Sick Sinus Syndrome

Sick sinus syndrome, also known as sinus node disease or sinus node dysfunction is a term that describes a group of heart rhythm disorders (arrhythmias) in which the sinus node — the heart's natural pacemaker stops working properly. The sinus node constitutes an area of specialized cells in the upper right chamber of the heart that control your heart rhythm.

In normal conditions, the sinus node creates a steady pace of regular electrical impulses. In sick sinus syndrome, these signals get abnormally paced. A person with sick sinus syndrome will have abnormal heart rhythms that are too fast, too slow, interrupted by long pauses, or an alternating combination of all these rhythm problems.

Sick sinus syndrome is a relatively rare condition, but the risk of developing sick sinus syndrome increases with age.

A majority of patients with sick sinus syndrome may gradually need an implantation of an artificial pacemaker to maintain a regular heart rhythm.

Initially, most patients with sick sinus syndrome may not have any symptoms at all. Over a period of time, when it becomes difficult for your heart to pump an adequate amount of blood, symptoms appear, and may include:

• Slower pulse than normal (bradycardia) 
• Fatigue 
• Dizziness or lightheadedness
• Fainting or sensations of fainting 
• Feeling short of breath or difficulty in breathing
• Chest pains
• A feeling of rapid, fluttering heartbeats (palpitations) 
• Disturbed sleep
• Mental confusion
• Problems with memory

Many of these signs and symptoms are because of reduced blood flow to your brain when the heart beats either too fast or too slowly.  

When to see a doctor?

If you have symptoms such as palpitations, lightheadedness, dizziness, fainting, fatigue, or shortness of breath, seek your doctor's advice. Several medical conditions can also cause these signs and symptoms — including sick sinus syndrome — and it is necessary to identify the cause of your problem.

The causes of sick sinus syndrome vary depending on its type.

Your heart consists of four chambers — two upper chambers (atria) and two lower chambers (ventricles). The sinus rhythm of your heart is controlled by the sinoatrial (SA) node — or sinus node — an area of specialized cells located in the right atrium. This is a natural pacemaker, and produces regular electrical impulses that are required to initiate or trigger each heartbeat.

From the sinus node, electrical impulses travel across the atria to the reach the ventricles, resulting in contraction of ventricles and pumping of blood out to your lungs and other body organs. In sick sinus syndrome, there is malfunctioning sinus node because of which your heart rate becomes too slow (bradycardia), too fast (tachycardia) or irregular. 

Types of sick sinus syndrome and their causes include: 

• Sinoatrial block: Electrical signals travel very slowly through the sinus node causing an abnormally slow heart rate. 
• Sinus arrest: The sinus node stops sending electrical signals or sinus node activity pauses. 
• Bradycardia-tachycardia syndrome: The heart rate follows a pattern of alternating abnormally fast and slow heart rhythms, usually with a long pause (asystole) in between heartbeats.

What causes the sinus node to misfire?

Diseases and conditions that cause scarring or damage to your heart's electrical system are the reason for malfunctioning of the sinus node. Scar tissue that may occur as a result of a previous heart surgery also may be the cause, especially in children. Sick sinus syndrome may also be triggered by certain group of medications, such as calcium channel blockers or beta blockers that are used in the treatment of high blood pressure, heart diseases or other conditions. However, in some cases, the sinus node does not work properly because of age-related wear and tear of the heart muscle.

Making a diagnosis of sick sinus syndrome is done by performing several tests.

Symptoms of sick sinus syndrome, even if they are present, may be so mild enough that they often go unnoticed. For this reason, sick sinus syndrome remains unidentified until it reaches an advanced stage at which risk of complications is high. You may call your family doctor or general practitioner if you have symptoms of sick sinus syndrome. When you call to set up an appointment, you may be referred to a doctor trained in diagnosis and treatment of heart conditions (cardiologist). Here is some information that can help you prepare for your appointment. 

What you can do?

Be aware of your pre-appointment restrictions, such as changing your activity level or your diet while preparing for diagnostic tests. Make a list of the following:

• Symptoms you have been experiencing, and their duration. 
• Key personal information, including major stresses or recent changes in your life. 
• Key medical information, including other medical problems for which you have recently been on treatment and all the medications you are taking, including over-the-counter medications, vitamins, and supplements. 

Ask a family member or friend to accompany you to the appointment, if possible. Someone who comes with you can help you remember what the doctor says. 

Write down the questions you want to ask your doctor.

For sick sinus syndrome, some basic questions to ask your doctor include: 

• What is the most likely cause of my symptoms? 
• Are there any other causes for my symptoms? 
• What kinds of diagnostic tests do I need? 
• What treatment approach will you suggest? 
• What procedure is recommended for a pacemaker implantation? 
• Will I need to stay in the hospital? 
• What risks are involved with pacemaker implantation procedure?
• What will the recovery from surgery be like? 
• Will I be able to resume normal activity and when? 
• Will a pacemaker be able to manage my symptoms permanently? 
• Will I need any additional surgery to maintain or will there be a need to replace my pacemaker? 
• How will my health be monitored long term? 
• I am being treated for another health problem. Will I need to change the treatments to manage that condition? 
• Should my children or other close relatives be screened for heart problems?

What to expect from your doctor?

   Your doctor may ask you a number of questions such as:

• What are your symptoms? 
• When did you first notice your symptoms? 
• Have your symptoms changed over a period of time? If so, how?
• Do your symptoms include a feeling of lightheadedness or dizziness?
• Do you feel rapid, fluttering or pounding heartbeats (palpitations)? 
• Have you experienced squeezing, pressure, heaviness, tightness or pain in your chest (angina)?
• Does exercise or physical exertion make your symptoms worse? 
• Are you aware of any history of heart problems in your family? 
• Are you undergoing treatment for any other health conditions?

What you can do in the meantime?

You may check with your family members to find out if any of your relatives have been diagnosed with heart problems. Your family health history can be helpful in planning the right diagnostic tests and treatments taking into account on your individual risks. Although sick sinus syndrome is rare, its symptoms mimic those of many other heart disorders. If exercise worsens your symptoms, avoid exercise until you have been seen by your doctor. 

Symptoms of sick sinus syndrome — such as dizziness, shortness of breath, and fainting — occur as symptoms of several other diseases and conditions. However, in sick sinus syndrome, these symptoms appear only when the heart beats abnormally.

In order to diagnose and treat sick sinus syndrome, your doctor needs to establish a connection between your symptoms and an abnormal heart rhythm.

Diagnostic tests include:

• Electrocardiogram: Tests for sick sinus syndrome includes a standard electrocardiogram (ECG). However, if your abnormal heart rhythms are transient in nature, these cannot be detected during the brief time period for which a standard ECG records electrical activity of your heart. You may need additional types of ECG: 
• Standard ECG: During this test, special type of electrodes are attached to your chest and limbs to record the electrical signals traveling through your heart. This test may reveal patterns that indicate sick sinus syndrome, including fast heart rate, slow heart rate or a long pause in the heartbeat (asystole) after a fast heart rate. 
• Holter monitor: This is a portable device that can be carried in your pocket or in a pouch on a belt or shoulder strap. It automatically records electrical activity of your heart for an entire 24- to 48-hour period, which provides your doctor, an extended look at your heart's activity and rhythms. This type of monitoring is very helpful to identify sick sinus syndrome. 
• Event recorder: This is also a portable electrocardiogram device that can be taken along with you in your pocket or worn on your belt or shoulder strap for home monitoring of your heart's activity. This device will be worn for up to a month. Whenever you feel symptoms, you can push a button so that a brief ECG recording gets saved for that period. This helps your doctor to identify your heart rhythm at the time of your symptoms, which helps to accurately pinpoint sick sinus syndrome. 
• Implantable loop recorder: This is a small device that is implanted just below the skin of your chest, and is required for continual, long-term monitoring of your heart's electrical activity. An implantable loop recorder may be worn for several months to years. This device gets automatically triggered by an irregular heart rhythm (arrhythmia) or can be manually triggered whenever you feel the symptoms. 
• Electrophysiologic testing: In some cases, electrophysiologic testing helps in checking the function of your sinus node as well as other electrical properties of your heart. During this test, thin, flexible tubes with their tips attached with electrodes are passed through your blood vessels to reach various regions along the electrical pathways in your heart. Once in place, these electrodes can accurately map the spread of electrical impulses during each beat, and may also recognize the source of heart rhythm problems.

The goal of treatment of sick sinus syndrome is elimination or reduction of unpleasant symptoms. If you do not have any symptoms, regular checkups are sufficient to monitor your condition. For people who have symptoms, the treatment of choice is an implanted electronic pacemaker.

Medication changes

Your doctor may start by evaluation of your current medications to check whether any of these are interfering with the function of your sinus node. Medications taken to control high blood pressure or heart disease — such as beta blockers or calcium channel blockers — can further worsen abnormal heart rhythms. Sometimes, modification of these medications may relieve some of the symptoms.   

Pacing the heart

Most patients with sick sinus syndrome will eventually require an implantation of permanent artificial pacemaker to regulate their heartbeat. Pacemaker is a small, battery-powered electronic device that is implanted underneath the skin near your collarbone through a minor surgical procedure. The pacemaker is programmed such that it stimulates your heart as required to make it beat normally. The type of pacemaker needed depends on the type of irregular heart rhythm you have.

Some cases may be treated with a single chamber pacemaker, which uses only one wire (lead) to pace any one chamber of the heart — in this case, the atrium. However, most people may find dual chamber pacemaker (one lead paces the atrium and one lead paces the ventricle) beneficial. 

You can resume your normal or near-normal activities once you recover from pacemaker implantation surgery. 

Additional treatment for fast heart rate

 If rapid heart rate exists as part of your sick sinus syndrome, you may need additional treatment to control these rhythms:

•  Medications: If you have an implanted pacemaker, but still your heart rate is too fast, your doctor may advise anti-arrhythmia medications to prevent fast heart rhythm. If you have atrial fibrillation or other abnormal heart rhythm that can increase your risk of stroke, you may be advised to take a blood-thinning medicine, such as warfarin (Coumadin) or dabigatran (Pradaxa).
• AV node ablation: This procedure is indicated in control of fast heart rhythms in people with implanted pacemakers. It involves application of radiofrequency energy using a long, thin tube (catheter) to destroy the tissues around the atrioventricular (AV) node between the atria and the ventricles. This will prevent fast heart rates from reaching the ventricles and causing problems. 
• Radiofrequency ablation of atrial fibrillation: This procedure is same as AV node ablation, but in this, ablation is targeted to the tissues that trigger atrial fibrillation. This procedure eliminates the atrial fibrillation itself, rather than just preventing it from reaching the ventricles.

Lifestyle modifications are necessary in order to cope with sick sinus syndrome.

At times, inflammation and narrowing of arteries caused by underlying heart diseases can lead to sick sinus syndrome. Your doctor may advise lifestyle modifications in addition to other treatments to keep your heart as healthy as possible.

Take these self-care measures to eliminate risk factors that may lead to heart disease: 

• Regular exercise and healthy diet: Live a heart-healthy lifestyle by exercising regularly and eating a healthy, low-fat diet that is rich in fruits, vegetables, and whole grains such as cereals.
• Maintain a healthy weight: Being obese or overweight enhances your risk of developing heart disease. 
• Maintain blood pressure and cholesterol under control: Lifestyle changes and medications can help to bring high blood pressure (hypertension) or high cholesterol levels under control. 
• Quit smoking: If you smoke and cannot quit on your own, discuss with your doctor about strategies or programs that can help you stop your smoking habit. 
• Avoid drinking alcohol or do so in moderation: In some conditions, doctors recommend complete avoidance alcohol. Ask your doctor for advice specific to your condition. If you cannot control your alcohol use, ask your doctor about a program that helps quit drinking and manage other behaviors related to alcohol abuse. 
• Avoid use of illegal drugs: Your doctor can guide you through an appropriate program that helps in stopping illegal drug use. 
• Manage your stress effectively: Avoid getting subjected unnecessary stress and learn coping techniques that can help you handle normal stress in a right way.
• Do not skip your scheduled checkups: Get regular physical examinations and inform any signs or symptoms to your doctor.

There are several risks and complications associated with sick sinus syndrome.

Sick sinus syndrome may occur at any age, even in infants. As it usually develops in a slow manner over many years, it is most commonly seen in people around the age of 70. Rarely, sick sinus syndrome may also occur associated with certain conditions such as muscular dystrophy and other diseases that affect the heart. 

When your heart's natural pacemaker does not work properly, your heart cannot pump blood as efficiently as it should. This leads to a very slow heart rate, which causes fainting. In some cases, longer periods of slow heart rate or fast heart rate prevents pumping of enough blood from your heart to meet your body's needs — a condition called heart failure. 

If you have a type of sick sinus syndrome called bradycardia-tachycardia syndrome, you may be at a higher risk of formation of a blood clot in your heart that may lead to a stroke. This is because the fast heart rhythm that occurs in bradycardia-tachycardia syndrome is atrial fibrillation, which is a chaotic rhythm of the upper chambers of the heart that can cause pooling of blood in the heart. A blood clot may breakdown and travel to the brain, causing a stroke.