Sequential spectrum analysis in the follow-up of revascularized patients

Abstracts

BACKGROUND: Patients treated for peripheral arterial occlusive disease with lower limb revascularization (angioplasty or grafts) were followed up for a 2-year period after treatment with vascular ultrasound (segmental spectrum analysis, SSA). OBJECTIVE: To demonstrate that SSA can be used in the follow-up of patients treated for peripheral arterial occlusive disease. METHODS: The following SSA measurements were performed: peak systolic velocity (PSV), pulsatility index (PI), and flow velocity waveform (FVW). These measurements were performed and compared for each patient during the pre- and post-treatment periods (with 3-month intervals) for diagnosis of vascular patency. RESULTS: Measurements performed postoperatively in the arteries immediately distal to the treated segments showed a significant increase in PSV and PI, with a change of the FVW from a monophasic to a biphasic or triphasic configuration. PSV and PI increased, respectively, 92.26 and 98.2% (intervention in the aortoiliac segment), 112.83 and 62.39% (intervention in the femoral-popliteal segment), and 149.08 and 28.8% (in the popliteal-tibial segment). Such changes in flow velocity patterns occurred in all patients and remained almost unaltered during the period of patient follow up. When treatment failed (hemodynamically significant occlusion or stenosis), parameters fell to levels similar to those observed prior to treatment. If treatment failure was corrected by new revascularization (angioplasty or grafts), SSA parameters returned to patterns observed after initial treatment. CONCLUSION: SSA can be used in the follow-up of patients with lower limb revascularization due to peripheral arterial occlusive disease, demonstrating treatment patency and failure.

Atherosclerosis; Doppler ultrasound; ultrasound

CONTEXTO: Pacientes tratados por revascularização arterial (enxertos e angioplastias) nos membros inferiores acometidos por doença arterial oclusiva periférica foram seguidos por até 2 anos pós-tratamento usando ultrassom vascular (análise espectral segmentar, AES). OBJETIVO: Demonstrar que a AES pode ser utilizada no seguimento dos pacientes tratados por doença arterial oclusiva periférica. MÉTODOS: As medidas de AES realizadas foram: velocidade sistólica de pico, índice de pulsatilidade e forma da onda de velocidade de fluxo. Essas foram comparadas em cada paciente no pré e pós-tratamento (com intervalos de 3 meses) para diagnóstico de perviedade. RESULTADOS: Medidas realizadas no pós-operatório nas artérias imediatamente distais aos segmentos tratados mostraram aumento consistente de velocidade sistólica de pico e índice de pulsatilidade com mudanças na forma da onda de velocidade de fluxo de unifásica para bi ou trifásica. A velocidade sistólica de pico e o índice de pulsatilidade aumentaram respectivamente em 92,26 e 98,2% (tratamentos no segmento aorto-ilíaco), em 112,83 e 62,39% (tratamentos no segmento fêmoro-poplíteo) e em 149,08 e 28,8% (tratamentos no segmento poplíteo-tibial). Tais mudanças nos padrões de velocidade de fluxo ocorreram em todos os pacientes e permaneceram quase inalteradas enquanto os tratamentos estivessem pérvios. Quando ocorria falência nos tratamentos (oclusões ou estenoses hemodinamicamente significantes), os parâmetros caíam a níveis similares aos de antes do tratamento. Se a falência do tratamento era corrigida por nova revascularização (enxerto ou angioplastia), os parâmetros de AES voltavam a se comportar como após o tratamento inicial. CONCLUSÃO: A AES pode ser usada no seguimento dos pacientes com revascularização dos membros devido a doença arterial oclusiva periférica, demonstrando tanto a perviedade quanto a falência do tratamento.

Aterosclerose; eco-Doppler; ultrassom

ORIGINAL ARTICLE

Sequential spectrum analysis in the follow-up of revascularized patients

Domingos de Morais Filho; Fernando Thomazinho; Fernando Motta; Igor Schincariol Perozin; Wander Eduardo Sardinha; José Manuel da Silva Silvestre; Oswaldo Palma; Rodrigo Gomes de Oliveira

Hospital Universitário Estadual do Norte do Paraná (HURNP), Universidade Estadual de Londrina (UEL), Departamento de Clínica Cirúrgica, Setor de Cirurgia Vascular, Londrina, PR, Brazil

Correspondence

Abstract

Background: Patients treated for peripheral arterial occlusive disease with lower limb revascularization (angioplasty or grafts) were followed up for a 2-year period after treatment with vascular ultrasound (segmental spectrum analysis, SSA).

Objective: To demonstrate that SSA can be used in the follow-up of patients treated for peripheral arterial occlusive disease.

Methods: The following SSA measurements were performed: peak systolic velocity (PSV), pulsatility index (PI), and flow velocity waveform (FVW). These measurements were performed and compared for each patient during the pre- and post-treatment periods (with 3-month intervals) for diagnosis of vascular patency.

Results: Measurements performed postoperatively in the arteries immediately distal to the treated segments showed a significant increase in PSV and PI, with a change of the FVW from a monophasic to a biphasic or triphasic configuration. PSV and PI increased, respectively, 92.26 and 98.2% (intervention in the aortoiliac segment), 112.83 and 62.39% (intervention in the femoropopliteal segment), and 149.08 and 28.8% (in the popliteal-tibial segment). Such changes in flow velocity patterns occurred in all patients and remained almost unaltered during the period of patient follow-up. When treatment failed (hemodynamically significant occlusion or stenosis), parameters fell to levels similar to those observed prior to treatment. If treatment failure was corrected by new revascularization (angioplasty or grafts), SSA parameters returned to patterns observed after initial treatment.

Conclusion: SSA can be used in the follow-up of patients with lower limb revascularization due to peripheral arterial occlusive disease, demonstrating treatment patency and failure.

Keywords: Atherosclerosis, Doppler ultrasound, ultrasound.

Introduction

Since peripheral arterial occlusive disease (PAOD) has a segmental character and may present concomitant lesions, a thorough knowledge of its anatomical distribution and the hemodynamic relevance of lesions present in each case is of paramount importance. Changes in hemodynamic patterns after treatment also need to be assessed in detail in order to analyze efficacy and duration of treatment effects. Vascular ultrasound has been considered the best method for confirmation of initial diagnosis, as well as for relative quantification of the segments involved and for PAOD follow-up, mainly because this method can provide objective measurements for temporal comparisons.^1-12 One of the methods for the assessment of PAOD by vascular ultrasound was called segmental spectrum analysis (SSA),¹³ which evaluates parameters of arterial hemodynamics in a segmental manner. The objective of the present study was to determine patterns of hemodynamic alterations based on SSA measurements in different arrangements of PAOD lesions prior to treatment and to evaluate pattern changes after successful treatment or pattern behavior when treatment failed.

The objectives were:

- To demonstrate changes in SSA parameters used as a screening tool in the location and quantification of hemodynamically significant lesions of PAOD in the lower limbs;

- To correlate such measurements with local hemodynamic alterations and different arrangements of PAOD atherosclerotic lesions using SSA;

- To compare SSA measurements performed prior to treatment with those performed after treatment and relate them to changes in arterial hemodynamics after treatments;

- To follow up patients treated with lower limb revascularization using SSA to define patterns concerning parameters and their changes during the follow-up period;

- To show which SSA parameter alterations occur after PAOD treatment with arterial revascularization (angioplasty or grafts) and which alterations occur when treatment fails (occlusion or hemodynamically significant stenosis);

- To define changes in parameters after new revascularization and compare these patterns with those measured after initial treatment.

Methods

Between January 2005 and December 2007, 205 limbs were treated for arterial ischemia (in 193 patients) caused by PAOD in the lower limbs (117 men and 76 women). Such patients were submitted to revascularization procedures (angioplasty or grafts). All 193 patients received unilateral treatment and 12 patients received bilateral treatment. All patients received treatment in the vascular surgery sector. The study was approved by the Research Ethics Committee of Universidade Estadual de Londrina (UEL) (protocol no. 172/05), in Londrina, state of Parana, Brazil. All patients had critical ischemia (categories 5 and 6) of Society of Vascular Surgery/International Society of Cardiovascular Surgery (SVS/ISCVS).⁷ All patients were examined by vascular ultrasound prior to angiography and after revascularization (grafts or angioplasty with or without stents) before hospital discharge. After treatment, all patients were followed up using vascular ultrasound with SSA at 3-month intervals. All patients were submitted to angiography prior to treatment, for treatment planning, and when treatment failed.

Patients were assigned to different groups according to angiographic findings, such as hemodynamically significant lesions (requiring graft revascularization or endovascular procedures) in one or more arterial segments. Groups were divided as follows: patients with lesions only in the aortoiliac segment (group 1, Tables 1 and 2), patients with significant lesions only in the femoropopliteal segment (group 2, Tables 3 and 4), patients with significant lesions only in the popliteal-tibial segment (group 3, Tables 5 and 6), and patients with significant lesions both in the aortoiliac and femoropopliteal segments (group 4, Tables 7 and 8).

Table 1
- Group 1: spectrum analysis in the common femoral artery and ABI of patients with pre- and post-treatment PAOD exclusive in the aortoiliac segment (means)

Aortoiliac	Pre (n = 65)	Post (1 month) (n = 65)	6 months (n = 53)	12 months (n = 49)	24 months (n = 46)	Pre/post (1 month) (%)
ABI	0.48	0.80	0.77	0.74	0.75	66.6
PSV	61.27	117.80	112.54	93.74	119.2	92.26
PI	2.23	4.42	4.30	3.33	4.37	98.2
FVW	LAM	B/T	B/T	B/T	B/T	B/T

Table 2
- Group 1: patients with PAOD exclusive in the aortoiliac segment and treated with angioplasty who showed occlusions or hemodynamically significant stenoses in the aortoiliac segment after treatment
(treatment failure) (means)

	Pre-failure*				Post-failure†				Repair‡
Patients	PSV	PI	FVW		PSV	PI	FVW		PSV	PI	FVW
1 (65)	130.6	3.43	T		56.7	1.8	LAM		100.93	4.02	B
2 (103)	186.2	3.9	T		63.16	2.46	LAM		122.34	3.97	B
3 (50)	128.33	3.07	T		42.11	1.52	LAM		98.44	3.5	B
4 (89)	92.69	3.45	B		36.46	1.68	LAM		96.72	4.2	T
5 (29)	104.54	5.58	T		60.02	0.55	LAM		104.7	3.2	B
6 (60)	98.04	3.69	T		50.32	3.24	LAM		79.27	3.1	HAM
7 (76)	102.7	4.8	T		48.2	2.12	LAM		75.32	3.3	B
Mean	120.94	3.98	T/B		50.99	1.91	LAM		96.81	3.61

Table 3
- Group 2: spectrum analysis measurements performed in the popliteal artery and ABI of patients with pre- and post-treatment PAOD exclusive in the femoropopliteal segment (means)

Femoropopliteal	Pre (n = 54)	Post (1 month) (n = 54)	6 months (n = 49)	18 months (n = 46)	Pre/post (1 month) (%)
ABI	0.51	0.83	0.87	0.81	62.74
PSV	33.27	70.81	72.34	67.87	112.83
PI	2.34	3.80	3.59	4.45	62.39
FVW	LAM	B/T	B/T	B/T	B/T

Table 4
- Group 2: patients with revascularization in the femoropopliteal segment who showed treatment failure (hemodynamically significant stenoses or occlusions) (means)

	Pre-failure*				Post-failure†				Repair‡
Patients	PSV	PI	FVW		PSV	PI	FVW		PSV	PI	FVW
1	70.65	3.45	T		17.17	1.92	LAM		68.17	3.87	T
2	56.67	4.61	T		12.22	1.01	LAM		54.38	4.88	B
3	68.86	2.44	T		6.38	0.92	LAM		62.46	3.69	B
4	59.89	5.27	B		17.92	1.41	LAM		63.7	3.98	T
5	76.62	5.92	T		23.61	1.05	LAM		70.2	4.22	B
T6	77.58	4.35	T		31.58	1.88	LAM		72.5	3.89	T
7	69.83	4.98	T		17.98	1.02	LAM		66.4	4.7	T
8	65.29	5.67	T		26.53	0.98	LAM		64.3	3.68	T
Mean	68.17	4.58	1B/7T		19.17	1.27	LAM		61.67	4.14	3B/5T

Table 5
- Group 3: patients with revascularization in the popliteal-tibial segment,
SSA and ABI measurements (means)

Popliteal-tibial	Pre (n = 50)	Post (1 month) (n = 50)	6 months (n = 45)	13 months (n = 42)	Pre/post (%)
ABI	0.52	0.73	0.78	0.81	40.38
PSV	35.06	87.33	82.14	81.87	149.08
PI	1.70	2.19	2.98	2.45	28.8
FVW	LAM	HAM/B/T	HAM/B/T	HAM/B/T

Table 6
- Group 3: patients with revascularization in the popliteal-tibial segment who showed treatment failure (means)

	Pre-failure*				Post-failure†
	PSV	PI	FVW		PSV	PI	FVW
1	70.65	3.45	T		17.17	1.92	LAM
2	56.67	4.61	B		12.22	1.01	LAM
3	68.86	2.44	T		6.38	0.92	LAM
4	67.68	3.45	HAM		16.67	1.2	LAM
5	71.87	3.67	B		24.35	1.02	LAM
6	54.28	2.98	B		21.83	1.01	LAM
Mean	64.98	3.34	2T/3B/HAM		16.43	1.18	LAM

Table 7
- Group 4: spectrum analysis in the common femoral artery and ABI of patients with hemodynamically significant lesions both in the aortoiliac and femoropopliteal segments (means)

AI-FP	Pre (n = 36)	Post (1 month) (n = 36)	6 months (n = 35)	12 months (n = 32)	Pre/post (%)
ABI	0.37	0.54	0.59	0.63	45.94
PSV	49.65	93.57	90.78	78.87	88.46
PI	1.55	3.51	3.59	3.67	126.45
FVW	LAM	B/T	B/T	B/T

Table 8
- Group 4: spectrum analysis in the popliteal artery and ABI of patients with hemodynamically significant lesions both in the aortoiliac and femoropopliteal segments (means)

AI-FP	Pre (n = 36)	Post (1 month) (n = 36)	3 months (n = 35)	12 months (n = 32)	Pre/post (%)
ABI	0.37	0.54	0.59	0.63	45.94
PSV	17.68	23.67	27.56	30.34	33.88
PI	0.91	1.14	1.34	1.23	25.27
FVW	LAM	LAM	LAM	LAM

The protocol of ultrasound examination was: with patients in supine position, external iliac, common femoral, anterior and posterior tibial, and peroneal arteries were examined, and, with patients in prone position, popliteal arteries were examined. SSA measurements described in a previous study¹³ were performed in each patient in the common femoral and external iliac arteries (at the level of the inguinal crease), in the popliteal artery (in the popliteal hollow), in leg arteries (anterior and posterior tibial), an at the level of the ankle. The following spectrum analysis measurements were performed (Figure 1): flow velocity waveform (FVW), peak systolic velocity (PSV), and pulsatility index (PI). FVW was classified according to its phases (Figures 1 and 2) as follows: triphasic (T), biphasic (B), or monophasic (M). Triphasic and biphasic configurations were considered normal. Monophasic waveforms were classified in two subgroups: high-acceleration monophasic waveforms (HAM, example C) considered normal (due to distal vasodilation) (Figure 1, HAM) and low-acceleration monophasic waveforms (LAM, Figure 1D), abnormal, due to loss of flow velocity wave energy, resulting from hemodynamically significant changes (stenoses or occlusions) proximal to the measurement site. PSV was measured at the highest point of the flow velocity waveform (Figure 1) and pulsatility and resistive indices were calculated using ultrasound equipment.

During patient follow-up, whenever we observed changes in pulse palpation previously present, signs of ischemia, SSA measurements with a decrease higher than 50% in previously measured numeric parameters with a change of the FVW (from a biphasic or triphasic to a low-acceleration monophasic configuration), revascularization procedure (angioplasty or grafts) failure was a possible diagnosis. Patients were then submitted to confirmatory angiographic examination. All cases with suspicion of hemodynamically significant lesions or SSA-diagnosed occlusion of angioplasty or grafting sites were confirmed by angiography.

For comparison purposes, we added a group of patients (group n) without significant PAOD, with demographic data similar to those observed in the groups studied, composed of 102 patients (204 limbs) who had been examined in our service for other purposes (such as carotid artery, deep venous thrombosis [DVT], varicose vein, and renovascular hypertension examination). All patient in this group had normal peripheral pulse, with no arterial bruits, and ankle-brachial index (ABI) greater than 0.9. This was called normal group (group n) (Table 9).

Table 9
- SSA measurements in patients without PAOD (group n) in the lower limbs (means)

Measurement site:	PSV	PI
CF	92.18 (±18.14)	8.1 (±4.88)
Pop	68.71 (±15.9)	9.06 (±6.5)
AT	59.81 (±17.78)	9.56 (±3.71)
PT	62.17 (±18.63)	8.4 (±3.74)

Inclusion criteria were as follows:

- Patients submitted to treatment for peripheral arterial insufficiency caused by PAOD in the lower limb with clinical indication for revascularization;

- Patients with pre- and post-treatment vascular ultrasound examination, according to SSA protocol;

- Patients without atherosclerotic lesions (hemodynamically significant stenoses, occlusions) in the thoracic and abdominal aorta;

- Patients with hemodynamically significant lesions only in the aortoiliac, femoropopliteal, or popliteal-tibial segments;

- Patients with hemodynamically significant atherosclerotic lesions both in the aortoiliac and femoropopliteal segments;

- Patients with complete pre-treatment angiographic examination;

- Patients with angiographic examination in cases suspected of having lesions (hemodynamically significant stenoses or occlusions) in post-treatment angioplasty and grafts;

- Patients without major amputations in the examined limb.

Exclusion criteria included:

- Patients without pre-treatment vascular ultrasound examination;

- Patients with non-conclusive angiographic examination;

- Patients without angiographic examination in cases suspected of having lesions (hemodynamically significant stenoses or occlusions) in post-treatment grafts, stents, and angioplasty;

- Patients with hemodynamically significant lesions both in the femoropopliteal and in the popliteal-tibial segments or in the aortoiliac, femoropopliteal, and popliteal-tibial segments, concomitantly;

- Patients with incomplete follow-up (less than one examination in a 6-month post-treatment interval);

- Patients with arterial aneurysms.

Results

In the group of patients with exclusive aortoiliac disease (group 1), 60 patients (65 procedures) were followed for up to 24 months (mean of 19.5 months) (Table 1). In such group, 11 aortoiliac grafts and 54 angioplasties (all of them with stent placement) were performed. The statistical analysis applied to the study consisted of a comparison between arithmetic means of SSA numeric parameters, PSV and PI, this being the objective of the study.

The mean of SSA numeric parameter measurements (PSV and PI) obtained in the common femoral artery (artery defining hemodynamically changes in the aortoiliac segment), in group 1, increased significantly in over 90% of pre-treatment levels (after 1 month in Table 1, Figures 3 to 5). FVW was monophasic (LAM in Table 1, pre) prior to treatment, changing to a biphasic (B) or triphasic (T) configuration after revascularization, in all cases (Table 1, in 1 post-treatment month). Such changes remained constant during follow-up of patients who did not need reintervention (Table 1, in 6 months, 12 months and 24 months).

Immediate postoperative increases, in relation to pre-treatment measurements, were 92.26% in PSV (from 61.27 cm/s to 117.8 cm/s) and 98.2% in PI (from 2.23 to 4.42) (Table 1, in 1 post-treatment month, and Figure 5).

In group 1, 4 occlusions and 3 (hemodynamically significant) stenoses occurred during follow-up, these events occurring only in angioplasty-treated patients (Table 2). Occlusions and hemodynamically significant stenoses were considered revascularization failures. All seven patients who showed significant changes in SSA numeric parameters with a fall in PSV values to 42.16% of pre-failure values (from 120.94 cm/s to 50.94 cm/s) and in PI to 47.98% of pre-failure values (from 3.98 to 1.91) (Table 2, Figures 6 to 8). Post-treatment biphasic or triphasic FVW changed to monophasic (LAM) in all cases of treatment failure (Table 2, post-failure, LAM). All seven patients were treated for occlusions and stenoses with new angioplasties and showed a significant increase in numeric parameters and FVW returning to biphasic and triphasic patterns (Table 2, Figures 6 to 8). PSV increased 89.86% after post-failure angioplasty (from 50.99 cm/s to 96.81 cm/s). PI increased 89% after post-failure angioplasty (from 1.91 to 3.61) (Table 2, Figure 8).

The group of patients with exclusive femoropopliteal disease (group 2), composed of 54 patients (54 procedures) was followed for up to 18 months (mean of 13.2 months) (Table 3, Figures 3 to 5). The patients were treated with grafts (23 cases) or stent angioplasty (31 cases). In these cases, there was a significant and steady increase in SSA numeric parameters measured in the popliteal artery (which defines the hemodynamic conditions of the femoropopliteal segment), compared to pre-treatment values (Table 3, Figures 3 to 5). PSV showed an increase of 112.83% (from 33.27 cm/s to 70.81 cm/s) and PI showed an increase of 62.39% (from 2.34 to 3.8) (Figures 5 and ⁹) with a change of the FVW from a monophasic (LAM) to a biphasic or triphasic configuration in all cases (Table 3).

In group 2, 6 occlusions occurred among angioplasty-treated patients and 2 hemodynamically significant stenoses occurred among those treated with grafts. Here occlusions and hemodynamically significant stenoses were also considered revascularization failures. In such patients, PSV and PI measured in the popliteal artery showed great changes. PSV decreased on average to 28.12% of pre-failure values (from 68.17 cm/s to 19.17 cm/s) and PI decreased on average to 27.73% of pre-failure values (from 4.58 to 1.27) (Table 4, Figures 6, 7 and ⁹). FVW also changed from a biphasic or triphasic to a monophasic (LAM) configuration in all patients (Table 4). When submitted to new revascularization (grafts and stenosis repair), measurements performed in the popliteal artery had a behavior similar to that observed in the initial revascularization, with PSV and PI increase and a change of the FVW from a monophasic (LAM) to a biphasic or triphasic configuration (Table 4, Figures 6 to ⁹). In these cases, PSV increased 221.7% (from 19.17 cm/s to 61.67 cm/s) and PI increased 225% (from 1.27 to 4.14) (Figures 6, 7 and ⁹).

Patients with disease only in the popliteal-tibial segment (group 3), composed of 44 patients (50 procedures) were followed up for a mean of 13.47 months (up to 15 months) (Table 5, Figures 3 to 5). In this group, 41 limbs were treated with grafts and 9 limbs were treated with angioplasty. SSA measurements used for pre- and post-treatment comparisons refer only to those performed in the treated (anterior or posterior) tibial arteries.

In group 3, SSA numeric parameters (PSV and PI) and post-treatment FVW had a behavior similar to that observed in the previous two groups (Table 5, Figures 3 to 5). PSV showed an increase of 149.08% (from 35.06 cm/s to 87.33 cm/s) and PI showed an increase of 28.8% (from 1.7 to 2.19) (Table 5, Figures 3 to 5), with a change of the FVW from a monophasic (LAM) to a biphasic or triphasic configuration in most cases (in one case to HAM) (Table 5). In the case of graft occlusion, SSA parameters had a behavior similar to that observed in the previous cases (patients with disease only in the aortoiliac and femoropopliteal segments) with a fall in PSV and PI and a change in FVW from a biphasic or triphasic to a monophasic (LAM) configuration (Table 6, Figures 6 and 7). PSV had a reduction of 74.16% (64.98 cm/s to 16.43 cm/s) and PI of 64.67% (from 3.34 to 1.18).

In the group of patients with disease both in the aortoiliac and femoropopliteal segments (group 4), 35 patients (36 procedures) were followed up for a mean of 15.2 months (up to 16 months). This group included only patients submitted to disease repair in the aortoiliac segment (Tables 7 and 8). Patients with sequential revascularization (aortoiliac and femoropopliteal) were excluded, since they accounted for only 3 patients. Measurements performed in the common femoral artery with proximal (aortoiliac) revascularization showed an increase in SSA numeric parameters of 88.46% in PSV and 126.45% in PI with a change of the FVW from a monophasic (LAM) to a biphasic or triphasic configuration (Table 7). However, regarding measurements performed in popliteal arteries (with no revascularization in the segment), PSV and PI increases were only 33.8 and 25.27%, respectively, with no changes in FVW (Table 8).

Discussion

The use of vascular ultrasound for the diagnosis and treatment planning of PAOD had its diagnostic ability and accuracy demonstrated in several studies,¹-12 both in the supra and infrainguinal segments, its use being currently considered part of the vascular propedeutics.

Follow-up of patients treated with revascularization of the lower limb (grafts or endovascular treatment) using vascular ultrasound has been considered a reliable and safe method.^14-23 Graft follow-up using vascular ultrasound examination may even increase primary patency, which is called assisted patency.^19-23 In patients with grafts using brachial veins, vascular ultrasound follow-up examination revealed that more than 40% of grafts needed postoperative intervention, for maintenance of patency.²⁴ In another case series,²⁵ follow-up of femorofemoral grafts using vascular ultrasound increased patency (primary) from 86% (in 1 year), 78% (in 3 years), and 62% (in 5 years) to an assisted patency of 95% (1 year) and 88% (3 and 5 years). It was also demonstrated²⁶ that infrainguinal graft postoperative follow-up in the treatment of critical ischemia using vascular ultrasound was less expensive and resulted in less amputations than follow-up based on ABI or based on clinical examination alone.

However, in classical treatment follow-up protocols using vascular ultrasound, the limb is examined to the fullest extent including donor and receptor artery (in grafts) or angioplasty site (in endovascular treatments). The examination is performed in color mode with velocity measurements in points indicated by color changes ^{14,19,24,27,28} at rest and occasionally after physical exercise or reactive hyperemia.³ Stenoses are graded by proximal PSV correlation (ratio) and in the lesion site. SSA measurements to calculate this correlation should have a corrected angle of insonation, which is sometimes difficult to be achieved, such as in the aortoiliac segment, where the segment arteries show a natural tortuosity. Angle correction may also be hindered in anastomosis sites. Other causes that may hinder the measurement of PSV correlations in the arteries include muscle mass in the femoropopliteal segment, intra-abdominal gases, lesions in the origin of arteries, diameter disproportion between grafts and donor or receptor arteries, as well as segments with calcified atherosclerotic plaques, which impede local insonation. All these situations may be complicated by the examiner's level of experience.²⁹ On the other hand, the measurement of PSV relative increase (ratio) in a stenosis does not allow a sequential stenosis evaluation.¹¹

There are discrepancies between measurements to define pressure gradient present in post-treatment stents when pressure measurements with catheters and intraluminal PSV changes are compared,⁹ probably due to catheter positioning or angulation of the flow axis in relation to the ultrasound beam and intraluminal turbulence. It was also demonstrated that graft PSV measurements do not usually show a fixed pattern, also hindering their application in temporal comparisons.²⁹ All these difficulties may be minimized in the examination using the SSA technique, because measurements are performed in sites relatively distant from the point of stent insertion or even from graft anastomoses.¹³

Several methods for the analysis of arterial hemodynamics were used by other authors such as local measurement of PSV,^{24,25,27,30-32} PI,^33,34 resistive index (RI),^33,34 or FVW analysis.^6,30,31,35 Decreased PSV compared to a previous measurement in the same arterial segment was used to indicate the presence of hemodynamically significant stenosis proximal to the measurement site in grafts using brachial veins.²⁴ On the other hand, low PSV in the midthird of polytetrafluoroethylene (PTFE) grafts^30,31 has already been correlated to failure of such grafts, but parameters were not analyzed in a temporal or segmental manner.

In a study using patients treated for renovascular hypertension³² with renal revascularization (angioplasty or grafts), PSV measured in the renal parenchyma (therefore distal to treatment site) increased 42% postoperatively in relation to pre-treatment measurements. Another recent study²⁵ on femorofemoral graft follow-up showed that in grafts in which hemodynamically significant proximal stenoses developed postoperatively, PSV was lower than 60 cm/s in five of eight cases, this PSV increasing threefold after proximal stenosis repair. Reports of low flow velocities (PSV) measured at a random point of a graft may be indicative of a trend toward occlusion.²⁷

It has also been demonstrated that pulsatility and resistive indices, in addition to acceleration indices, measured in the intrarenal arteries in patients with renal artery stenosis increase and return to normal levels after treatment with angioplasty.³³ In patients with post-treatment stent stenosis (restenosis), the parameters decreased returning to pre-treatment levels.³³ After endovascular treatment in renal transplant patients with stenosis in the afferent arteries, RI increased distally in a significant manner.³⁴ Improvement of local hemodynamics was confirmed by functional tests and angiography.

In the analysis of FVW, monophasic waves are considered the abnormal flow pattern, mainly low-acceleration waves, and were defined in several studies as indicative of significant occlusive disease proximal to the examination site.^6,30,31 Other authors used a formula combining PSV, RI and FVW measured in the common femoral artery to diagnose significant disease in the aortoiliac segment.¹² PSV and FVW measurements generated by magnetic resonance had a behavior similar to that produced by ultrasound.³⁵

In our study, we measured SSA parameters (PSV, PI, and FVW) in a segmental manner, in the common femoral, popliteal and tibial arteries of patients with pre- and post-treatment PAOD (groups 1 to 4) (Tables 1 to 8), which showed great correlation with angiographic findings from a previous study.¹³ Such data were also compared to SSA measurements performed in patients without significant disease (group n) (Table 9), confirming that values obtained for these parameters were consistently different from those measured in the corresponding arteries of patients without PAOD.

After revascularization in the lower limb with arterial ischemia caused by PAOD, values of SSA numeric parameters (PSV and PI) measured in the segment distal to the receptor artery (or distal to the angioplasty-treated segment) increased significantly and remained like this while revascularization remained patent (Tables 1, 3 and 5, Figures 3 and 4). PSV increased more than 90% (Tables 1, 3 and 5, Figure 5) after revascularization, indicating a significant increase in FVW kinetic energy.^2,36 Regarding PI, the increase was 98% after treatment of lesions in the aortoiliac segment, 62% after treatment in the femoropopliteal segment, and 28.8% after treatment in the popliteal-tibial segment. These differences might have occurred due to distal, collateral vasodilation or changes in arterial wall compliance. FVW also changed (Figures 1 and 2) from a pre-treatment low-acceleration monophasic (LAM) to a biphasic or triphasic configuration.

When treatment failed (occlusion or hemodynamically significant stenosis of grafts or angioplasty), SSA numeric indices measured in the segment distal to the receptor artery (or distal to angioplasty-treated segment) decreased significantly, and FVW changed returning to monophasic (LAM) patterns (Tables 2, 4 and 6, Figures 6 to 9). PSV and PI decreased in all groups. Pre-failure values in patients treated for lesions in the aortoiliac segment fell more than 40%, 28 and 27%, respectively, in patients with femoropopliteal lesions, and 25 and 35%, respectively, in patients with popliteal-tibial lesions. In patients treated with stenosis repair or new revascularizations (repair, in Tables 3 and 5, Figures 6 to 9), there was an increase in PSV and PI values both in the aortoiliac (increase of 89%) (Table 2) and in the femoropopliteal (increase greater than 220%) segments (Table 4). FVW changed from a monophasic to a biphasic or triphasic configuration in all cases in which repair was needed after treatment failure (Tables 2 and 5).

In terms of length of a classical ultrasound examination, reports show that the examination lasts about 1 hour,⁸ even in services with well-trained examiners. The time spent in the examination should be longer in services where trainee residents perform the tests. In the case of SSA, examination length is reduced because only three or four measurements are necessary in each limb. There are several SSA advantages, in addition to a shorter duration of examination. With SSA, it is possible to examine patients with treatment sites less accessible to ultrasound, such as abdomen, adductor channels, proximal third of the leg. It is also possible to define numeric values that are easy to understand and can be used in temporal comparisons, which is an useful tool for follow-up. In cases in which there are doubts regarding SSA measurements at rest, it is always possible to perform this analysis after reactive hyperemia or exercise.

To compare our results, we chose to use percentage of changes in SSA numeric values because we believed that such values directly define local hemodynamic changes, which can be used in a temporal comparison, are more easily understood, and do not depend on absolute values for definition (Figures 8 and ⁹). Regarding PSV absolute measurement, it is known that it shows changes when measured in a site where arterial lumen is altered, and may be affected by cardiac hemodynamics, and which also has an inversely proportional relation with vessel diameter, since the greater the vessel diameter the lower blood flow velocity will be, when flow is constant.

Increased SSA numeric measurements (PSV, PI) and changes in FVW from a monophasic to a biphasic or even triphasic configuration, together with clinical signs of improved local perfusion (ulcer healing, abolished pain at rest) and increased ABI, demonstrate that local hemodynamics changed to patterns similar to those of patients without significant PAOD (Table 9). Therefore, without hemodynamically significant lesions. Maintenance of such SSA parameters while treatments (grafts, angioplasty and stents) were patent and a fall in these parameters when treatments failed, with the subsequent increase in parameters when the problem was resolved, confirms that these parameters may be used as revascularization patterns, mainly in temporal comparisons.

Conclusions

Consistent changes in SSA numeric values and in FVW when treatments were successful and no failure occurred, returning to post-treatment patterns when a new revascularization was performed, show that SSA may be used as a useful tool in the follow-up of PAOD in the lower limbs. This enables an early and non-invasive diagnosis of possible hemodynamically significant stenoses or occlusions of the surgical procedures performed. The correlation between such measurements and local hemodynamic alterations and the different arrangements of atherosclerotic lesions may be inferred by the behavior of pre- and post-treatment SSA measurements.

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Publication Dates

• Publication in this collection
  02 Oct 2009
• Date of issue
  June 2009

History

• Received
  27 Apr 2008
• Accepted
  30 Mar 2009