The sinus node is the pacemaker of the heart. The sinus node is a group of cells in the upper right hand corner of the heart, specifically in the right atrium near the entrance of the superior vena cava. In some instances the cells of the sinus node may traverse a line passing on a course into the lower portion of the right atrium. The sinus node generates electrical impulses that stimulate the heart muscle to contract. The impulses are initially passed through both atrium, then transmitted through the AV node to the ventricles. More information can be found in the article on normal electrical conduction.
Primary disorders of the sinus node are very uncommon in children. They are seen most commonly in children who have undergone surgery with incisions on the right atrium. This includes procedures such as the Fontan procedure or the Mustard or Senning operation for transposition of the great arteries.
Children or infants presenting with episodes of a slow heart rate, termed bradycardia, are much more likely to have a secondary cause of the slow heart rate as opposed to a primary abnormality of the sinus node. For example, changes in the autonomic nervous system may influence the vagus nerve to cause a slowing of the heart rate. This is commonly seen in premature infants with disordered breathing or other problems such as gastroesophageal reflux. In many instances a slow heart rate is a normal variant found in otherwise healthy, well conditioned children. Evaluation for disorders of the sinus node may include such tests as an ECG or Holter monitor. In addition, a stress test may be necessary.
In those individuals with a true disorder of the sinus node, a pacemaker may be required. A pacemaker provides an electrical impulse to the heart muscle from a small battery-powered electrical generator placed under the skin of either the abdomen or chest wall.