Revascularization for CMI and AMI is increasingly being performed with PTA/S. For CMI, PTA/S is associated with lower in-hospital mortality, shorter length of stay, and fewer bowel resections. For AMI, bypass was typically employed in more advanced cases requiring bowel resection making comparison with PTA/S difficult. However, after controlling for the need for bowel resection, there was a lower mortality with PTA/S. Revascularization procedures for CMI are increasing overall with a dramatic rise in PTA/S and a constant rate of surgical procedures, while revascularization for AMI is relatively constant with PTA/S apparently replacing surgery in some cases.
The increase in revascularization procedures for CMI may be due to many reasons. There may be increasing awareness of the disease particularly now that a minimally invasive treatment is available and being more widely utilized. The advancing age of the population may be contributing although this would also be expected to demonstrate a rise in AMI as well unless the increase in elective procedures is preventing AMI. With the less invasive approach there may expansion of treatment indications to include those previously considered to be at prohibitive risk for surgery. In this series PTA/S patients were older with greater comorbidity. Additionally, indications may have expanded to include treatment of those with symptoms that are less severe or those in whom the diagnosis is in question. If this is the case, this may bias the results in favor of PTA/S while treatment of those at prohibitive risk for surgery would potentially bias in favor of surgery. Finally, it is well documented that PTA/S is associated with a greater risk of restenosis and recurrent symptoms.15
This is certainly playing some role in the increase in overall CMI interventions. Additionally, patients undergoing re-intervention for restenosis may have a different risk for inhospital mortality which could again influence the comparison of PTA/S with surgery. Clearly, there is a need for longitudinal follow-up to determine whether there is any long term benefit to PTA/S over surgery. It has been suggested that a strategy of initial PTA/S would allow for correction of the malnourished state so that the patient may more safely undergo surgical revascularization after the early onset of recurrent stenosis and symptoms prior to a severe deterioration in nutritional status.12, 23
The decline in surgical procedures for AMI appears to be primarily in those undergoing embolectomy. This is likely due to an increasing utilization of anticoagulation for dysrhythmias such as atrial fibrillation. A recent study from the Mayo clinic found an increase in rates of anticoagulation and a decrease in embolic strokes in patients with atrial fibrillation between 1980–2000.24
A recent review by Kougias et al summarized the largest series of PTA/S for CMI.15
They found a 30-day mortality rate of 3%, and a restenosis rate of 28% at a mean follow up of 2 years with 27% undergoing repeat PTA/S. Mortality from large series of open revascularization for CMI range from 0% to 12%.1–7, 13, 14
The broad range reflects the small number of patients undergoing revascularization for CMI even at large referral centers. Derrow et al reviewed the NIS database for surgical revascularization of CMI from 1993–1997 and found a mortality rate of 14.7% which corresponds to our findings from a broader period using the same database.8
Therefore, the numbers from the current study better reflect the true risk of open surgical revascularization and demonstrate the potential benefit of PTA/S.
Mortality with revascularization for AMI is typically >50%. 1, 5, 9, 10
We found that surgical revascularization mortality was highest with embolectomy and lowest with bypass. This is likely due to the lack of an established collateral circulation with embolization. Since PTA/S is felt by most to be inappropriate treatment for most cases of embolism we focused on comparison of PTA/S with bypass. We found that the need for bowel resection was the primary predictor of mortality with AMI more so than the use of PTA/S versus bypass. Unlike CMI, the need for bowel resection with AMI likely reflects the severity of ischemia at the time of vascular consultation rather than a complication of revascularization.9, 10
Given that resection was required in a much larger proportion of those undergoing bypass it is likely that the two cohorts are dissimilar and this biases the comparison in favor of PTA/S. There is general agreement that in most cases of AMI there is a need to inspect the bowel viability and perform resection as needed. The diagnosis of AMI is often made at laparotomy in an operating room setting that may not be amenable for angiography and intervention which may limit the broader application of this technology. Retrograde stenting of the SMA via an arteriotomy has been advocated as a means to provide rapid revascularization through the open abdomen at the time of laparotomy.18, 21, 22
We do not have the ability to determine whether percutaneous antegrade or open retrograde PTA/S was employed in patients undergoing laparotomy in the NIS database and cannot comment on the potential merits of this approach. With the expansion of operating room endovascular suites and the increasing use of rapid multi-row detector computed tomographic angiography for diagnosis, PTA/S may be utilized with greater frequency when the diagnosis is entertained prior to laparotomy. However, PTA/S would not be expected to obviate the need to inspect bowel viability.
Our study has several limitations. This is a retrospective study with clear selection bias in the choice of therapy. This is most evident in AMI where more patients with advanced ischemia underwent bypass than PTA/S. There may have been other factors in addition to the need for bowel resection that were unmeasured that impacted the decision to choose bypass rather than PTA/S. We do not have anatomic details about number of vessels treated, lesion length, or stenosis versus occlusion which are likely to impact revascularization strategy and could impact outcome. The large numbers in this study (20% sample of non-federal hospitals) obtained from hospital discharge data are the strength of the study. This is evidenced by comparison to the recent review of the literature of mesenteric PTA/S by Kougias et al with a total of 292 patients that would represent a <5% sample of patients undergoing this procedure. However, discharge databases such as NIS are subject to coding errors. This is highlighted by the 3% of patients who were coded as undergoing embolectomy for CMI. A nearly 3-fold higher percentage of CMI patients undergoing embolectomy had atrial fibrillation/flutter compared to those undergoing another method of repair. Additionally, the diagnosis of CMI is often a difficult one and may be made without a complete workup particularly when percutaneous therapy is attempted. We also cannot identify patients undergoing repeat mesenteric procedures. The increasing number of endovascular procedures may be reflective of either of these and bias mortality in favor of PTA/S. The inability to definitively state whether a bowel resection is done at the time of mesenteric operation, during a “second look” procedure, before revascularization, or as a complication of the mesenteric operation is one more limitation of the NIS database. There is a variable for day of operation, but this was infrequently recorded and thus was an unreliable method to further clarify this.