2D perfusion angiography: an alternative method to evaluate endovascular intervention for acute lower limb ischemia

Patient selection

Patients diagnosed with acute ischemia of the lower extremity and undergoing mechanical thrombectomy in our center between August 2015 and August 2018 were screened. The diagnostic criteria for ALI included acute lower extremity ischemia, a disease duration of less than 2 weeks, and obvious signs and symptoms of lower extremity ischemia (lower extremity pain, numbness, skin pallor, decreased skin temperature, and sensory disturbance). Patients who met the imaging conditions of iFlow imaging technology and who had consistent imaging parameters were further enrolled in this study. Patients with severe cardiac, pulmonary, hepatic and renal insufficiency were excluded. Patients whose affected limb has been treated with amputation were also excluded from this study. Finally, a total of 47 patients diagnosed with ALI between August 2015 and August 2018 were screened for the evaluation of endovascular intervention in this single-center study. The process for cohort establishment is shown in Fig. 1. The severity of ALI in the 47 limbs was characterized using the Rutherford classification system [10]. Demographic and clinical data were obtained from the hospital’s medical database. This retrospective study was approved by the institutional review board of the First Affiliated Hospital of Jinan University. All procedures were in accordance with the ethical standards of the national research committee and with the 1964 Helsinki Declaration.

Fig. 1figure 1

The flow diagram of the patient selection

Endovascular intervention

Under local anesthesia, contralateral common femoral artery access was obtained with a 6-F crossover sheath. The lesion was crossed intra-luminally with a guide wire (Terumo, Japan). Next, a rheolytic percutaneous mechanical thrombectomy (PMT) device (AngioJet, Boston Scientific) was placed into the lesion. After thrombectomy, if the stenosis caused by thrombus was greater than 50% and the patient had no contraindications to catheter-directed thrombolysis (CDT), a 5-F thrombolysis catheter (Uni-Fuse, Angio Dynamics, NY) was inserted into the residual thrombus. The patient was administered urokinase (Abbokinase) via the thrombolytic catheter (400,000–800,000 U/24 h) for thrombolysis. The duration of thrombolysis was not more than 7 days, and angiography was performed every 2 to 3 days. After thrombolysis, if the stenosis was still greater than 50%, balloon angioplasty was performed. After angioplasty, stenting was implemented if the residual stenosis exceeded 50%.

Technical success and clinical outcomes

The criteria for technical success included residual stenosis ≤ 30% and at least one artery below the knee reached the foot, as revealed by angiography. All 47 patients met these criteria for technical success in this study. The clinical outcomes included complete response (CR), partial response (PR), no response (NR), and amputation (AM). The definitions of the different outcomes were as follows: 1) CR: return to normal pulse in the distal limb after treatment, no gangrene, no sensory and motor impairment; 2) PR: recovery of distal limb pulse after treatment, weaker than the opposite side, and improvement of symptoms; 3) NR: partial recovery of blood flow in the distal artery of the limb after treatment, still with ischemic symptoms; and 4) AM: the distal end of the limb was removed and divided into major and minor amputations.

Image acquisition

DSA images were obtained using an angiographic system (Artis Zeego; Siemens, Germany). Medical restraint bands were used to limit the movement of the affected limb during the angiography, so as not to affect the quality of image acquisition. A 5-F catheter was placed through the 6F contralateral sheath in the affected limb through the common femoral artery for all arteriographic procedures. Four successive DSA scans were performed over the entire lower extremity. The first segment contained the catheter tip and the femoral head, and the C-arm was tilted 30° medially to fully view the superficial and deep femoral arteries. The second segment observed from the anteroposterior view included the knee joint as the lower boundary of the field of view (FOV). The upper boundary of the third segment observed from the anteroposterior view was 5 cm above the upper edge of the patella. The fourth segment of the lower boundary observed from lateral view contained the entire affected foot. A power-injector was set to deliver the contrast material (320 mg iodine/ml) at a flow rate of 3 cc/s. The dose of contrast material was 9 cc for the first three segments and 15 cc for the last segment. A high-pressure syringe was set to a pressure of 300 PSI and the number of angiographic frames was 15 per second.

DSA image postprocessing

The DSA data were immediately transferred to and reconstructed with a Siemens workstation (Artis Zeego Leonardo; Siemens) to generate color-coded images. Regions of interest (ROIs) in the femoral head, knee joint, and ankle joint with a size of 1000 mm2 were selected in the iFlow images. The TTP in each region was measured. The differences in TTP between the knee region and the femoral head region (TTP difference in the knee area) and between the ankle area and the knee area (TTP difference in the ankle area) were calculated. The above angiographic procedures and measurements were performed by two experienced interventional vascular surgeons (Fig. 2).

Fig. 2figure 2

Standard DSA and iFlow images of the lower extremity. a, c Arteriography before (a) and after (c) endovascular intervention. b, d iFlow processed the same DSA sequence before (b) and after (d) endovascular intervention

Measurement of ABI and TcPO2

Pre- and post-operative ABI measurements were performed using an ABI meter. Before measurement, the patient was allowed to rest for 5–10 minutes in a supine position, and blood pressure cuffs were placed on the patient's upper arms and lower extremities at the foot and ankle, and measured using ultrasonic Doppler, with the auscultation site in the upper arm located at the pulsating brachial artery in the elbow fossa and the auscultation site in the foot and ankle located at the dorsalis pedis or posterior tibial artery. Theystolic pressure of the upper extremity was taken as the higher limit, and the ratio of the systolic pressure of the lower extremity to the systolic pressure of the upper extremity was calculated.

TcPO2 was measured using a TcPO2 detector. The patient was allowed to rest for 5–10 minutes in a supine position at room temperature before measurement, with the dorsum of the affected foot as the measurement site, avoiding skin ulcers, large blood vessels, hair, and bony prominence. The skin was cleaned at the measurement area with 75% ethanol, and after drying, take the electrode fixation patch was applied to the skin between the first toes. We then added an appropriate amount of electrode solution in the patch hole, aligned and connected the arrow mark on the electrode with the patch hole, rotated the electrode 90° clockwise, fixed it in the patch hole, waited for approximately 10 minutes for the value to stabilize, and then recorded the result.

Statistical analysis

Continuous data are presented as the mean ± standard deviation (median), and categorical data are presented as the count (percentage). Statistical analysis was performed using SPSS 16.0 statistical software (version 16.0; IBM Corporation, USA). Any change in the TTP, TTP difference, ABI, and TcPO2 for each ROI before and after an intervention was analyzed using the paired t test. The TTP, ABI, and TcPO2 between the CR, PR, NR, and AM groups were compared using one-way analysis of variance. The correlations between ΔTTP and ΔABI/ΔTcPO2 were analyzed using Pearson’s analysis. A confidence level of 95% was used, and a p value < 0.05 was considered statistically significant.

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