Clinical Briefs

By Louis Kuritzky, MD

Impaired Fasting Glucose vs Impaired Glucose Tolerance

In the absence of postglucose load measurements, most clinicians diagnose diabetes mellitus (DM) on the basis of an elevated fasting blood glucose (FBG), most recently defined as diabetic if > 125 mg/dL. Because glucose derangement typical of incipient diabetes is heralded by modest perturbations of FBG, the category of impaired fasting glucose (IFG = 110-125 mg/dL) designates a population at substantially increased risk for development of frank DM. Whereas IFG is often the first measurable glucose homeostatic defect in those ultimately destined to develop DM, impaired glucose tolerance (IGT = 2-hour post 75-g oral glucose load 140-199 mg/dL) becomes evident earlier in some persons.

This study examined the concordance between FBS and IGT, by selecting patients (n = 279) whose clinical circumstances suggested screening for metabolic abnormalities (exclusive of those already known to have DM). By including measurement of insulin resistance, Schianca and colleagues were also able to define the relationship between insulin resistance and the presence of IFG, IGT, or both.

Schianca et al found that persons with IFG were characterized by a presence of insulin secretory deficiency, whereas IGT was generally accompanied by insulin resistance. The combination of both tests disclosed an additional 17% of persons with disturbed glucose metabolism compared to relying on FBS alone. Since IFG and IGT reflect different pathogenetic underpinning, using both tests not only discovers a larger group of persons with disturbed glucose homeostasis, it may also help direct which therapeutic tool best matches the associated metabolic defect.

Schianca GPC, et al. Diabetes Care. 2003;26:1333-1337.

Risk Stratification in Long-QT Syndrome

On EKG, prolongation of the QT interval (QTI) may be a marker for increased susceptibility to life-threatening arrhythmias. With normal heart rates (60-100), the QTI (from the beginning of the QRS complex to the return of the T wave to baseline) generally ranges from 0.30-0.40 seconds, and the duration is typically 10% longer in females. Since the QTI is heart rate dependent, a calculation is made using Bazett’s formula to give a "corrected" QTI. Factors that can cause QTI prolongation include myocardial ischemia, myocarditis, antiarrhythmics, psychotropic agents, hypokalemia, hypomagnesemia, hypocalcemia, and cerebral events like subarachnoid hemorrhage. Additionally, there is a genetic long-QT syndrome (Romano Ward Variant), in which risk stratification for arrhythmia has been poorly defined, which is the subject matter of this investigation.

Priori and colleagues studied 647 patients from 193 families for 3 different genotypes associated with long QTI. In untreated individuals during a 28-year mean observation period, 13% of long-QTI individuals had a cardiac arrest or died suddenly before age 40. Beta-blocker therapy is believed to be efficacious in this population. Because different genetic varieties of long-QT syndrome, varying degrees of corrected QTI, and gender all impact the predictive model, clinicians should refer such patients to facilities where appropriate genetic testing can be accomplished.

Priori SG, et al. N Eng J Med. 2003; 348:1866-1874.

EBCT, Motivation, Behavioral Change, and Cardiovascular Risk Profile

It has been suggested that as much as 75% of clinical CHD can be predicted on the basis of traditionally recognized risk factors (eg, lipids, BP, smoking). Because of the ponderous effect of cardiovascular disease upon mortality, heightened awareness and motivation of the at-risk population is a shared clinician-patient goal.

EBCT (Electron Beam Coronary Tomography) is a recent technology, which allows noninvasive imaging of the coronary vasculature calcification, a substantiated marker for cardiovascular risk. This study investigated whether providing patients an EBCT photograph would enhance their motivation to alter their cardiovascular risk factors.

Study subjects (n = 559) comprised ostensibly healthy US Army Personnel aged 39-45 who were scheduled for mandated periodic physical examination. After EBCT, one group of subjects received intensive case management (ICM) including counseling on diet, smoking cessation, lipids, and exercise. Impact of intervention was measured by change in Framingham Risk Score (FRS).

After 1 year of follow-up, providing EBCT results to study subjects resulted in no statistically significant effect upon FRS. On the other hand, subjects who received intensive case management showed a significant decline in FRS. This study calls into question the belief that dramatization and concretization of potential or real target organ damage is a strong motivator. Encouragingly, favorable effect of intensive counseling about cardiovascular risk factors did result in measurable risk reduction.

O’ Malley PG, et al. JAMA. 2003;289:2215-2223.

Dr. Kuritzky is Clinical Assistant Professor, University of Florida, Gainesville.