Pericardial fat a better predictor of CHD than BMI

by Lisa Nainggolan

Technorati Tags: coronary heart disease,chest pain,Acute myocardial infarction,angina pectoris

Winston-Salem, NC- A new study has shown that fat around the heart—so-called pericardial fat—predicts coronary heart disease (CHD) independent of conventional risk factors [1].

In fact, pericardial fat may be a better predictor of an individual's future risk of CHD than either body-mass index (BMI) or waist circumference, say Dr Jingzhong Ding (Wake Forest University School of Medicine, Winston-Salem, NC) and colleagues in their paper in the September 2009 issue of the American Journal of Clinical Nutrition.

Ding told heartwire: "We and other groups have previously found in cross-sectional studies that pericardial fat is related to coronary artery disease. Our new study extends the findings to demonstrate that pericardial fat predicts the future development of clinical events of CHD and that this kind of prediction is beyond that conferred by conventional obesity measures—the first time this has been shown."

Inflammatory cytokines secreted by pericardial fat could be the culprits

Ding et al conducted a case-cohort study in 998 individuals randomly selected from the more than 6000 participants of the Multi-Ethnic Study of Atherosclerosis (MESA), who had no history of CVD. The volume of pericardial fat was measured using cardiac CT scans performed at baseline in MESA.

Of the 998 individuals, 26 developed incident CHD during follow-up, from 2000 to 2005. Pericardial fat was positively correlated with both BMI (correlation coefficient=0.45; p<0.0001) and waist circumference (correlation coefficient=0.57; p<0.0001).

In unadjusted analyses, pericardial fat (relative hazard per one standard deviation increment 1.33), but not BMI (1.00), was associated with the risk of CHD. Waist circumference was marginally associated with CHD risk (1.14; p=0.1). The relation between pericardial fat and CHD remained significant after further adjustment for BMI and other cardiovascular disease risk factors (1.26).

"Our data support the idea that pericardial fat is a better predictor of incident CHD than are more general measures of adiposity (eg, BMI or waist circumference)," say Ding et al. "The present study extends the findings of other research in this field by relating pericardial fat to incident CHD in community-based adults without a history of CVD," they add.

Ding says he and his colleagues have a theory as to the possible mechanism underlying the link between pericardial fat and CHD. "The pericardial fat secretes many chemicals, such as inflammatory cytokines like IL-6," he noted. "We can postulate that direct secretion of such substances might lead to the development of atherosclerosis in the coronary arteries." Pericardial fat is also known to secrete such inflammatory cytokines at a higher rate than subcutaneous fat, he adds.

More research needed on pericardial fat

He told heartwire that much more research is needed on pericardial fat. In general, older people have been found to have more pericardial fat than younger ones, and the volume of pericardial fat does seem to correlate with BMI and other obesity measures, as shown in the current study. But slim people also have pericardial fat, he noted, and it is not known what amount is "normal," if any. Whether babies have pericardial fat present at birth, for example, is unclear. Nor is it known whether there is any kind of cutoff amount of this fat above which it becomes hazardous.

Future studies should also examine whether pericardial fat is the primary fat depot regarding the risk of developing CHD, after other regional fat depots are controlled for, say he and his colleagues. "If the hypothesis is confirmed, pericardial fat may serve as a more specific and sensitive marker of CHD than other fat measures."

However, they note that routine CT scans are not feasible for mass screenings at the present time, but the echocardiographic measurement of pericardial fat "has potential for CHD risk stratification."

"Ultimately, with a better understanding of the determinants of pericardial fat accumulation and the underlying mechanism of the link between pericardial fat and CHD, new therapeutic targets may be identified in the prevention of CHD," they conclude.

Source

1. Ding J, Hsu F-C, Harris TB, et al. The association of pericardial fat with incident coronary heart disease: the multi-ethnic study of atherosclerosis (MESA). Am J Clin Nutr 2009; 90:499-504.

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Teachable software may help diagnose endocarditis, study shows

Technorati Tags: Arrhytmias,Cardio Diagnstic,Endocarditis

by Barbara Boughton

San Francisco, CA - Artificial neural networks—teachable software designed to mimic the human brain—could one day be used to diagnose endocarditis related to implanted cardiac rhythm devices.

In a proof-of-concept study, investigators from the Mayo Clinic in Rochester, MN devised a neural network that could correctly identify 72 of 73 generator pocket infections and 12 of 13 cardiac rhythm management device-related infective endocarditis (CRMD-IE), according to research presented here at the American Society for Microbiology 2009 Interscience Conference on Antimicrobial Agents and Chemotherapy.

If proven, the software could benefit some patients by helping them avoid the risk, discomfort, and expense of transesophageal echocardiography (TEE), according to lead author Dr M Rizwan Sohail (Mayo Clinic). "In some cases, it might enable us to correctly diagnose patients without performing TEE or to select patients who might benefit from additional testing," Sohail said. "The result would be reduced healthcare costs and improved outcomes."

The researchers used data from 189 patients admitted to the Mayo Clinic with a diagnosis of CRMD infection to "train" the software to recognize variables that signaled infection. Of the patients, 23% actually had CRMD-IE.

In testing the artificial neural network, the researchers used three configurations of clinical variables to test how accurate the software could be. They found that the most reliable variables were blood-culture results, presenting signs and symptoms, tenderness at the infection site, ejection fraction, and fever. By using these variables, they increased the overall sensitivity of the artificial neural network to 86.4%, Sohail said.

In developing their model, they focused primarily on clinical features of CRMD infection, rather than laboratory parameters, because these findings are readily available to clinicians. However, the inclusion of positive blood cultures and presenting signs and symptoms were the variables that most improved the sensitivity of their model, Sohail said.

The scientists used the final neural network on six cases with an "unknown" diagnosis. They found that the trained software correctly identified all four cases without CRMD-IE (pocket-only infections) but missed one of the two CRMD-IE cases.

The scientists are continuing to work with the artificial neural network and have already used more than 400 cases to continue "training" the software. They also plan to expose it to 200 cases with unknown diagnoses to see how reliable the software is. If the model proves reliable, the artificial neural network might eventually be used to diagnose other types of infection, such as pneumonia, Sohail said.

"In training the artificial neural network, you have to be very careful about what data you feed into it, and expose it gradually to different variables," he said. Like humans, too much extraneous data can cause the artificial neural network to "become distracted," he said.

"These results are very encouraging," commented Dr Vance G Fowler Jr (Duke University, Durham, NC). "If appropriately validated, it could help clinicians make a sometimes-difficult diagnosis."

Yet Fowler pointed out that the artificial neural network correctly identified only a handful of CRMD-IE cases, while it was more successful in pinpointing generator pocket infections, which are fairly easy for clinicians to recognize, he said. "But it's a novel and innovative approach, and it clearly warrants further investigation," he said.

Source

Sohail MR, Saadah LM, Uslan DZ, et al. Using artificial neural networks to predict cardiac rhythm management device-related infective endocarditis. American Society for Microbiology 2009 Interscience Conference on Antimicrobial Agents and Chemotherapy; September 12, 2009; San Francisco, CA. Abstract K-268.

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Cardiac MRI shows promise in European study

by Marlene Busko

Essen, Germany - A pilot study in 20 German centers suggests that cardiac magnetic resonance (CMR) imaging is safe, used frequently in clinical practice, provides high-quality images, and strongly affects patient care [1].

The main indications for CMR imaging were for patients with hypertrophic cardiomyopathy, CHF, and CAD.

Importantly, in 16% of cases, CMR imaging led to a new, unsuspected final diagnosis, and in 45% of cases, patient treatment was altered as a result of CMR findings.

"Having a constantly growing number of sites clearly demonstrates that CMR has already made its way into clinical routine," lead author Dr Oliver Bruder (Elisabeth Hospital, Essen, Germany) told heartwire. "However, more widespread use in some countries is still limited by the availability of CMR scanners, trained personnel, and low reimbursement rates."

The study is published online August 12, 2009 in the Journal of the American College of Cardiology.

Three main clinical indications

In the past five years CMR has been increasingly used in clinical practice in European countries such as Germany, Spain, the United Kingdom, and Portugal, coauthor Dr Anja Wagner (Drexel University College of Medicine, Philadelphia, PA) told heartwire. However, little information existed about the impact of this procedure on clinical practice.

To evaluate the indications, image quality, safety, and impact on patient management from using CMR imaging, the researchers analyzed data from the European Cardiovascular Magnetic Resonance (EuroCMR) registry for 11 040 consecutive patients who underwent CMR imaging in 20 centers in Germany.

Two-thirds of the patients had prior echocardiography, but CMR imaging was the first imaging procedure for 23% of the patients.

Severe complications requiring an overnight stay in hospital occurred in only five patients and were related to stress testing. No patients died during or due to the procedure. Mild complications occurred in 1.1% of patients.

Most patients (86%) did not require further imaging tests after CMR imaging.

The top three indications of CMR were workup of myocarditis/cardiomyopathies (32% of patients), risk stratification in CAD (31%), and myocardial viability imaging (15%).

"The presence and pattern of late gadolinium enhancement of the left ventricular myocardium is particularly helpful to differentiate the etiology of reduced left ventricular function in patients with new onset of heart failure," Bruder said.

Risk stratification in patients with suspected CAD is another important application, he added, noting that "single-center data, such as studies from the Eike Nagel group [2], have clearly demonstrated that patients with a normal stress CMR have an excellent prognosis."

These findings from multiple centers with imaging instruments from multiple vendors document the potential of CMR imaging for clinical, routine use, since CMR was capable of answering relevant clinical questions in more than 98% of cases, the authors write.

Impact of CMR on prognosis

Next, the researchers will analyze data from the EuroCMR registry to determine the prognosis for patients who undergo CMR imaging for the three most common indications.

"As soon as these prognostic data are available, we speculate that CMR will become the main imaging procedure in many major clinical indications," Bruder said.

Unlike other procedures, CMR does not involve ionizing radiation. The current study also suggests that a substantial number of invasive coronary angiographies can be avoided in patients undergoing CMR stress testing for workup of suspected CAD, he added.

"We are very excited that we will soon expand our research [from currently more than 50 European centers] to the United States," Wagner, who will coordinate the US research, said.

Implications for US practice

"In the US, CMR is available in clinical practice but is limited to large hospitals, academic centers, and advanced outpatient clinics," Dr Ricardo C Cury (Baptist Cardiac and Vascular Institute, Miami, FL), who was not involved in the study, commented to heartwire.

He identified three key findings:

• The main clinical indications that MRI was used for in this registry are similar to those in the US.
• MRI is a very safe procedure, even during pharmacological stress.
• In two-thirds of patients, CMR affected patient management, and in 16% of patients there was a new important finding that was not suspected before the MRI study.

CMR can be used to replace or supplement more invasive procedures, he noted, and although the use of CMR in clinical practice is growing, this is occurring at a slower pace than in research, he added.

According to Cury, "More physicians need to be trained in CMR, and referring cardiologists need better education about CMR."

Sources

1. Bruder O, Schneider S, Nothnagel D, et al. EuroCMR (European Cardiovascular Magnetic Resonance) registry: Results of the German pilot phase. J Am Coll Cardiol 2009; DOI: 10.1016/j.jacc.2009.07.003. Available at: http://content.onlinejacc.org.
2. Jahnke C, Nagel E, Gebker R, et al. Prognostic value of cardiac magnetic resonance stress tests. Circulation 2007; 115:1769-1776.

Technorati Tags: CMR,cardiac MRI,cardiomyopathy,CHF,CAD

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