Critical Limb Ischemia (CLI) is the most severe pattern of peripheral artery disease. It is defined by the presence of chronic ischemic rest pain, ulceration, or gangrene [1]. Limb pain at rest, or the imminent risk of amputation due to the inadequate blood supply, are hallmarks of critical limb ischemia [2]. Chronic limb ischemia (CLI) represents the "last stage" of Peripheral arterial disease (PAD) [3]. Chronic limb ischemia (CLI) is a disease process that develops over the course of months to years and, if left untreated, leads to limb loss due to a lack of blood flow and oxygenation in the limbs, this should not be confused with abrupt blockage of the distal arterial tree. Critical limb ischemia being a severe PAD symptom, these individuals would be placed in the most advanced stages of the Fontaine classification (stages III–IV) or the Rutherford classification (grades 4-6) [4] Table 1.

Although CLI patients may fall anywhere on the PAD spectrum, it is generally agreed that they experience the most severe type of PAD [5], and that the medical community should place the utmost emphasis on techniques to improve surgical and nonsurgical treatment and optimize early detection [6]. The vascular examination, the ankle-brachial index (ABI), and a number of imaging modalities make it easy to diagnose CLI, but it is less obvious how best to treat people who have CLI, whether surgically or therapeutically [7].

Diabetic complications in the lower extremity are common and diverse. These complications result from complex interactions between diabetic vasculopathy, neuropathy, structural deformity, and decreased immunity [8]. Diabetes mellitus is associated with 4–5 times increased likelihood of critical limb ischemia and lower limb amputation [9]. Lower limb atherosclerosis in patients with diabetes tends to occur more distally. Arteries below the knee are preferentially affected particularly the peroneal and posterior tibial arterie [10]. Atherosclerosis in DM: Classic atherosclerosis has been described in the proximal arteries of diabetic limbs, and it manifests itself as illnesses of the iliac, femoral, and popliteal arteries [11]. Conventional atherosclerotic lesions are found in diabetic patients’ proximal sites at the same frequency as they are in nondiabetic patients’ proximal sites [12]. The blockage is typically multisegmented and has inadequate growth of collateral vessels [13]. Diabetes patients typically experience the onset of atherosclerosis ten years earlier than people who do not have the condition [14].

Diabetic foot disease is one of the most feared complications of DM, refers to a collection of several pathologies, some of which include diabetic neuropathy, peripheral vascular disease, Charcot’s neuroarthropathy, foot ulceration, osteomyelitis, and limb amputation, which is an endpoint that may or may not be prevented. It is estimated that more than a million people with diabetes require limb amputation each year [15]. The lifetime of a person with diabetes developing foot ulceration is reported to be as high as 25% [16]. Ulcer Diabetic neuropathy, peripheral vascular disease, and traumas that occur in the foot are the most significant risk factors for foot ulcers. Even relatively minor injuries, especially when infection complicates the situation, can increase the demand for blood in the foot. If the blood supply is insufficient, this can result in foot ulceration, which can then potentially lead to amputation of the limb [17]. These injuries can eventually result in foot ulceration, which can then be followed by infection of the ulcer, which can ultimately result in foot amputation [18].

The measurement of the Ankle-Brachial Index (ABI) is based on comparing the blood pressure in the lower extremities to the blood pressure in the systolic blood pressure in the arm. The systolic blood pressure in the lower extremities should be equal to both the central systolic blood pressure in the aorta and the systolic blood pressure in the upper extremities under normal conditions, which is the basis for the test. This means that the ratio between the two values should be 1 [19]. After measuring the systolic blood pressure of both the brachial and lower extremity. After that, a ratio is obtained, and the two values are divided by one another [20]. The duplex ultrasound (DUS) method, a technology that allows direct observation of the artery, can both locate the anatomic site of arterial lesions and assess the hemodynamic effects of these lesions by measuring the speed at which blood flows across the affected areas [21]. According to this concept, the ultrasonic waveform. There is a correlation between the changes in the observed velocity of red blood cells and the degree of stenosis [22]. duplex ultrasound, in contrast to testing that is solely physiologic, can distinguish between occlusion and stenosis [23]. A healthy lower limb artery at rest, the arterial flow is pulsatile and laminar, and triphasic which consist of the sharp systolic upstroke, sharp descending systolic down stroke, Negative diastolic component, Positive diastolic rebound, and then Return to baseline [24] Figure 1.

Biphasic waveforms may be considered normal as long as they maintain a sharp systolic upstroke unless there is an abrupt change from triphasic waveforms. Also, the biphasic wave pattern is initially produced as atherosclerosis develops because the elastic and muscular recoil of the artery wall is lost. This causes a lack of forward flow during late diastole [24]. Figure 2.

(1) a rapid ascending branch (systolic rise time less than or equal to 70 ms, (2) a rapid descending branch, (3) a negative diastolic component, (4) a positive diastolic rebound, and (5) a return to baseline. The spectral window is clear. VMax systolic corresponds to the maximum systolic velocity and VEnd-diastolic corresponds to the end diastolic velocity, so multiphasic with rapid systolic acceleration, sharp systolic peak, reverse diastolic flow, and low, or absent, end-diastolic forward flow [25].

Normal monophasic waveforms following exercise or resulting from increased body temperature. The increased flow demand and decreased vascular resistance associated with exercising muscle, increased body temperature, or focal inflammation results in continuous forward flow with normal peak systolic velocity (PSV) and normal acceleration time [26] Figure 3.

Abnormal Monophasic Waveform: A monophasic waveform has an antegrade systolic flow that is blunted, slow, and persists into diastole. Monophasic arterial waveforms, which are frequently observed downstream from stenoses or in collateral arteries created around the occlusive illness, are always abnormal [27] Figure 4.

Normal Velocity in Lower Limb Arteries: In a control group of 68 patients with normal ABIs (1.08 \(\pm\) 0.09), PSVs in the anterior tibial artery varied from 69 to 71 cm/s. PSVs in the posterior tibial artery varied from 67 to 81 cm/s. In the peroneal artery, PSVs are lower and vary from 48 to 69 cm/s [28].

Acceleration Time (AT): Acceleration time is the time from the start of systole to peak systole. In a healthy subject rapid ascending branch (systolic rise time) less than or equal to 70 ms, Few recent studies, have established the accuracy of AT of distal arteries to diagnose severe peripheral arterial disease. As such, they recommend that PAT be added to the WIFI classification in the evaluation of ischemic limb disease [29] Figure 5.

The term "stenosis" should only be used to describe lesions that cause a change in hemodynamics [5]. If there is constriction following a specific reduction in lumen diameter, the arterial flow that is recorded will be altered. Alterations in the morphology of the Doppler waveforms are examples of what are recognized as direct indicators or signs of stenosis. [30].

Changes in the Doppler waveforms’ shape are recorded upstream and downstream from this point whenever there is a considerable amount of stenosis (which is traditionally defined as a diameter reduction of at least 70%). These shifts in the flow of water upstream and downstream are referred to as indirect signals [31]. If the collaterals are of high quality and efficiency, there may not be any indirect symptoms present. At the point where the artery lumen is reduced, the flow velocity begins to progressively increase, according to the schematic [32].

The degree to which the arterial lumen is reduced is directly correlated to the increase in flow velocity. Indirect indications will only become apparent further downstream when the stenosis is equal to or higher than 70% (decrease in diameter) and when there are no collaterals that are of a high grade or efficiency. When one moves further away from the stenosis, one sees a reduction in the severity of these alterations [33].

Regarding the decreased availability of oxygen further downstream from the stenosis, the downstream symptoms that have been seen include an increase in the systolic rise time (acceleration time) as well as an increase in the positive diastolic component. On the other hand, if the vasodilatation capacities of the region are pushed to their limits, this component might not be there. Last but not least, there is a substantial drop in the maximum systolic velocity. The indications that can be seen upstream include a reduction in systolic velocity as well as a lack of triphasic characteristics [34].

A. Patients

A prospective study includes 40 adult patients (31 male and 9 female), their age range (32y-78y), mean age 61.52\(\pm\) 9.49 years, after obtaining their informed written consents, who had been referred to AL-Najaf cardiology center in Al - Sadir medical city, Najaf – Iraq with signs and symptoms of critical limb ischemia. (rest pain, ulceration, and gangrene) for angiographic revascularization procedures. The study was carried out between 1/3/2022 -1/10/ 2022.

B. Inclusion Criteria

The patients with any symptoms including claudication, pain at rest, ulceration, and gangrene of more than 2 weeks duration were selected to enroll in our study. These symptoms are considered as critical limb ischemia.

C. Exclusion Criteria

1. Patients who refused any revascularization due to personal issues.

2. Patients with renal impairment and drug allergy who are contraindicated for iodine contrast.

3. Patients with signs and symptoms of infection.

4. Patients who had not been followed by Doppler ultrasound after the re- vascularization or missed clinical follow-up.

D. Methods

All patients undergo a Doppler study with a single ultrasound machine (VOLUSON, S10, GE, AUSTRIA) by the same expert radiologist. The Doppler study includes a color Doppler map and pulse wave Doppler for all lengths of the lower limbs concentrated on CFA, SFA, POPA, ATA, and PTA, the following measurement are recorded including PSV, EDV, and AT for the distal parts of PTA, and ATA (at the level of the ankle); all the data were collected in CD and printed photographs. The patients were categorized into different groups according to Acceleration Tim (AT); class I AT = 40-120 ms, class II AT= 121- 180 ms, class III AT = 181-225, and class 1V more than 225 ms. The procedures of the Doppler study were done in the supine position after resting for 10 minutes to avoid increased diastolic flow due to exercise, using lubricating gel with a high-frequency linear probe. On the same day, all patients enrolled were subjected to interventional procedures of the stenotic segment.

E. Procedure of Angioplasty

All patients undergone catheterization under local anesthesia starting with access selection either antegrade or retrograde approach, followed by diagnostic angiography for proper visualization of the lesion then putting a plan of intervention which include balloon dilatation, only two patients need stenting in addition to balloon dilatation, 38 patients out of 40 were catheterized through femoral arteries, only two patients the catheterization done through the brachial artery. After finishing the catheterization, the patient was admitted to the recovery ward center for 8 hours with dressing at the site of the arterial puncture. Within the first 2-3 hours of the angioplasty, a second session of doppler study of the affected limb was done, recording distal arterial PSV, EDV, and AT. All patients were followed for three months after the procedures, asking them for clinical improvement regarding pain, ulcer healing, and state of gangrene.

F. Statistical Analysis

Data were entered and analyzed using the statistical package for social sciences (SPSS) version 22. All categorical and ordinal variables were determined by their frequencies in each subgroup. The scale variables were defined by mean and standard deviation. Comparison between values of acceleration time of pre- and post- revascularization was done by paired T-test and the p-value of less than 0.05 was considered significant. Correlation between values of acceleration times and improvement of the limb affected was done by Pearson correlation which the p-value of less than 0.05 was considered significant.

A total of 40 patients were enrolled in this study, the mean age of the patients was 61.52\(\pm\) 9.49 years. Figure 6 shows the histogram of the patient’s age, the dispersion of age which is demonstrating that the dispersion is higher in the ages of above 61.52. Out of 40 patients, 31 were male and 9 were female and 30 patients had DM, 31 hypertensives, 11 with IHD, 1 patient with IHD and HT, 1 patient with IHD, H, T, and DM and 1 patient had IHD and DM. Out of 40 patients; 19 were nonsmokers, and 25 patients had a family history of PAD Table 2.

The left limb is affected more with CLI representing 65% while the RT limb represents 35%, 30 patients not complaining of claudication, 25 limbs had ulceration and 4 patients had gangrene, out of the 40 patients 9 of them had a previous vascular intervention Table 3.

The mean AT of the anterior tibial artery was 120 .72 ms pre angioplasty while post angioplasty it was 90.52 ms with a significant difference, P = 0.006. PSV of ATA was 17.47 cm/s in pre angioplasty in post angioplasty the velocity was higher 28.72 highly significant, p = 0.0001 while the EDV of ATA was 4.97 pre-angioplasty and 5.25 post-angioplasty with no significant difference = 0.792 Table 4.

Regarding the PTA, the mean of AT was 169.17 pre-angioplasty and 115.65 post-angioplasty with a highly significant difference, P=0.0001. Also, there is a significant difference in the PSV in pre- and post-angioplasty with P= 0.0001, while there was no significant difference in the EDV, P=0.76. The mean value of AT of both ATA and PTA shows a significant difference, P = 0.0001as well as there was a significant difference in the mean value of PSV of both ATA and PTA between pre- and post-angioplasty, while there was no significant difference in the mean value of EDV of both ATA and PTA. The common site of stenosis was the SFA seen in 21 patients out of 40. Out of 40 patients, 32 showed total occlusion, 7 showed subtotal, and one patient with mild occlusion. During the revascularization based on the site of occlusion (Table 5) two methods of approach were used, in 24 patients (60%) retrograde approach and 16 (40%) antegrade approaches were used. In 10 of 40 (25%) a stent was used and 30 0f 40 (75%) underwent revascularization without any stent.

Eleven patients were in class 2, nine of them remain in class 2 and two of them became in class I. Eleven patients were in class III, seven remained in class III and four patients became in class I. Nine patients were in class IV after intervention all became in class III and II. After the revascularization, the improvement of the patients was evaluated based on three categories: no improvement, partial and complete improvement Tables 6,7 and 8.

The threat of lower limb loss is seen commonly in diabetes and peripheral vascular disease. The primary goal of limb salvage is to restore vascularity in the ischemic leg and providing a stable walking surface for trophic ulcers. Endovascular procedures are gaining importance and have reduced the extent of surgery and increased amputation-free survival period. So, predicting limb salvage in patients with diabetic feet is an emerging issue.

Ankle-brachial indices (ABI) are not a reliable indication of perfusion in the foot in patients who have noncompressible tibial vasculature and/or infra geniculate arteries that are difficult to view [35, 36, 37, 38]. In diabetic patients, ABI has a low specificity when it comes to predicting arterial occlusive disease [39, 40]. It is possible that medial wall calcifications and arterial stiffness are to blame for this phenomenon. Both of these factors contribute to an increase in the amount of external pressure required for a blood pressure cuff to compress an artery. This can result in inaccurately inflated ABI values, which may inaccurately depict the severity of PAD or even the presence of PAD in diabetic patients [41].

The Duplex US technique is a simple, non-invasive approach which allows direct real-time visualization of the arteries and perfusion characteristics [42]. Arterial duplex ultrasound (DUS) had a good correlation with angiography findings on proximal lower limbs arteries (iliac and femoral arteries) but was still weak on distal arteries. Hence, the place of DUS with Doppler waveforms (DWs) analysis to estimate distal perfusion remains poorly known even if many consider it a helpful tool to evaluate PAD severity through distal perfusion [43].

Acceleration time seems to be more and more described in the literature as associated with PAD. And they studied the usefulness of acceleration time in proximal lower limb arteries, Yagyu, et al.2020 [44], stated that (DUS) plays a major role in less invasive diagnosis and assessment of lesion severity in lower proximal extremity peripheral artery disease (PAD). In this study, they had been evaluated the efficacy of each DUS parameter measured in patients with PAD and established a simple method for PAD evaluation and they stated that AT and AT ratio is simple and reliable parameters for evaluating aortoiliac and femoropopliteal artery disease [45].

A Study [46], studied patients with non- diabetic PAD, they measured the AT in the lateral plantar artery of 250 nondiabetic patients divided into four classes: Class 1=89.9\(\pm\)15.5 ms; Class 2=152.3\(\pm\)28.4 ms; Class 3= 209.8\(\pm\)25.5 ms and Class 4 =270.2\(\pm\)35.3 ms. ABI scores and clinical symptoms were used to further categorize patients into four distinct groups. significant link between ABI, clinical presentation, and AT (p-value 0.001) and the 4 classes’ categorization of AT. An ABI of 0.90-1.3 correlates with AT of 0-120 ms, an ABI of 0.69-0.89 correlates with AT of 121- 180 ms, an ABI of 0.40-0.68 correlates with AT of 181-224 ms, and an ABI of 0.00-0.39 correlates with AT that is greater than 225 msec. So, they confirmed that Plantar AT had a high correlation with ABI in patients with compressible arteries. The correlation between AT classes and the clinical improvement in our study was comparable with Sommerset et al 2019 [47].

In our study,3 patients had their AT changed from class IV to II, two of them show partial improvement, and one with no improvement seen, this suggests that our goal in the re-vascularization procedure is to get a significant decline in the AT to improve the clinical state of the limb. The one class change show variable outcome according to the change from pre catheterization class; change from class II to class I show 81% complete improvement versus 18% partial improvement and 0% no improvement, so in our study change in AT from class II to class I is a reliable predictor for limb salvage. In class IV,6 patients were descended to class III, all these patients had no complete or partial improvement, this finding may rule out the uses of re- vascularization in those patients.

The Doppler ultrasound was assessed, along with its link with ABI and toe brachial index (TBI) [48], Their objectives were as follows: (i) to evaluate the correlation between DUS parameters of distal arteries of the lower extremities with TBI in patients with PAD; (ii) to evaluate the correlation between DUS parameters of distal arteries with ABI; and (iii) to assess the diagnostic accuracy of maximal acceleration time of pedal arteries to detect toe pressure 30 mmHg. To evaluate the correlation between DUS parameters of distal arteries with TBI in patients with PAD Both the univariate analysis (r = 0.78, p=0.0001) and the multivariate analysis (p=0.0001) showed that the greatest acceleration time of either DPA or LPA (ATmax) was the most strongly connected to TBI. The association between DUS parameters and ABI was not as strong. ATmax values greater than 215 milliseconds demonstrated high diagnostic accuracy to a toe pressure of 30 mmHg or below [sensitivity of 86% [0.57–0.98] and negative predictive value of 97% [0.89–1.00]]. In patients with PAD, ATmax reveals a good association with TBI and high diagnostic accuracy for the diagnosis of critical limb ischemia. In patients with advanced lower extremity PAD, the ATmax can be considered the next step in determining the severity of PAD using DUS.

These findings confirm the value of AT as a predictor for CLI assessment, this finding supports our aim for using AT which is a simple, cheap, available, non-invasive procedure for the assessment of CLI. The current study revealed that there were no significant changes in the EDV between pre and post -catheterization.

Tibial Acceleration time had a high correlation with clinical fate in predicting healing of the limbs in CLI and diabetic foot. Patients with diabetic foot, if the AT is within class I-II will get good clinical, improvement while a patient with class III will get partial improvement. If the AT is high in class IV, no improvement will be gained. So can use tibial Acceleration Time in vascular practice for the management of critical limb ischemia patients.

None.

No conflicts of interest have been declared by the authors.

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