Spinal Cord Stimulator and Warfarin

1. Spinal Cord Stimulator and Warfarin Humphrey Lam MD Vanderbilt University Medical Center Department of Anesthesiology, CA-2

2. Case Presentation • 76 y/o female with a history of atrial fibrillation on warfarin, lumbar degenerative disc disease, s/p lumbar laminectomies of L2-S1 back in 2007. She presented at that time with lower back pain, bilateral foot numbness, as well as left leg pain. The back pain had subsided since her surgery, and the left leg pain was milder, but the foot numbness never truly went away. She then noted an increase in lower back pain and had an acute episode of bilateral lower extremity numbness from the knees down. The sensation slowly returned, but has intermittent relapses of the same symptoms. A MRI was obtained that showed multilevel disease most severe at L5-S1 with decreased signal noted in the left neural foramina; contrast enhancement encasing the L5 nerve root, likely indicating scar formation. • Lower back pain is 5/10 on the pain scale, 7/10 on worse days. She is able to walk 2-3 miles a day, or for at least 45 minutes. • Interventions thus far- ESI x2 prior to surgery, left L5 TF Epidural Injection, RACZ Caudal Epidural Adhesiolysis • What’s next? The patient will have a spinal cord stimulator trial. If she demonstrates a good response, then she may benefit from a long-term implant.

3. Spinal Cord Stimulator • Neurostimulation sprung from the pioneering work on SCS for the treatment of pain at the University Hospitals of Cleveland in the 1960s by Dr. Norman Shealy • Used to treat pain from failed back surgery, radicular pain, complex regional pain syndrome, vascular insufficiency, peripheral neuropathy, headache, angina, abdominal pain, and pelvic pain. Spinal Cord Stimulation Complications in Order of Decreasing Frequency • COMPLICATIONREPORTED FREQUENCY (BY REFERENCE) • Lead migration with need for revision 7%,[18] 10%,[19] 5%,[20] 14%,[21] 11%[22] • Lead breakage with need for revision 13%,[18] 23%,[19] 0%,[20] 13%,[21] 6%[22] • Infection 4%,[19] 7%,[20] 3%,[21] 5%[22] • Neurologic injury Case reports, rare [24,25]

4. Atrial Fibrillation • Found in 1 % of persons > 60 years to more than 5 percent of patients > 69 years. • lifetime risk of developing atrial fibrillation after age 40 has been found to be 26.0 percent for men and 23.0 percent. • 4 things to consider are treatable contributing factors, control of the ventricular rate, prevention of recurrences, and prevention of thromboembolic episodes • risk of systemic emboli as a result of circulatory stasis • risk of stroke in patients with nonvalvular atrial fibrillation is five to seven times greater than that in controls without atrial fibrillation • Risk factors that predict stroke in patients with nonvalvular atrial fibrillation include- previous stroke or transient ischemic attack (relative risk, 2.5), diabetes (relative risk, 1.7), history of hypertension (relative risk, 1.6), and increasing age (relative risk, 1.4 for each decade). Patients with any of these risk factors have an annual stroke risk of at least 4 percent if untreated. • < 60 years of age without any clinical risk factors or structural heart disease do not require antithrombotic therapy for stroke prevention because of their low risk. • stroke rate is < 2 percent/year in patients between the ages of 60 and 75 years with lone atrial fibrillation. These patients may be adequately protected from stroke by aspirin therapy. • >75 years patients with atrial fibrillation, anticoagulation should be used with caution and carefully monitored because of the potentially increased risk of intracranial hemorrhage

5. Warfarin • Oral anticoagulant that acts on vitamin K dependent clotting factors (II, VII, IX, X) • Activity level of 40% for each factor is adequate for normal or near normal hemostasis (INR < 1.5) • PT and INR are most sensitive to factors VII and X • INR >1.2 occurs when factor VII activity is reduced to 55% of baseline • Age, diet, race, drug interactions, sex, body weight, and comorbidities

6. ASRA Guidelines • Warfarin must be stopped 4-5 days prior to the procedure • PT/INR should be measured prior to the neuraxial procedure • Concurrent use of meds that affect the clotting cascade should be checked • Patients on low-dose warfarin therapy during epidural analgesia should have their PT/INR monitored daily • Neuraxial catheters should be removed when the INR is <1.5 • Neurological testing should be performed routinely on patients on warfarin therapy • Reduce or withhold warfarin dose in patients with indwelling catheters with an INR >3

7. References • Horlocker, Terese T. et al. Regional Anesthesia in the Anitcoagulated Patient: Defining the Risks (The Second ASRA Consensus Conference on Neuraxial Anesthesia and Anticoagulation). Regional Anesthesia and Pain Medicine 2003, 28: 172-197 • Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, Peter Libby et al. 8th ed. • Raj's practical management of pain/editors, Honorio T. Benzon…[et al.]. 4th ed. • Shah, RV and Kaye AD. Bleeding risk and interventional pain management. Current Opinion in Anesthesiology 2008, 21:433-438 • Woods DM et al. Complications of neurostimulation. Techniques in Regional Anesthesia and Pain Management 2007, 11:178-182