CLEVELAND, OHIO. Brain natriuretic peptide (BNP), a cousin of atrial natriuretic peptide (ANP), is a hormone released from the walls of the ventricles when stretched such as during unusually strenuous activity. It is stored as a prohormone within secretory granules in the ventricles and is secreted as an N-terminal fragment, N-terminal pro-brain natriuretic peptide (nt-pro-BNP), and the smaller active hormone BNP. BNP has effects similar to those of ANP, that is, it decreases sodium reabsorption rate, renin release, and aldosterone release; it also increases vagal (parasympathetic) tone and decreases adrenergic (sympathetic) tone. Because nt-pro-BNP is easier to measure than BNP it is often used as a marker for BNP.

It is well established that BNP and nt-pro-BNP levels are elevated in heart failure and that the degree of elevation is directly proportional to the seriousness of the failure. However, researchers at the Massachusetts General Hospital have reported that lone afibbers also have elevated nt-pro-BNP values even when in sinus rhythm.

Now researchers at the Cleveland Clinic report that an elevated BNP level is a strong predictor of the recurrence of atrial arrhythmia (atrial fibrillation, flutter or tachycardia) after pulmonary vein isolation (PVI). Their study involved 726 lone afibbers undergoing their first PVI. The average age of the patients was 57 years, 71% were male, and 78% had paroxysmal AF. All study participants underwent a thorough medical examination to exclude known causes of AF and had their BNP level determined on the day of the procedure (median value 52 pg/mL). An elevated BNP level was found to be associated with older age, longer duration of AF, non-paroxysmal (persistent or permanent) AF, and larger left atrial size.

Over a median follow-up of 26 months, excluding a 2-month blanking period, 78.8% of ablatees remained arrhythmia-free. The following variables independently predicted arrhythmia recurrence:

• Higher body mass index (BMI)
• Non-paroxysmal AF
• Longer duration of AF
• Lower left ventricular ejection fraction
• Larger left atrial size.

However, the most important predictor of ablation failure was an elevated BNP level. Afibbers with a pre-ablation BNP level above 126 pg/mL had a 6 times greater risk of recurrence than did those with a BNP level of less than 31 pg/mL.

The Cleveland researchers speculate that in lone afibbers, the source of BNP, typically secreted by the ventricles, is actually the atria and may reflect intrinsic atrial disease such as inflammation, fibrosis or even subclinical atrial myocardial ischemia.

Hussein, AA, Wazni, OM, et al. Plasma B-type natriuretic peptide levels and recurrent arrhythmia after successful ablation of lone atrial fibrillation. Circulation, Vol. 123, May 17, 2011, pp. 2077-82

Editor's comment: The role of BNP was discussed in detail in an earlier research report. See The Role of BNP in Atrial Fibrillation. The conclusion of this report was that BNP is an important hormone released from the walls of the ventricles and, to some extent, the atria when stretched. It is well established that a high BNP level is associated with heart failure, but it is now also clear that elevated BNP levels are closely associated with atrial fibrillation including lone AF. BNP levels are higher in afibbers than in non-afibbers and those in permanent afibbers are higher than those in paroxysmal afibbers. A high BNP level is associated with a lower probability that cardioversion will be successful and also predicts a poor outcome of catheter ablation. There is also evidence that an elevated BNP level in paroxysmal afibbers is associated with a quicker progression to the permanent state. Finally, some very recent research provides convincing evidence that an elevated BNP level is strongly associated with the risk of developing AF over a 10-year period following the baseline BNP determination. It is to be hoped that electrophysiologists will soon include a measurement of BNP or nt-pro-BNP in their initial evaluation of all afibbers and their relatives.