B-type natruretic peptide, or BNP, is a hormone that is manufactured by the ventricular muscle in human hearts. The physiologic effects of BNP include the following: Diuresis (increased urination), loss of sodium, and vasodilation. It is expressed in response to either a pressure or volume load on the ventricle. This can be seen in a number of different settings, including valve stenosis (narrowing), an enlarged and poorly functioning heart muscle, or a heart muscle that is stressed by having to pump excess blood.
BNP levels in the bloodstream can easily be measured. In the late 1990s it became widely appreciated that measuring BNP levels in older adults who presented with difficulty breathing could be helpful in distinguishing respiratory from heart related causes. Several studies confirmed this, and BNP was adopted as a rapid screening test in emergency rooms throughout the country.
The question from a pediatric standpoint is whether BNP can be helpful in managing children with heart disease. Several studies have addressed this very question. Currently BNP seems to be potentially helpful in the following settings. First, in the management of premature babies with a patent ductus arteriosus, BNP has been shown to be helpful in decision-making. Babies with high levels of BNP are more likely to benefit from early treatment compared to those with lower levels.
BNP levels in children have also been demonstrated to be useful in distinguishing babies who present with respiratory symptoms. In this setting, often an urgent decision needs to be made as to whether the baby potentially has a life-threatening heart condition. A recent study demonstrated that in a baby between 0-7 days of age presenting with possible heart related findings, a BNP level over 170 pg/ml indicates a greater than 90% chance that the baby has heart disease.
BNP also appears to be useful to help monitor and guide decision-making in the setting of dilated cardiomyopathy and chronic heart failure. One recent large study in pediatric patients found that a persistently elevated BNP level despite adquate therapy predicted a worse long-term outcome compared to patients with lower levels.
Less is known at this point about the utility of BNP monitoring in children with congenital heart defects, including both acyanotic and cyanotic forms. BNP levels do seem to rise in proportion to the amount of left to right shunting in patients with a ventricular septal defect. In addition, in patients with single ventricles levels have been shown to correlate with the degree of volume overload or stress on the heart. BNP levels have also been used following open heart surgery to track recovery. Finally, studies are ongoing to determine whether a BNP level might assist in predicting the timing and need for a pulmonary valve replacement in older patients who have pulmonary valve insufficiency following repair of tetralogy of Fallot.
In summary, blood levels of BNP have become commonplace in adult cardiology to assist in decision-making. Whether this ultimately becomes a useful tool in pediatric cardiology remains to be seen.
Penn Laird II, M.D.