The use of iodine-123 meta-iodobenzylguanidine (123I-mIBG) scintigraphy is able to detect cardiac sympathetic nervous system abnormalities that are prognostic of heart failure and permanent atrial fibrillation (AF), according to a study in the January issue of Journal of the American College of Cardiology: Imaging.
Researchers noted that AF facilitates the development or progression of heart failure (HF) by reduction of cardiac output, which results from "enlargement of left atrial size, rapid ventricular rate, irregular rate, valvular inefficiency and left ventricular dysfunction with tachycardia-induced cardiomyopathy."
However, not all patients with paroxysmal AF and HF have reduced left ventricular ejection fraction (LVEF), unlike those with permanent AF and HF, and not everyone with paroxysmal AF progresses to permanent AF. Therefore, various researchers are trying to noninvasively identify key components of cardiovascular remodeling factors that promote AF in patients with preserved LVEF.
In that regard, Yasushi Akutsu, MD, and colleagues from Showa University School of Medicine in Tokyo evaluated cardiac sympathetic nervous system activity presented as the heart/mediastinum (H/M) ratio in 98 consecutive patients with idiopathic paroxysmal AF and preserved LVEF (more than 50 percent).
Researchers also measured C-reactive protein (CRP) and plasma brain natriuretic peptide (BNP).
During nearly five years of follow-up, the transition to permanent AF was associated with the occurrence of heart failure (HF) in 34.3 percent of patients with permanent AF versus 6.3 percent of patients without.
The investigators found that sympathetic nervous system activity, left atrial dimension, BNP levels and LVEF were the factors that perpetuated AF, but a multivariable analysis identified sympathetic nervous system abnormality as an independently powerful factor perpetuating AF.
In addition, BNP levels, left atrial dimension, sympathetic nervous system activity, LVEF and age were the factors resulting in the occurrence of HF with permanent AF; however, a multivariable analysis again identified sympathetic nervous system abnormality as an independently powerful predictor resulting in HF with permanent AF.
"Our major finding is that sympathetic nervous system abnormality was an independently powerful factor for predicting not only the transition to permanent AF, but also the occurrence of HF with permanent AF in patients with paroxysmal AF and preserved cardiac function," Akutsu and colleagues concluded.
In addressing the underlying mechanisms, they suggested that in patients with paroxysmal AF, electrical remodeling of atria occurs before structural remodeling and the electrical remodeling prolongs the duration of paroxysmal AF, which results in HF in patients with paroxysmal AF.
"It may result from similar causes that the value of sympathetic nervous system abnormality was superior to that of large left atrial dimension for predicting both events. The electrical remodeling of atria may influence sympathetic nervous system activity indirectly by the triggering of myocardial damage that AF causes, for example, oxidative stress."