.A SVG Grafts (NoJprocedure) &we MeanzkSD
SVG harvest site (No. of patients) Left leg
Riht leg Bilateral legs No SVG harvested Study day (No. of days after surgery) Range Mean t SD DVT prophylaxis (No. of patients) Graded elastic compression stockings Aspirin therapy (No. of patients) LIMA, Left internal mammary artery graft; SVG, saphenous
40-83 2 10.4 26 1 ‘2
2-s 3.1 “i 0.7 19 6
5-11 6.5 f 1.4
29 29
artery graft; RIMA, right internal mammary vein graft; SD, standard deviation.
There were 23 men and six woman with a mean age of 65.4 r?~10.4 years (Table I). had an internal mamm (65.5 % ), six (20.7 % left, right, and bila for grafts, reap have either saphenous vein harvested. We detected a 49.3% frequeq rate (14 of 29) of clinically silent DVT (95%, ax&dame interval 30.1 to 66.4%). One patient had pr DVT (Fig. l), which required stay (5 days) for initiation of anti
II). Ten clota (50.0 %
edema (34.5%), i tenderness (3.4% ) more than one sign. ation between any of these DVT. The presence of DVT was not suspected clinically in any patient.
480
Reis et al.
August 1991 Heart Journal
American
Fig. 1. Longitudinal vein. Tip of thrombus
sonogram taken at knee level showing large nonobstructing thrombus in popliteal (open arrows) is free floating and partly anchored to more distal portion of vein
(closed arrows).
II. Results of venous ultrasound (N = 29)
examination
Results
N
fable
Table III. Signs present in the lower legs at the saphenous vein harvest site Sign
No. of patients with DVT No. of patients with superficial vein thrombosis Total number with DVT Location of clots Popliteal vein (proximal) Muscular veins (soleus, sural, gastrocnemius) Peroneal vein Posterior tibia1 vein Leg with DVT (compared to SVG harvest site) Ipsilateral Contralateral SVG, Saphenous
14 2 20
Edema (n = 10) Drainage (n = 10) Tenderness (n = 1) None
(n = 8)
D VT present (N = 14)
No DVT present (N = 15)
4 6 0 4
6 4 1 4
1 14 4 1
10 10
vein graft.
Risk factors for DVT, excluding the inherent risk related to the surgical procedure and postoperative rehabilitation, werepresent in 27.6% of the patients (Table IV). These included current cigarette use (17.2%), past history of malignancy (6.9%), and presence of varicose veins (3.4%). None of the patients had more than one putative risk factor or a prior history of DVT. Two patients had a diagnosis of malignancy after CARG surgery. One patient underwent thoracotomy for lung adenocarcinoma within 7 months, and onepatient underwent cystectomy for bladder cancer within 1?4 months. There
was no statistically significant association between any of these factors and formation of DVT. None of the four patients who underwentfollow-up venous ultrasound studies after hospital discharge showedproximal extensionof clot. At follow-up examination 5 to 11 months after CARG surgery, no patients described episodesof clinically suspected DVT or pulmonary embolism. Follow-up findings wereobtained from 28 of 29 patients, including all of those with DVT. The patient with an identified popliteal thrombus took warfarin for less than 4 months after dischargewith no apparentrecurrences. One patient was seenat another hospital 3 weeksafter dischargewith new atrial fibrillation of unknown cause.She had had sural and soleusclots identified postoperatively but denied subsequent lower extremity or pulmonary symptoms. Another patient describedpoor incisional healing at the vein harvesting site in the leg with identified soleusand peroneal thrombi. Results of follow-up ultrasound exami-
volume 122 Numbar 2
Deep vein thrombosis
after C’ABG
481
Fig. 2. Sonogram showing early nonobstructive thrombus measuring 1.5 X 0.5 cm within a muscular vein sinusoid (arrows). This particular sinusoid communicates with posterior tibia1 veins (PTI. This small thrombus has not entered paired tibia1 veins.
nation, however, thrombi.
showed
resolution
of these calf
DISCUSSION
It is important to study the frequency of DVT after CABG surgery because more than 250,000 CABGs are performed annually in the United States. The contribution of DVT to postoperative morbidity has not been defined adequately in this patient population. Our data indicate that postoperatively CABG patients have a surprisingly high frequency (48.3 % ) of clinically silent DVT as documented by results of venous ultrasound examination performed before hospital discharge. The formation of DVT postoperatively in CABG patients may be explained by pathophysiologic mechanisms that are common to other high-risk surgical procedures. These include venous stasis, endothelial damage,5 and a local hypercoagulable state6 resulting from the effects of anesthetic agents and immobilization. Patients who undergo CABG surgery may be at additional risk for DVT because of positioning and immobilization of the lower legs during saphenous vein harvest and immobilization in the intensive care unit during postoperative recuperation. The documented thromboses in this study were not suspected clinically. Although signs suggestive of DVT may have been masked by local edema at the saphenous vein harvest site, the number of clots located in the leg ipsilateral to the harvest site was similar to the number found in the contralateral leg. This suggests that direct trauma related to saphenous vein harvest does not explain the high frequency
Table
IV. Potential risk factors for DVT Risk factor
D VT present (N = 14)
Cigarette use (n = 5) Past malignancy (n = 2) Varicose veins (n = 1) None (n = 21)
3 0 0 11
No DVT present ;n: = 15)
.-
” 2 : IO
of DVT in CABG patients and that physical examination is not a sensitive screening test for DVT in these patients. Calf veins were the source of the majority of thromboses identified in this report, which is similar to the 44% frequency of calf DVT reported by Liu et al7 among asymptomatic patients after totaI hip replacement or repair of hip fracture. Our 44.8% frequency of calf DVT in postoperative CABG patients may also be compared with the 462% frequency of venographically documented calf DVT in 638 patients who underwent knee arthroptasty as reported by Stulberg et aLa Only 6 % of theee patients had clinical findings suggestive of DVT. However, this study of orthopedic surgical patients reported only a 3.2% frequency of DVT in the contralateral calf, which suggests that the predisposition and pathophysiologic mechanisms responsible for formation of DVT differ between orthopedic and CABG patients. Furthermore, orthopedic patients appear to be more susceptible to proximal extension of DVT and to pulmonary embolism. The documented high rate of asymptomatic calf
482
Reis et al.
vein thrombosis in CARG patients is of unknown significance.Lagerstedtet al9 demonstrateda 28.6% recurrencerate of untreated symptomatic calf DVT within 3 months of diagnosis.Although it is difficult to extrapolate these data to our population with asymptomatic calf DVT, the potential sequelaeof calf vein thrombosis-such as proximal propagation to the thigh, pulmonary embolism, and chronic venous insufficiency- justify further investigation.‘O*l1 The subsequent clinical course of patients followed in this study suggeststhat the majority of asymptomatic DVTs in the calf in post-CABG patients may be benign. Although repeat studies were performed in only 4 of 14 patients with documented DVT, there is no evidence of clinically related acute sequelae.One patient described an event (atria1fibrillation) that may havebeen attributable to pulmonary embolism, but many other causesexist. Most patients who undergo CABG surgery are treatedroutinelywith antiplateletagentsin an attempt to prevent graft occlusion.All patients in this report weretreated with aspirin, which (aswith orthopedic patients)appearsto be inadequateprophylaxisagainst calf vein thrombosis. Graded elastic compression stockings were worn by all patients as routine prophylaxisagainstDVT. The frequencyof DVT in postoperative CABG patients who do not wear graded elastic compressionstockings may be even higher. Our report has certain limitations with regard to detection of DVT, the relatively small sample size, and potential selection bias. First, although venous ultrasound examination is highly accuratein the detection of proximal vein DVT, it may underestimate the frequency of DVT in the calfn2Our findings were not confirmed by other techniques such as venography or fibrinogen scanning.Also, ultrasound evaluation of the legthat underwent saphenousvein harvest may have been technically limited becauseof the presence of edema. Therefore the actual rate of asymptomatic DVT in postoperativeCABG patients may be evenhigher than the rate we report. Second, the small sample size resulted in wide confidence limits for detection of DVT, ranging from 30% to 66%. Third, selection bias may have occurred becausepatients were chosenon the basisof the availability of oneinvestigator (J.F.P.) to perform the ultrasound examination.
American
August 1891 Heart Journal
Results of our survey suggestthat asymptomatic DVT is a surprisingly frequent postoperative complication of CABG surgery.However,the ultrasound evaluation that we undertook before dischargedoes not addressthe rate of DVT formation during postdischarge outpatient recuperation. Future studies should follow patients systematically after discharge to determine this frequency. Postdischargestudies should also be performed to addressthe natural history of documentedDVT in this patient population to determine the clinical importance of this finding and the needfor treatment of recognizedthrombus. Additional investigations should assessthe needfor and efficacyof routine mechanicaland/or pharmacologic prophylaxis against DVT in the more than 250,000patients who undergo CABG surgery each year. We thank the technologists of the Noninvasive Vascular Laboratory and the nurses of the Venous Thromboembolism Research Group for their invaluable assistance.
REFERENCES
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