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Can Ulnar Artery Velocity Changes Be Used as a Preoperative Screening Tool for Radial Artery Grafting in Coronary Artery Bypass?
Can Ulnar Artery Velocity Changes Be Used as a Preoperative Screening Tool for Radial Artery Grafting in Coronary Artery Bypass? V.V. Sullivan, MD,1 C. Higgenbotham, RDMS, RVT,1 C.J. Shanley, MD,2 J. Fowler, RN,1 R.M. Lampman, PhD,1 W.M. Whitehouse, Jr., MD,1 and S.W. Wolk, RVT, MD,1 Ann Arbor and Royal Oak, Michigan
Radial artery harvesting for coronary revascularization may result in digit ischemia if collateral circulation is inadequate. The purpose of this study was to compare changes in ulnar artery flow velocity during radial artery compression (RAC) with changes in first- and second-digit pressures during RAC, a previously validated predictor of digital ischemia. Photoplethysmography was used to measure first- and second-digit arterial pressures before and during RAC on 80 extremities. Color flow duplex imaging was used to measure distal ulnar artery peak systolic velocity before and during RAC. Seventy-eight of eighty extremities had a slight increase in ulnar artery velocity with RAC. There was no correlation between ulnar artery velocity changes and digit pressure changes. Measurement of ulnar artery velocity during RAC is not a useful predictor of digit pressure changes. Measurement of segmental upper extremity pressures with first- and second-digit pressure measurement during radial artery compression should remain the preferred preoperative screening tool for radial artery harvest prior to CABG.
INTRODUCTION Over 170,000 coronary artery bypass grafting (CABG) procedures are performed in the United States each year.1 Carpentier et al. popularized the use of the radial artery as a conduit for CABG in the early 1970s.2 This conduit was initially abandoned secondary to high occlusion rates. With the advent of atraumatic harvesting techniques and the use of 1 Section of Vascular Surgery, Department of Surgery, Michigan Heart and Vascular Institute, St. Joseph Mercy Hospital, Ann Arbor, MI. 2
Department of Surgery, Beaumont Hospital, Royal Oak, MI.
Presented at the 25th World Congress of the International Society for Cardiovascular Surgery, Cancun, Mexico, September 10, 2001. Correspondence to: S.W. Wolk, RVT, MD, St. Joseph Mercy Hospital, Department of Surgery, 5333, McAuley Drive, RHB-2111, P.O. Box 995, Ann Arbor, MI 48106, USA, E-mail: [email protected] Ann Vasc Surg 2003; 17: 253-259 DOI: 10.1007/s10016-001-0248-8 Annals of Vascular Surgery Inc. Published online: 22 April 2003
calcium channel blockers and nitrates to minimize vasospasm during radial artery harvest, there has been renewed interest in radial artery conduits for CABG.3-11 Both short- and long-term patency rates for radial artery conduits approach those of internal mammary artery conduits and are superior to those for greater saphenous conduits.4,5,12 With the increasing need to find alternative conduits, a dramatic increase in radial artery harvesting has occurred. Concurrently, the potential for digit ischemia has become a concern, exemplified by recent reports of digit ischemia13 and reduced digit perfusion14 after radial artery harvest. The radial and ulnar arteries normally communicate in the hand through the superficial palmar arch (SPA) and deep palmar arch (DPA). However, Doppler ultrasound,15-17 arteriographic,18 and autopsy studies19 have found incomplete arches in 11-66% of individuals. These studies suggest that some patients may be at significant risk for severe 253
254 Sullivan et al.
digit ischemia after radial artery harvesting.13 An objective and standardized method needs to be established to accurately predict adequacy of digit perfusion, should the radial artery be harvested. Such a screening method should not underestimate potential conduit donors yet must accurately predict the risk for digit ischemia. Pressure changes in first and second digits during radial artery compression (RAC) have been recently validated as an objective but technically demanding method for preoperative radial artery harvest evaluation.20,21 The purpose of this study was to compare ulnar artery velocity changes during RAC with first- and second-digit pressures changes during RAC in an attempt to develop a simpler preoperative screening method prior to radial artery harvest for CABG.
METHODS Forty normal subjects volunteered for this study and were recruited via notices posted throughout the medical center. Informed consent was obtained from each subject prior to participation in this study according to the guidelines and approval of the Institutional Review Board, St. Joseph Mercy Hospital. Exclusion criteria included a history of known vasospastic disorders, peripheral vascular occlusive disease, or significant tobacco use. A single registered vascular technologist (RVT) examined 80 upper extremities in 40 volunteers without knowledge of recorded parameters of interest. Values were recorded independently by one of the co-investigators. The examination was performed with the subject in a supine position. A temperature probe was placed on the index finger and a heating pad was placed on the hand to maintain skin temperature between 36 and 37.5C for all studies. Equilibration of temperature was allowed for 5 min prior to initiation of measurements. Segmental upper extremity arterial pressures were measured for the brachial, radial, and ulnar arteries to exclude a proximal stenosis. Digit arterial blood pressure measurements were obtained before and during RAC using 2.5-cm digit pressure cuffs placed around the proximal phalynx of the first and second digits using a photoplethysmography (PPG) probe attached to the distal phalynx of these digits. All digit pressure measurements preceded the ulnar artery velocity measurements. A minimum of 5 min was allowed to elapse prior to measuring flow velocities before and during RAC. Pressure readings were processed through a digital recording system
Annals of Vascular Surgery
(Nicolet VasoGuard, Golden, CO) for 10 individuals (20 extremities) and through an analog system (DEC PC CP 4335x, Bellevue, Washington) for 30 patients (60 extremities). A 15L 8-MHz continuous wave Doppler probe was used to compress the radial artery at the wrist to ensure complete radial artery occlusion for 15 sec prior to and during a repeat digit pressure measurement. Identical procedures were performed on the contralateral extremity. Ulnar artery peak systolic velocity (PSV) was measured using color flow duplex imaging of the distal ulnar artery at the level of the wrist (Sequoia 128, Acuson, Mountain View, CA). A 15L 8-MHz continuous wave Doppler probe (Parks-Mini Lab IV model 3000-LA, Aloha, OR) was used to compress the radial artery at the wrist to ensure complete radial artery occlusion for 15 sec prior to and during a second ulnar artery PSV measurement. The same tests were repeated on the contralateral extremity. A random sample of 20 subjects of the total 40 subjects served as a subgroup to assess reproducibility of the digit pressure and ulnar artery PSV measurements. Two separate identical measurements were made, 1 hr apart, using the analog system for the first 10 subjects and the digital system for the second 10 subjects. The use of two different PPG systems allowed for examination of reproducibility for each system. All statistical analyses were conducted with JMP for Windows version 4.0.0 (SAS Institute Inc., Cary, NC). The reproducibility of digit pressure measurements was examined with Pearson’s correlation coefficients and paired t-tests. The correlation coefficient measured overall association between repeated tests for the parameters of interest and was used to determine if a relationship existed for the total cohort (n = 80 extremities) between changes in digit pressure (digits 1 and 2) and changes in ulnar artery PSV during RAC. Paired t-tests assessed whether a significant difference existed between the mean values of continuous parametric variables.
RESULTS Descriptive Statistics There were 35 female and 5 male Caucasian participants. Mean age was 35.9 ± 7.8 years (range, 23-58 years). There was no statistically significant difference between the mean ages of subjects when stratified by gender (unpaired t-test). The dominant hand was right in 30 subjects and left in 10.
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Preoperative screening for radial artery grafting in CABG 255
Table I. Correlation coefficient (r) and significance (p) for reproducibility study (initial vs. 1-hr repeat measurement) DP (mmHg) = digit pressure ) digit pressure during RAC Extremity
First digit
Second digit
DV (m/sec) = ulnar artery PSV ) ulnar artery PSV during RAC
Dominant hand (n = 40) Nondominant hand (n = 40) Dominant + nondominant hand (n = 80)
0.7 (p < 0.01) 0.73 (p < 0.01) 0.72 (p < 0.01)
0.38 (p = 0.10) 0.76 (p < 0.01) 0.59 (p < 0.01)
0.33 (p = 0.16) 0.41 (p = 0.07) 0.37 (p = 0.02)
Table II. Correlation coefficient (r) and significance (p) for analog vs. digital PPG systems DP (mmHg) = digit pressure ) digit pressure during RAC System
First digit
Second digit
Analog system (n = 20) Digital system (n = 20)
0.53 (p = 0.02)
0.6 (p < 0.01)
0.82 (p < 0.01)
0.7 (p < 0.01)
Test Reproducibility Twenty of the 40 normal volunteers were studied. Repeated change in digit pressure (DP = digit pressure ) digit pressure during RAC) for both hands correlated for the first digit (r = 0.72; p < 0.01) as well as the second digit (r = 0.59; p < 0.01) (Table I). Student’s t-test results showed no difference between the initial test and the repeat 1-hr test (first digit, p = 0.l5; second digit, p = 0.24). Reproducibility was also compared using different PPG systems—analog and digital (Table II). The analog system had a lower overall correlation for digit pressures between the initial test and the 1-hr retest (first digit DP: r = 0.53, p = 0.02 and second digit DP: r = 0.6, p < 0.01), whereas the digital system showed a close relationship (first digit DP: r = 0.82, p < 0.01 and second digit DP: r = 0.7, p < 0.01). Ulnar artery PSV changes (DV = ulnar artery PSV ) ulnar artery PSV during RAC) for dominant plus nondominant extremities correlated significantly between the initial test and the 1-hr test (r = 0.37, p = 0.02), though to a lesser degree than the digit pressures (Table I). Change in Digit Pressures versus Change in Ulnar Artery PSV Forty normal volunteers (80 extremities) were included. The mean ± SD are grouped by dominant
Fig. 1. First-digit pressure changes versus ulnar artery PSV changes during radial artery compression.
hand versus nondominant hand (Table III). There was little correlation (r = )0.16, p = 0.17) between the first DP and the ulnar artery PSV changes (DV = ulnar artery PSV ) ulnar artery PSV during RAC) (Fig. 1). There was no correlation (r = )0.01, p = 0.95) between the second digit DP and the ulnar artery PSV changes (DV) (Fig. 2).
DISCUSSION The noninvasive vascular laboratory at our institution currently utilizes a preoperative screening protocol based on our previous work demonstrating the superiority of measuring digit pressure changes during RAC over results using the modified Allen’s test20,21 (Fig. 3, gray box). This protocol can be labor-intensive, requires patient cooperation, and may be difficult to complete at the bedside. The examination of ulnar artery PSV
DP; change in digit pressure; DV; change in ulnar artery PSV during radial artery compression; UA PSV; ulnar artery peak systolic velocity; w/RAC, during radial artery compression.
Second digit pressure w/RAC (mmHg) Second digit pressure (mmHg) DP first digit (mmHg) First digit pressure w/RAC (mmHg) Extremity
a
UA PSV w/RAC (m/sec)
To examine the accuracy of digit pressure reproducibility between different time points, both a digital and an analog PPG system was used for
DP second digit (mmHg)
UA PSV (m/sec)
Test-Retest Reproducibility Study
First digit pressure (mmHg)
changes to determine the patency of the SPA would simplify this protocol as digit pressures would not need to be measured in those individuals with a patent SPA (Fig. 3). If digit pressure changes stay constant during RAC, this should correspond to an increase in ulnar PSV if the SPA is complete. Conversely, individuals with an incomplete SPA should not have a significant change in ulnar artery PSV during RAC. These findings would allow individuals without a complete SPA to be easily differentiated from those with complete palmar arches. Pola et al. examined the utility of ulnar artery velocity combined with measurement of SPA and digit artery velocities via a resistance index.22 However, the relationship between these variables and the change in digit pressures was not evaluated by these authors. The difficulty in accurately insonating the SPA and DPA vessels also limits the practical utility of velocity measurements obtained from these vessels.21,23 Lohr et al. investigated the utility of ulnar artery PSV measurements and digit pressure changes in 27 patients undergoing radial artery harvest for CABG.24 They demonstrated a significant increase in ulnar artery PSV and no significant changes in first- or second-digit pressure following radial artery harvest. However, no attempt was made to examine the relationship between these measurements as was done in the present study.
Table III. Mean ± SD pressure and velocity values before and during radial artery compression
Fig. 2. Second-digit pressure changes versus ulnar artery PSV changes during radial artery compression.
Dominant hand 109.9 ± 16.4 97.2 ± 16 13.1 ± 10.8 114.7 ± 19.6 101.2 ± 21.1 13.5 ± 10.38 0.5 ± 0.18 0.74 ± 0.24 0.24 ± 0.17 (n = 40 extremities) Nondominnat 117.75 ± 14.3 104.95 ± 13.53 11.8 ± 9.15 120.6 ± 17.23 109.75 ± 15.62 10.9 ± 9.39 0.51 ± 0.11 0.76 ± 0.17 0.25 ± 0.12 hand (n = 40 extremities)
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DV UA PSV (m/sec)
256 Sullivan et al.
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Preoperative screening for radial artery grafting in CABG 257
Fig. 3. Current algorithm (gray box) versus proposed modified algorithm for preoperative screening protocol prior to radial artery harvest in CABG.
repeat measures. The overall reproducibility for the measurement of digit pressures was acceptable in this study as previously demonstrated.20 The ulnar artery PSV changes were reproducible between the two different time points with a significant, though not high, correlation. Both systems showed these measures to be reproducible, although a higher correlation was demonstrated with the digital system (Table II). Regardless, the analog system, used in most noninvasive vascular laboratories in the United States, still provides a valuable tool. It has been reported that ischemia will not likely occur unless a decrease of ‡40 mmHg occurs in digit pressure changes during RAC.20,23,25,26 Analog versus digital data were reexamined in this study. Despite somewhat lower correlation with the analog system, no subject in the reproducibility portion of this study was found to have this magnitude of a pressure drop (‡40 mmHg). This suggests that the study population had adequate ulnar blood supply to the digits. Therefore, in this study, analog or
digital measurement variability would not have made a clinical difference. One limitation of this study is the relatively small number of subjects studied. All individual extremity measurements were assumed to be independent observations; by combining dominant and nondominant extremities in this manner, overall sample size was increased. Another limitation of the present study was that subjects did not have angiographic identification of palmar arch anatomy prior to noninvasive testing, since an invasive modality would subject normal volunteers to an unacceptable risk. Change in Digit Pressures versus Change in Ulnar Artery PSV For ulnar artery PSV changes during RAC to be clinically useful, they must relate to a known measure used for preoperative radial artery screening prior to CABG. Previous work has shown
258 Sullivan et al.
that measurement of digit pressure changes in the first and second digits during RAC is more accurate and objective than the Allen’s test or the modified Allen’s test using a continuous-wave probe to insonate the SPA.20,21,23 In this study, we hypothesized that an increase in ulnar artery PSV during RAC, if associated with no significant decrease in digit pressure change during RAC, could be used instead of digit pressure measurements to predict ischemia. Individuals without an increase in ulnar artery velocities (suggesting an incomplete SPA) would only then be considered for additional measurement of digit pressures. The results of this study demonstrated that no correlation existed between the first- or seconddigit pressure changes during RAC and the change in ulnar artery PSV changes during RAC. This suggests that velocity changes cannot be used clinically to determine if digits would become ischemic if the radial artery were harvested. Until ulnar artery velocity changes and their utility in predicting an incomplete SPA are better understood, complete extremity arterial evaluation consisting of segmental pressure measurements, arterial waveform analysis, and measurement of first- and seconddigit pressure before and during RAC should remain the preferred preoperative screening tool prior to radial artery harvest for CABG.
CONCLUSION Measurement of the change in ulnar artery PSV during RAC did not predict digit artery pressures in this study. The authors do not advocate using changes in ulnar artery PSV during RAC as a sole preoperative screening tool prior to CABG. Measurement of segmental upper extremity pressures with first- and second-digit pressure measurement during RAC should remain the preferred preoperative screening tool for radial artery harvest prior to CABG.
REFERENCES 1. Database NCS. 174,906 Isolated CAB Procedure performed in US/year. Society for Thoracic Surgeons 1999. 2. Carpentier A, Guermonprez JL, Deloche A, et al. The aortato-coronary radial artery bypass graft. A technique avoiding pathological changes in grafts. Ann Thorac Surg 1973;16:111-121. 3. Acar C, Jebara VA, Portoghese M, et al. Revival of the radial artery for coronary artery bypass grafting. Ann Thorac Surg 1992;54:652-659; discussion 659–660.
Annals of Vascular Surgery
4. Acar C, Ramsheyi A, Pagny JY, et al. The radial artery for coronary artery bypass grafting: clinical and angiographic results at five years. J Thorac Cardiovasc Surg 1998;116:981-989. 5. Possati G, Gaudino M, Alessandrini F, et al. Midterm clinical and angiographic results of radial artery grafts used for myocardial revascularization. J Thorac Cardiovasc Surg 1998;116:1015-1021. 6. Manasse E, Sperti G, Suma H, et al. Use of the radial artery for myocardial revascularization. Ann Thorac Surg 1996;62:1076-1082; discussion 1082–1083. 7. Dietl CA, Benoit CH. Radial artery graft for coronary revascularization: technical considerations. Ann Thorac Surg 1995;60:102-109; discussion 109–110. 8. Fremes SE, Christakis GT, Del Rizzo DF, et al. The technique of radial artery bypass grafting and early clinical results. J Card Surg 1995;10:537-544. 9. Ronan JW, Perry LA, Barner HB, et al. Radial artery harvest: comparison of ultrasonic dissection with standard technique. Ann Thorac Surg 2000;69:113-114. 10. Kaufer E, Factor SM, Frame R, Brodman RF. Pathology of the radial and internal thoracic arteries used as coronary artery bypass grafts. Ann Thorac Surg 1997;63:11181122. 11. Chen AM, Brodman RF, Frame R, et al. Routine myocardial revascularization with radial artery: a multicenter experience. J Card Surg 1998;13:318-327. 12. Brodman RF, Frame R, Camacho M, et al. Routine use of unilateral and bilateral radial arteries for coronary artery bypass graft surgery. J Am Coll Cardiol 1996;28:959963. 13. Nunoo-Mensah J. An unexpected complication after harvesting of the radial artery for coronary artery bypass grafting. Ann Thorac Surg 1998;66:929-931. 14. Brodman RF, Hirsh LE, Frame R. Effect of radial artery harvest on colateral forearm blood flow and digital perfusion. J Thorac Cardiovasc Surg 2002;123:512-516. 15. Coleman S, Anson BJ. Arterial patterns in the hand based upon studies of 650 specimens. Surg Gynecol Obstet 1961;113:409-424. 16. Hosono M, Suehiro S, Shibata T, et al. Duplex scanning to assess radial suitability for coronary artery bypass grafting. Jpn J Thorac Cardiovasc Surg 2000;48:217-221. 17. Rodriguez E, Ormont ML, Lambert EH, et al. The role of preoperative radial artery ultrasound and digital plethysmography prior to coronary artery bypass grafting. Eur J Cardiothorac Surg 2001;19:135-139. 18. Varro J, Horvath L, Varga G. Anatomy of the hand arteries based on angiographic studies [author’s transl]. Magy Traumatol Orthop Helyreallito Seb 1978;21:127-134. 19. Doscher W, Viswanathan B, Stein T, et al. Hemodynamic assessment of the circulation in 200 normal hands. Ann Surg 1983;198:776-779. 20. Starnes SL, Wolk SW, Lampman RM, et al. Noninvasive evaluation of hand circulation before radial artery harvest for coronary artery bypass grafting. J Thorac Cardiovasc Surg 1999;117:261-266. 21. Wolk S, Moores H, Lampman R, et al. The use of preoperative noninvasive vascular studies for the evaluation of radial artery conduits for coronary artery bypass grafting. Vasc Surg 1998;32:249-253. 22. Pola P, Serricchio M, Flore R, et al. Safe removal of the radial artery for myocardial revascularization: a Doppler study to prevent ischemic complications to the hand. J Thorac Cardiovasc Surg 1996;112:737-744.
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23. Husum B, Berthelsen P. Allen’s test and systolic arterial pressure in the thumb. Br J Anaesth 1981;53:635-637. 24. Lohr JM, Paget DS, Smith JM, et al. Upper extremity hemodynamic changes after radial artery harvest for coronary artery bypass grafting. Ann Vasc Surg 2000;14:5662.
Preoperative screening for radial artery grafting in CABG 259
25. Palm T. Evaluation of peripheral arterial pressure on the thumb following radial artery cannulation. Br J Anaesth 1977;49:819-824. 26. Lassen NA. [Strain-gauge measurement of the distal systolic blood pressure in occlusive arterial conditions] Ugeskr Laeger 1975;137:365-369.
Radial artery harvesting for coronary revascularization may result in digit ischemia if collateral circulation is inadequate. The purpose of this study was to compare changes in ulnar artery flow velocity during radial artery compression (RAC) with changes in first- and second-digit pressures during RAC, a previously validated predictor of digital ischemia. Photoplethysmography was used to measure first- and second-digit arterial pressures before and during RAC on 80 extremities. Color flow duplex imaging was used to measure distal ulnar artery peak systolic velocity before and during RAC. Seventy-eight of eighty extremities had a slight increase in ulnar artery velocity with RAC. There was no correlation between ulnar artery velocity changes and digit pressure changes. Measurement of ulnar artery velocity during RAC is not a useful predictor of digit pressure changes. Measurement of segmental upper extremity pressures with first- and second-digit pressure measurement during radial artery compression should remain the preferred preoperative screening tool for radial artery harvest prior to CABG.
INTRODUCTION Over 170,000 coronary artery bypass grafting (CABG) procedures are performed in the United States each year.1 Carpentier et al. popularized the use of the radial artery as a conduit for CABG in the early 1970s.2 This conduit was initially abandoned secondary to high occlusion rates. With the advent of atraumatic harvesting techniques and the use of 1 Section of Vascular Surgery, Department of Surgery, Michigan Heart and Vascular Institute, St. Joseph Mercy Hospital, Ann Arbor, MI. 2
Department of Surgery, Beaumont Hospital, Royal Oak, MI.
Presented at the 25th World Congress of the International Society for Cardiovascular Surgery, Cancun, Mexico, September 10, 2001. Correspondence to: S.W. Wolk, RVT, MD, St. Joseph Mercy Hospital, Department of Surgery, 5333, McAuley Drive, RHB-2111, P.O. Box 995, Ann Arbor, MI 48106, USA, E-mail: [email protected] Ann Vasc Surg 2003; 17: 253-259 DOI: 10.1007/s10016-001-0248-8 Annals of Vascular Surgery Inc. Published online: 22 April 2003
calcium channel blockers and nitrates to minimize vasospasm during radial artery harvest, there has been renewed interest in radial artery conduits for CABG.3-11 Both short- and long-term patency rates for radial artery conduits approach those of internal mammary artery conduits and are superior to those for greater saphenous conduits.4,5,12 With the increasing need to find alternative conduits, a dramatic increase in radial artery harvesting has occurred. Concurrently, the potential for digit ischemia has become a concern, exemplified by recent reports of digit ischemia13 and reduced digit perfusion14 after radial artery harvest. The radial and ulnar arteries normally communicate in the hand through the superficial palmar arch (SPA) and deep palmar arch (DPA). However, Doppler ultrasound,15-17 arteriographic,18 and autopsy studies19 have found incomplete arches in 11-66% of individuals. These studies suggest that some patients may be at significant risk for severe 253
254 Sullivan et al.
digit ischemia after radial artery harvesting.13 An objective and standardized method needs to be established to accurately predict adequacy of digit perfusion, should the radial artery be harvested. Such a screening method should not underestimate potential conduit donors yet must accurately predict the risk for digit ischemia. Pressure changes in first and second digits during radial artery compression (RAC) have been recently validated as an objective but technically demanding method for preoperative radial artery harvest evaluation.20,21 The purpose of this study was to compare ulnar artery velocity changes during RAC with first- and second-digit pressures changes during RAC in an attempt to develop a simpler preoperative screening method prior to radial artery harvest for CABG.
METHODS Forty normal subjects volunteered for this study and were recruited via notices posted throughout the medical center. Informed consent was obtained from each subject prior to participation in this study according to the guidelines and approval of the Institutional Review Board, St. Joseph Mercy Hospital. Exclusion criteria included a history of known vasospastic disorders, peripheral vascular occlusive disease, or significant tobacco use. A single registered vascular technologist (RVT) examined 80 upper extremities in 40 volunteers without knowledge of recorded parameters of interest. Values were recorded independently by one of the co-investigators. The examination was performed with the subject in a supine position. A temperature probe was placed on the index finger and a heating pad was placed on the hand to maintain skin temperature between 36 and 37.5C for all studies. Equilibration of temperature was allowed for 5 min prior to initiation of measurements. Segmental upper extremity arterial pressures were measured for the brachial, radial, and ulnar arteries to exclude a proximal stenosis. Digit arterial blood pressure measurements were obtained before and during RAC using 2.5-cm digit pressure cuffs placed around the proximal phalynx of the first and second digits using a photoplethysmography (PPG) probe attached to the distal phalynx of these digits. All digit pressure measurements preceded the ulnar artery velocity measurements. A minimum of 5 min was allowed to elapse prior to measuring flow velocities before and during RAC. Pressure readings were processed through a digital recording system
Annals of Vascular Surgery
(Nicolet VasoGuard, Golden, CO) for 10 individuals (20 extremities) and through an analog system (DEC PC CP 4335x, Bellevue, Washington) for 30 patients (60 extremities). A 15L 8-MHz continuous wave Doppler probe was used to compress the radial artery at the wrist to ensure complete radial artery occlusion for 15 sec prior to and during a repeat digit pressure measurement. Identical procedures were performed on the contralateral extremity. Ulnar artery peak systolic velocity (PSV) was measured using color flow duplex imaging of the distal ulnar artery at the level of the wrist (Sequoia 128, Acuson, Mountain View, CA). A 15L 8-MHz continuous wave Doppler probe (Parks-Mini Lab IV model 3000-LA, Aloha, OR) was used to compress the radial artery at the wrist to ensure complete radial artery occlusion for 15 sec prior to and during a second ulnar artery PSV measurement. The same tests were repeated on the contralateral extremity. A random sample of 20 subjects of the total 40 subjects served as a subgroup to assess reproducibility of the digit pressure and ulnar artery PSV measurements. Two separate identical measurements were made, 1 hr apart, using the analog system for the first 10 subjects and the digital system for the second 10 subjects. The use of two different PPG systems allowed for examination of reproducibility for each system. All statistical analyses were conducted with JMP for Windows version 4.0.0 (SAS Institute Inc., Cary, NC). The reproducibility of digit pressure measurements was examined with Pearson’s correlation coefficients and paired t-tests. The correlation coefficient measured overall association between repeated tests for the parameters of interest and was used to determine if a relationship existed for the total cohort (n = 80 extremities) between changes in digit pressure (digits 1 and 2) and changes in ulnar artery PSV during RAC. Paired t-tests assessed whether a significant difference existed between the mean values of continuous parametric variables.
RESULTS Descriptive Statistics There were 35 female and 5 male Caucasian participants. Mean age was 35.9 ± 7.8 years (range, 23-58 years). There was no statistically significant difference between the mean ages of subjects when stratified by gender (unpaired t-test). The dominant hand was right in 30 subjects and left in 10.
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Preoperative screening for radial artery grafting in CABG 255
Table I. Correlation coefficient (r) and significance (p) for reproducibility study (initial vs. 1-hr repeat measurement) DP (mmHg) = digit pressure ) digit pressure during RAC Extremity
First digit
Second digit
DV (m/sec) = ulnar artery PSV ) ulnar artery PSV during RAC
Dominant hand (n = 40) Nondominant hand (n = 40) Dominant + nondominant hand (n = 80)
0.7 (p < 0.01) 0.73 (p < 0.01) 0.72 (p < 0.01)
0.38 (p = 0.10) 0.76 (p < 0.01) 0.59 (p < 0.01)
0.33 (p = 0.16) 0.41 (p = 0.07) 0.37 (p = 0.02)
Table II. Correlation coefficient (r) and significance (p) for analog vs. digital PPG systems DP (mmHg) = digit pressure ) digit pressure during RAC System
First digit
Second digit
Analog system (n = 20) Digital system (n = 20)
0.53 (p = 0.02)
0.6 (p < 0.01)
0.82 (p < 0.01)
0.7 (p < 0.01)
Test Reproducibility Twenty of the 40 normal volunteers were studied. Repeated change in digit pressure (DP = digit pressure ) digit pressure during RAC) for both hands correlated for the first digit (r = 0.72; p < 0.01) as well as the second digit (r = 0.59; p < 0.01) (Table I). Student’s t-test results showed no difference between the initial test and the repeat 1-hr test (first digit, p = 0.l5; second digit, p = 0.24). Reproducibility was also compared using different PPG systems—analog and digital (Table II). The analog system had a lower overall correlation for digit pressures between the initial test and the 1-hr retest (first digit DP: r = 0.53, p = 0.02 and second digit DP: r = 0.6, p < 0.01), whereas the digital system showed a close relationship (first digit DP: r = 0.82, p < 0.01 and second digit DP: r = 0.7, p < 0.01). Ulnar artery PSV changes (DV = ulnar artery PSV ) ulnar artery PSV during RAC) for dominant plus nondominant extremities correlated significantly between the initial test and the 1-hr test (r = 0.37, p = 0.02), though to a lesser degree than the digit pressures (Table I). Change in Digit Pressures versus Change in Ulnar Artery PSV Forty normal volunteers (80 extremities) were included. The mean ± SD are grouped by dominant
Fig. 1. First-digit pressure changes versus ulnar artery PSV changes during radial artery compression.
hand versus nondominant hand (Table III). There was little correlation (r = )0.16, p = 0.17) between the first DP and the ulnar artery PSV changes (DV = ulnar artery PSV ) ulnar artery PSV during RAC) (Fig. 1). There was no correlation (r = )0.01, p = 0.95) between the second digit DP and the ulnar artery PSV changes (DV) (Fig. 2).
DISCUSSION The noninvasive vascular laboratory at our institution currently utilizes a preoperative screening protocol based on our previous work demonstrating the superiority of measuring digit pressure changes during RAC over results using the modified Allen’s test20,21 (Fig. 3, gray box). This protocol can be labor-intensive, requires patient cooperation, and may be difficult to complete at the bedside. The examination of ulnar artery PSV
DP; change in digit pressure; DV; change in ulnar artery PSV during radial artery compression; UA PSV; ulnar artery peak systolic velocity; w/RAC, during radial artery compression.
Second digit pressure w/RAC (mmHg) Second digit pressure (mmHg) DP first digit (mmHg) First digit pressure w/RAC (mmHg) Extremity
a
UA PSV w/RAC (m/sec)
To examine the accuracy of digit pressure reproducibility between different time points, both a digital and an analog PPG system was used for
DP second digit (mmHg)
UA PSV (m/sec)
Test-Retest Reproducibility Study
First digit pressure (mmHg)
changes to determine the patency of the SPA would simplify this protocol as digit pressures would not need to be measured in those individuals with a patent SPA (Fig. 3). If digit pressure changes stay constant during RAC, this should correspond to an increase in ulnar PSV if the SPA is complete. Conversely, individuals with an incomplete SPA should not have a significant change in ulnar artery PSV during RAC. These findings would allow individuals without a complete SPA to be easily differentiated from those with complete palmar arches. Pola et al. examined the utility of ulnar artery velocity combined with measurement of SPA and digit artery velocities via a resistance index.22 However, the relationship between these variables and the change in digit pressures was not evaluated by these authors. The difficulty in accurately insonating the SPA and DPA vessels also limits the practical utility of velocity measurements obtained from these vessels.21,23 Lohr et al. investigated the utility of ulnar artery PSV measurements and digit pressure changes in 27 patients undergoing radial artery harvest for CABG.24 They demonstrated a significant increase in ulnar artery PSV and no significant changes in first- or second-digit pressure following radial artery harvest. However, no attempt was made to examine the relationship between these measurements as was done in the present study.
Table III. Mean ± SD pressure and velocity values before and during radial artery compression
Fig. 2. Second-digit pressure changes versus ulnar artery PSV changes during radial artery compression.
Dominant hand 109.9 ± 16.4 97.2 ± 16 13.1 ± 10.8 114.7 ± 19.6 101.2 ± 21.1 13.5 ± 10.38 0.5 ± 0.18 0.74 ± 0.24 0.24 ± 0.17 (n = 40 extremities) Nondominnat 117.75 ± 14.3 104.95 ± 13.53 11.8 ± 9.15 120.6 ± 17.23 109.75 ± 15.62 10.9 ± 9.39 0.51 ± 0.11 0.76 ± 0.17 0.25 ± 0.12 hand (n = 40 extremities)
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Fig. 3. Current algorithm (gray box) versus proposed modified algorithm for preoperative screening protocol prior to radial artery harvest in CABG.
repeat measures. The overall reproducibility for the measurement of digit pressures was acceptable in this study as previously demonstrated.20 The ulnar artery PSV changes were reproducible between the two different time points with a significant, though not high, correlation. Both systems showed these measures to be reproducible, although a higher correlation was demonstrated with the digital system (Table II). Regardless, the analog system, used in most noninvasive vascular laboratories in the United States, still provides a valuable tool. It has been reported that ischemia will not likely occur unless a decrease of ‡40 mmHg occurs in digit pressure changes during RAC.20,23,25,26 Analog versus digital data were reexamined in this study. Despite somewhat lower correlation with the analog system, no subject in the reproducibility portion of this study was found to have this magnitude of a pressure drop (‡40 mmHg). This suggests that the study population had adequate ulnar blood supply to the digits. Therefore, in this study, analog or
digital measurement variability would not have made a clinical difference. One limitation of this study is the relatively small number of subjects studied. All individual extremity measurements were assumed to be independent observations; by combining dominant and nondominant extremities in this manner, overall sample size was increased. Another limitation of the present study was that subjects did not have angiographic identification of palmar arch anatomy prior to noninvasive testing, since an invasive modality would subject normal volunteers to an unacceptable risk. Change in Digit Pressures versus Change in Ulnar Artery PSV For ulnar artery PSV changes during RAC to be clinically useful, they must relate to a known measure used for preoperative radial artery screening prior to CABG. Previous work has shown
258 Sullivan et al.
that measurement of digit pressure changes in the first and second digits during RAC is more accurate and objective than the Allen’s test or the modified Allen’s test using a continuous-wave probe to insonate the SPA.20,21,23 In this study, we hypothesized that an increase in ulnar artery PSV during RAC, if associated with no significant decrease in digit pressure change during RAC, could be used instead of digit pressure measurements to predict ischemia. Individuals without an increase in ulnar artery velocities (suggesting an incomplete SPA) would only then be considered for additional measurement of digit pressures. The results of this study demonstrated that no correlation existed between the first- or seconddigit pressure changes during RAC and the change in ulnar artery PSV changes during RAC. This suggests that velocity changes cannot be used clinically to determine if digits would become ischemic if the radial artery were harvested. Until ulnar artery velocity changes and their utility in predicting an incomplete SPA are better understood, complete extremity arterial evaluation consisting of segmental pressure measurements, arterial waveform analysis, and measurement of first- and seconddigit pressure before and during RAC should remain the preferred preoperative screening tool prior to radial artery harvest for CABG.
CONCLUSION Measurement of the change in ulnar artery PSV during RAC did not predict digit artery pressures in this study. The authors do not advocate using changes in ulnar artery PSV during RAC as a sole preoperative screening tool prior to CABG. Measurement of segmental upper extremity pressures with first- and second-digit pressure measurement during RAC should remain the preferred preoperative screening tool for radial artery harvest prior to CABG.
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