epidural blood patch was per- formed in a female patient taking 1.3 mg/kg of enoxaparin twice daily, 30 h after the last dose was given. A 39-yr-old female taking enox- aparin, 100 mg orally twice a day, underwent an uneventful lumbar puncture by her neurologist to ex- clude pseudotumor cerebri. Soon afterwards the patient developed a debilitating headache in the occipi- tal region that became excruciating in the upright position. Her history was significant for deep venous thrombosis (DVT). The patient was treated with IV hydration and IV caffeine for 24 h without relief. Thirty hours after the last dose of enoxaparin, an epidural blood patch was performed with 20 mL of autolo- gous blood with complete resolution of her postural headache. Low molecular weight hepari- noids (LMWH) are increasingly pre- scribed for systemic anticoagulation therapy and DVT treatment and pro- phylaxis (1–3). Gaiser et al. (4) re- ported a partially successful epidural blood patch in a female patient 24 h after 190 mg of LMWH administered subcutaneously. There appears to be a predictable and reproducible dose response to enoxaparin when dosed on a weight-adjusted basis in small doses for thromboprophylaxis (5). With the lack of predictability at larger doses pharmacokinetic simu- lation is extremely difficult. The terminal half-life of plasma anti-Xa activity of enoxaparin is be- tween 3– 4 h. Therefore, we elected to wait for more than 7 half-lives to perform an epidural blood patch. To our knowledge, a successful epidural blood patch on a patient receiving enoxaparin more than 1.5 mg/kg/day has not been reported. Nalini Vadivelu, MD Craig Freiberg, MD James Kim, MD Mathew Wallace, MD Raymond Sinatra, MD, PhD Department of Anesthesiology Yale University School of Medicine New Haven, CT nalini.vadivelu@yale.edu REFERENCES 1. Horlocker TT, Wedel DJ, Benzon H, et al. Regional anesthesia in the anticoagu- lated patient: defining the risks (the second ASRA Consensus Conference on Neuraxial Anesthesia and Antico- agulation). Reg Anesth Pain Med 2003;28:172–97. 2. Horlocker TT, Wedel DJ. Neuraxial block and low-molecular-weight heparin: bal- ancing perioperative analgesia and thromboprophylaxis. Reg Anesth Pain Med 1998;23:164 –77. 3. Horlocker TT, Heit JA. Low molecu- lar weight heparin: biochemistry, phar- macology, perioperative prophylaxis regimens, and guidelines for regional anesthetic management. Anesth Analg 1997;85:874 – 85. 4. Gaiser RR, Mauney DL, Imbesi SG. Epi- dural blood patch in a patient with an arachnoid cyst. J Clin Anesth 2002;14:42–5. 5. Yin B, Barratt SM, Power I, Percy J. Epi- dural haematoma after removal of an epidural catheter in a patient receiving high-dose enoxaparin. Br J Anaesth 1999;82:288 –90. DOI: 10.1213/01.ANE.0000227136.73526.F0 Acute Right Bundle Branch Block as a Presenting Sign of Acute Pulmonary Embolism To the Editor: Rosenberger et al. (1) described the limited utility of intraoperative transesophageal echocardiography (TEE) as a primary diagnostic tool for obtaining a definitive diagnosis of pulmonary embolism (PE). We wish to highlight the role of the electrocardiogram (ECG) in diag- nosing PE. A 51-yr-old patient presented to the operating room for reduction of a hip dislocation. The patient’s pre- operative ECG, obtained earlier the same day, revealed sinus bradycar- dia (Fig. 1). Immediately before a planned induction of general anes- thesia, we attached an ECG monitor and noted a new right bundle branch block (RBBB). We post- poned induction and obtained a 12-lead ECG in the operating room (Fig. 2). The ECG revealed new findings, including normal sinus rhythm, (RBBB), multiple ST seg- ment abnormalities, S1Q3T3 pat- tern, and T wave inversion V1-V3. A subsequent computerized to- mography (CT) scan revealed mul- tiple, deep-venous thrombi and massive PE. The usefulness of ECG findings in the diagnosis of PE is controver- sial (1). As with clinical presenta- tion and physical examination, an ECG is of limited value in diagnos- ing PE: findings are often incon- sistent and nonspecific (1). ECG changes may vary with the size of the embolus, impact upon hemody- namics, and cardiopulmonary re- serve (1,2). Classically described findings are often absent, or they are equally prevalent in patients suspected of having PE in whom an alternative diagnosis is ultimately made (2). Although approximately 90% of patients with PE have at least one abnormality on ECG, many of these findings are nonspe- cific and therefore limited in their diagnostic utility in cases of sus- pected PE (3). Given the wide- spread use of imaging modalities for diagnosis of PE, the primary function of the ECG in modern clinical practice is to raise or rein- force suspicion (4). In our case it was a new RBBB, indicative of impairment in right- sided cardiac conduction, that prompted further evaluation. Its significance for diagnosing PE is unclear. One study found new RBBB in 80% of patients with mas- sive trunk embolism but in no cases of peripheral embolism in the pul- monary artery (4). Another study found RBBB present in 10% of pa- tients with confirmed PE, although the severity of PE failed to correlate with the presence or absence of RBBB (5). In that same study, a pattern of subepicardial ischemia (T-wave inversions) in the precor- dial leads was the finding most often noted in PE and also the find- ing most closely correlated with se- verity. Inverted T-waves, however, present in many other processes, are thus of limited diagnostic util- ity. In another study, 28 different ECG abnormalities were analyzed in patients suspected of having PE Vol. 103, No. 3, September 2006 © 2006 International Anesthesia Research Society 789 Letters to the Editor