"More than 80 percent of all cases of sudden cardiac death occur in people who have significant coronary artery disease, but we currently do not have a medical test that consistently identifies patients at risk," said Sumeet S. Chugh, M.D., associate director of the Cedars-Sinai Heart Institute and director of Clinical Electrophysiology. Chugh is first author of an article in Circulation , now appearing online ahead of print. This research was conducted with colleagues in the Emergency Medicine and Pathology Departments at Oregon Health and Science University in Portland, as part of the ongoing Oregon Sudden Unexpected Death Study.
"Abnormal QT prolongation has significant potential for evaluating risk and developing prevention strategies, but there are many factors “ some known and some not known “ that contribute to QT prolongation. Diabetes and the use of certain medications were significant predictors of QT interval prolongation and sudden cardiac death risk in our study. However, the most interesting and somewhat unexpected finding was that abnormally prolonged QT interval of unknown etiology “ independent of diabetes, medications and other factors “ was an even more powerful predictor of sudden cardiac death, with a five-fold increase in odds," said Chugh, who holds the Pauline and Harold Price Chair in Cardiac Electrophysiology Research.
The researchers noted that several gene variations have been linked to prolonged QT intervals, and the discovery of new genetic associations are likely to improve risk-assessment and intervention strategies. "The continued identification of gene variants that determine QT interval duration has become an important scientific priority in the field," Chugh said.
"QT interval" refers to electrical activity that occurs in the main pumping chambers of the heart, the ventricles. It includes the Q, R, S, and T waves seen on an electrocardiogram. Unlike heart attacks, which are typically caused by clogged coronary arteries, sudden cardiac arrest is the result of defective electrical impulses.
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Used in solar cells, quantum dots may be quickly weathered by acid rain, he said. Another concern is that acids in the body could break down dots used in such medical applications as in vivo imaging. "If they degrade faster than they can be excreted, there's the potential for heavy metals to be released into the body," said Alvarez. "Then their impact becomes a question of dose."
The team tested its theories on common bacteria that serve as models of cell toxicity and indicators of environmental health. At near-neutral pH, bacteria exposed to quantum dots containing cadmium and selenium showed decreased rates of growth but did not die.
But in moderately acidic or alkaline conditions, quantum dot shells decomposed more rapidly, killing the bacteria in a matter of hours.
On the positive side, the study also found certain proteins and such natural organic matter as humic acids may mitigate the effects of decomposing quantum dots by coating them or by complexing the metal ions released, making them less toxic.
The researchers cautioned that short-term studies can't easily predict whether toxins released by quantum dots will build up in the body over time. "We hope our work will stimulate research by other labs into the release dynamics," said Alvarez.
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