Equipment for Intraoperative Assessment of Sternal Collaterals

by Mark M. Levinson , MD
Hutchinson Hospital
Hutchinson, KS, USA

April 21, 2001


In an attempt to determine if the absence of sternal collaterals predisposes to sternal wound complications following IMA harvesting, I have searched for a method that would reliably and inexpensively assess chest wall collateral flow. A 5 mm endoscopic straight tip doppler probe (as used by general surgeons during laparoscopic procedures) proved to be inadequate.

Recently, I have been very successful in detecting doppler flow signals in the intercostal arteries using a special bayonet doppler probe supplied by Koven Technology . This is the only probe I have found that has the correct angle at the tip. The bayonet probe can be positioned correctly over the intrathoracic portion of the intercostal spaces and doppler flow signals easily detected in the intercostal arteries. Flow signals have also been detected in the subcostal and superior epigastric vessels with this probe.

The photograph below shows the bayonet probe tip.

This probe is connected to a Koven (or Hadeco) hand held MiniDop ES-100x unit. Signal acquisition requires a 10 MHz amplifier . Only the probe tip needs to be sterilized. The photograph below shows the MiniDop ES-100x and the 10 MHz amplifier. The probe inserts into the amplifier. There is an on-off button on the amplifier.

Use of this equipment has allowed me to locate intercostal and subcostal flow signals in every case so far. Digital compression of the IMA against the chest wall one or two interspaces proximal to the signal eliminates all intercostal or subcostal flow in about 10% of cases. In the remaining 90%, the signal either remains or is increased.

It is my hypothesis that complete loss of the flow signal at all interspaces indicates absent chest wall collaterals. This finding implies that chest wall blood supply is completely IMA dependent and thus contraindicates IMA harvesting. However, proof of this hypothesis is not possible yet as the data is preliminary. A multicenter study is currently being organized to help determine if the incidence of sternal wound complications is higher in patients with absent collateral flow. If you wish to participate in this study, please email Mark M. Levinson

 

 

CHANGING FLOW PATTERN OF THE INTERNAL THORACIC ARTERY UNDERGOING CORONARY BYPASS GRAFTING: CONTINUOUS-WAVE DOPPLER ASSESSMENT

RAYMOND CARTIER, MD, OMAR SEMPER DIAS, MD, MICHEL PELLERIN, MD, YVES HÉBERT, MD, YVES LECLERC, MD

Surgeons have limited ability to evaluate intraoperatively the patency of internal thoracic artery graft as a bypass for coronary artery revascularization. We used continuous-wave Doppler ultrasonography to study the velocity of the internal thoracic artery before harvesting and after grafting (scanning probe, 8 MHz). Systolic and diastolic frequency shift (in kilohertz) and systolic frequency/diastolic frequency index were analyzed. Twenty four internal thoracic artery grafts in 15 patients were studied. Fourteen internal thoracic artery grafts were anastomosed to the left anterior descending artery, one to a diagonal artery, and nine to the circumflex artery. The mean systolic frequency before harvesting was 1.19 ± 0.40 KHz and no significant differences were found between the right and the left internal thoracic artery (right, 1.17 ± 0.37; left, 1.19 ± 0.42 KHz). There was a 40% drop in sytolic frequency related to the harvesting. Mean sytolic frequency decreased after grafting (1.19 ± 0.40 versus 0.87 ± 0.32 KHz; p < 0.01) whereas mean diastolic frequency doubled (0.32 ± 0.12 versus 0.83 ± 0.4 KHz; p < 0.001) and mean diastolic frequency/systolic frequency index increased from 28% ± 11% to 101% ± 39% (p < 0.001), indicating an increased myocardial vascularization during diastole. No significant difference was found between grafted arteries (left anterior descending versus circumflex) .All patients had an uneventful postoperative course and no perioperative myocardial infarction was reported. Doppler flow quantification of internal thoracic artery bypasses may give the surgeon an opportunity to evaluate intraoperatively the physiologic features and patency of the internal thoracic artery before and after coronary artery bypasses.(J Thorac Cardiovasc Surg 1996; 112:52-8)

Internal thoracic artery (ITA) is universally recognized as the optimal conduit for myocardial revascularization.1,2 However, despite its universal acceptance, intraoperative ITA graft patency assessment remains mostly qualitative. Indirect signs of antegrade flow such as distal vascular bed filling or spontaneous electrical myocardial activity at the unclamping of the ITA pedicle are used as indices of patency. However, these do not give the surgeon a direct flow quantification. Traditionally, cardiac and vascular surgeons have used an electromagnetic flow probe to evaluate saphenous vein bypasses, with which magnitude of the blood flow is derived from voltage variation of ions flowing across a fixed magnetic field.3


During the past 15 years, surgeons have become familiar with the use of ultrasonography for blood flow evaluation. Continuous-wave Doppler ultrasonography has been commonly used by vascular surgeons for noninvasive evaluation of peripheral vascular disease and also by cardiac surgeons for assessment of coronary artery bypass.4-8 Continuous-wave Doppler ultrasonography applies the principle of the Doppler shift described by the physicist and mathematician Christian Johann Doppler (1803-1853).9 Instead of producing a magnetic field, the piezoelectric crystal contained inside the Doppler probe transmits an ultrasonic beam that is reflected by the circulating red blood cells. A separate transducer crystal receives the reflected sound waves. The velocity of the blood flow is proportional to the frequency shift between transmitted and reflected ultrasonic beam. Contrary to the magnetic flow probe, the ultrasonic flow probe is effective without vessel denudation and only requires a limited access to the vessel circumference. However, continuous-wave Doppler ultrasonongraphy measures flow velocity whereas the electromagnetic "encircling" flowmeter as a result of known cross- sectional area can measure volumetric flow. Therefore the former is not as accurate as the latter. Nevertheless, the continuous Doppler assessment allows systolic and diastolic flow velocity characterization of the ITA flow pattern during a complete cardiac cycle. Native ITAs are predominantly perfused during systole, whereas coronary arteries are mainly perfused during diastole. Evaluation of systolic and diastolic velocity of ITA graft flow may provide the surgeon with a quantitative evaluation of the flow pattern changes as the ITA grafts adapts its hemodynamics to the coronary artery circulation and therefore could become useful in determining graft patency.


The purpose of this work was to evaluate intraoperatively the use of continuous- wave Doppler ultrasonographic assessment of ITA phasic flow pattern before harvesting and after coronary artery grafting and to establish its usefulness as a noninvasive means of evaluating ITA graft patency.


PATIENTS & METHODS

Population
The study was done in 15 patients undergoing elective coronary operation. There were 12 men and 3 women whose ages averaged 60 ± 7.6 years (52 to 82 years). The majority underwent operation of isolated coronary artery insufficiency although two patients had concomitant valve operations. A total of 24 ITA grafts were completed. Before operation all patients had New York Heart Association functional class II or III symptoms.

Doppler Evaluation
Velocity of the ITA flow was measured first in situ before any dissection and manipulation of the vessel, a second time after the pedicle dissection, and then after completion of the ITA- coronary artery anastomosis once the patient had been weaned off the extracirculatory support. To standardize the experimental conditions, ITA graft Doppler measurement was completed after the patientâs condition was hemodynamically stabilized, which included a systolic pressure 100 mm Hg or greater, a pulse rate less than 100 beats/min, a pulmonary wedge pressure less than 20 cm H2O, and a body temperature 35° C or higher.


The continuous-wave Doppler device used was a Smartdop apparatus (Koven Technology, Inc., St. Louis, Mo.) coupled to an 8 MHz transducer recorder. Systolic and diastolic ITA blood flow velocities were evaluated by quantification of the magnitude of the Doppler shift (Df) recorded in kilohertz. Doppler frequency shift readings were obtained with a probe angle manually maintained at 75 to 80 degrees toward antegrade ITA blood flow. To obtain this orientation with minimal variability, the probe was first perpendicularly oriented to the ITA pedicle and then pulled back by 10 to 15 degrees to face blood flow stream. Recordings were always done on the midsegment of the ITA because phasic flow has been reported to vary along the course of the ITA.10 This segment was always easy to reach and required minimal manipulation. Sterile acoustic gel was uniformly used to couple the ultrasonic transducer to the ITA pedicle to decrease air attenuation coefficients. Systolic and diastolic frequency shift values represent peak velocity of each phase of the cardiac cycle.

Coronary Artery Assessment
All ITA grafts included in the present study were anastomosed to the left coronary artery territory. To quantify vessel runoff, each coronary artery was evaluated according to a standardized scoring system. A score of 1 was attributed to left anterior descending artery (LAD) terminating before or at the apex of the heart. A score of 2 was attributed when the LAD terminated beyond the apex. An additional score of 1 was added for any major diagonal artery connected to the LAD. In a similar fashion, in the case of ITA bypass to the circumflex territory a score of 1 was given for any marginal artery distal to the anastomotic site whose caliber and runoff were surgically accessible.

Clinical Assessment
After the surgical procedure, the patient's postoperative course was evaluated according to routine hemodynamic and cardiac assessment. Perioperative myocardial creatine kinase activity (CK-MB) 1 and 16 hours after operation (normal range, 0 to30 IU/L), ventricular arrhythmia necessitating treatment, and New York Heart Association functional class at hospital discharge were recorded. Perioperative myocardial infarction (MI) was diagnosed by a new Q wave and CK-MB count greater than 100 IU/L.

Data Analysis
Results are expressed as mean and standard error of the mean. Statistical analysis of the data was done by one-way analysis of variance for intergroup observations. Paired Student's t test was used for between-subject paired observations. Results were considered significant for a p value less than 0.05.

RESULTS

Evaluation Before and After Harvesting
The average systolic and diastolic frequency shifts assessed in situ before harvesting were, respectively, 1.19 ± 0.40 and 0.32 ± 0.12 KHz and were comparable for both right and left ITAs (Table I). Systolic frequency significantly dropped after harvesting, but the diastolic/systolic ratio remained stable, indicating that the blood flow pattern was not affected (Table II).


Evaluation After Grafting
The ITA systolic frequency significantly decreased from 1.19 ± 0.40 to 0.87 ± 0.32 KHz (p < 0.01) after coronary artery grafting once patients were weaned off cardiopulmonary bypass. In contrast, diastolic frequency increased drastically from 0.32 ± 0.12 to 0.83 ± 0.4 KHz (p < 0.001), which was reflected also by an increase of the diastolic/systolic frequency ratio (28% ± 11% to 101% ± 39%, p < 0.001), indicating a significant change in the pattern of ITA blood flow (Fig. 1). Fig. 2 illustrates an example of a right (A) and left (B) ITA assessment as recorded in situ, after pedicle dissection, and after grafting. As pointed out, in both cases the diastolic frequency shift increased considerably once the graft was submitted to the coronary vascular network and even occasionally overrode the systolic one (as seen in Fig. 2 with the right ITA).

 

Coronary Anatomy
Site of revascularization (LAD or circumflex territory) affected neither systolic (LAD, 0.89 ± 0.32, versus circumflex, 0.88 ± 0.30 KHz, p = NS*) nor diastolic (LAD, 0.85 ± 0.50 KHz, p = NS) frequency shift. Similarly, the distal runoff, as characterized by the coronary score, did not affect the velocity pattern. Even though a better diastolic score was observed in vessels with larger runoff (scores of 2 and 3), this did not reach statistical significance (Fig. 3).

Postoperative Follow-up
All patients had an uneventful postoperative course. No perioperative MI was recorded on routine electrocardiography and cardiac isoenzyme (CK-MB) values remained less than the critical level for MI in our institution at 1 hour (44 ± 17 IU/L, maximum, 80 IU/L) and 16 hours (23 ± 9 IU/l, maximum, 36 IU/L).


DISCUSSION

The pulsatile aspect of coronary blood flow has been recognized since the seventeenth century.11 The arterial and venous flows are generally out of phase, which indicates a change in intramyocardial blood volume during the heart cycle.12, 13 The arterial blood flow decreases during systole whereas venous blood flow increases. These changes appear mostly related to changing stiffness of the heart muscle, rather than pressure in the pumping chamber of the heart, although controversy still exists.14-16 Coronary blood flow pattern is more affected in the left than the right coronary arteries. Right coronary artery flow follows the aortic pressure during systole in contrast to the left coronary arterial flow that is submitted to "systolic inhibition".17 Experimentally, these differences are abolished when the right side of the heart is facing pulmonary hypertension, which supports the cavity pressure concept.


Other experimental evidence suggests that the myocardial tissue pressure decreases from ventricular pressure in the subendocardium to atmospheric pressure in the subepicardium, explaining the subendocardial flow reduction observed in vivo.18,19 Noninvasive evaluation of coronary blood flow has confirmed the biphasic pattern of these arteries.20 On Doppler echocardiography blood flow in the LAD displays a monophasic peak in early systole followed by a rapid falling, the former corresponding to the first heart sound and the latter to the second heart sound. Diastole is characterized by an abrupt increase, maximal in early diastole, that gradually decreases thereafter.

The predominant diastolic flow pattern of the ITA graft supplying the coronary arterial network has been previously recognized.7, 21 By Doppler assessment, the in situ ITA is mainly perfused during systole, as shown in our study, and displays a high resistance flow velocity pattern (strong systolic peak, negative or absent protodiastolic velocity, and low diastolic peak). Once grafted to the left coronary network, the ITA flow pattern instantly adapts to the left ventricular hemodynamics. As shown in Fig. 1, the Doppler shift frequency drops during systolic phase and becomes more prominent during diastolic phase as left ventricular and wall tension decreases. This "diastolization" of the ITA blood flow is also related to the low resistance and large capacitance of the coronary artery network and to the ITA self-regulated property on vascular tone. Fusejima and associates,22 combining two-dimensional and Doppler echocardiography, compared postoperative hemodynamics of saphenous vein and ITA coronary bypass grafts to the LAD. They found a higher diastolic velocity with ITA graft compared with saphenous vein graft, suggesting a smoother flow pattern with no stagnation with the former conduit. They attributed this observation to a better caliber match between the ITA graft and the coronary artery.


Compared with the saphenous vein, the intima of the ITA releases larger amounts of endothelium-derived relaxing factor, such as nitric oxide, which accounts for the vasodilating capacity of this conduit.23 In large arteries, endothelial cells mediate flow- dependent release of endothelium-derived relaxing factor, then initiate a self-dependent compensatory mechanism in situations of increased needs.24, 25 Clinically, it has been reported that the ITA grafts could adjust their diameter to coronary flow demand.26 Our observations also confirm that, under resting conditions, right and left ITA flow patterns are quite constant from one patient to another. Surgical dissection significantly affects ITA flow as shown by a 40% drop in systolic frequency although the phasic pattern remains unaffected. This is mostly caused by side branch ligations and distal vasospasm during manipulation. This also reflects the clinical observation of a decreased ITA free blood flow after dissection that is normally overcome by the use of vasodilating agents.3


Neither the runoff score nor the vascular network (LAD versus circumflex) affected the ITA velocity after grafting, although a trend toward better diastolic flow was seen with a higher score. De Bono and colleagues,27 assessing ITA to coronary artery graft blood flow by transcutaneous ultrsonography, reported similar observations. They found a positive correlation between ITA graft flow velocity and quality of coronary arterial bed, confirming again the dynamic physiological adaptability of the ITA.27 Nasu and colleagues10 have suggested that systolic velocity peak depends on ITA pedicle side branches and consequently is less affected than diastolic velocity by the coronary flow. The variable amount of side branches left after pedicle dissection may account for the systolic Doppler shift variability observed from one conduit to another (as shown in Fig. 2, A and B). Analyzing phasic flow patterns, Bandyk and associates21, showed that anastomotic stricture or pedicle torsion were identified by low or absent diastolic flow whereas ITA vasospasm was associated with a sustained high-velocity flow during the cardiac cycle.

Clinical outcome was excellent for all of our patients. However, because no routine coronary arteriography was done, one cannot extrapolate the predictive value of these observations on long-term patency. Nevertheless, considering an average probe angle of 75 degrees (such a wide angle had to be used to ensure optimal probe contact with ITA pedicle) and an average diastolic frequency of 0.83 KHz, we can estimate an average flow velocity of 32 cm/sec, which approximates the LAD velocity of 33.5 ± 5.1 cm/sec found by Fusejima20 in normal subjects. Because the velocity pattern in native recipient LAD and ITA graft has been reported to be quite comparable we may conclude that the value found in our study truly reflects a normal ITA graft flow (appendix). Consequently, despite its limitation, Doppler frequency shift assessment of the coronary phasic flow may provide the surgeon with a valuable piece of information on ITA to coronary artery bypass physiologic conditions by allowing evaluation of ITA patency before harvesting and of ITA graft patency after coronary revascularization. Other authors have used pulsed Doppler ultrasonography coupled to a vessel cuff to evaluate ITA to coronary artery bypass flow with good success.28 The use of a cuff allows direct flow measurement although more ITA dissection and manipulation are needed. The continuous Doppler apparatus we used in the study is a simple and inexpensive piece of equipment that can be used by vascular and cardiac surgeons and does not necessitate any ITA dissection. The velocity quantification through the Doppler shift frequency obtained is valuable complementary information to clinical evaluation.

In conclusion, intraoperative assessment of ITA grafts before and after coronary bypass by continuous Doppler assessment is a useful noninvasive technique. It allows phasic quantification of the ITA graft flow pattern and a better understanding of myocardial physiologic processes. It may help in detecting preexisting pathologic conditions of the ITA and intraoperative technical errors.

REFERENCES

1.       Galbut DL, Traad EA, Dorman MJ, et al.12 year experience with bilateral internal mammary artery grafts. Ann Thorac Surg 1985; 40: 264-70.

2.       Barner HB, Standeven JW, Reese J. 12 year experience with internal mammary artery for coronary artery bypass. J. Thorac Cardiovasc Surg 1985; 90: 668-75.

3.       Louagie YAG, Haxhe J-P, Buche M, Schoevaerdts J-C, Intraoperative electromagnetic flow meter measurements in coronary artery bypass grafts. Ann Thorac Surg 1994; 57: 357-64.

4.       Beard JD, Scott DJA, Evans JM, Skidmore R, Horrocks M. A Doppler flowmeter for use in vascular surgery. Proc Biol Eng Soc 1988;6-12.

5.       Simpson IA, Spyt TJ, Wheatley DJ, Cobbe SM. Assessment of coronary artery bypass graft flow by intraoperative Doppler ultrasound technique. Cardiovac Res 1988;22: 484-8.

6.       Bandyk DF, Galbraith TA, Haasler GB, Almassi GH. Blood flow velocity of internal mammary artery and saphenous vein grafts to the coronary arteries. J Surg Res 1988; 44: 342-51.

7.       Van der Meulen J, van Son JAM, van Asten WNJC, Skotnicki SH, Lacquet LK. Intraoperative Doppler spectrum analysis of blood flow in the internal mammary artery used for myocardial revascularization. Thorac Cardiovasc Surg 1991; 39: 281- 3.

8.       Fujiwara T, Kajiya F, Kanazawa S, et al. Comparison of blood flow velocity waveforms in different coronary artery bypass grafts; sequential saphenous vein grafts and internal mammary artery grafts. Circulation 1988; 78: 1210-7.

9.       Doppler C. Uber das farbige Licht der Doppelsterne und einiger anderer Gestrine des Himmels, Prague; Abhandinger der koniglichen bohmischer Gessellsghaft der Wissenschafter, 1842: 465.

10.    Nasu M, Akasaka T, Okazaki T, et al. Postoperative flow characteristics of left internal thoracic artery grafts. Ann Thorac Surg 1995; 59: 154-62.

11.    Scaramucci J. De motu cordis, theorema sexton. Theoremata Familiara de physico- medicics lucubrationibus Iucta leges mechanicas. 1695: 70-81.

12.    Sabiston DC, Jr, Gregg DE. Effect of cardiac contraction on coronary blood flow. 1957; 15: 14-20.

13.    Spaan Jae, Bruinsma P, Laird JD. Coronary flow mechanics of the hypertrophied heart. In: Terkeurs HEJD, Schipperheijn JJ, rds. Cardiac left hypertrophy. Dordrecht, The Netherlands: Martinus Nijhoff, 1983: 171-201.

14.    Krams R, Sipkema P, Zegers J, Westerhof N. Contractilty is the main determinant of coronary systole flow impediment. Am J Physiol 1989; 257: H1936-44.

15.    Krams R, Sipkema P, Westerhof N. Varying elastance concept may explain coronary systolic flow impediment. AM J Physiol 1989; 257: H1471-9.

16.    Spaan JAE, Breuls NPW, Laird JD. Diastolic-systolic coronary flow differences are caused by7 intramyocardial pump action in the anesthetized dog. Circ Res 1981; 49: 584-93.

17.    Lowensohn HS, Khouri EM, Greegg DE, Pyle RL, Patterson RE. Phasic right coronary artery flow in conscious dogs with normal and elavated right ventricular pressures. Circ Res 1976; 39: 760-6.

18.    Arts T, Veenstra Pc, Reneman RS. Epicardial deformation and left ventricular wall mechanics during ejection in the dog. Am J Physiol 1982; 243: H379-90.

19.    Heineman FW, Grayson J. Transmural distribution of intramyocardial pressure measured by micropipette technique. Am J Physiol 1985; 249: H1216-23.

20.    Fusejima K. Noninvasive measurement of coronary artery blood flow using combined two- dimensional and Doppler echocardiography. J Am Coll Cardiol 1987; 10: 1024-31.

21.    Bandyk DF, Galbraith TA, Haasler GB, Almassi GH. Blood flow velocity of internal mammary artery and saphenous vein grafts to the coronary arteries. J Surg Res 1988; 44: 342-51.

22.    Fusejima K, Takahara Y, Sudo Y, et al. Comparison of coronary hemodynamics in patients with internal mammary artery and saphenous vein coronary artery bypass grafts: a noninvasive approach using combined two- dimensional and Doppler echocardiography. J AM Coll Cardiol 1990; 15: 131-9.

23.    Luscher TF, Diedrich D, Siebenmann R, et al Differences between endothelium- dependant relaxation in arterial and in venous coronary bypass grafts. N Engl J Med 1988;319: 462-7.

24.    Kaiser L, Hull SS, Sparks HV Jr. Methylene blue and ETYA block flow- dependent dilation in canine femoral artery. Am J Physiol 1986; 250: H974-81.

25.    Kaiser L, Sparks HV Jr. Mediation of flow- dependent arterial dilution by endothelial cells. Circ Shock 1986; 18: 109-14.

26.    Singh RN, Beg RA, Kay EB. Physiological adaptability: the secret of success of the internal mammary artery grafts. Ann Thorac Surg 1986; 41: 247-50.

27.    De Bono DP, Samani NJ, Spyt TJ, Hartshorne T, Thrush AJ, Evans DH. Transcutaneous ultrasound measurement of blood flow in internal mammary artery to coronary artery grafts. Lancet 1992; 339: 379-81.

28.    Louagie YAG, Haxhe JP, Jamart J, Buche M, Schoevaerdts JC. Intraoperative assessment of coronary artery bypass grafts using a pulsed Doppler flow meter. Ann Thorac Surg 1994; 58: 742-9.


APPENDIX

Velocity (V) is obtained by the equation

V = C x Df / 2fo x Cosq, where C is the sound velocity (1.56x 105 cm/sec) in blood, Df the Doppler shift in kilohertz (0.83), fo the transmitted frequency by the probe (8x103 KHz), and q the angle which sound beam intersects velocity vector (75 degrees).

 

  (1.56 x 105 cm/sec) x (0.83 KHz)          

 

 

V =         2 x (8 x 103 KHz) x (Cos 75°)       = 32 cm/sec

 

(Kempczinski RF, Yao JST, eds. Practical noninvasive vascular diagnosis. 2nd ed. Chicago, London, Boco Raton: Year Book Medical Publishers, 1987:44-55)

 

 

 

ARTERIAL DISEASE OF THE LOWER EXTREMITIES

This first article of a series reviews test techniques to identify and characterize occlusions of the leg arteries.

DALE BUCHBINDER, MD AND D. PRESTON FLANIGAN, MD

Whether used in the primary-care setting or in the vascular laboratory after referral, non-invasive arterial tests provide reliable, reproducible data that can confirm a diagnosis, clearly related symptoms to anatomy, and guide the angiographer, should invasive studies prove necessary. Such data not only aid in planning for surgery, when required, but also serve as a baseline for immediate postoperative comparisons and for long-term follow-up. This month's article will review noninvasive strategies for assessing arterial disease of the legs. Subsequent installments of the series will describe tests for venous thrombosis and for head-and-neck arterial disease. Our recommendations will be in accord with the protocols of the University of Illinois vascular laboratories, which perform more than 10,000 blood-flow studies each year.

LIMITATIONS OF EXAMINATION

Intermittent claudication suggests arterial disease; rest pain means that it is severe. The differential diagnosis, however, must include such other disorders as diabetic neuropathy, phlebitis, myositis, tendinitis, rupture of the plantaris tendon, other trauma, skeletal abnormalities, pseudoclaudication, and osteoarthritis (table).

Often, the individual's account of the onset, location, and duration of pain will strongly suggest one of these other causes. The pain of pseudoclaudication, for example, does not follow the predictable pattern of true claudication: The type and amount of exercise necessary to produce pain varies; it lasts longer than the pain of occlusive disease and is not relieved solely by resting. When such neurologic symptoms as bilateral numbness or paresthesias in the legs or feet accompany unilateral claudication, consider the possibility of undiagnosed diabetes.

Inspection of the extremities may disclose evidence of occlusive disease, but generally not until eschemia is already severe. At that point, the affected limb may feel cool, and be characterized by dry, scaly, or thin skin; scant hair; and thickened toenails. Color changes - pallor after the foot is elevated, rubor after it's brought down - and venous filling time of more than 15 seconds are further diagnostic indications.

NONISCHEMIC CAUSES OF LEG PAIN


Diabetic neuropathy
Myositis-tendinitis
Nocturnal cramps
Osteoarthritis
Phlebitis
Ruptured or strained plantaris tendon
Skeletal abnormalities
Trauma (old or new)

Diminished or absent pulses may indicate occlusion. Palpate from the femoralis down to the dorsalis pedis artery. Auscultate for bruits over the lower abdomen and the femoral artery.

When symptoms and examination findings are suggestive, non-invasive testing is indicated to provide more-definitive and quantitative evidence of a vascular problem. Researchers found little correlation between the results of palpating femoral pulses and the significance of occlusive disease. (1)

SEGMENTAL PRESSURES

The standard battery of tests for evaluating arterial flow in the legs begins with segmental Doppler pressures and calculation of an ankle/brachial index (ABI). Properly sized blood pressure (BP) cuffs are placed at the ankle, calf, lower thigh (above the knee), and upper thigh. Pressures at each location are taken with a Doppler ultrasound flow detector. The ABI is derived from the ratio of ankle to brachial pressures. In the supine position, the ratio is normally 1.0. Values between 0.71 and .096 suggest mild ischemia, 0.31 to 0.7 moderate ischemia, and 0.0 to 0.3 severe ischemia. (2)

Although ABI is generally a reliable indicator of arterial flow at rest, patients with hemodynamically subcritical arterial stenoses may have normal resting pressures. These individuals usually require additional testing - as described later in this article - to locate and evaluate such lesions.

The value of segmental pressures is also limited in the elderly and in diabetics whose vessels are calcified and not normally compressible. The use of a directional Doppler ultrasound recorder is helpful for assessing blood flow in non-compressible vessels. The normal Doppler arterial wave is triphasic (figure 1): The first portion, with its steep peak, represents the high flow of systole. The second portion, dipping down, indicates the reverse flow in early diastole. The third segment of the wave, a small peak, represents the small forward flow of later diastole (aortic recoil).

FIGURE 1. The normal triphasic Doppler arterial wave has an initial steep peak, representing the high flow of systole. The second portion, dipping down, indicates the reverse flow in early diastole. The third segment of the wave, a small peak, signifies the forward flow of late diastole.

In contrast, the wave form recorded below a point of arterial stenosis or occlusion changes to a biphasic or monophasic pattern (figure 2). Uptake is slower, no reverse flow can be seen, and the second and third wave components are lost. Collateral circulation also produces this same pattern of flow.

FIGURE 2. The wave form recorded below a point of arterial stenosis or occlusion changes to a biphasic or monophasic pattern. Uptake is slower, no reverse flow can be seen, and the second and third wave components are lost.

Thus, normal resting pressures but abnormal Doppler waveforms in patients strongly suggest segmental large-vessel disease. A decreased popliteal wave in the presence of a normal femoral wave, for example, would indicate occlusion or stenosis of the superficial femoral artery. Progressive degeneration in wave forms and pressures seen segmentally down the leg would signal multisegmental disease (figures 3 and 4).

TRANSMETATARSAL AND TOE PRESSURES

Segmental pressures can also be used to evaluate circulation between the ankle and toes. Segmental pressures are obtained with a photoplethysmograph instead of Doppler ultrasound. A photosensitive transducer is placed on the toe and a small cuff is placed around the metatarsal area. The cuff is inflated until the wave form recorded by the plethysmographic transducer is obliterated. When the cuff is deflated, the systolic transmetatarsal pressure can be measured. Similarly, smaller cuffs can be wrapped around the toes, with transducers placed distal to the cuffs. This procedure can be used to obtain individual toe pressures (figures 5 and 6).

 

Normally, toe pressures should be at least 60% of systemic pressure. (3) The absolute toe and transmetatarsal pressures correlate with the potential for healing after toe or forefoot amputations. Pressures as low as 20 mmHg in the toes and between 20 mm and 40 mmHg at the transmetatarsal region may be associated with adequate healing after amputations at their respective levels. (4,5) Ankle pressures may be normal, yet large gradients occur between the ankle, transmetatarsal, and toe pressures, should there be incomplete pedal arches or should small-vessel disease exist at the level of the foot or toes.

STRESS TESTING

The aforementioned tests provide information about lower-extremity circulation at rest but do not reflect the dynamic state and may, in fact, be misleading if patients have hemodynamically subcritical stenoses. Therefore, it is necessary to evaluate blood flow after stress or exercise.

The treadmill test is the most commonly used technique. Segmental pressures and Doppler tracings are first recorded at rest. The patient then steps onto a treadmill adjusted to a rate of one-and-a-half miles per hour, and set at a 12º incline. After five minutes' walking, ankle pressures are retaken.

Patients who cannot tolerate treadmill exercise can be tested, instead, with a pedal ergometer. (6) Inducing reactive hyperemia is an alternative test for those who are not able to exercise. A BP cuff, wrapped around the thigh, is inflated to above systolic pressure for three to five minutes. When the cuff is released, leg BPs are measured again. Because ischemia causes vasodilation, producing an effect similar to stressing the leg with exercise, this procedure can also demonstrate stenoses that are not hemodynamically significant at rest.

KEYPOINTS


When such neurologic symptoms as bilateral numbness or paresthesias in the legs or feet accompany unilateral claudication, suspect undiagnosed diabetes.


Diminished or absent pulses indicate occlusion; to pursue the finding, palpate from the femoralis down to the dorsalis pedis artery.

PAPAVERINE TESTING

In patients with suspected aortoiliac disease despite normal resting blood flow, intra-arterial pressure monitoring and papaverine testing facilitate assessment of the aortoiliac system. These procedures are minimally invasive.

Under sterile conditions, a small arterial cannula is placed in the common femoral artery and connected to a pressure transducer after an injection of 20 mg papaverine HCI, diluted to 10 mL in normal saline, pressures are recorded via the transducer. At the same time, a directional Doppler probe, positioned below the injection site, records Doppler velocity tracings. This technique detects arterial flow elevations, indicated by increases in velocity, and drops in the femoral/brachial index. A greater than 15% decrease in the femoral/brachial indices (7) or an increase in arterial flow of less than 100% indicates a hemodynamically significant stenosis proximal to the site of the papaverine injection.

Papaverine testing is particularly helpful for evaluating the hemodynamics of the iliac system when a femorofemoral bypass may be required. Abnormal results indicate that the artery is not a suitable donor vessel. The procedure is also useful in preoperative planning for patients with multisegmental vascular disease. Demonstrating hemodynamic soundness of the iliac artery, for example, would indicate that only a distal procedure is needed. Disclosure of hemodynamically abnormal aortoiliac arteries might also call for an inflow procedure.

PENILE PERFUSION

Noninvasive evaluation of penile blood flow may be warranted to rule our vascular cause of impotence. A photoplethysmographic sensor is placed on the glans of the penis and a small BP cuff around the base can measure penile pressure, and a penile/brachial index (PBI) can be calculated. (5) An index of greater than 0.7 is considered evidence of adequate penile blood flow, ruling out vascular causes of impotence. A PBI of less than 0.7 indicates decreased blood flow, but the possible role of medications, diabetes, and other factors must be considered before importence can be attributed to vascular problems.

CLINICAL APPLICATIONS

In patients with exercise-induced leg pain, a finding of absent, diminished, or equivocal pulses is bound to raise the possibility of arterial insufficiency. When the pulses seem normal, however, noninvasive testing will distinguish arterial insufficiency from other causes of leg pain.

Another valuable application of these procedures is documenting the severity of disease. This is particularly important when symptoms, such as rest pain, might signify either severe ischemia or significant neuropathy. The noninvasive laboratory will document whether there is a significant amount of ischemia present. Most patients with claudication usually have absolute ankle/brachial pressures between 70 mm and 100 mmHg, and ABI's of 0.5 to 0.8. Those with rest pain or gangrene usually will have absolute ankle pressures of less than 50 mmHg and ABIs of 0.3 or less. (8) Patients with diabetes mellitus, Buerger's disease, and chronic renal failure may have stiffer, calcified vessels, and their pressures may be falsely high for the extent of disease. (2)

These tests are reasonably accurate, too, in pinpointing the specific site of disease. For example, superficial femoral artery occlusion is diagnosed in patients with normal upper-thigh pressures and Doppler tracings, decreased popliteal tracings, and decreased calf pressures. Suspect aortoiliac disease when femoral tracings are abnormal and upper-thigh pressures are decreased. The latter finding, however, may also be associated with high superficial femoral occlusions and profunda femoris disease. Normal popliteal results and decreased ankle tracings point to tibial vessel disease. In general, a pressure gradient of 30 mmHg or more between segments indicates arterial occlusive disease somewhere between the two pulse points.

Segmental pressures are also valuable in planning therapy, as they can help predict the likelihood that foot lesions and amputations will heal. In one study, foot lesions healed in 92% of nondiabetic patients and in 76% of diabetic patients when ankle pressures were less than 55 mmHg, unless patients underwent arterial reconstruction. Virtually all foot ulcers healed in nondiabetics who had toe pressures of 30 mmHg or more; 94% of lesions healed in diabetics whose toe pressures exceeded 55 mmHg. (9) In general, spontaneous healing of foot ulcers is likely, and conservative therapy should be attempted if ankle pressure is more than 55 mmHg in nondiabetics and 80 mmHg in diabetics.

In several studies, healing of below-knee amputations occurred in 88% to 100% of patients with calf pressures greater than 60 mmHg. (10, 11, 12) Because diabetics' vessels may be calcified, yielding falsely high readings, it is extremely important to use these values cautiously in planning amputations: In one study, only 10% of below-knee amputations healed when calf pressures were less than 55 mmHg. (13)

Finally, these non-invasive tests are powerful tools for long-term follow-up, to identify the causes of changes in symptoms, to track the progression of disease, and to identify patients who are candidates for arterial reconstructive surgery. At the University of Illinois, we retest such surgical patients at three-month intervals for the first two years after surgery, every six months for the next two years, and annually after that. In persons with functioning arterial grafts, slight changes in Doppler wave forms and decreases in segmental pressures represent early warnings of restenosis. These studies have led to timely diagnosis of impending failure of the graft in several patients. As a result, problems were easily corrected by minor surgical procedures so that vascular grafts, along with the patients' extremities, were salvaged.

REFERENCES

1. Sobinsky, KR, Borozan, PG, Gray, B, et al; Is femoral pulse palpation accurate in assessing the hemodynamic significance of aortoiliac occlusive disease? Am J Surg 148:214, 1984

2. Kempczinsky, RF; Clinical application of noninvasive testing in extremity arterial insufficiency. In: Kempczinsky, RF, and Yao, JST, eds:; Pratical Noninvasive Vascular Diagnosis. Yearbook Medical, Chicago, 1982, pp 343-367.

3. Bridges, RA, and Barnes, RW; Segmental limb pressures. In: Kempczinsky, RF, and Yao JST, eds: Practical Noninvasive Vascular Diagnosis. Yearbook Medical, Chicago, 1982, pp 79-93.

4. Schwartz, JA, Schuler, JJ, O'Connor, RJA, et al; Predictive value of distal perfusion pressure in the healing of amputation of digits and the forefoot. Surgery 154:865, 1982.

5. LaRosa, MP, Buchbinder, D, Gray B, et al; Penile arterial study by photoplethysmography. Bruit 8:225, 1984.

6. Sobinsky, KR, Williams, LR, Gray, B, et al; Supine exercise testing in the selection of suprainguinal versus infrainguinal bypass in patients with multisegmental arterial occlusive disease (presented at the 1984 meeting of the Association of Veterans administration surgeons).

7. Williams, LR, Gray, B, Ryan, TJ, et al; Preoperative hemodynamic assessment of multisegmental lower extremity arterial disease using papaverine hydrocloride. Bruit 8:19, 1984.

8. Yao, JST; New techniques in objective arterial evaluation. Arch Surg 106:600, 1973.

9. Carter, SA; The relationship of distal systolic pressures to healing of skin lesions in limbs with arterial occlusive disease, with special reference to diabetes mellitus. Scand J Clin Lab Invest 31 (suppl.128):239, 1973.

10. Raines, JK, Darling, RC, Buth, J, et al; Vascular laboratory criterial for the management of peripheral vascular disease of the lower extremities. Surgery 79:21, 1976.

11. Dean, RH, Yao, JST, Thompson, RC, et al; Predictive value of ultrasonically derived arterial pressures in determination of amputation level. Am J Surg 41:731, 1975

12. Barnes, RW, Shanik, GD, and Slaymaker, EE; An index of healing in below-knee amputation. Surgery 79:13, 1976.

13. Gibbons, GW, Wheelock, FC, Jr, Siembieda, C, et al; Noninvasive prediction of amputation level in diabetic patients. Arch Surg 114:1253, 1979.