Adjusting for bias introduced by instrumental variable estimation in the Cox Proportional Hazards Model

Instrumental variable (IV) methods are widely used for estimating average treatment effects in the presence of unmeasured confounders. However, the capability of existing IV procedures, and most notably the two-stage residual inclusion (2SRI) procedure recommended for use in nonlinear contexts, to account for unmeasured confounders in the Cox proportional hazard model is unclear. We show that instrumenting an endogenous treatment induces an unmeasured covariate, referred to as an individual frailty in survival analysis parlance, which if not accounted for leads to bias. We propose a new procedure that augments 2SRI with an individual frailty and prove that it is consistent under certain conditions. The finite sample-size behavior is studied across a broad set of conditions via Monte Carlo simulations. Finally, the proposed methodology is used to estimate the average effect of carotid endarterectomy versus carotid artery stenting on the mortality of patients suffering from carotid artery disease. Results suggest that the 2SRI-frailty estimator generally reduces the bias of both point and interval estimators compared to traditional 2SRI.Comment: 27 pages, 8 figures, 4 table

Using Risk Models to Improve Patient Selection for High-Risk Vascular Surgery

Vascular surgeons frequently perform procedures aimed at limiting death, stroke, or amputation on patients who present with diseases such as aortic aneurysms, carotid atherosclerosis, and peripheral arterial occlusive disease. However, now more than ever surgeons must balance the potential benefits associated with these interventions with the risks of physiologic insult for these elderly patients, who often have significant comorbidity burdens and the potential for costly complications. In this paper, we highlight how regional and national datasets can help surgeons identify which patients are most likely to benefit from vascular operations and which patients are most likely to suffer complications in the postoperative period. By using these guidelines to improve patient selection, our risk models can help patients, physicians, and policymakers improve the clinical effectiveness of surgical and endovascular treatments for vascular disease

Assembling and Validating Data from Multiple Sources to Study Care for Veterans with Bladder Cancer

Despite the high prevalence of bladder cancer, research on optimal bladder cancer care is limited. One way to advance observational research on care is to use linked data from multiple sources. Such big data research can provide real-world details of care and outcomes across a large number of patients. We assembled and validated such data including (1) administrative data from the Department of Veterans Affairs (VA), (2) Medicare claims, (3) data abstracted by tumor registrars, (4) data abstracted via chart review from the national electronic health record, and (5) full text pathology reports

Consistency of Hemoglobin A1c Testing and Cardiovascular Outcomes in Medicare Patients With Diabetes

Background: Annual hemoglobin A1c testing is recommended for patients with diabetes mellitus. However, it is unknown how consistently patients with diabetes mellitus receive hemoglobin A1c testing over time, or whether testing consistency is associated with adverse cardiovascular outcomes. Methods and Results: We identified 1 574 415 Medicare patients (2002–2012) with diabetes mellitus over the age of 65. We followed each patient for a minimum of 3 years to determine their consistency in hemoglobin A1C testing, using 3 categories: low (testing in 0 or 1 of 3 years), medium (testing in 2 of 3 years), and high (testing in all 3 years). In unweighted and inverse propensity‐weighted cohorts, we examined associations between testing consistency and major adverse cardiovascular events, defined as death, myocardial infarction, stroke, amputation, or the need for leg revascularization. Overall, 70.2% of patients received high‐consistency testing, 17.6% of patients received medium‐consistency testing, and 12.2% of patients received low‐consistency testing. When compared to high‐consistency testing, low‐consistency testing was associated with a higher risk of adverse cardiovascular events or death in unweighted analyses (hazard ratio [HR]=1.21; 95% CI, 1.20–1.23; P\u3c0.001), inverse propensity‐weighted analyses (HR=1.16; 95% CI, 1.15–1.17; P\u3c0.001), and weighted analyses limited to patients who had at least 4 physician visits annually (HR=1.15; 95% CI, 1.15–1.16; P\u3c0.001). Less‐consistent testing was associated with worse results for each cardiovascular outcome and in analyses using all years as the exposure. Conclusions: Consistent annual hemoglobin A1c testing is associated with fewer adverse cardiovascular outcomes in this observational cohort of Medicare patients of diabetes mellitus

Development and Pilot Feasibility Study of a Health Information Technology Tool to Calculate Mortality Risk for Patients with Asymptomatic Carotid Stenosis: The Carotid Risk Assessment Tool (CARAT)

Patients with no history of stroke but with stenosis of the carotid arteries can reduce the risk of future stroke with surgery or stenting. At present, a physicians’ ability to recommend optimal treatments based on an individual’s risk profile requires estimating the likelihood that a patient will have a poor peri-operative outcomes and the likelihood that the patient will survive long enough to gain benefit from the procedure. We describe the development of the CArotid Risk Assessment Tool (CARAT) into a 2-year mortality risk calculator within the electronic medical record, integrating the tool into the clinical workflow, training the clinical team to use the tool, and assessing the feasibility and acceptability of the tool in one clinic setting

Tibiopedal arterial minimally invasive retrograde revascularization (TAMI) in patients with peripheral arterial disease and critical limb ischemia. On behalf of the Peripheral Registry of Endovascular Clinical Outcomes (PRIME)

Objectives and backgroundComplex peripheral arterial disease (PAD) and critical limb ischemia (CLI) are associated with high morbidity and mortality. Endovascular techniques have become prevalent in treatment of advanced PAD and CLI, and use of techniques such as tibiopedal minimally invasive revascularization (TAMI), have been proven safe in small, singleâ center series. However, its use has not been systematically compared to traditional approaches.Methods and resultsThis is a retrospective, multicenter analysis which enrolled 744 patients with advanced PAD and CLI who underwent 1,195 endovascular interventions between January 2013 and April 2018. Data was analyzed based on access used for revascularization: 840 performed via femoral access, 254 via dual access, and 101 via TAMI. The dual access group had the highest median Rutherford Class and lowest number of patent tibial vessels. Median fluoroscopy time, procedure time, hospital stay, and contrast volume were significantly lower in the TAMI access group when compared to both femoral/dual access groups. There was also a significant difference between all groups regarding location of target lesions: Femoropopliteal lesions were most commonly treated via femoral access; infrapopliteal lesions, via TAMI, and multilevel lesions via dual access.ConclusionsStandâ alone TAMI or tibial access as an integral part of a dual access treatment strategy, is safe and efficacious in the treatment of patients with advanced PAD and CLI who have infrapopliteal lesions. Larger prospective and randomized studies may be useful to further validate this approach.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154326/1/ccd28639.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154326/2/ccd28639_am.pd

Upper Extremity Arteriovenous Grafts are Less likely to be Abandoned Compared to Autogenous Fistulas Despite a Higher Reintervention Rate

BackgroundUpper-extremity arteriovenous (AV) access often requires reintervention. However, the frequency of reinterventionsand subsequent access failure is not well-characterized. Our goal was to evaluate the frequency and type of reinterventions, risk-factors, and outcomes after AV access creation.MethodsWe performed a retrospective review of index upper extremity AV access creations (2017-2019) within the VQI Medicare-linked Vascular Implant Surveillance and Interventional Outcomes Network dataset for patients on hemodialysis (HD). Reinterventionswere defined as open or endovascular procedures on the access occurring at 1 day or more after access creation. Access abandonment was defined as any new access creation, peritoneal dialysis, kidney transplant, or death following index access creation. Univariable, multivariable, Kaplan-Meier, and Cox regression analyses were performed.ResultsThere were 2,551 patients with an index AV graft (AVG) (19.5%) or AV fistula (AVF) (80.5%). Patients who underwent an AVG were more likely older, female sex, of non-White race, nonambulatory, not living at home, and to undergo the procedure as an inpatient (P < 0.05). Reintervention rates were 1.64/person-year for AVG and 1.17/person-year for AVF. On Kaplan-Meier analysis, freedom from new AV access creation at 3 years was 72% for AVG and 78% for AVF (P < 0.001). Freedom from tunneled dialysis catheter (TDC) placement at 3 years was 66% for AVG and 71% for AVF (P = 0.19). On multivariable analysis, undergoing placement of an AVG was independently associated with an increased risk of any reintervention compared to AVF (rate ratio (RR) 1.40 95% confidence interval (CI) 1.3-1.6; P = <0.001). TDC placement was increasingly associated with each subsequent reintervention but did not vary by access type. There was an elevated risk of access abandonment with subsequent reinterventions; however, long-term access abandonment was lower with an AVG compared to an AVF (RR 0.82 95% CI 0.7-0.96; P = 0.015).ConclusionReinterventions to support HD access are common, and more than 60% of patients required at least one procedure within the first year of access placement. While patients with AVG require more reinterventions, they also have a lower rate of long-term access abandonment and similar rates of TDC placement compared to patients who receive an AVF

BEST-CLI International Collaborative: planning a better future for patients with chronic limb-threatening ischaemia globally.

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