Travel and Risk for Venous Thromboembolism

Editor's notes:
The body of evidence on the epidemiology of long-distance travel and venous thromboembolism (VTE) is heterogeneous and inconclusive. The reviewers found 14 eligible studies, which had significant between-study heterogeneity, and the pooled relative risk for VTE was 2.0 (95% CI, 1.5 to 2.7). The reviewers eliminated the heterogeneity by excluding 6 case control studies with biased selection of control participants. The relative risk was 2.8 (CI, 2.2 to 3.7) in the remaining included studies and 1.2 (CI, 0.9 to 1.6) in the excluded studies. By excluding studies with control participants who had a different risk for VTE than the source population for the case-patients, the authors clarified a confusing body of evidence.

BACKGROUND: The potential risk for travel-related venous thromboembolism (VTE) has become an important public health concern because of rapid increases in long-distance travel; however, previous studies on this relationship are surprisingly contradictory. PURPOSE: To estimate the risk for VTE in travelers, determine whether a dose-response relationship exists, and identify reasons for the contradictory results of previous studies. DATA SOURCES: MEDLINE, EMBASE, BIOSIS, CINAHL, grey-literature sources, contact with investigators, and reference lists of studies, without language restrictions. STUDY SELECTION: Reports were selected if they investigated the association between travel and VTE for persons that used any mode of transportation and had nontraveling persons for comparison. DATA EXTRACTION: Data on study and patient characteristics, risk estimates, and quality parameters were independently extracted by 2 investigators. Pooled effect estimates were obtained by using random-effect meta-analysis. DATA SYNTHESIS: Of 1560 identified abstracts, 14 studies (11 case-control, 2 cohort, and 1 case-crossover) met inclusion and exclusion criteria, including 4055 cases of VTE. Compared with nontravelers, the overall pooled relative risk for VTE in travelers was 2.0 (95% CI, 1.5 to 2.7). Significant heterogeneity was present because of the method for selecting control participants (P = 0.008): Whether the studies used control participants who had been referred for VTE evaluation or nonreferred control participants. Excluding the studies that used referred control participants, the pooled relative risk for VTE in travelers was 2.8 (CI, 2.2 to 3.7), without significant heterogeneity. A dose-response relationship was identified, with an 18% higher risk for VTE for each 2-hour increase in duration of travel by any mode (P = 0.010) and a 26% higher risk for every 2 hours of air travel (P = 0.005). Limitation: All available studies were from Western countries; generalizability to non-Western populations is expected but needs confirmation. CONCLUSION: Travel is associated with a nearly 3-fold higher risk for VTE, with a dose-response relationship of 18% higher risk for each 2-hour increase in travel duration. Heterogeneity in results of previous studies was identified as being due to selection bias toward the null from use of referred control participants.

Chandra D, Parisini E, Mozaffarian D. Travel and Risk for Venous
Thromboembolism. Ann Intern Med. 2009 Jul 6. [Epub ahead of print] PubMed PMID:
19581633.

Early CT scan of low risk patients with chest pain: A reduction in length of stay and expense

Low-Risk Patients With Chest Pain in the Emergency Department: Negative 64-MDCT Coronary Angiography May Reduce Length of Stay and Hospital Charges
American Journal of Roentgenology. 2009; 193:150-154
PMID: 19542407

Researchers at the University Of Washington School of Medicine in Seattle hypothesized that a negative coronary CTA combined with negative ECG and negative cardiac enzyme tests discovered early in the patient evaluation in low-risk patients with chest pain can shorten the length of stay in the emergency department as well as reduce the cost of care. Cardiac CT scan
versus the current standard-of-care (SOC) workup of low-risk patients with chest pain could rule out coronary artery disease early on. Three types of patient workups were analyzed for length of stay and charges incurred: (1) Standard of care, (2) Coronary CTA with observation, and (3) Coronary CTA without observation. Qualifying patients all had chest pain and a low TIMI risk score of 0-2.

ABSTRACT: The current standard-of-care workup of low-risk patients with chest pain in an emergency department takes 12-36 hours and is expensive. We hypothesized that negative 64-MDCT coronary angiography early in the workup of such patients may enable a shorter length of stay and reduce charges. The standard-of-care evaluation consisted of serial cardiac enzyme tests, ECGs, and stress testing. After informed consent, we added cardiac CT early in the standard-of-care workup of 53 consecutive patients. Fifty patients had negative CT findings and were included in this series. The length of stay and charges were analyzed using actual patient data for all patients in the standard-of-care workup and for two earlier discharge scenarios based on negative cardiac CT results: First, CT plus serial enzyme tests and ECGs during an observation period followed by discharge if all were negative; and second, CT plus one set of enzyme tests and one ECG followed by discharge if all were negative. Comparisons were made using paired Student's t tests. For standard of care and the two CT-based earlier discharge analyses, the mean lengths of stay were 25.4, 14.3, and 5.0 hours; mean charges were $7,597, $6,153, and $4,251. Length of stay and charges were both significantly less (p < 0.001) for the two CTbased analysis. In low-risk patients with chest pain, discharge from the emergency department based on negative cardiac CT, enzyme tests, and ECG may significantly decrease both length of stay and hospital charges compared with the standard of care.

Are you a part of global health at Duke? Share your story!

In conjunction with the upcoming "Against the Odds" global health exhibit, the Medical Center Library is collecting stories and images from Duke students, faculty and staff who have participated in global health activities. Please share your favorite digital photograph or a brief story (500 words or so) about your experiences around the world or here in Durham.

Images will be digitally displayed at the "Against the Odds" exhibit reception on September 3, from 5:30 - 7:00 pm. The reception is open to all in the Duke community and we hope that you will be able to join us!

Images and stories will also be added to the new Duke Global Health Stories Archive created by the Medical Center Archives. This online site will showcase and preserve the service and impact of global health activities at Duke.

To ensure that your photograph is included in the digital showcase at the September 3 reception, please submit your image file no later than August 17. Photographs and stories submitted after that date will still be added to the online exhibit and archive.

Submit your photographs and stories online today at http://digitaldukemed.mc.duke.edu/global_health/contribution

The "Against the Odds" exhibit will be on display from August 3 to September 11 in the Medical Center Library. This touring exhibition was developed and produced by the National Library of Medicine, National Institutes of Health and is sponsored by the Duke Medical Center Library and Archives, the Duke Global Health Institute and the Hubert-Yeargan Center for Global Health. It features stories of community health, food for life, action on AIDS, the legacy of war, disease prevention and global collaboration.

For more information about the exhibit or about submitting your story, please contact Megan von Isenburg at 919-660-1100 or Adonna Thompson at 919-383-2653. If you are interested in being contacted about recording an audio version of your story, please contact Jessica Roseberry at 919-383-2653.

Statin-associated Myopathy and Muscle Damage

Statins have been proven safe, effective and are widely prescribed for hypercholesterinemia therapy. Statin-associated myopathy can include pain and muscle weakness. Researchers at the University of Bern in Switzerland and Tufts-New England Medical Center in Boston biopsied the vastus lateralis muscle to determine muscle injury in patients. Significant injury was defined as 2% or more damaged fibres per biopsy sample. Patients identified as having statin-associated myopathy had complaints of myalgia, cramps or muscle weakness predominately in the trunk area.

ABSTRACT: Many patients taking statins often complain of muscle pain and weakness. The extent to which muscle pain reflects muscle injury is unknown. We obtained biopsy samples from the vastus lateralis muscle of 83 patients. Of the 44 patients with clinically diagnosed statin-associated myopathy, 29 were currently taking a statin, and 15 had discontinued statin therapy
before the biopsy (minimal duration of discontinuation 3 weeks). We also included 19 patients who were taking statins and had no myopathy, and 20 patients who had never taken statins and had no myopathy. We classified the muscles as injured if 2% or more of the muscle fibres in a biopsy sample showed damage. Using reverse transcriptase polymerase chain reaction, we
evaluated the expression levels of candidate genes potentially related to myocyte injury. Muscle injury was observed in 25 (of 44) patients with myopathy and in 1 patient without myopathy. Only 1 patient with structural injury had a circulating level of creatine phosphokinase that was elevated more than 1950 U/L (10x the upper limit of normal). Expression of ryanodine receptor 3 was significantly upregulated in patients with biopsy evidence of structural damage (1.7, standard error of the mean 0.3). Persistent myopathy in patients taking statins reflects structural muscle damage. A lack of elevated levels of circulating creatine phosphokinase does not rule out structural muscle injury. Upregulation of the expression of ryanodine receptor 3 is suggestive of an intracellular calcium leak.

Association between statin-associated myopathy and skeletal muscle damage
CMAJ. 2009 Jul 7;181(1-2):E11-8. PMID: 19581603.

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