Intra-Abdominal Obesity and Cardiovascular Risk

Intra-Abdominal Obesity and Cardiovascular Risk

Manesh R Patel

Cardiology Fellow, Duke University, Atlanta, GA USA

This paper will address the clinical perceptions surrounding cardiovascular risk factors, while keeping a particular focus on intra-abdominal adiposity and the metabolic syndrome. The results of a survey on intra-abdominal adiposity and the definition of the metabolic syndrome according to the current National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) guidelines are discussed. Prof Ballantyne's perspectives on the survey results will be provided along with comments from various thought leaders in the area of metabolic syndrome and cardiovascular disease prevention.

Survey participants

A six-question survey evaluating perceptions on intra-abdominal adiposity and the metabolic syndrome in the context of cardiovascular risk factors was completed by 1436 healthcare professionals. Of these respondents, physicians made up the largest group (879 participants or 61%), with cardiology representing the largest medical specialty (634 participants or 72%).

Waist circumference as a cardiovascular risk factor

The most recent NCEP ATP III guidelines (the 2002 update) emphasize the use of the metabolic syndrome as a therapeutic target beyond lowering of LDL. In fact, the guidelines provide criteria for the clinical recognition of the metabolic syndrome. For evaluation of intra-abdominal adiposity, the guidelines recommend looking at waist circumference. When asked what the most accurate indicator of cardiovascular risk was (weight, body mass index, waist circumference, or waist-to-hip ratio), only 49% of respondents identified waist circumference as the most accurate indicator. These survey confirm the previous observations and epidemiological data that have demonstrated that fat distribution is an important factor with intra-abdominal fat being of increased concern. In Ballantyne's view, weight-associated measurements provide a continuum of cardiovascular risk prediction with weight being the poorest predictor, followed by body mass index, waist-to-hip ratio, and waist circumference. He notes, that waist-to-hip ratio does not provide more information than waist circumference, and that "waist circumference is one simple measurement." Dr Steven Haffner commented that the literature supports that elevated waist circumference despite a decreased BMI might be indicative of an increased risk of diabetes.

CLINICAL IDENTIFICATION OF THE METABOLIC SYNDROME

Risk Factor	Defining Level
Abdominal Obsevity	Waist Circumference
Men	>102 cm (>40 in)
Women	>88 cm (35 in)
Triglycerides	150 mg/dl

HDL Cholesterol
Men	< 40 mg/dl
Women	< 50 mg/dl
Blood Pressure	130 / 85 mmHg
Fasting Glucose	110 mg/dl

Measuring waist circumference

When asked how often they perform waist circumference measurements to evaluate cardiovascular risk, 54% of all healthcare professionals from all geographic regions and specialties responded that they perform the measurement less than 25% of the time or never, although it was identified as an accurate predictor of cardiovascular risk and part of the clinical definition of the metabolic syndrome. Unfortunately, cardiologists around the world perform the measurement as infrequently if not less than other physicians. These findings are not surprising and it though physicians find waist circumference important, but do not measure it. He also stated that "waist circumference should be a vital sign. Physicians should have it on the chart when they walk into a room. Much like other vital signs, there needs to be a system in place to get it before the physician sees the patient." For instance, nurses at some metabolic clinics routinely measure waist circumference along with the other vital signs and provide it to the doctor when they are seeing their patients. The waist circumference is one simple measurement of the mid-abdominal line, near the anterior superior iliac crest, at the end of expiration. Care should be taken not to measure near the hips, where patients often wear their pants if they have intra-abdominal adiposity.

Waist-to-hip ratio was initially used to help determine adipose distribution in patients with abdominal adiposity versus their lower extremities, often referred to as "apple" versus "pear" morphologies. However, waist circumference identifies intra-abdominal adiposity accurately in one measurement. Additionally due to the simplicity of the measurement patients could follow their progress at home.

Waist circumference in different populations

When asked if they felt that the "at-risk" standards for waist circumference were appropriate, 64% of healthcare professionals responded "yes". However, 28% felt that the "at-risk" standards should be lowered. Additionally, 52% of respondents thought that the "at-risk" standards should be adjusted by race.

It has been shown that the NCEP ATP III guideline recommendations for "at-risk" waist circumference were based on epidemiological data across one entire population, which may not accurately represent all ethnic populations. In fact, there is emerging data that certain ethnicities such as South Asians may require a lower "at-risk" waist circumference. However, it is felt that the guidelines provided a starting point for evaluating intra-abdominal adiposity, and that increasing the number of measurements and data from different populations is likely to improve our understanding. Future recommendations may be modified for special populations diagnosed with metabolic syndrome at lower waist measurements with multiple marginal risk factors, based on future research and published data.

Importance of cardiovascular risk factors

The majority of respondents; 61%, voted diabetes mellitus to be the most important of five cardiovascular risk factors (smoking, hypertension, hypercholesterolemia, diabetes mellitus, and abdominal obesity), followed by smoking, hypertension, and hypercholesterolemia. Abdominal obesity was rated as the lowest risk factor. These perceptions are common. Physicians are still focused on measurable disease entities, and intra-abdominal adiposity is not as high on the radar screen. The goal of the NCEP ATP III guidelines is to refocus clinicians on the preventive mechanism by emphasizing the importance of the metabolic syndrome. It is agreed that diabetes, hypertension, and hypercholesterolemia clearly are significant cardiovascular risk factors, but how do you get there? Obesity and specifically intra-abdominal adiposity plays a major pathophysiologic role in the development of these conditions. Clinicians should focus on the causal nature of intra-abdominal adiposity in hopes of treating its consequences, which include diabetes and hypercholesterolemia. Drs Stone and Haffner both reiterated the significance of the "hypertriglyceridemic waist" as identified in several studies where the presence of increased waist circumference and increased triglycerides was associated with specific increases in the risk factors for heart disease.

Metabolic syndrome as a specific disease entity

When asked if they consider the metabolic syndrome as a specific disease entity or a cluster of individual risk factors, 49% of global healthcare professionals responded that the metabolic syndrome is a cluster of individual risk factors. This was in keeping with the perceptions on the relative importance of cardiovascular risk factors discussed above.

Additionally, there were geographic variations for the identification of the metabolic syndrome as a specific disease entity, with European healthcare providers identifying this at a higher rate than their North American colleagues — 54% of North American healthcare professionals consider the metabolic syndrome as a cluster of individual risk factors while 55% of Europeans see it as a specific disease entity itself. Dr Haffner provides one explanation. He states that there are structural differences in definitions, with the ATP III guideline definition requiring three out of five criteria and the World Health Organization (WHO) definition (mostly used by European clinicians), which necessitates insulin resistance or some form of glucose intolerance. Dr Scott Grundy discussed the recent consensus definition of metabolic syndrome from the International Diabetes Federation (IDF) presented in April 2005, which recognizes increased waist circumference or abdominal obesity to be at the forefront of diagnosis. Dr Grundy commented that this revision took into consideration a relationship between increased abdominal obesity and potential insulin resistance, with the focus of the IDF definition being an attempt to emphasize the clinical utility of making the diagnosis and driving lifestyle changes (ie, weight loss and increased physical activity).

Dr Ballantyne concluded that these findings highlight the need for making physicians and patients appreciate that all of these factors are related, especially with regards to intra-abdominal adiposity. As an example, Dr Ballantyne described his method for getting patients to focus on abdominal obesity. He stated that to get the message across, he often has patients tighten their abdominal muscles in the clinic room. He then presses on the abdomen and describes to them how he can feel their abdominal muscles. This technique is used to drive home the point that the abdominal adipose is intra-abdominal. The fat in the abdominal cavity is next to the two most vital organs for metabolic control, the liver and the pancreas, which are in charge of blood sugar and lipid management.

This understanding is also crucial for physicians as Dr Ballantyne mentioned. Recognizing the metabolic syndrome identifies patients with a disease entity strongly related to intra-abdominal adiposity. Recommended weight loss and lifestyle modifications have a significant effect on the disease state. For instance, he cited the Diabetes Prevention Trial, which demonstrated that a modest weight loss (5-7%) led to a decrease in the incidence of diabetes, which will likely be translated into a decrease in cardiovascular disease. Therefore, understanding the relationship between intra-abdominal adiposity and standard cardiovascular risk factors is crucial to both recognize and prevent cardiovascular disease. In order to bring about cardiac risk factor reduction and lifestyle modifications, healthcare providers must be proactive and continue to increase their knowledge of the metabolic syndrome and published guidelines. The acquired knowledge must result in clinical application. Additional efforts such as making waist circumference the "fifth vital sign" can help identify patients at increased risk early.

Available Volumes

EDITOR IN CHIEF

Dr. Rajeev Gupta
(MD PhD FACC)

HON. EDITOR

Dr. Soneil Guptha
(MD FACC FESC)

Editorial Board

Available Volumes

USEFUL LINKS