Sinus node dysfunction

Overview

The sinus node, the natural pacemaker of the heart, is located in the heart's upper chamber, called the atrium. It is responsible for initiating the electrical impulse that travels through the heart, causing it to beat in a regular rhythm and heart rate. This normal transmission is called normal sinus rhythm, with a regular heartbeat of 60 to 100 times per minute. If the sinus node is not functioning normally — due to damage from surgery, drugs, congenital heart defects or other causes — the heartbeat may become very slow with a decrease in blood pressure. Sinus node dysfunction may lead to an abnormally slow heart rhythm called bradycardia.

Signs & symptoms

Sinus Node Dysfunction may cause the following symptoms:

• Chest pressure or pain
• Fainting, also known as syncope, or near-syncope
• Fatigue
• Lightheadedness or dizziness
• Palpitations, which can be skipping, fluttering or pounding in the chest
• Shortness of breath

It is important to note that children with sinus node dysfunction may not know how to describe what they are feeling. They may have trouble keeping up with other children or realize they are having "spells" and want to sit down and rest. Some children do not experience any symptoms at all.

Diagnosis

Sinus node dysfunction may occur spontaneously with unpredictable timing. Therefore, in many cases, specialized tests are needed to make an accurate diagnosis. If your doctor suspects that your child has an arrhythmia caused by sinus node dysfunction, he or she will order one or more of the following diagnostic tests to determine the source of your child's symptoms.

• Electrocardiogram (ECG or EKG) — An ECG records the heart's electrical activity. Small patches called electrodes are placed on your child's chest, arms and legs, and are connected by wires to the ECG machine. The electrical impulses of your child's heart are translated into a graph or chart, enabling doctors to determine the pattern of electrical current flow in the heart and to diagnose arrhythmias.
• Electrophysiology (EP) Study — In an EP study, doctors insert special electrode catheters — long, flexible wires — into veins and guide them into the heart. These catheters sense electrical impulses and also may be used to stimulate different areas of the heart. Doctors can then locate the sites that are causing arrhythmias. The EP study allows doctors to examine an arrhythmia under controlled conditions and acquire more accurate, detailed information than with any other diagnostic test.
• Exercise Stress Test — An exercise stress or treadmill test records the electrical activity of your child's heart during exercise, which differs from the heart's electrical activity at rest.
• Event Monitor — This is a small monitor about the size of a pager that your child can have for up to a month. Since the arrhythmia may occur at unpredictable times, this will help to record the abnormal rhythm when your child is experiencing symptoms. He or she can just push a button on the pager and record the heartbeat. The recording can then be transmitted by phone to the doctor.
• Holter Monitor — A Holter monitor is a small, portable machine that your child wears for 24 hours. It is about the size of a portable tape player and provides a continuous 24-hour recording of your child's heartbeat onto a tape. You will be asked to keep a diary of your child's activities and symptoms. This monitor may detect arrhythmias that might not show up on a resting electrocardiogram, which only records a heartbeat for a few seconds at rest.

Treatment

Sinus node dysfunction can be treated with the implantation of a permanent pacemaker. A pacemaker is a medical device that regulates the heart beat. It consists of two parts — the generator and the lead. The generator is a small metal container with a battery and tiny computer. The lead is an insulated wire that carries electrical impulses to the heart to ensure a stable heartbeat.

The computer in the pacemaker is constantly monitoring your child's heartbeat. This is called sensing. When the pacemaker senses your child's heartbeat, it continues to "watch" or monitor your child's heart and does not send a signal to stimulate the heart to beat. If no electrical impulse is sensed by the pacemaker, it sends out a signal to stimulate your child's heart to beat.

For information on how a pacemaker is implanted, please see Pediatric Pacemaker Procedure.