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1
Department of Radiology, University of California—San Diego, 200 W.
Arbor Dr., San Diego, CA 92103.
2
Present address: Department of Radiology, Kaweah Delta Hospital, 400 W.
Mineral King, Visalia, CA 93291-6263.
Received August 30, 1999;
accepted after revision January 4, 2000.
Presented at the annual meeting of the American Roentgen Ray Society, San
Francisco, April-May 1998.
Abstract
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MATERIALS AND METHODS. Thirty-four patients with initial successful thrombolysis were referred for repeated thrombolysis because of early rethrombosis. Repeated thrombolysis occurred within 1 month of initial thrombolysis. Technical success and patency rates were calculated. Causes of graft thrombosis and procedural modifications were analyzed.
RESULTS. The 39 rethrombosed grafts were successfully treated using pharmacomechanical thrombolysis, and patients underwent subsequent hemodialysis. The underlying flow-limiting stenoses were treated with balloon angioplasty using a larger balloon (41%), a same-size angioplasty balloon (18%), stent placement (15%), or increased anticoagulation (5%). A new stenosis location was discovered in 18%. Mean primary patency was 80.9 days (2.6 months) and secondary patency was 235.4 days (7.8 months). With life table analysis, 1-, 3-, 6-, and 12-month primary patency rates were 72%, 31%, 23%, and 15%, and secondary patency rates were 77%, 62%, 51%, and 31%, respectively. Graft patency rates in our study were compared with our institutional historic graft patency rates, with no significant difference noted (p = 0.76). No major procedural complications occurred.
CONCLUSION. Adequate technical success and patency rates for pharmacomechanical thrombolysis occur even for hemodialysis grafts that rethrombose within 1 month. After thrombolysis, aggressive search for and treatment of additional stenoses are warranted.
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We hypothesized that grafts with early failure after thrombolysis would have significantly lower technical success and long-term patency rates from repeated thrombolysis compared with a hemodialysis graft without a history of early graft failure. To test this hypothesis, we retrospectively compared the results of repeated thrombolysis in this subset of patients with results in the average population of patients with a thrombosed hemodialysis graft [3].
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Technique
All thrombolysis procedures followed previously published pulsed-spray
pharmacomechanical thrombolysis technique
[2,
3] with subsequent
modifications. A vial of 250,000 U of urokinase (Abbokinase; Abbott
Laboratories, North Chicago, IL) was reconstituted and combined with 5000 U of
heparin and sterile water. The 10-ml mixture was injected via pulsed-spray
technique, with the dose split between two 5-French multisidehole catheters
(AngioDynamics, Queensbury, NY) placed in crisscross fashion into the graft. A
second dose of 250,000 U of urokinase (Abbokinase) without additional heparin
was injected if a large volume of residual clot was present. Aspirin and IV
heparin (usually 2000-3000 U) were routinely administered. The hemodialysis
graft was evaluated using contrast material injections, and the arterial plug
was displaced with mechanical balloon thrombectomy. Balloon angioplasty (and
sometimes stent placement) was used to treat the underlying stenosis. Initial
treatment in one patient was performed with a mechanical device (Amplatz
thrombectomy device; Microvena, White Bear Lake, MN) that was converted to
thrombolysis because of the inability to establish flow.
Definitions
Technical success and patency rates were calculated on the basis of
intention to treat. Patients who were lost to follow-up or deceased were
considered to have a thrombosed graft at point of last recorded successful
dialysis. Initial technical success was defined as restoration of flow with
the presence of a palpable thrill in the graft and no angiographically evident
residual thrombus or stenosis exceeding 30% of lumen diameter. Clinical
success was defined as patency of the hemodialysis graft for at least two
sequential dialysis sessions. Primary graft patency was defined as time from
repeated thrombolysis to first subsequent intervention. Secondary patency was
defined as the time from repeated thrombolysis to either abandonment of the
graft or surgical revision. The treatment interval refers to the elapsed time
between initial and repeated thrombolysis.
Data Analysis
Cumulative graft patency was analyzed by the life table method
[4]. Primary and secondary
patency rates were calculated at 1, 3, 6, 12, and 18 months. Primary and
secondary patency rates were compared with the treatment interval, using
Pearson's correlation coefficient. The cause of graft failure was determined
from review of angiograms and angiography reports. The pharmacomechanical
thrombolysis technique typically precludes a direct side-by-side analysis of
early fistulograms. Any modifications in technique between the first and
second thrombolysis and resulting patency rates were compared using analysis
of variance. Patency rates were also compared between grafts with no prior
percutaneous intervention and re-treated grafts, using the unpaired Student's
t test. The time interval between treatments and patency rates are
reported with mean ± standard deviation.
The results of the present study were compared with pharmacomechanical thrombolysis patency rates at our institution [3]. Cumulative hemodialysis graft survival (secondary patency) was compared at 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 21, 24, 30, and 36 months using the Kaplan-Meier (product-limit) method.
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An average time interval of 8.8 ± 7.3 days ensued between the initial and repeated thrombolysis treatments. No significant correlation was noted between the thrombolysis treatment interval and primary or secondary patency rates (r = 0.08 and 0.18, respectively). The most frequent cause of graft failure was a venous anastomosis or proximal outflow stenosis (67%), followed by central venous stenosis (13%), intragraft stenosis (10%), and stenosis at the arterial anastomosis or inflow artery (10%).
The treatment method used to remedy the cause of graft rethrombosis is given in Table 1. The most common technique change involved the use of an angioplasty balloon of larger diameter (41%) during the second thrombolysis. In one case, balloon diameter was 2 mm larger, and in the remaining cases, balloon diameter was 1 mm larger. Identical thrombolysis technique to treat the causative stenosis was used in 18%, using balloon angioplasty with a balloon of the same diameter. Review of a single case (2.6%) failed to reveal a clear change in approach between the first and repeated treatments. Using analysis of variance, no significant difference was noted between the specific treatment technique to correct the cause of the restenosis and either the primary patency rate (p = 0.29) or the secondary patency rate (p = 0.16).
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Of the 39 re-treated grafts, 17 (43.6%) had never been managed percutaneously before initial thrombolysis treatment; 22 (56.4%) had been managed with angioplasty or thrombolysis of graft before initial thrombolysis treatment. Patency of thrombosed grafts with no prior treatment averaged 120.4 ± 151.9 days versus 113.2 ± 173.9 days for thrombosed grafts with a history of intervention before initial thrombolysis. No significant differences in patency rates were noted between grafts not previously treated and those with prior angioplasty or thrombolysis (p = 0.89). Secondary patency rates in our study were compared with our published institutional graft patency rates (Fig. 3), with no significant difference noted (p = 0.76).
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No major procedural complications occurred during initial or repeated thrombolysis. One minor complication that occurred consisted of a balloon that ruptured and then became adherent to a previously placed subclavian vein stent. Venous access was obtained through the contralateral jugular vein to assist in freeing the balloon from the stent. The graft subsequently underwent successful thrombolysis and hemodialysis. Metallic expandable stents were used in seven patients, two in central veins and five at the venous anastomosis or proximal outflow. Stents were placed generally for salvage with six of the seven stents placed during the second thrombolysis treatment. Of these six, four failed within 3 months, but two remained patent for more than 1 year.
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In grafts with early rethrombosis, the ultimate technical success or patency did not correlate with the time interval between the initial thrombolysis and the early rethrombosis. It might be expected that grafts that thrombose quickly could be associated with a higher failure rate than grafts that did not have early rethrombosis. However, our results do not support this viewpoint. In fact, repeated thrombolysis for very early graft thrombosis (within the first few days or week) is just as likely to succeed as those grafts that remain patent for longer periods of time.
It is noteworthy that the technique used to treat the flow-restrictive stenosis that caused graft thrombosis was often modified between the initial and repeated thrombolysis. Changes in technique between the first and the repeated thrombolysis treatments must be emphasized; few cases (seven of 39 rethrombosed grafts) were treated without any significant change in technique. An unsuspected cause of graft failure (different from what was originally believed to be the cause during the first thrombolysis) was discovered in seven cases. A balloon of larger diameter at the venous anastomosis was also used in most cases. This more aggressive approach did not lead to an increase in complications. When no cause for graft failure was determined, long-term anticoagulation therapy was used to extend graft patency. Part of the improved patency of the second thrombolysis treatment may have been caused by increased vigilance on the part of the interventional radiologist to detect subtle lesions that were missed at the time of initial thrombolysis.
Several guidelines for the management of venous access for dialysis have been published [11, 12]. The National Kidney Foundation's Dialysis Outcomes Quality Initiative [xx] is a comprehensive set of practice recommendations, many of which are pertinent to hemodialysis graft access. Our aggressive approach supports the overall goal of vein preservation (limited venous access sites). In addition, our technique supports achievement of several specific guidelines. The stated primary patency goal is 40% at 3 months. Although our rate of 35% falls short of this guideline, the overall primary goal of vein preservation is clearly met. The technical success rate is targeted at 85%, which we were able to achieve. The usefulness of using stents is unclear because of the small number of stents that were used. However, stents may have assisted salvage in two cases, showing acceptable long-term patency.
Potential bias exists in a retrospective study like this one. The aggressive approach toward hemodialysis graft with early rethrombosis developed over time. The degree of aggressiveness depended on the experience of the particular radiologist and the patient's available alternative access sites. Even arbitrary factors such as a busy angiography schedule may have played a role in patient selection. It is possible that selection bias created a group of hemodialysis grafts that were ultimately more likely to benefit from thrombolysis than an "average" thrombosed graft, thereby accounting for our good results. However, even if this premise were true, the alternative to this aggressive approach is surgery, which leads to the loss of an access site or additional vein. Our study is based on a relatively low number of grafts treated, which may limit the ability to measure statistically significant differences in patency rates.
The additional drawbacks of subset analysis make it more difficult to generalize the impact of technical modifications to remedy any underlying stenosis. However, other studies in the literature evaluating graft patency involve comparable numbers [6, 8, 13, 14]. Although no significant difference was noted between secondary graft patency rates in our study compared with our published institutional graft patency rates, the trend toward divergence of late results might be significant if a larger number of grafts were evaluated (Fig. 3). Still, to our knowledge, our study reflects the largest series in the literature that specifically addresses this challenging subset of patients. We must note that a comparable study evaluating pharmacomechanical thrombolysis of 12 early surgical failures showed similar results, with a median primary patency of 69 days [14]. Finally, the thrombolytic agent in our study was urokinase, which is not currently available for use in the United States. There is no reason for us to believe that our results would not be generalizable to other thrombolytic agents or even mechanical devices.
In summary, the technical success and patency rates for pharmacomechanical thrombolysis of early rethrombosed hemodialysis grafts approach the efficacy of initial treatment. In fact, with aggressive search for and treatment of underlying stenoses, patency rates approach those published for recanalization of hemodialysis grafts that have not thrombosed during the previous month. No significant decrease in patency rates is noted when compared with established series. Interventional radiologists should enter the angiography suite in the setting of the "failed" graft with the mind-set that significant long-term function can be restored. Even rethrombosis within days of initial thrombolysis appears to not be correlated with decreased patency.
Acknowledgments
We are indebted to Troy H. Patience for statistical analysis.
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