Changes in peripheral hemodynamics after percutaneous transluminal angioplasty

Changes in peripheral hcmodynamics after percutaneous transluminal angioplasty Sergio X. Salles-Cunha, P h l ) , G e o r g e Andros, M D , L e o p o l d o B. Dulawa, M D , R o b e r t W. Harris, M_D, and R o b e r t W. Oblath, M D , Burbank, Calif. We measured ankle/arm pressure indexes and blood flow rates before and after performing percutaneous transluminal angioplasty in 36 extremities. Flow rates through the leg were determined with a magnetic resonance blood flow scanner. All patients had claudieation; one had gangrene, another had an ulcer, and two complained of rest pain. The median age was 65 years, and 72% were men. There were 25 dilations of the lilac artery, 12 of the superficial femoral artery, and eight of the popliteal arteries; nine patients had two arterial segments dilated. Nineteen legs had ankle/arm pressure indexes before percutaneous transluminal angioplasty of less than 0.80 (range 0.51 to 0.75); their flow rates averaged 40 - 20 (SD) ml/min. After percutaneous transluminal angioplasty flow and pressure increased significantly in 14 of these 19 legs, and three had no hemodynamie improvement; in one leg only pressure and in another only flow increased significantly. The remaining 17 extremities had ankle/arm pressure indexes before percutaneous transluminal angioplasty ranging from 0.81 to 1.09; their flow rates averaged 53 - 27 (SD) ml/min. Abnormal flow rates were detected in 15 of these 17 extremities. With nearnormal ankle/arm pressure indexes no significant increase in pressure was anticipated. Flow rates augmented to 75 -+ 28 (SD) ml/min after percutaneous transluminal angioplasey; a significant increase in flow was noted in 12 legs (71%). For patients with ano kle/arm indexes before percutaneous transluminal angioplasty of less than 0.80, either pressure or flow measurements should corroborate the benefits of the operation, whereas if the ankle arm index is greater than 0.80, flow measurements are most likely to substantiate changes in peripheral hemodynamics. (J VAse SuRG 1989;10:338-42.)

The measurement o f ankle pressures has been advocated as a quantifier o f the results obtained with percutaneous transluminal angioplasty (PTA). 13 Indeed, the ankle/brachial systolic pressure ratio, or ankle/arm index (AAI), has been recommended as an integral part o f the evaluation o f vascular reconstructions affecting the lower extremity. 4 However, several impediments have been recognized. 1-3's7 In practice, the inability to measure systolic pressure in calcified, incompressible arteries is common knowledge. Less evident is the fact that pressure measurements obtained in partially incompressible vessels (i.e., arteries in the process o f becoming incompressible) are misleading. 7 In theory, the simplest model devised relates three variables: pressure, flow, and peripheral resistance; two o f the three must be mea-

PATIENTS AND METHODS

From St. Joseph Medical Center. Presented at the Thirteenth Annual Meeting of the Southern Association for Vascular Surgery, Key West, Fla., Jan. 25-28, 1989. Reprint requests: Sergio Salles-Cunha, PhD, TechnicalDirector, Vascular Laboratory,Saint JosephMedicalCenter, BuenaVista and Alameda, Burbank, CA 91505. 24/6/13613

Pressure and flow rates were measured before and after 36 PTA interventions in 35 lower extremities o f 27 patients. Eight patients had bilateral iliac dilations, and one o f these patients had an additional procedurc to dilate the superficial femoral artery 3 months later. Twenty-seven o f the 36 procedures, were performed in men (75%), and nine were performed in women (25%). The median age was 65

338

sured to characterize the system. In addition, clinical improvement has been reported after PTA despite little or no change in the ankle pressures. 3,6 A subset o f this group o f patients includes those with claudication who have normal or near-normal systolic ankle pressures. Despite lack o f a demonstrated hemodynamic deficit, PTA has been performed based on the patient's symptoms and the finding o f an anatomic defect on the arteriogram. Because the vascular origin o f symptoms o f claudication and the significance o f an arteriographic stenosis may be debatable, we incorporated the measurement o f blood flow rates to the noninvasive hemodynamic assessment o f patients undergoing PTA.

Volume l0 Number 3 September 1989

years. Smoking (78%), hypertension (47%), heart disease (36%), and diabetes (11%) were risk factors noted. Table I lists the various dilations performed. All patients had clandication. One had gangrene, another had a nonhealing ulcer, and two others complained of rest pain.

Hemodynamic assessment Pressure and flow rates were measured before and after PTA. Measurements after PTA were not performed in the same day of the intervention to avoid transient effects of anesthetic or drugs or to avoid vasoreactivity. Approximately 90% or more of the injected dose of contrast material iohexol is excreted within the first 24 hours, with the peak urine concentrations occurring in the first hour after administration. Twenty eight of the 36 measurements tal~en after PTA were performed 24 hours later, on the day after the procedure; five legs were studied within 5 days, and three were studied within 1 month. Standard methods were used to measure systolic pressure at the ankle and arm. The preintervention and postintervention pressure measurements taken at the posterior tibial artery were compared. Blood flow rates were measured with a Metriflow (Metriflow Medical Systems Inc., Milwaukee, Wis.) blood flow scanner. 8 This magnetic resonance (MR) flowmeter averaged flow from 20 cardiac cycles. The output of the instrument, in milliliters per minute, represented flow rate through the entire cross section of the leg. We analyzed the flow rates detected across a section located 30 cm proximal to the malleoli. Before in vivo measurements the M R flowmeter was calibrated in vitro against an electromagnetic flowmeter. 9 A pulsatile pump propelled saline in a 5 mm tube through the electromagnetic flowmeter in series with the M R flowmeter. The saline was doped with copper sulfate to mimic the M R characteristics of blood. Blood flow rates were varied from 0 to 200 ml/min and the M R signal was correlated to the electromagnetic measurement. Linear regression provided the calibration factor for the following in vivo measurements. Based on our initial observations of increased blood flow after PTA performed in patients with claudication and near-normal ankle pressures, ~° we analyzed two groups: (1) extremities with clearly abnormal ankle pressures (AAIs <0.80) and (2) extremities with near-normal anlde pressures (AAIs ->0.80). We assumed that an increase of 0.10 in the AAI was significant, nq2 Based on our own studies on the variability of blood flow measurements, we selected an increase of 20% to be significant.la-~4 Flow

Changes in peripheralhemodynamics 339

Table I. Percutaneous transluminal angioplasties Cormnon iliac artery External iliac artery C o m m o n + external iliac arteries Superficial femoral artery Popliteal artery Superficial femoral + poplkeal arteries

13 2 5 8 4 4

rates below 75 ml/min (at 30 cm from the malleoli) were considered decreased when compared to flow rates measured in normal young adults. 13-14

RESULTS Table II summarizes AAIs, flow rates, type of dilation performed, and follow-up for extremities with abnormal preintervention AAIs (<0.80). Table III presents similar data for extremities with nearnormal AAIs (>0.80). The increase in blood flow rates after PTA was statistically significant in both groups (paired t test, p < 0.00i). The increase in AAIs was statistically significant in the group with abnormal pressures (p < 0,001). When we compared pre-PTA blood flow rates, we found the group with abnormal AAIs had significantly less flow than the group with nearnormal AAIs (unpaired t test, p < 0.1). The postPTA variance in flow and pressure between the two groups were not statistically significant (p > 0.1). In the group of patients with abnormal AAIs (Table II), 14 of 19 extremities had significant increase in flow rates and ankle pressure. Two of these 14 arteries occluded at 2 and 8 months after PTA (cases 4 and 5). In three extremities both pressure and flow failed to increase significantly. One patient continues to have claudication without benefit from the PTA (case 17). Another patient had bilateral iliac PTAs followed by femoropopliteal bypass grafting (cases 11 and 13). Although flow increased by over 50% in one extremity (case 10), it changed only from 21 to 33 ml/min, whereas the ankle pressures remained unchanged; this patient later received adjunctive femoropopliteal bypass grafting. Finally a patient had an increase in pressure only after dilation of the superficial femoral artery (case 15). As expected, in the group of patients with nearnormal ankle pressures (Table III), the average AAI increased by 4% only. In contr~ist, the flow rates augmented by 42% on average. Blood flow augmented significantly in 12 extremities (71%) but failed to improve in five. In one extremity the flow rate was high even before PTA (case 21); another

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Salles-Cunha et al.

Table II. Group I: Pre-PTA ankle/arm pressure index <0.80 Ankle~arm index

Flow rates (ml / min)

Case

Pre-PTA

Post-PTA

Pre-PTA

Post-PTA

IntErvention/fbllow-up

1 2 3 4 5 6 7 8 9 10 11 12 13 I4 15 16 17 18 19

0.51 0.55 0.56 0.61 0.62 0.62 0.62 0.63 0.63 0.64 0.64 0.65 0.68 0.70 0.71 0.74 0.74 0.75 0.75

0.74 0.94 0.77 1.00 0.90 0.95 0.91 0.95 1.02 0.63 0.58 1.12 0.60 0.81 0.84 0.97 0.63 0.98 1.10

27 20 70 98 43 38 45 18 20 21 27 31 29 56 61 33 25 33 59

56 65 108 172 93 94 73 63 43 33 19 47 23 68 68 40 25 51 84

0.65

0.87

40

64

Average value

0.07

0.16

20

35

SD

EIA/9 mo CIA, EIA/8 mo CIA/12 mo POP/failed 2 mo/fempop SFA POP/failed 3 mo POP/13 mo SFA/ POP/6 mo SFA/6 mo CIA/Fempop 9 mo CIA EIA/Fempop 7 mo SFA/8 mo CIA/Fempop 7 mo SFA/8 mo SFA/12 mo CtA/5 mo CIA/No benefit 10 mo CIA/10 mo SFA POP/15 mo

CIA, Comanon iliac artery; EIA, external iliac artery; SFA, superficial femoral artery; POP, popliteal artery; Fempop, femoropopliteal bypass; mo, months of follow-up.

patient had the superficial femoral artery dilated at a later date (case 25), and the other three had apparent clinical benefits from PTA (cases 27, 30, and 34). DISCUSSION Despite claims that balloon dilation is an economically attractive and clinically effective alternative to bypass revascularization, 15in our practice PTA and bypass grafting have been complementa U procedures. Patients submitted for PTA usually did not have limb-threatening ischemia or were not disabled enough by daudication to warrant surgery. On the opposite end of the spectrum, patients with severe ischemia but who pose a prohibitive risk could benefit from PTA. The results of PTA may be judged clinically, angiographically (anatomically), and in many instances hemodynamically. However, in a subgroup of patients with near-normal ankle pressures, standard methods are insufficient or inadequate to evaluate the patient hemodynamically. The limitations of pressure measurements compounded with the subjectiveness of clinical symptoms and the inability t ° assess the significance of focal stenoses seen on arteriography, raise questions about the effectiveness of PTA in patients with claudication whose ankle pressure is minimally decreased.I° By incorporating the measurement of blood flow

rates in our noninvasive assessment of PTA patients, we observed that (1) blood flow rates can be abnormally low as compared to blood flow rates in normal young adults, 13,14 even if the AAIs are near-normal; and (2) blood flow rates can increase after revascularization despite insignificant changes in ankle pressures. It is plausible that in some of the extremities with low flow rates and near-normal pressures, a process of calcification rendering the arteries partially incompressible may be underway. The pressure measurements could then be falsely elevated. 7 However, the incidence of this observation is more common in patients with diabetes, and in this sample population only 11% of the PTAs were performed in patients with diabetes. We suspect partial vessel incompressibility of the arteries at the ankle when the toe pressure is decreased, the ankle pressure measurements fluctuate from study to study, the velocity waveforms are monophasic, and the arteries at the thigh are incompressible. 7 Toe pressures are informative ha the evaluation of the distal circulation complementing ankle pressure and flow measurements. 12 Toe pressures were measured in 13 of the 17 extremities with nearnormal anlde pressures. Eight were minimally decreased (toe/brachial index in the 0.6 to 0.8 range), three were normal (toe/brachial index >0.8),

Volume 10 Number 3 September 1989

Changes in peripheralhemodynamics 341

Table III. Group I: Pre-PTA ankle/arm pressure index <0.80 Flow rates (ml/min)

Ankle~arm index Case

Pre-PTA

Post-PTA

Pre-PTA

Post-PTA

Int~wention/)bllow-up

20 21 22 23

0.81 0.83 0.83 0.84

0.74 0.86 0.81 0.85

23 129 38 28

51 110 97 74

24 25

0.84 0.88

0.92 0.95

68 36

92 28

26 27 28 29 30 31 32 33 34 35 36

0.90 0.91 0.93 0.95 0.96 0.97 0.97 0.99 1.05 1.09 1.09

0.85 1.01 1.27 1.04 1.09 0.99 1.02 0.96 1.09 1.03 0.98

90 74 64 28 36 38 62 57 54 44 31

I32 74 98 66 37 67 104 81 47 73 40

SFA, POP/12 mo CIA/12 mo CIA/13 mo SFA, POP/Fempop 9 mo S F A / l l mo CIA, EIA/SFA PTA 6 mo SFA/10 mo CIA/12 mo P O P / i 2 mo CIA, EIA/12 mo CIA/6 mo CL& EIA/12 mo SFA/12 mo CIA113 mo CIA/5 mo EIA/16 mo CIA/10 mo

0.93

0.97

53

75

Average value

0.09

0.12

27

28

SD

CIA, Common iliac artery; EIA, external iliac artery; SFA, superficial femoral artery; POP, popliteal artery; Fempop, femoropopliteal bypass; mo, months of follow-up.

and two were clearly abnormal 'toe/brachial index <0.40). In one of the latter patmnts ~(case 20) the toe/ankle index nearly tripled after PTA, raising the suspicion of tibial incompressibility. Velocity waveforms of the tibial arteries were monophasic despite near-normal pressures in four extremities. This finding can be attributed to occlusive disease or partial arterial incompressibility. In one of these extremities, incompressibility of the femoral arteries in the thigh was observed (case 33). We now rarely use the continuous-wave Doppler for velocity waveform analysis. The origin of the velocity wavcform can be precisely and rapidly identified with color Doppler. Nevertheless, waveforms can be normal with low flow rates, or in contradistinction, the ultrasonic beam may fail to penetrate and insonate the lumen of the vessel adequately. We continue to investigate the measurements of pressure and flow rates at rest and after exercise. However, for practical purposes the simplicity of measurements at rest far outweighs the complexity of exercise testing. In most patients with significant disease exercise testing does not increase diagnositc yield? 6 In patients with mild claudication we may have to prolong the exercise until the ankle pressure drops significantly. Such a protocol has been avoided, particularly in elderly or disabled patients or in patients with cardiac risk. Finally, for time-series eval-

uation, the reproducibility of the patient's perception of claudication is questionable. Nevertheless, we performed pre-PTA exercise testing (toe raises) in eight of the 17 extremities with near-normal anne pressures. Our standard procedure limited the number of toe raises to a maximum of 50. This limited exercise was enough to elicit a significant drop in ankle pressures in only one extremity. Changes in peripheral resistance caused by arteriosclerotic occlusivc disease should result in a decrease in distal pressure or flow, either concomitantly or independently. Either of the two variables may be affected more so than the other. The data in this article emphasize cases in which the blood flow rate was more sensitive than the systolic pressure to detect hemodynamic changes after PTA. Other general conditions of the patient may also affect blood flow. Indeed, we attempt a rigorous control of peripheral vasodilation/vasoconstriction during the performance of the tests. We recommend that the sldn temperature of the foot be within 26°C to 29°C and that the Doppler velociW tracings of the posterior tibial artery do not show diastolic flow at the time of the measurement of blood flow rates. Previous studies desribing the variance of noninvasivc hemodynamic parameters have shown that systolic pressures measured at the arm, ankle, or toe fluctuate less than mean volumetric flow rates. 12-~4

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Salles-Cunha et al.

This represents a physiologic variation in flow. Recently we calculated the coefficient of variance (standard deviation divided by the mean) for the calibration factor of the M R flowmeter to be only 1.5%; thus we consider changes in flow greater than 3% as physiologic rather than instrumental at the 95% level of confidence. Blood flow may be a highly sensitive parameter to detect change; however, in practice we must specify the main cause of change in blood flow rates. When the post-PTA flow measurements were performed, the systemic effects of the operation had already subsided, and the patients were ready to resume normal activities. As evidence, the post-PTA flow rates measured in the contralateral leg of patients who had unilateral procedures were on average 97% _+ 9% (SD) of the pre-PTA value in 16 of 19 extremities (84%). Only three legs (16%) had significant (>20%) increases in flow rates; two of these extremities had abnormally low AAIs before PTA (group 1); in the third patient who had decreased toe pressures (case 20), partial arterial incompressibiIity was suspected and this patient probably should not belong to the exceptional group of patients with claudication with near-normal pressures. Therefore, in the cases reported herein, the PTA intervention was the major contributing factor, and the increase in flow rates observed can be specifically ascribed to the arterial dilation. In summary, we have presented evidence to justify the measurement of blood flow rates in addition to the determination of systolic pressures during the noninvasive hemodynamic evaluation of the peripheral circulation. In a subset of patients undergoing PTA the changes detected in blood flow rates were important quantitative indicators of the benefits of the intervention. In practice, if AAIs are less than 0.80, either pressure or flow rates can indicate improvement on peripheral hemodynamics; however, even in these cases, pressure measurements may be false if the distal arteries arc in the process of calcification leading to "partial vessel incompressibility." If AAIs are larger than 0.80, the measurement of blood flow rates is most likely to show quantitatively the hemodynamic improvement.

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10.

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13.

14.

15.

16. REFERENCES

1. Nehnan HL, Bergan JJ, Yao JST, Bran& TD, Greenberg M, O'Maha CS. Hemodynamic assessment of transluminat an-

gioplasty for lower extremity ischemia. Radiology 1982; 143:639-43. Borozan PG, Schuler JJ, Spigos DG, Flanigan DP. Longterm hemodynamic evaluation of lower extremity percutaneous transluminal angioplasty. J VAse SUV~G1985;2:78593. Mofin JF, Johnston KW, Rac M. Improvement after successful percutaneous transluminal dilation treatment of occlusive peripheral arterial disease. Surg Gynecol Obstet 1986',163:453-7. Rutherford RB, Flanigan DP, Gupta SK, et al. Suggested standards for reports dealing with lower extremity ischemia. J VASC SURG 1986;4:80-94. Samson RH, Sprayregen S, Veith FJ, Gupta SK, Ascer E, Scher LA. Inadequacy of the noninvsaivehemodynamic evaluation of percutaneous transluminal angioplasty. Am J Surg 1984;147:212-5. Cumberland DC. Percutaneous transluminal angioplasty: experience in balloon dilatation of peripheral, coronaty and renal arteries. Br J Radiol 1982;55:33-7. Vincent DG, Salles-Cunha SX, Bernhard VM, Towne JB. Noninvasive assessment of toe systolic pressures with special reference to diabetes mellims. J Cardiovasc Surg [Torino] 1983;24:22-8. Battodetri JB, Halbach RE, Salles-Cunha SX, Sances A Jr. The NMR blood flowmeter: theory and history.. Med Phys 1981;8:435-43. Salles-Cunha SX, Halbach RE, Battocletti JB, Sances A Jr. Nuclear magnetic resonance (NMR) cylindrical blood flowmeter: in vitro evaluation. J Clin Eng 1980;5:205-13. Salles-Cunha SX, Dutawa LB, Andros G, Harris RW, Oblath RW. Peripheral transluminal angioplas~ (PTA) in clandicants with minimal decrease in ankle pressures: is it warranted? In: Boccalon H, ed. Angiologie: Strategie du Diagnostic et de !a Terapeutique. Paris, France: John Libbey Eurotext, 1988:209-11. Johnston KW, Rae M, Hogg-Johnston SA, et al. 5-Year resuits of a prospective study of percutaneous transluminal angioplasty. Ann Surg 1987;206;403-13. Sondgeroth TR, Salles-Cunha SX, Vollrath KD, Towne lB. Variability of toe pressure measurements. Bruit t982;6; 14-6. Salles-Cunha SX, Cosman P, Andros G. Variance of arterial blood flow rates in the leg. Proceedings of the San Diego Symposium on Non-invasive Diagnostic Techniques in Vascular Disease. San Diego: 1988:t25. Salles-Cunha SX, Tolan D. Evaluation of a magnetic resonance arterial blood flowmeter: comparison with venous occlusion strain-gauge plethysmography. J Vasc Tech (In press). Doubilet P, Abrams HL. The cost of underutilization: percutaneous transluminal angioplasty for peripheral vascular disease. N Engl J Med 1984;310:95-102. Outiel K, McDonnell AE, Metz CE, Zarins CK. A critical evaluation of stress testing in the diagnosis of peripheral vascular disease. Surgery 1982;91:686-93.