Proton MRS spots early heart problems in diabetics

At a time when bad press about cardiovascular crises dogs diabetes drug manufacturers, cardiac proton MR spectroscopy is proving itself in identifying early signs of heart dysfunction in patients with impaired glucose tolerance. This finding has important implications for intervention and drug development.

Animal studies have shown that cardiac myopathy is related to the buildup of lipids and other products of fatty acid metabolism. The new multicenter study from researchers at the University of Texas Southwestern Medical Center in Dallas and other institutions in the same area shows for the first time that this is also the case for humans (Circulation 2007;116(10):1170-1175).

Researchers analyzed results from 134 patients with no history of heart disease and concluded that myocardial triglyceride buildup was more than twice as high in those with impaired glucose tolerance and type 2 diabetes compared with lean patients.

The technically demanding cardiac MRS was more accurate in detecting cardiac steatosis than standard serum measurements for triglycerides. The findings indicate that lipid buildup occurs prior to heart failure and type 2 diabetes diagnosis, raising prospects for effective interventions following imaging studies.

In an accompanying editorial, Dr. Frederick Ruberg, codirector of the advanced cardiac imaging program at Boston University, noted that this is the largest study of cardiac spectroscopy in human subjects. Thanks to this research, he wrote, "myocardial lipid content may one day be used as a biomarker to predict development of cardiac dysfunction in patients with insulin-resistant states and may serve as a measurable target for intervention before the development of cardiomyopathy."

Drugs that reduce fat accumulation in blood vessel walls have been shown to reduce risk of heart attack and stroke, said Ruberg in an interview with Diagnostic Imaging. Drugs in the TZD class, for example, which are used to reduce blood sugar levels in people with diabetes, are known to reduce fat content in liver and skeletal muscle cells. Perhaps they may do so in heart cells as well.

Drugs that may reduce fat accumulation in heart cells may likewise slow or avert the progression to heart dysfunction in diabetes. Cardiac MRS may be used as a means to test the efficacy of known drugs or agents in development in the treatment of cardiovascular disease, Ruberg said.