What is Atrioventricular Nodal Reentry Tachycardia?
The atrioventricular (AV) node is a small structure located within the heart, specifically in the lower back part of the right atrium. In an average adult, it’s about the size of a grain of rice. It’s situated in an area surrounded by the coronary sinus ostium at the back, the tendon of Todaro at the top, and the septal tricuspid valve annulus at the front. This area is also known as the triangle of Koch. The blood supply to the AV node comes mainly from the right coronary artery (90%) and also from the left circumflex artery (10%), depending on whether the right or left side predominantly supplies blood to the heart. The first septal perforator of the left anterior descending artery also provides blood to the AV node.
Atrioventricular nodal reentrant tachycardia (AVNRT) is a kind of intermittent rapid heart rate condition that occurs due to a loop circuit in or near the AV node. Diagnosing AVNRT requires an electrocardiogram (ECG). In most cases, the ECG will show a heart rate of 140 to 280 beats per minute and, if there’s no unusual conduction, a QRS complex of less than 120 milliseconds. The QRS complex is a specific pattern seen on the ECG. Depending on the reentrant circuits, the type of AVNRT can be identified as follows:
‘Slow-Fast AVNRT’ is indicated by a Pseudo-S wave in leads II, III, and AVF and a Pseudo-R’ in lead V1. ‘Fast-Slow AVNRT’ is characterized by P waves between the QRS and T waves. ‘Slow-Slow AVNRT’ shows late P waves after a QRS; this often appears as atrial tachycardia.
What Causes Atrioventricular Nodal Reentry Tachycardia?
Atrioventricular nodal reentry tachycardia, a type of heart rhythm disorder, isn’t typically found in people with structural heart issues. The type of this disorder depends on the path the electrical impulses take through the heart’s natural pacemaker, the AV node.
The most common type, slow-fast AVNRT, makes up about 90% of cases. In this type, the electrical signals move forwards through the slow pathway of the AV node and backwards through the fast pathway.
Fast-slow AVNRT is the next most common and comprises about 5-10% of cases. Here, electrical signals move forward through the fast AV node pathway and backwards through the slow pathway.
The rarest type is slow-slow AVNRT, accounting for only 1-5% of cases. In this, electrical impulses travel both forwards and backwards through the slow AV node pathways and slow atrial pathways.
Risk Factors and Frequency for Atrioventricular Nodal Reentry Tachycardia
Atrioventricular nodal reentry tachycardia, or AVNRT, is a type of rapid heart rhythm. The number of people around the world who have this condition is about the same as in the United States. It makes up about 60% of all instances of a sudden, fast heartbeat condition known as paroxysmal supraventricular tachycardia. Of these, two-thirds occur in women. Most people start to show symptoms of AVNRT during their twenties, but in some cases, it might not happen until they are in their seventies or eighties.
- AVNRT is a common, rapid heart rhythm and is found in similar numbers worldwide as it is in the US.
- About 60% of fast heart rate conditions, known as paroxysmal supraventricular tachycardia, are diagnosed as AVNRT.
- Two-thirds of the people affected by AVNRT are women.
- Most people with AVNRT begin to experience symptoms in their twenties.
- In some cases, symptoms might not begin until their seventies or eighties.
Signs and Symptoms of Atrioventricular Nodal Reentry Tachycardia
Atrioventricular nodal reentrant tachycardia (AVNRT) is a heart condition that often leads to symptoms like dizziness, fainting, breathlessness, irregular heartbeats, discomfort in the neck and chest, feelings of anxiety, and increased urination. These symptoms can occur due to increased heart activity. People with AVNRT who also have heart disease might experience a heart attack due to the extra strain on their heart. In some cases, those with heart failure might have a worsened condition and decreased heart efficiency due to AVNRT.
Fainting is not common with AVNRT, but it can occur in cases where the heart rate exceeds 170 beats per minute. This can happen because the heart doesn’t have enough time to fill with blood before pumping, reducing the amount of blood available to the brain. Decreased heart activity due to high heart rates may also cause these symptoms.
Patients with AVNRT generally have heart rates between 140 and 280 beats per minute. If they also have heart failure or heart disease, they may experience chest pain and other symptoms indicative of heart failure like rapid breathing, wheezing, and swelling in the lower body parts. Doctors can sometimes observe specific features on physical examination, such as simultaneous contraction of the chambers of the heart, resulting in pronounced neck veins. Low blood pressure due to insufficient heart filling can also be detected during the examination.
- Dizziness
- Fainting
- Shortness of breath
- Irregular heartbeats
- Neck and chest discomfort
- Anxiety
- Increased urination
- Potential heart attack or heart failure symptoms in those with pre-existing conditions
- Chest pain
- Rapid breathing and wheezing
- Swelling of the lower body parts
- Pronounced neck veins
- Low blood pressure
Testing for Atrioventricular Nodal Reentry Tachycardia
If someone shows signs of a heart condition known as atrioventricular nodal reentrant tachycardia (AVNRT), the first step is to take their medical history and do a physical examination. This includes checking the patient’s vital signs like their breathing rate, blood pressure, temperature, and heart rate. An electrocardiogram, which is a medical test that measures the electrical activity of the heart, will also be done.
The doctor will also want to check if the patient has any unidentified heart issues, like coronary artery disease or heart failure. The doctor will mainly determine if the patient is stable by looking at their blood pressure, mental state, and breathing rate.
More tests may be done, such as thyroid and lung function tests, routine blood work, and echocardiography. Echocardiography is a type of ultrasound test that shows a picture of the heart’s movements and structures.
Treatment Options for Atrioventricular Nodal Reentry Tachycardia
When someone comes in with an abnormally fast heart rhythm — a condition known as atrioventricular nodal reentry tachycardia, or AVNRT — the first thing doctors need to do is assess how stable the patient is. If the fast heart rate is causing other dangerous symptoms like low blood pressure, chest pain, confusion, trouble breathing, or shock, then the doctor may need to restore a normal heart rhythm quickly using a technique called electrical cardioversion.
But if the patient is stable, the doctor will first try some techniques to slow the heart rate down. This could involve something called vagal maneuvers, which are simple exercises like coughing, holding breath, or immersing the face in cold water. If these don’t work after a couple of tries — or if they’re not suitable for the patient — the doctor will then move on to medical treatment.
The first drug doctors usually use in these situations is adenosine, which is given through an IV. If adenosine doesn’t work or isn’t suitable, the doctor may then consider other medications like calcium channel blockers, beta-blockers, or digoxin. The choice between these depends on the individual patient’s needs. For example, if the patient also has low blood pressure, digoxin might be the best choice because it doesn’t lower blood pressure. Conversely, if the patient has breathing difficulties due to conditions like asthma, they might start with a calcium channel blocker.
Adenosine can stop about 80 percent of AVNRT cases. But if it and the other initial treatments don’t work or cause bad side effects, the next option could be catheter ablation. This involves threading a tube into the heart to destroy the tiny area causing the rapid heartbeat. This treatment has a great success rate, up to 95 percent. If patients don’t want to or can’t have catheter ablation, then the doctor might put them on long-term medication with antiarrhythmic drugs. This includes drugs like flecainide, propafenone, amiodarone, dofetilide, or sotalol, with the choice depending on the patient’s other medical conditions and the side effects of the drugs.
What else can Atrioventricular Nodal Reentry Tachycardia be?
When a certain type of fast heartbeat, known as a narrow QRS complex tachycardia, shows up on a heart rhythm test (electrocardiogram), and the rhythm is found to be regular, it could indicate various conditions:
- Atrioventricular nodal reentrant tachycardia: an abnormal heart rhythm caused by a loop of electrical signals in the heart
- Atrioventricular reentrant tachycardia: a fast heartbeat caused by an additional pathway in the heart
- Intra-atrial reentrant tachycardia: a type of abnormal heart rhythm characterized by rapid, regular heartbeats
- Sinoatrial nodal reentrant tachycardia: a fast heart rhythm originating in the natural pacemaker of the heart
- Junctional ectopic tachycardia: a fast, abnormal heart rhythm that starts in a part of the heart called the junctional region
- Atrial tachycardia: a category of heart rhythms characterized by a rapid heartbeat that originates in the heart’s upper chambers
- Atrial flutter: a condition where the heart’s upper chambers beat too quickly
- Sinus tachycardia: a condition where the heart beats faster than normal while at rest
- Inappropriate sinus tachycardia: a condition where the resting heart rate is abnormally high, and the rate increases excessively with minimal exercise
What to expect with Atrioventricular Nodal Reentry Tachycardia
The outlook is typically positive if a healthcare provider quickly identifies the heart rhythm.
Possible Complications When Diagnosed with Atrioventricular Nodal Reentry Tachycardia
If symptoms like fainting, tiredness, or dizziness are not quickly recognized and treated, they can lead to complications.
Preventing Atrioventricular Nodal Reentry Tachycardia
Teaching patients who are prone to this heart rhythm about their condition can greatly improve how it’s managed. Ensuring regular and open communication between these patients and their healthcare providers also plays a crucial role in the effective management of these heart rhythms.
