NEW ORLEANS -- High levels of the amino acid cystine in the blood may indicate an increase in oxidative stress that can cause atrial fibrillation in patients following cardiac catheterization procedures, researchers suggested here.
About 90% of patients with a level of cystine less than the median of 97 µM were free from atrial fibrillation four years after undergoing catheterization compared with about 77% of patients who had higher levels of cystine (P=0.04), said Nima Ghasemzadeh, MD, a resident in internal medicine at Emory University in Atlanta.
"Higher oxidative stress burden, as measured as higher plasma cystine, is an independent predictor of left atrial size and of new onset atrial fibrillation," Ghasemzadeh told MedPage Today at his poster presentation at the American College of Cardiology meeting.
Co-author Ibrahim Kassas, MD, a resident in cardiology at Emory, told MedPage Today that their work suggests that treatment that normalizes measures of oxidation "needs to be investigated for the prevention of atrial fibrillation."
In their study, the Emory team reviewed outcomes of 629 patients who underwent cardiac catheterization and were then followed for a median of about two years to determine if they developed atrial fibrillation.
The researchers also followed a subgroup of 233 patients who had undergone two-dimensional echocardiograms to measure left atrium size.
Patients with prevalent atrial fibrillation were excluded from the analysis.
Of the 629 patients, 38 experienced atrial fibrillation. Those patients were generally older -- 68 versus 63 (P=0.006) and were also more likely to be men (84%, P=0.01).
The researchers also noted that the patients who developed atrial fibrillation had lower left ventricular ejection fraction -- 43% versus 51% (P=0.001) -- and a larger left atrium size -- 4.5 cm versus 4 cm (P<0.01).
Kassas pointed out that they excluded atrial fibrillation within 30 days after the procedure to avoid counting cases that might have been caused by the procedure itself.
Ghasemzadeh noted that the plasma cystine levels correlated with left atrium size (P=0.006).
When the researchers performed multivariate adjustment for traditional variables such as statin use, beta-blocker use, mitral regurgitation and left ventricular ejection fraction, independent predictors of left atrium size were observed to be cystine levels in the plasma (P=0.04), male gender (P<0.001), left ventricular ejection fraction (P<0.017), and high blood pressure (P=0.02).
They also performed multivariate analyses to determine predictors of the time to incident atrial fibrillation and determined those to be higher levels of cystine (P=0.04), male gender (P=0.009), and mitral regurgitation (P=0.001).
"This study adds to the evidence that there is something to oxidative stress and its impact on atrial fibrillation," said David Murdock, MD, medical director at the Cardiology Research and Education Foundation at the Aspirus Heart and Valvular Institute, in Wausau, Wis.
He told MedPage Today that there appears to be "compelling" data that effects on the sodium pathways may play a role in atrial fibrillation.
Ghasemzadeh noted that previous experimental studies had shown a link between oxidative stress and atrial fibrillation, and that aminothiol compounds -- cysteine, cystine, and glutathione -- can be used to measure levels of oxidative stress.
Kassas said the researchers were able to correlate levels of cystine with left atrium size and atrial fibrillation, but not the other compounds. They did observe a correlation between the ratio of cystine to glutathione, but not to the level of glutathione alone.
"The next step to take is to see if we can target cystine to prevent the occurrence of atrial fibrillation," Kassas said during the poster presentation.
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