Pressure Wire Used to Measure Gradient in Chronic Mesenteric Ischemia

Abstract

Chronic mesenteric ischemia is a rare disorder in the United States. Frequently, its symptoms correlate poorly with the angiographically apparent degree of mesenteric artery stenosis. Measuring the pressure gradient with a small-caliber catheter is an established means of determining whether a particular stenosis is flow-limiting, thus guiding the interventional decision when stenoses are of indeterminate angiographic significance. Using a 0.014-in guidewire, however, is potentially more accurate because it eliminates any measurement error attributable to the use of a larger, potentially obstructive catheter. We present a case of chronic mesenteric ischemia in a 70-year-old woman who had abdominal pain with multiple possible causes. We used a 0.014-in pressure wire to calculate pressure gradients and guide our decision to stent tandem lesions in the superior mesenteric artery. After revascularization, the patient's symptoms improved dramatically. To the best of our knowledge, this is the first published case in which a pressure wire was used to measure a pressure gradient in chronic mesenteric ischemia.

Recent technical advances in vascular imaging have led to increased recognition of pervasive atherosclerotic plaques. The resulting clinical challenge has been to correlate anatomic findings with the clinical presentation. Using angiography alone may lead one to underestimate or overestimate the significance of visually apparent stenoses.^1,2 Techniques for measuring stenosis severity physiologically have been introduced to help overcome these problems. The pressure gradient across a lesion, measured directly and in vivo, is likely to be the most helpful guide in this regard. The use of small-caliber catheters to measure intravascular gradients has been well established, but the results must be interpreted with caution because of the potential flow obstruction caused by the measuring catheter itself. For this reason, using a 0.014-in pressure wire to measure the translesional pressure gradient can provide more precise information.

We present the case of a 70-year-old woman whose symptoms, although atypical, had features that suggested chronic mesenteric ischemia (CMI). We measured the pressure gradient across 2 tandem stenoses of uncertain severity in the proximal superior mesenteric artery (SMA) to guide our decision to stent. We believe that this is the first published case in which a pressure wire was used to measure translesional pressure gradients in a patient with CMI.

Case Report

A 70-year-old woman with a history of coronary artery disease, severe peripheral vascular disease, diabetes mellitus, hypertension, hyperlipidemia, pulmonary fibrosis, and recently diagnosed lung cancer presented with abdominal pain that had become increasingly severe during the past year. Although this pain was typically located over the left lower quadrant and occurred after meals, the patient stated that it was sometimes generalized over the entire abdomen and lasted all day or night. The patient also reported significant bloating, constipation, and fecal urgency with occasional fecal incontinence, none of which was necessarily related, in time, to the abdominal pain. The pain, however, was predictably more intense after eating. She reported no nausea, vomiting, melena, or hematochezia. During the past 2 years, she had lost 12 kg, half of that amount in the previous 6 months.

She had seen multiple physicians for abdominal pain and had been given multiple associated diagnoses, including irritable bowel syndrome, hiatal hernia, diverticulitis, and gastroesophageal reflux; however, treatment of those conditions had not improved her symptoms. Past procedures included aortocoronary bypass, bilateral femoral–popliteal bypasses, bilateral iliac artery stenting, and hysterectomy with bilateral salpingo-oophorectomy.

Results of her physical examination upon admission were normal except for minimal tenderness in the left lower quadrant and a right carotid bruit. No abdominal bruit was heard. Pertinent laboratory findings were negative except for mild anemia (hemoglobin, 11.4 mg/dL; and hematocrit, 32.6%) and an elevated blood glucose level of 269 mg/dL. Liver function test results, amylase levels, and lipase levels were normal.

Further evaluation with contrast-enhanced abdominal computed tomography (CT) revealed a new left hepatic-lobe mass measuring 1.2 cm, a small hiatal hernia, and diverticula particularly affecting the descending and sigmoid colon. No diverticular inflammation was identified. The CT scan also showed extensive vascular calcification in the abdominal aorta and its major branches. Given her symptom complex and the extent of vascular calcification, a CT angiogram (CTA) of the abdomen and pelvis was obtained to evaluate for possible mesenteric artery stenosis; the CTA revealed a heavily calcified aorta with narrowing of the SMA origin. The celiac artery was patent, but the inferior mesenteric artery could not be identified and was presumed to be occluded. A diagnostic liver biopsy for the newly diagnosed mass confirmed metastatic lung adenocarcinoma.

Selective angiography was then performed from the right radial approach with a 6F Amplatz Right 1 catheter to further evaluate the mesenteric vasculature. The celiac artery was widely patent (Fig. 1), whereas the inferior mesenteric artery was completely occluded. Evaluation of the SMA in the left anterior oblique (LAO) projection revealed an apparently moderate stenosis at its origin and a more distal, calcified stenosis of questionable severity. Despite evaluation in multiple projections, we were unable to conclusively ascertain the severity of these stenoses. Given the patient's atypical presentation, a definitive study was needed to determine whether revascularization was warranted. Although we considered using a small (4F) catheter to measure a pullback gradient across the ostial stenosis, we decided that the pressure gradient across both lesions could be more safely and accurately measured by using a smaller-caliber device: the 0.014-in Pressure Wire™ Certus FFR Measurement System (St. Jude Medical, Inc.; St. Paul, Minn).

Fig. 1 The celiac artery is seen to be widely patent on angiography.

When the pressure wire was positioned with the transducer distal to both lesions of interest, the pressure was recorded at 60 mmHg, while the guiding catheter recorded a pressure of 160 mmHg—a 100-mmHg pressure drop. To evaluate the significance of each stenosis individually, a pullback was performed that revealed a 70-mmHg drop across the distal lesion and a 30-mmHg drop across the proximal lesion (Fig. 2). Given this demonstration of a 60-mmHg head of pressure supplying the SMA circulation in a patient with an occluded inferior mesenteric artery, we concluded that stenting both lesions would be an effective means of maximizing blood flow into the SMA.

Fig. 2 Angiograms. By using the pullback technique, we measured the pressure gradient across the distal stenosis (most visible in A) and across the proximal stenosis (most visible in B; see arrow).

Scoring balloon angioplasty was performed at both sites with a 5 × 20-mm AngioSculpt® Scoring Balloon Catheter (AngioScore, Inc.; Fremont, Calif). Subsequently, 6 × 18-mm and 6 × 14-mm Express® Biliary SD Monorail® Stents (Boston Scientific Corporation; Natick, Mass) were deployed. Post-balloon dilation was performed with a 6 × 15-mm Rx Viatrac™ 14 Plus Peripheral Dilatation Catheter balloon (Abbott Vascular, part of Abbott Laboratories; Redwood City, Calif), producing excellent angiographic results (Fig. 3). A post-interventional gradient was not obtained.

Fig. 3 Angiograms show the superior mesenteric artery after stenting of the A) distal and B) proximal stenoses.

The patient noted some mild improvement in her symptoms the day after the procedure. Over the next 4 to 5 days, she described a diffuse mild ache across her abdomen that was new and different from her previous pain. Then her symptoms dramatically improved, and at 4-month follow-up, she reported complete resolution of her abdominal pain, minimal bloating and constipation, and no fecal urgency or incontinence.

Discussion

Chronic mesenteric ischemia is an uncommon disorder that affects the mesenteric vasculature. Although CMI is most often due to atherosclerotic plaques in the SMA,³ other disorders can lead to CMI, such as fibromuscular dysplasia,⁴ Buerger's disease, and aortic dissection.³ Usually, CMI presents with intestinal angina: postprandial abdominal pain and food aversion that leads to significant weight loss. Less common symptoms include nausea, vomiting, hematochezia, diarrhea, and constipation.

After common causes of abdominal pain are ruled out, the diagnosis of CMI should arise from the constellation of symptoms and the finding of high-grade stenoses affecting at least one of the mesenteric arteries on imaging studies. Duplex ultrasonography is a reasonable first screening method but is limited by operator experience, patient body habitus, prior abdominal surgery, and overlying bowel gas.

Both CTA⁵ and magnetic resonance angiography (MRA)⁶ are now widely used in the abdominal vasculature as alternatives to more invasive conventional diagnostic angiography. Nonetheless, traditional diagnostic angiography is still considered the gold standard. When the results of CTA or MRA are unavailable, anteroposterior and lateral aortography can be performed to evaluate the collateral vessels and the ostia of the mesenteric arteries, respectively. When CTA or MRA has been performed beforehand, global aortography is often skipped in favor of selective mesenteric angiography.

Measuring translesional pressure gradients with a 0.014-in guidewire can provide accurate information about the blood pressure in and flow through the stenotic part of the artery. This technique also accurately evaluates the amount of residual pressure distal to a particular stenosis. Each stenosis has complex anatomic features, and conventional angiography is limited in its ability to give clinicians a complete understanding of a lesion's anatomy. With proper angulation, angiography can be used to measure the length and minimal luminal diameter of a stenotic arterial segment. However, other features such as flow entrance, exit angle, orifice shape, and degree of turbulence are not well evaluated angiographically but are incorporated within pressure-gradient measurements.

Pressure-gradient measurements have been widely used to identify patients who will benefit from revascularization. In renal artery stenosis, a ratio of post-stenotic pressure to aortic pressure of 0.90 (as measured by a 0.014-in pressure-monitoring guidewire) has been proposed as a threshold for activating the renin-angiotensin system and causing renovascular hypertension, therefore mandating intervention.⁷ Pullback techniques can be helpful in isolating the segment most responsible for pressure gradients in patients with fibromuscular dysplasia who have diffuse renal artery stenoses.⁸

Pressure-gradient measurement has previously been used in evaluating patients with mesenteric ischemia; in these cases, a mean gradient exceeding 20 mmHg was considered significant in the presence of corresponding clinical symptoms.⁹ It is important to note that in this series, the investigators measured the pressure by placing a catheter in the aorta and another 4F catheter beyond the stenosis: a technique not likely to be as accurate as using the 0.014-in pressure wire.

Because mesenteric artery stenosis in asymptomatic elderly patients neither contributes to mortality risk nor develops into a symptomatic disease at 7-year follow-up,¹⁰ most authors recommend medical management only. However, patients with symptoms that can be attributed to CMI will probably benefit from revascularization.

Acute mesenteric ischemia, which has a very poor prognosis, often presents in patients who have had no previous abdominal symptoms. However, upon detailed questioning, symptoms attributable to CMI can be elicited in up to 43% of patients who later present acutely.¹¹ This association suggests that patients who have symptomatic CMI might be at risk for acute mesenteric ischemia and that revascularizing such patients might be beneficial.

The treatment of CMI has evolved during the past decade. Endovascular treatment with percutaneous transluminal angioplasty with or without stenting (that is, PTA/S) has replaced the surgical approach as the treatment of choice for symptomatic CMI. Although PTA/S was first introduced as an alternative to bypass surgery for high-risk patients, it quickly became the treatment of choice, especially for patients who have short lesions (<2 cm) with minimal calcification and thrombus. According to Schermerhorn and colleagues,¹² who reviewed data from all patients in the United States Nationwide Inpatient Sample who were treated for mesenteric ischemia (acute and chronic) from 1988 through 2006, the PTA/S volume surpassed the volume of all surgical procedures for CMI treatment in 2002. In addition, percutaneous treatment was associated with lower mortality rates than was surgical treatment.

Our case provides an example of the diagnostic challenges that CMI often poses. The patient was known to have a complex medical history that included malignancy, severe vasculopathy, and abdominal symptoms with typical and atypical features of mesenteric ischemia. In this case, measuring pressure gradients to correlate the angiographic findings with the clinical presentation was particularly helpful. The test revealed a 30-mmHg ostial gradient and a 100-mmHg pressure drop from the aorta to the 2nd stenosis, yielding a pressure head of 60 mmHg to the territory of the SMA, as well as to its collateral vessels to the inferior mesenteric artery territory. The presence of inferior mesenteric artery occlusion in this setting might have contributed to the gradient's severity by eliminating a source of competitive flow in the vascular bed.

Given the demonstrated functional significance of these tandem stenoses, we decided that percutaneous revascularization would be appropriate. The patient had prompt partial symptomatic improvement followed by a dull ache for several days that could have been related to reperfusion of chronically hypoxic bowel. At the 4-month follow-up examination, the patient reported complete resolution of the pain that she had tolerated for several years and a dramatic improvement in her quality of life.

Although hyperemia is routinely induced pharmacologically when a pressure wire is used to study the coronary vasculature, the importance of inducing splanchnic hyperemia to mimic the postprandial state (together with the dosing and technique) is as yet unclear; therefore, we did not induce splanchnic hyperemia in this patient. Doing so could augment the baseline pressure differential, which could be particularly useful in patients whose baseline gradient is less than 20 mmHg at rest. Further investigations with a larger case series would be instructive in this population.

Conclusion

In consideration of the high prevalence of mesenteric arterial stenosis and the rarity of CMI, functional tests are required to correlate anatomic and clinical findings, in order to ensure that only symptomatic stenoses are treated. Although we believe that measuring pressure gradients can provide such information, further studies are required to ascertain how best to use this relatively simple but valuable test—considering that ours appears to be the first published case in which the pressure wire was used to measure pressure gradient in CMI.

Acknowledgment

Stephen N. Palmer, PhD, ELS, contributed to the editing of the manuscript.