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Lack of Association Between Limb Hemodynamics and Response to Infrapopliteal Endovascular Therapy in Patients With Critical Limb Ischemia
Abstract: Background. Non-invasive limb hemodynamics may aid in diagnosis of critical limb ischemia (CLI), although the relationship with disease severity and response to endovascular therapy is unclear. Methods and Results. This prospective, single-center study enrolled 100 CLI patients (Rutherford class 4-6) who underwent infrapopliteal endovascular revascularization (175 lesions) in the Peripheral RegIstry of Endovascular Clinical OutcoMEs (PRIME) registry. Hemodynamic measures included ankle-brachial index (ABI), toe-brachial index (TBI), and toe pressure (TP). Procedure success following revascularization was defined as stenosis ≤30%. Hemodynamic success was defined as an increase >0.15 in ABI or TBI relative to baseline. Freedom from amputation was defined as no major or minor amputation during follow-up. Clinical success was defined as a decrease of at least one Rutherford class during follow-up. Treatment success was defined as procedure success, freedom from amputation, and clinical improvement. Median baseline hemodynamic values were 0.90 for ABI, 0.39 for TBI, and 54 mm Hg for TP. Twenty-nine patients (29%) did not meet the common hemodynamic diagnostic criterion for eligibility in CLI trials (ABI ≤0.5, TBI ≤0.5, or TP <50 mm Hg). Main outcomes included 96% procedure success, 95% freedom from amputation, 64% clinical success, and 62% treatment success. There was no relationship between baseline (or with the pretreatment to posttreatment change) limb hemodynamic values and the response to infrapopliteal endovascular therapy. Conclusion. Non-invasive hemodynamic studies may have limited clinical usefulness in patients with CLI. The usefulness of these parameters to confirm eligibility and to assess response to therapy in interventional CLI clinical trials should be re-evaluated.
J INVASIVE CARDIOL 2017;29(5):175-180.
Key words: critical limb ischemia, endovascular, hemodynamic, infrapopliteal
Symptomatic peripheral artery disease affects 15%-20% of older adults and is associated with a 4-fold increase in all-cause mortality risk and an 8-fold increase in cardiovascular mortality risk.1 Peripheral artery disease may insidiously progress to critical limb ischemia (CLI), defined as the presence of rest pain requiring analgesia and/or ischemic tissue loss.2 Prognosis following CLI diagnosis is grave, with 1-year mortality and major amputation rates ranging from 20%-50%.3-5 These statistics underscore the importance of early diagnosis and intervention to improve tissue perfusion, relieve pain, and promote wound healing.6-10
The diagnosis of CLI is routinely based on clinical symptoms and confirmed by measurements of non-invasive limb hemodynamics such as ankle-brachial index (ABI), toe-brachial index (TBI), and/or toe pressure (TP).11 Limb hemodynamic measures are often used to confirm eligibility in CLI clinical trials where ABI ≤0.5, TBI ≤0.5, and/or TP <50 mm Hg are required for enrollment.6,11-16 These measures are also used to quantify response to therapy in CLI clinical trials where ABI or TBI increases >0.15 are taken as evidence of hemodynamic success.17,18 However, recent studies have shown that many CLI patients do not meet these diagnostic hemodynamic criteria.6,11,19 Furthermore, the association between changes in these hemodynamic parameters and clinical outcomes following endovascular therapy is unclear. The purpose of this study was to assess the relationship of limb hemodynamics with response to infrapopliteal endovascular revascularization in patients with CLI.
Methods
Patients. This is a prospective, single-center study of consecutive CLI patients who underwent infrapopliteal endovascular revascularization in the Peripheral RegIstry of Endovascular Clinical OutcoMEs (PRIME) registry. Institutional review board approval and patient consent were obtained prior to any procedures or data collection. Eligible patients were adults ≥18 years with symptomatic CLI (Rutherford class 4-6) and angiographically confirmed infrapopliteal disease that required endovascular revascularization. Patients underwent clinical examination and noninvasive limb hemodynamic measurements, including ABI, TBI, and TP prior to revascularization and within 3 months post intervention on the affected limb.
Procedures. Hemodynamic measures were obtained after subjects rested supine for 5 minutes. Systolic pressures were measured in both arms (brachial artery) and at the dorsalis pedis and posterior tibial arteries using a MultiLab Series 2-CP (Unetixs Vascular) or Dopplex D900 Doppler waveform analyzer (Huntleigh). ABI was calculated as the ratio between the higher of the ankle pressures and the higher brachial pressure. Systolic TP was evaluated at the hallux using a MultiLab Series 2-CP (Unetixs Vascular) or Vista Doppler waveform analyzer (Wallach Surgical Devices) by photoplethysmography. TBI was calculated as the ratio between toe pressure and the higher brachial pressure.
Endovascular revascularization was attempted on all study subjects. Intervention included angiographic evaluation of arterial stenosis of the infrainguinal and infrapopliteal arteries by physician estimate, prior to infrapopliteal intervention of the target lesions. Revascularization method was determined by the treating physician and included one or a combination of the following: atherectomy, percutaneous transluminal angioplasty, drug-coated balloon angioplasty, and/or bare-metal or drug-eluting stent placement. Angiography was performed to assess procedure success post revascularization.
Outcomes and definitions. Procedure success following revascularization was defined as stenosis ≤30% determined by physician visual estimate. Hemodynamic success was defined as an increase >0.15 in ABI or TBI relative to baseline following endovascular therapy. Freedom from amputation was defined as no major (above the ankle) or minor (below the ankle) amputation during follow-up. Clinical success was defined as a decrease of at least one Rutherford class during follow-up. Treatment success was a composite endpoint that comprised procedure success, freedom from amputation, and clinical improvement.
Data analysis. Continuous data were reported as mean and standard deviation or median and interquartile range, depending on normality assumptions. Categorical data were reported as frequencies and percentages. Group comparisons were performed with independent samples t-test for normally distributed continuous data, Mann-Whitney U-test for non-normally distributed continuous data, or Fisher’s exact test for categorical data. Longitudinal changes in clinical outcomes were assessed with paired t-tests or Wilcoxon signed-rank test, based on normality. Univariate logistic regression assessed the relationship of baseline characteristics on treatment success. Variables that loaded into the univariate model at P<.10 were evaluated in a multivariable model using backward elimination (likelihood ratio method). A P-value <.05 was considered statistically significant. Data were analyzed using Predictive Analytics Software version 22 (SPSS, Inc).
Results
A total of 100 patients clinically diagnosed with CLI (Rutherford class 4-6) underwent infrapopliteal endovascular revascularization between January 2013 and January 2016. Mean age was 75 years and 67% were male. The most common comorbidities were dyslipidemia (92%), hypertension (89%), and diabetes mellitus (68%). Over 50% of patients presented with at least chronic kidney disease stage 3 (glomerular filtration rate <60 mL/min). Median baseline hemodynamic values were 0.90 for ABI, 0.39 for TBI, and 54 mm Hg for TP (Table 1). There was no significant association between baseline ABI and TBI values (Figure 1). Twenty-nine patients (29%) did not meet the common hemodynamic diagnostic criterion for eligibility in CLI trials (ABI ≤0.5, TBI ≤0.5, or TP <50 mm Hg).
Revascularization was performed in 175 infrapopliteal lesions. Treated segments included the popliteal artery (P3 segment) (25%), anterior tibial artery (24%), tibioperoneal trunk (15%), peroneal artery (15%), posterior tibial artery (13%), dorsalis pedis (3%), lateral plantar artery (2%), medial plantar artery (1%), lateral calcaneal artery (1%), and pedal loop (1%). Main outcomes included 96% procedure success, 95% freedom from amputation, 64% clinical success, and 62% treatment success.
When comparing patients based on hemodynamic diagnostic eligibility, there were no observable differences in baseline characteristics or in response to infrapopliteal endovascular therapy (Table 2). Baseline ABI (Figure 2A) and TBI (Figure 2B) were not different in patients with treatment success or treatment failure. In the univariate logistic regression model, lower Rutherford class, absence of diabetes, higher glomerular filtration rate, and higher hemoglobin were associated with treatment success and subsequently included in the multivariate model. Notably, neither ABI (P=.20), TP (P=.23), nor TBI (P=.31) predicted treatment success after endovascular therapy. In the multivariate logistic regression model, only lower Rutherford class (odds ratio, 19.8; 95% confidence interval [CI], 5.5-71.6; P<.001) was associated with treatment success (Table 3).
Despite the high procedure success rate following endovascular therapy, only minimal (albeit statistically significant) increases in limb hemodynamics were observed. Hemodynamic success was 56%, ABI increased from 0.93 ± 0.35 to 1.06 ± 0.26 (P<.001), TBI increased from 0.42 ± 0.25 to 0.49 ± 0.25 (P=.04), and TP increased from 61 ± 38 mm Hg to 71 ± 37 mm Hg (P=.04). When comparing patients with hemodynamic success vs hemodynamic failure, there were no statistical differences in procedure success, freedom from amputation, clinical success, or treatment success (Figure 3).
Discussion
Data regarding the effectiveness of endovascular modalities for the treatment of infrapopliteal disease in patients with CLI are beginning to emerge with variable outcomes. The results of this study demonstrated a lack of association of non-invasive limb hemodynamic measures with baseline patient characteristics, disease severity, and response to infrapopliteal endovascular therapy among patients with CLI. Therefore, the clinical usefulness of these measures in patients with CLI is questionable.
The accuracy of non-invasive hemodynamic testing to identify patients with CLI with compromised infragenicular run-off has been studied by several authors. Bunte and colleagues6 showed that 29% of patients with CLI and abnormal infrapopliteal run-off had normal or mildly abnormal ABIs (defined as ABI >0.7 and <1.4), and that low TBI was not associated with abnormal infrapopliteal run-off. However, TBI values were somewhat higher with improved pedal perfusion, questioning the utility of these indices to assess limb hemodynamics in CLI patients with abnormal infrapopliteal anatomy. Shishehbor et al19 reported only 16% of CLI patients had abnormal ankle pressures and that abnormal TP had better specificity in CLI diagnosis. Still, 40% of patients in this study had normal TP values and neither ABI nor TP were associated with disease severity. Vallabhaneni et al20 reported that CLI patients with TP ≤10 mm Hg had higher amputation rates relative to those with TP of 31-50 mm Hg (60% vs 18%, respectively; P<.001); however, patients did not have exclusive infrapopliteal disease, as in our current study. Our results suggest only a weak association between limb hemodynamics and response to infrapopliteal endovascular therapy; instead, Rutherford class was the sole predictor of treatment success in multivariate analysis.
Commonly utilized non-invasive limb hemodynamic assessments can be misleading and unreliable in CLI, as they frequently failed to identify patients with severe disease and limb-threatening angiographic anatomies in the current study. No differences were observed in outcomes after endovascular therapy among patients with CLI regardless of baseline ABI, TBI, or TP, many of which would have been otherwise considered “normal” and possibly resulted in denial of therapy that could have otherwise proven beneficial. Ongoing studies designed to identify patients with CLI who would benefit from specific methods of endovascular therapy have used ABI, TBI, and TP values of ≤0.5, ≤0.5, and/or <50 mm Hg, respectively, as inclusion criteria (and hence as surrogate diagnostic criteria for CLI). Results from the current study suggest that the use of limb hemodynamic measures as inclusion/exclusion criteria in studies of infrapopliteal therapies is questionable, since many appropriate patients are excluded using these thresholds. Furthermore, this study questions the necessity of performing non-invasive studies as surveillance tools after infrapopliteal revascularization procedures in patients with CLI given the lack of association between hemodynamic success and clinical outcomes. Clinicians should maintain a high index of suspicion and a low threshold to proceed with repeat revascularization when dictated by clinical judgment regardless of the information provided by the aforementioned tests. Emerging modalities such as evaluation by skin perfusion pressure, transcutaneous oxygen pressure, fluorescent angiography through the use of indocyanine green dye, subcutaneous implantation of oxygen microsensors, or use of two-dimensional perfusion imaging software are promising, and given further study, may prove useful in diagnosis and prognosis of patients with complex peripheral arterial disease and CLI.21-25
Study limitations. There were several limitations of this study that may impact interpretability. First, patient outcomes were reported through 3 months post treatment. Therefore, the relationship of limb hemodynamics with longer-term clinical outcomes after endovascular therapy in patients with infrapopliteal disease cannot be evaluated in this study. Second, physicians involved in patient follow-up were not blinded to the intervention and the results of the preprocedural non-invasive limb hemodynamics. Finally, the study represents a single-center experience, where patients were not randomized and were treated by experienced operators specifically trained in CLI therapy.
Conclusion
Non-invasive hemodynamic studies may have limited clinical usefulness in patients with CLI. The use of these measures to confirm eligibility and to assess response to therapy in interventional CLI clinical trials should be re-evaluated.
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From 1Metro Health Hospital, Wyoming, Michigan; 2Rex Healthcare and University of North Carolina Health Systems, Raleigh, North Carolina; 3Newton Wellesley Hospital, Boston, Massachusetts; 4Mount Sinai Medical Center, Miami, Florida; and 5Miller Scientific Consulting, Inc, Asheville, North Carolina.
Funding. L. Miller was compensated by Metro Health Hospital for statistical analysis and interpretation. The remaining authors received no compensation for their contributions to this work.
Disclosure. The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report unrestricted research grants to Metro Health Hospital to support the PRIME registry from Bard Peripheral Vascular, Terumo Interventional Systems, Cardiovascular Systems, Inc, Access Closure, Medtronic, Boston Scientific, and Spectranetics. Dr Mustapha reports personal fees from Bard Peripheral Vascular, Terumo Interventional Systems, Cardiovascular Systems, Inc, Medtronic, Boston Scientific, and Spectranetics. Dr Diaz-Sandoval reports personal fees from Bard Peripheral Vascular, Terumo Corporation, and Cardiovascular Systems, Inc. Dr Adams reports personal fees from Bard Peripheral Vascular, Terumo Interventional Systems, Cardiovascular Systems, Inc, Medtronic, Boston Scientific, and Spectranetics. Dr Jaff reports non-financial support (non-compensated advisor) from Medtronic, Boston Scientific, Abbott Vascular, and Cordis; personal fees from Cardinal Health, Volcano, and VIVA Physicians, a 501c3 not-for-profit education and research organization (board member); equity investment in PQ Bypass. Dr Beasley reports personal fees from Bard Peripheral Vascular, Cook, Abbott Vascular, Cardinal Health, Cardiovascular Systems, Inc, Medtronic, Boston Scientific, and Spectranetics. Dr Miller reports personal fees from Metro Health Hospital, Spectranetics, and Medtronic. Dr Saab reports personal fees from Bard Peripheral Vascular, Terumo Interventional Systems, Cardiovascular Systems, Inc, Medtronic, Boston Scientific, and Spectranetics. Theresa McGoff, Sara Finton, and Dr Ansari report no conflicts of interest regarding the content herein.
Manuscript submitted January 4, 2017, final acceptance given January 11, 2017.
Address for correspondence: Jihad A. Mustapha, MD, Metro Health Hospital, 5900 Byron Center SW, PO Box 9490, Wyoming, MI 49519. Email: jihad.mustapha@metrogr.org
