Primecuts – This Week In The Journals

January 3, 2012

By Alexandra Sowa, MD

Faculty Peer Reviewed

Happy New Year!

For nostalgia’s sake, let’s take a look back before we begin to look forward. The December 21st edition of the Journal of the American Medical Association (JAMA) detailed a fascinating study on resting heart rate.

Although resting heart rate is widely recognized as an independent predictor of cardiovascular risk, little is known about the temporal effects of resting heart rate (RHR) on mortality (Fox). Researchers in Norway attempted to bridge this gap by examining the relationship between RHR and mortality in a prospective study involving 13,499 men and 15,826 women, all without known cardiovascular disease.  http://content.onlinejacc.org/cgi/content/full/j.jacc.2007.04.079v1

In the study, RHR was measured twice; once at baseline and then approximately ten years later. Compared with participants with a resting heart rate of less than 70 beats/min at both measurements, those with an initial RHR of 70 at the first measurement, but with a RHR greater than 85 at the second reading, were nearly two times as likely to die from ischemic heart disease (adjusted hazard ratio (AHR) of 1.9; 95% CI 1.0-3.6). Similarly, all cause mortality was found to be modestly, but not significantly increased in the group with elevated RHR over time (AHR of 1.3; 95% CI 0.9-1.8).

Interestingly, the association between changes in RHR and IHD was not linear. Participants whose RHR decreased over time demonstrated no decrease in ischemic heart disease-related mortality. Although further research is warranted, the results of this study suggest that heart rate may serve as a marker for patients who could benefit from primary prevention measures.

Speaking of hearts, the final 2011 edition of JAMA detailed research on a new potential biomarker for diagnosing heart attacks. Researchers at the University of Hamburg studied the utility of using a newly developed highly sensitive troponin I (hsTnI) in comparison to contemporary troponin I (cTnl) in the diagnosis of acute myocardial infarction. http://jama.ama-assn.org/content/306/24/2684.full

For diagnosis of acute MI on admission, the highly sensitive assay had a higher area under the receiver operating characteristic curve (AUC) than the older assay (0.96 versus 0.92). The hsTnl was better than cTnl in detecting lower concentrations of troponin I in the first three hours after presenting to the hospital with chest pain.

Although overall results from the two assays were not statistically different, combining information from admission and the serial change in troponin I concentrations improved the performance of both assays. The positive predictive value for hsTnl increased from 75.1% on admission to 95.8% after 3 hours, and for cTnl, increased from 80.9% at admission to 96.1% after 3 hours. The researchers acknowledge that future studies are needed to determine whether the use of relative changes in troponin I could improve patient care outcomes. http://jama.ama-assn.org/content/306/23/2579.full

Finally, it wouldn’t be a proper New Years-themed edition without addressing weight loss: America’s number one resolution. While many people use the mantra “think with your brain and not your stomach” when choosing healthy foods for weight loss, a new article from of the Journal of Clinical Investigation questions whether the brain is immune to the negative effects of obesity. http://www.ncbi.nlm.nih.gov/pubmed/22201683

Researchers at the University of Washington examined the effect of high-fat diets on the brains of mice and rats. The researchers found that unlike inflammation in peripheral tissues, which develops over weeks to months after consistent exposure to a high-fat diet, inflammation in the brain occurs within 24 hours of a high-fat diet. Remarkably, evidence of inflammatory signaling in the hypothalamus, a crucial area of the brain for body weight control, was evident even prior to weight gain.

The researchers then undertook a retrospective analysis of young adults, with a range of BMIs, who underwent brain MRI. As compared to lean individuals, obese individuals had significantly increased hyperintensity of the T-2 weighted signal in the mediobasal ganglia, a finding indicative of gliosis, or brain injury.

These findings, which show a link between damage to the hypothalamus and obesity, may help explain why individuals attempting to lose weight find themselves fighting against a “set weight.” Perhaps it is actually our brains, and not our stomachs, dictating our ability to lose weight.

Dr. Alexandra Sowa is a 1st  year resident at NYU Langone Medical Center

Peer reviewed by Robert Gianotti, MD, associate editor, Clinical Correlations

Image courtesy of Wikimedia Commons

References:

Fox K,Borer JS,Camm AJ, et al; Heart Rate Working Group. Resting heart rate in cardiovascular disease. J Am Coll Cardiol. 2007; 50(9):823-830.  http://content.onlinejacc.org/cgi/content/full/j.jacc.2007.04.079v1

Keller T, Zeller T, Ojeda F, et al. Serial Changes in Highly Sensitive Troponin I Assay and Early Diagnosis of Myocardial Infarction. JAMA. 2011; 306 (24): 2684-2693.  http://jama.ama-assn.org/content/306/24/2684.full

Nauman J, Janszky I, Vatten L, et al. Temporal Changes in Resting Heart Rate and Deaths from Ischemic Heart Disease. JAMA. 2011; 306 (23): 2579-2587.  http://jama.ama-assn.org/content/306/23/2579.full

Thaler JP, Yi CX, Schur EA, et al. Obesity is associated with hypothalamic injury in rodents and humans. J Clin Invest. 2011.  http://www.ncbi.nlm.nih.gov/pubmed/22201683

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