What is Sinus Node Dysfunction (Sick Sinus Syndrome)?
The sinoatrial node, often called the SA node, acts like the main “traffic controller” for your heart, telling it when to beat. The SA node is located where the superior vena cava (the large vein that carries deoxygenated blood from the upper half of your body back to your heart) meets the right atrium (one of the four chambers of your heart). The SA node sends out signals that cause your heart to contract, pumping blood throughout your body.[1]
If the SA node isn’t working right, it can lead to a condition called sinus node dysfunction, which used to be known as sick sinus syndrome. It’s like the SA node’s “traffic signals” aren’t strong enough for your heart’s needs. That means your heart rate – the number of times your heart beats in a minute – might not be as fast as it needs to be. You have sinus node dysfunction if you have symptoms and abnormal results on an electrocardiogram or EKG, a test that checks how your heart is functioning. These might include a slow heart rate (sinus bradycardia), periods when the heart stops beating for a while (sinus pauses or arrest), problems with the exit path of heartbeats from the sinus node (sinus exit blocks), or an ability to increase the heart rate with activity as needed (chronotropic incompetence). Another sign of sinus node dysfunction could be that the SA node doesn’t start working again after a procedure to correct an abnormal heart rhythm (electrical cardioversion).[2] Sometimes, sinus node dysfunction can occur along with a rapid heart rate – this is known as tachycardia-bradycardia syndrome.
What Causes Sinus Node Dysfunction (Sick Sinus Syndrome)?
Sinus node dysfunction is a condition where there is a problem with the heartbeat’s natural pacemaker (the sinus node) and nearby tissues. This could be because of how these tissues conduct electricity, creating the heartbeat, or how the sinus node keeps the heart’s rhythm, or both. This dysfunction can happen due to a few different reasons, like when fibrous tissue replaces the normal tissue, when arteries harden (atherosclerosis), or due to certain inflammatory disease processes infiltrating the heart tissues.
The most common cause of sinus node dysfunction is when fibrous tissue takes the place of the normal tissue in the sinus node. This can also happen in other parts of the heart’s electrical system, including the AV node, which helps relay the electrical signals that keep the heart beating.
Certain prescription medications can also mess up the functioning of the sinus node and cause dysfunction. These include beta blockers, certain types of calcium channel blockers, digoxin, antiarrhythmic medications, and acetylcholinesterase inhibitors, which are drugs that help transmit electrical signals in the body.
Some illnesses can infiltrate or affect the tissue of the SA node, causing sinus node dysfunction. These illnesses include amyloidosis, sarcoidosis, scleroderma, hemochromatosis, and pericarditis.
Sinus node dysfunction can also occur if the blood supply to the sinus node is reduced. The sinoatrial nodal artery, which provides blood to the sinus node, comes from the right coronary artery about 60% of the time and from the left circumflex artery the rest of the time. If these arteries narrow, it can affect the functioning of the sinus node. This can sometimes be reversed. Most such cases occur in inferior myocardial infarction, which is a type of heart attack.
In rare instances, sinus node dysfunction can be due to gene mutations related to the heart’s sodium channels. These are coded by the SCN5A and HCN4 genes.
Other less common culprits of sinus node dysfunction include hypothyroidism (an underactive thyroid), hypothermia, and hypoxia (a lack of sufficient oxygen).
Risk Factors and Frequency for Sinus Node Dysfunction (Sick Sinus Syndrome)
Understanding the number of people affected by sinus node dysfunction can be tough because symptoms and ECG scan results vary greatly. However, a record of two big studies including over 20,000 patients, averaging 59 years of age, offers some insight. For 17 years, researchers followed these patients, of which 43% were males. They found that on average, for every 1000 people observed per year, less than one person developed sinus node dysfunction. Also, it was observed that age played the most significant role in increasing the risk of this condition.
Signs and Symptoms of Sinus Node Dysfunction (Sick Sinus Syndrome)
Sinus node dysfunction, a condition affecting the heart’s natural pacemaker, is determined by a combination of symptoms and findings from an EKG test. Symptoms of this condition can be vague and include feeling light-headed, tired, near-fainting, or fainting. If the patient also has tachy-brady syndrome, another heart condition, they may also experience heart palpitations. For those with other heart-related health issues like coronary artery disease, symptoms of sinus node dysfunction may present as an increase in usual symptoms like chest pain and shortness of breath.
- Feeling light-headed
- Tiredness
- Near-fainting or fainting
- Heart palpitations (for those with tachy-brady syndrome)
- Increase in usual symptoms like chest pain or shortness of breath (for those with other heart issues)
Testing for Sinus Node Dysfunction (Sick Sinus Syndrome)
Sick sinus syndrome is a condition that is determined by a combination of specific Electrocardiogram (ECG) results and symptoms. However, it is essential to note that, on its own, an ECG displaying a slow heartbeat (known as sinus bradycardia) does not signal the existence of Sick sinus syndrome.
The ECG results indicative of this syndrome are:
* Extended periods of an unnaturally slow heartbeat, which can often be severe.
* Instances of sinus pauses, sinus arrests, and sinus exits blocks, which may be present both with and without an appropriate alternate heartbeat rhythm.
* A combination of a rapid heartbeat (tachycardia) and a slow heartbeat (bradycardia), which is known as tachy-brady syndrome. This combination could also be associated with other unusually fast heartbeat conditions known as supraventricular tachycardias.
To accurately diagnose Sick sinus syndrome, doctors need to link patients’ symptoms to ECG results at the time the symptoms occur. It can also be helpful to compare current ECG results with previous ones to check for rhythm changes that coincide with the onset of symptoms.
If a diagnosis is not conclusive based on medical history and the ECG results, a doctor may use an exercise stress test. This test aims to assess whether a patient’s heart rate responds appropriately to physical exertion. This test can also rule out any heart muscle-related issues and help fine-tune any devices (like a pacemaker) eventually used to regulate the patient’s heart rate.
If the above procedures do not definitively diagnose Sick sinus syndrome, ambulatory ECG monitoring, which involves the patient wearing a ECG device as they go about their daily activities, might assist in diagnosis process. Certain long-term ECG monitoring devices, like Holter monitors and cardiac event monitors, have proven useful in tracking down the abnormal heart rhythms that cause symptoms. Sometimes, longer periods of monitoring are required for patients whose symptoms are infrequent.
Finally, doctors will review any medications the patients are taking that might contribute to their symptoms, such as beta blockers, calcium channel blockers, digoxin or antiarrhythmic drugs. They may stop these medications temporarily while monitoring changes in the patients’ symptoms and ECG results to ascertain if these medications may be causing the condition.
Treatment Options for Sinus Node Dysfunction (Sick Sinus Syndrome)
The first thing doctors do when dealing with sinus node dysfunction is to check if the patient is stable or not.
Patients who aren’t stable:
Patients with sinus node dysfunction are rarely unstable for a long time. However, if they are, guidelines for dealing with slow heart rates should be followed, especially if the patient is experiencing confusion, fainting, chest pain due to low blood supply, and general instability.
Doctors initially treat with atropine, a medication that can help speed heart rate. Even so, this treatment should not postpone the use of skin pacing (sending electrical pulses through the skin to stimulate the heart) or other drugs that increase heart rate.
If atropine is not effective, the patient can receive an infusion of drugs like epinephrine, dopamine or isoproterenol to increase heart rate.
Skin pacing should be started in patients who are unstable, but it’s only temporary until an internal pacing device can be put in.
Patients who are stable:
It’s important to check for possible reversible causes first. If the patient is taking a medication that might be causing the problem and it can be stopped or replaced, the patient should be monitored to see if symptoms improve. If the medication can’t be stopped, the patient should be treated as if there’s no reversible cause. The next step is to determine whether the patient has symptoms or not.
Patients without symptoms:
It’s often best to just monitor patients without symptoms. There’s no standard recommendation to put in a permanent pacemaker for patients with a slow heart rate or pauses if they display no symptoms.
Patients with symptoms:
Patients with sinus node dysfunction who have symptoms will need a permanent pacemaker. A pacemaker is a device which helps control abnormal heart rhythms. There are two types – one that only paces the top chambers of the heart (AAI) and one that controls both the top and bottom chambers (DDD). A single chamber pacemaker is a reasonable choice for patients without abnormal heart rhythms. However, patients with delayed or blocked heart rhythms would get more benefit from a dual chamber pacemaker.
There’s much to discuss about the types and modes of pacemakers, but to give you an idea, a large trial involving patients with sinus node dysfunction found that there was no difference in the overall death rate between the two types of pacemakers. However, the single chamber pacemaker was linked to more incidents of sudden irregular heartbeats and a higher rate of pacemaker replacement.
Use of blood thinners:
Patients with sinus node dysfunction may have episodes of irregular heart rhythms, especially those with tachy-brady syndrome, where the heart alternates between abnormally fast and slow heart rates. People who have a permanent pacemaker have a higher risk of developing irregular heart rhythms, so their devices should be checked regularly. If an irregular heart rhythm (like atrial fibrillation) is confirmed, it’s important to weigh up the risks of stroke and bleeding. Then a decision should be made on whether to use blood thinners or not.
What else can Sinus Node Dysfunction (Sick Sinus Syndrome) be?
When a doctor is trying to diagnose sinus node dysfunction, which can cause a slow heart rate and fainting, they must also consider other causes of these symptoms. These could include:
- Carotid sinus hypersensitivity, a condition where pressure changes in the neck arteries lead to changes in heart rate and blood pressure,
- Neurocardiogenic syncope with a dominant cardioinhibitory component, a kind of fainting caused by a sudden drop in heart rate and blood pressure,
- Sinus bradycardia in conditioned athletes, a condition where athletes have a lower resting heart rate due to great physical conditioning; note that while these individuals may have pauses in their heart rate, they do not typically experience fainting.
Additionally, sinus node dysfunction and carotid sinus hypersensitivity may often occur together.
What to expect with Sinus Node Dysfunction (Sick Sinus Syndrome)
Sinus node dysfunction is a condition that worsens over time. It can’t be cured, but it can be managed. In one study, 52 patients with this condition, which caused slow heartbeat and interruptions to the heart’s normal rhythm, took an average of 13 years for the condition to become fully developed.
Whether sinus node dysfunction affects a person’s lifespan is still not clear, as many people with this condition also have other heart-related health issues. In a study of 19,000 individuals observed over an average period of 17 years, only 213 people developed sinus node dysfunction. The study did find that people with sinus node dysfunction tend to have a higher rate of mortality, but this connection weakened when taking into account the onset of other heart diseases.
In summary, while sinus node dysfunction is associated with increased illness, it’s not yet clear if it directly impacts lifespan.
Possible Complications When Diagnosed with Sinus Node Dysfunction (Sick Sinus Syndrome)
Sinus node dysfunction is a disease that continues to progress without a cure. If a person with this dysfunction does not have a pacemaker, they could experience low blood pressure or fainting.
Possible Complications:
- Low blood pressure
- Fainting
Preventing Sinus Node Dysfunction (Sick Sinus Syndrome)
As with any other health condition, it’s crucial for patients to understand their disease to manage it properly. With conditions that require the placement of a permanent pacemaker, it’s especially important that patients know how to keep it functioning correctly. This involves regular appointments with their heart rhythm specialist, also known as an electrophysiologist. These check-ups help make sure the pacemaker is working as it should.
In addition to regular visits, it’s just as important for patients to know the signs that their pacemaker might not be working properly. These can often be the same symptoms they experienced before getting the pacemaker, such as fainting, feeling lightheaded, or getting tired easily. By knowing these signs, if they start to experience them again, they can quickly get the medical help they need.
