Endoleaks after endovascular aneurysm repair lead to nonuniform intra-aneurysm sac pressure

Patients 

Since 1993, 553 patients have undergone EVAR of AAA at our tertiary university center. Of these, 25 patients (18 men, 7 women); age 76 years old (IQR 68 to 80) underwent 31 DISP at 16 months (IQR 14 to 26) months after EVAR (Fig 1). The median duration of DISP was 174 minutes (IQR 141 to 209). DISP was performed in 21 patients while a type II endoleak was present or had been embolized. Three patients had type III endoleaks at the time of DISP, and one patient had a type I endoleak.

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Fig 1. Flow chart shows patients undergoing direct intra-aneurysm sac pressure measurements (DISP) according to the type of endoleak (EL) and abdominal aortic aneurysm (AAA) diameter change. Six patients underwent DISP after successful embolization of type II endoleaks. *Two patients with type II endoleaks underwent DISP twice; the initial measurement was after AAA diameter shrinkage, and the second occurred once the AAA had expanded.

Inclusion criteria for the study were based on anatomic suitability for direct sac puncture and the presence of an endoleak after EVAR or the status after endoleak embolization. Patients were grouped according to the type of endoleak or status after its embolization (Table I). Our initial experience with DISP in eight of these patients has been included in a previous report.7

Table I. Characteristics of patients

	Group	Patients (n)	Age	AAA diameter (mm)	Time between EVAR and DISP (months)
	Endoleak
	Type I	1	81	55	15
	Type II	19⁎	77(68-81)	62(53-73)	16(14-22)
	EL control	6†	74(70-79)	58(53-62)	30(20-48)
	Type III	3	73(64-75)	55(52-62)	41(2-97)

AAA, Abdominal aortic aneurysm; EVAR, endovascular aneurysm repair; DISP, direct intra-aneurysm sac pressure measurement; EL, endoleak. Values are shown as median with interquartile range in parenthesis

⁎ Two patients of the 19 patients with type II endoleaks were measured twice. The first time after diameter shrinkage and thereafter once the diameter had expanded. † Four of these patients were also measured before the embolization of the endoleak and are, therefore, also included in type II endoleak group (ie, 2 patients were measured only after a previous embolization of the endoleak).

The study was approved by the local ethics committee, and all patients gave informed consent before the procedure.

Imaging 

The imaging protocols included contrast-enhanced spiral-computed tomography (CT) scans preoperatively and yearly after EVAR. More frequent CT scans were performed when indicated. Preoperative CT scans included two spiral scans that were done before and after intravenous nonionic iodinated contrast injection. Postoperative CT studies included an additional delayed spiral scan. CT scans were reconstructed with 0.75-mm to 3-mm axial slices. An additional CT-scan was obtained the month before DISP (pre-DISP CT scan).

The shortest transverse diameter of the AAA was measured at its widest portion on axial CT scans by the same observer. Diameter changes were calculated to express the diameter evolution before DISP (diameter at the time of DISP - initial diameter).7 A 5-mm cutoff was used for grouping AAAs into those shrinking by ≥5 mm, unchanged, and expanding by ≥5 mm.1

At the time of DISP, a digital subtraction aortogram was performed. This included selective angiography of the superior mesenteric and hypogastric arteries whenever the origin of the type II endoleak was not clearly established by CT scan and nonselective aortography.

Endoleaks were classified according to the recommended reporting standards.1 Endoleak nidus was defined as the contrast filled area within the aneurysm sac. A pressure measurement was considered within the endoleak nidus when this location was verified by contrast injection and free blood flow was obtained from the needle.

Pressure measurement system and direct intra-aneurysm sac pressure technique 

Anatomic suitability was assessed in the pre-DISP CT scan and defined as the possibility of inserting a pressure sensor in the AAA sac without damaging any viscera or jeopardizing stent graft integrity.

The pressure measurement system and DISP technique have been previously described in detail.6, 7, 10 Wired tip-pressure sensors mounted on 0.014-inch guidewires were used (PressureWire4, RADI Medical AB, Uppsala, Sweden). The pressure guidewire used for intra-aneurysm sac pressure measurements had a shorter tip (1 mm instead of 3 cm) to allow precise placement of the sensor. Systemic pressure was measured in the lumen of the stent-graft.

Access to the AAA sac was obtained by translumbar puncture using fluoroscopic guidance in 28 occasions, including the six late embolization controls. Two DISP were done through direct transabdominal ultrasound-guided AAA puncture. During the direct puncture of the AAA sac, efforts were made to pinpoint the endoleak nidus (Fig 2, A). Measurements in the thrombus were made when the sensor was located approximately mid-way between the nidus and the stent graft. On one occasion, the pressure guidewire was passed through a coaxial catheter placed in the ostium of the inferior mesenteric artery through the superior mesenteric artery.

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Fig 2. A, Digital subtraction angiography shows contrast injection inside a type II endoleak nidus (arrowheads) through a translumbar puncture of the abdominal aortic aneurysm at the time of direct intra-aneurysm sac pressure measurement. Two lumbar arteries are filled (arrows). B, Status after embolization of the endoleak with Histoacryl (Braun, Tuttlingen, Germany) and Lipiodol (Laboratoire Guerbet, Aulnay-Sous-Bois, France). The glue fills the endoleak nidus and the proximal part of two lumbar arteries (arrow).

The system recorded systemic and AAA sac pressures simultaneously. Intra-aneurysm sac pressures were analyzed as systolic, diastolic, mean, and pulse pressures. Mean pressure index (MPI) was calculated as the percentage of the mean intra-aneurysmal pressure relative to the simultaneous mean systemic pressure [MPI = (mean AAA pressure/mean systemic pressure) × 100].

Measurements were only considered of good quality if the drift in recalibration of the pressure sensor did not exceed 5 mm Hg in the end of the measurements. DISP has been previously validated in patients with a median intraobserver variability of MPI of 0% (IQR −7 to 17%).10 The sensor was also tested in vitro with an accuracy of better than 2 mm Hg.10, 11

Endoleak embolization 

Embolization of the endoleak was performed once access to the endoleak nidus or its feeding vessels was achieved (Fig 2, B). The embolizing materials used were coils, radiopaque glue (Histoacryl, Braun, Tuttlingen, Germany and Lipiodol, Laboratoire Guerbet, Aulnay-Sous-Bois, France), or gel-foam sponge (Spongostan Standard, Johnson & Johnson Medical Ltd, Bracknell Berkshire, United Kingdom). Late embolization control was defined as DISP being performed on a different occasion than the embolization.

Statistical analysis 

Normal distribution was not assumed. Values are presented as medians and interquartile range (IQR), if not stated otherwise. Nonparametric exact tests were used for paired and unpaired comparisons. Results were considered significant at P < .05. Statistical analysis was done using SPSS 12.0.1 software (SPSS Inc, Chicago, Ill).

Type I endoleak 

One patient, an 81-year-old man (AAA diameter, 55 mm) with a proximal type I endoleak and unchanged AAA diameter (0 mm), underwent DISP 15 months after EVAR. MPI was 62% and pulse pressure was 21 mm Hg in the thrombus and 93% and 66 mm Hg in the nidus, respectively. The AAA expanded 9 mm in the 28 months after DISP until the patient consented to a reintervention.

Type II endoleaks 

Nineteen patients (12 men; Table I) underwent 21 DISP while a type II endoleak was present. Two patients underwent DISP twice, because no embolization was performed on the first occasion and the aneurysms subsequently expanded (6 mm after 8 months and 11 mm after 11 months, respectively). At the time of the pressure measurement four AAAs had decreased in size, 11 remained unchanged, and six had expanded. MPI, intra-aneurysm mean and pulse pressures were significantly lower in the thrombus of shrinking AAAs compared with AAAs that expanded or remained unchanged in size (P = .019, P = .030 and P = .019, respectively; Table II).

Table II. Intra-aneurysm sac pressure in the presence of type II endoleaks

	Diameter change before DISP	N	Follow-up before DISP (mo)	ΔAAA diameter (mm)	AAA mean pressure (mm Hg)	AAA pulse pressure (mm Hg)	MPI (%)
	Shrinking	4	19(7-43)	−6(−9,−5)	40(24-47)⁎	7(6-10)†	35(25-38)‡
	Unchanged	11	15(13-16)	2(0,3)	86(53-97)⁎	21(12-22)†	78(47-85)‡
	Expanding	6	22(20-31)	7(6,10)	76(59-109)⁎	17(11-31)†	74(58-87)‡

DISP, Direct intra-aneurysm sac pressure measurement; N, number of DISP performed; AAA, abdominal aortic aneurysm; MPI, mean pressure index. Grouping was done according to the AAA diameter change. Values are shown as median with interquartile range in parenthesis.

⁎ P = .019. † P = .030. ‡ P = .019.

Pressure in the thrombus and nidus of type II endoleaks 

Pressure was measured within the thrombus and inside the endoleak nidus during the same puncture in 7 patients (Fig 3). Pressure was significantly higher inside the endoleak nidus, with MPI at 79% (IQR, 70% to 90%) and pulse pressure of 22 mm Hg (IQR, 18 to 57 mm Hg) than within the thrombus, with MPI at 45% (IQR, 34% to 85%) and pulse pressure of 11 mm Hg (IQR, 7 to 21 mm Hg; P = .043 and P = .028, respectively). The median MPI difference between the nidus and the thrombus was 32% (IQR, 4% to 44%).

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Fig 3. Recording from direct intra-aneurysm pressure measurement. A, Measurement within the thrombus. B, Measurement in the endoleak nidus. Red curves represent the aortic pressure, and green curves represent the intra-aneurysm sac pressure. Each figure has three tracings. The large one to the left is the tracing obtained during each recording where the aortic and intra-aneurysm sac pressures are registered simultaneously. The pressure recorded during 10 heart cycles is gathered separately in two different tracings, one for the aortic (upper smaller tracing to the right) and the other intra-aneurysm sac pressures (lower smaller tracing to the right). The system calculates also the mean of the systolic, diastolic, and mean pressures for both the aortic and intra-sac pressures (values below the small tracings). In the smaller tracings the scale is adjusted by the software to the amplitude of the curves.

Type II endoleak embolization 

Thirteen patients underwent embolization of type II endoleaks at the time of DISP. Glue was used in 12 cases and coils and gel-foam particles in one. Twelve of the 13 procedures were considered successful, and the AAA diameter changed 0 mm (IQR, −7 to 2 mm) during the following 13 months (IQR, 6 to 37 months). In five of these patients, pressure was measured immediately after the embolization at the same procedure. MPI changed from 70% (IQR, 57% to 84%) before the embolization to 53% (IQR, 30% to 79%) immediately after (P > .05). Intra-aneurysm sac mean and pulse pressure changed from 86 mm Hg (IQR, 56 to 98 mm Hg) and 13 mm Hg (IQR, 12 to 19 mm Hg) before the embolization to, respectively, 56 mm Hg (IQR, 31 to 111 mm Hg) and 12 mm Hg (IQR, 8 to 40 mm Hg) after the embolization (P > .05). There was no association between the final MPI and the AAA diameter change afterwards.

One embolization was unsuccessful, and the endoleak persisted at the end of the procedure. This patient was considered unfit for any further reintervention and the aneurysm continued to expand (19 mm during the following 26 months).

Late control of type II endoleak embolization 

Six patients (5 men, 1 women) aged 74 years (IQR, 70 to 79 years; Table I) underwent DISP at 16 months (IQR, 6 to 31 months) after successful embolization of type II endoleaks. Three patients with MPIs of ≤31% at the late embolization control showed AAA shrinkage. The MPIs were lower after the embolization (Table III). Three patients with unchanged AAA diameter after the embolization of the type II endoleak had MPIs between 37% and 44% at the late embolization control. The MPIs had not changed significantly at the late control compared with before the embolization (Table III).

Table III. Pressure in six patients undergoing late endoleak embolization control

	Patient	MPI before embolization (%)	MPI after embolization (%)	Intra-aneurysm sac pressure (mm Hg)			Follow-up after embolization (mo)	ΔAAA diameter after embolization (mm)
				Systolic	Diastolic	Mean
	1	70	31	34	28	30	44	−7
	2	NA	13	22	19	20	72	−18
	3	67	19	25	18	21	50	−6
	4	NA	42	53	40	45	39	−1
	5	45	44	45	38	40	11	1
	6	39	37	60	57	58	9	−1

MPI, Mean pressure index; AAA, abdominal aortic aneurysm. The follow-up after the embolization also includes the imaging follow-up after the second direct intra-aneurysm sac pressure measurement.

Type III endoleaks 

Three patients (3 men, Table I) underwent DISP in the presence of a type III endoleak. One patient with a small type III endoleak persisting after EVAR underwent DISP 2 months after the EVAR. MPIs ranged from 70% close to the endoleak to 42% in the periphery of the AAA sac. The endoleak sealed spontaneously afterwards and the AAA diameter shrank by 12 mm.

The other two patients underwent DISP when late type III endoleaks were identified (one partial separation of the components of an aortouniiliac system and one small fabric disruption), and the AAAs remained unchanged in diameter (+2 and +1 mm, respectively). Intra-sac pressure within the thrombus decreased with increasing distance to the endoleak (MPIs range, 57% to 35% and 44% to 33%, respectively). No measurements were performed in the endoleak nidus. One patient refused any further reinterventions and died within 1 month of unknown cause. The other patient showed a 6-mm expansion of the AAA in the 4 months after DISP and was converted to open repair.