Atrioventricular Nodal Reentrant Tachycardia (AVNRT): Causes, Symptoms, and Treatments

Supraventricular tachycardia (SVT) falls into three main groups:

1. AVNRT: Atrioventricular Nodal Reentrant Tachycardia, the most common SVT, results from an additional pathway in the heart’s AV node disrupting the regular electrical flow.
2. AVRT: Atrioventricular Reciprocating Tachycardia, typically seen in younger individuals, is due to an abnormal link between the heart’s atria and ventricles, leading to a rapid heartbeat.
3. Atrial Tachycardia: Predominantly found in heart disease patients, this SVT type originates from fast-paced signals in the atria, excluding the AV node, elevating the heart rate.

Other types of supraventricular tachycardia include:

• Sinus tachycardia
• Sinus nodal reentrant tachycardia (SNRT)
• Inappropriate sinus tachycardia (IST)
• Multifocal atrial tachycardia (MAT)
• Junctional ectopic tachycardia (JET)
• Nonparoxysmal junctional tachycardia (NPJT)

We will discuss Atrioventricular Nodal Reentrant Tachycardia (AVNRT) today.

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

AVNRT is the most common form of SVT, accounting for approximately 60% of all cases. This form of tachycardia involves the atrioventricular node (AV node) – the heart’s electrical relay station between the atria and the ventricles.

Understanding AVNRT

Atrioventricular Nodal Reentrant Tachycardia (AVNRT) is a type of supraventricular tachycardia that occurs due to abnormal electrical pathways in the heart. To truly understand AVNRT, we must delve into the heart’s anatomy, physiology, and pathological changes leading to this condition.

1. Anatomical Perspective

The human heart has four chambers – two atria on top and two ventricles at the bottom. These chambers work in sync to pump blood throughout the body. The synchronization is managed by the heart’s electrical system, which includes the sinoatrial (SA) node, the atrioventricular (AV) node, and the His-Purkinje system.

The SA node in the right atrium is the heart’s natural pacemaker. It initiates an electrical impulse that travels through the atria, causing them to contract and pump blood into the ventricles. This electrical signal reaches the AV node at the junction of the atria and ventricles. The AV node delays the signal before passing it to the His-Purkinje system, which distributes the impulse to the ventricles, causing them to contract.

2. Physiological Perspective

In a normal heartbeat, the electrical signal travels along a single pathway from the atria to the ventricles. In AVNRT, an additional pathway exists within or near the AV node. This extra pathway can disrupt the normal flow of electrical signals, leading to a rapid and irregular heartbeat.

Typically, the electrical signal travels down the usual pathway and up the additional pathway, creating a circular or “reentrant” electrical loop. This rapid, continuous loop of electrical activity causes the heart to beat abnormally fast, resulting in AVNRT.

3. Pathological Perspective

The exact cause of the additional pathway in AVNRT is not known. It may be present at birth (congenital) or develop over time. Factors that may trigger AVNRT include stress, caffeine, alcohol, certain medications, and physical activity. Some medical conditions like heart disease, thyroid disorders, and pulmonary hypertension can increase the risk of AVNRT.

In addition to the rapid heart rate, the continuous electrical loop can cause other symptoms such as palpitations, lightheadedness, shortness of breath, chest pain, and, in severe cases, loss of consciousness. AVNRT may lead to serious complications, including heart failure, stroke, or sudden cardiac death if left untreated.

Risk Factors:

1. Gender: Women are at a higher risk of developing AVNRT than men.
2. Age: While AVNRT can occur at any age, it’s most common in young and middle-aged adults.
3. Stress: High emotional stress or physical exertion levels can trigger AVNRT episodes.
4. Stimulant Use: Consumption of caffeine, alcohol, or other stimulant drugs can stimulate the heart and potentially trigger AVNRT.
5. Smoking: Nicotine can stimulate the heart and increase the risk of various heart conditions, including AVNRT.
6. Underlying Heart Conditions: People with heart diseases, such as coronary artery disease or congenital heart disease, are at higher risk.
7. Certain Medications: Certain medications, such as cold and allergy drugs that contain pseudoephedrine, can trigger AVNRT.
8. Thyroid Disorders: Conditions like hyperthyroidism can increase the risk of developing AVNRT.
9. Electrolyte Imbalance: Abnormal levels of electrolytes such as potassium or calcium in the body can affect the heart’s electrical signals and increase the risk of AVNRT.
10. Family History: A family member with AVNRT or another form of supraventricular tachycardia may increase a person’s risk.

Signs of AVNRT:

1. Rapid heartbeat (tachycardia)
2. Heart palpitations
3. Regular or irregular heart rhythm (as detected on an electrocardiogram)
4. Abrupt start and stop of heart palpitations
5. Short periods of rapid heartbeat
6. Narrow QRS complex on the electrocardiogram during tachycardia
7. P waves buried within or occurring after the QRS complex on an electrocardiogram
8. Heart rate during an episode is typically between 150-220 beats per minute.
9. Inability to exercise or exert oneself due to rapid heartbeat
10. Typical heart structure (most AVNRT patients do not have heart disease)

Symptoms of AVNRT:

1. Heart palpitations – a sensation of rapid, fluttering, or pounding heartbeats
2. Lightheadedness or dizziness
3. Shortness of breath
4. Anxiety or a sense of impending doom
5. Chest pain or discomfort
6. Sweating
7. Fatigue or weakness
8. Syncope (fainting) or near-syncope
9. The feeling of being unwell (malaise)
10. Disruption in everyday activities due to symptoms

Diagnosis of AVNRT

1. Medical History and Physical Examination: The doctor will ask about the symptoms, their frequency, and duration, along with a thorough physical examination.
2. Electrocardiogram (ECG): An ECG records the heart’s electrical activity and can often detect AVNRT.
3. Holter Monitor: A device worn for 24-48 hours records every heartbeat, applicable if symptoms occur sporadically.
4. Event Recorder: A portable ECG device worn for a more extended period (weeks to months), activated by the patient when symptoms occur.
5. Exercise Stress Test: An ECG is performed while the patient exercises, often on a treadmill or stationary bicycle.
6. Tilt Table Test: This test monitors how body position and gravity changes can affect heart rate and blood pressure. It might be used if fainting (syncope) is one of the symptoms.
7. Echocardiogram: An ultrasound of the heart to ensure that the heart’s structure is typical.
8. Electrophysiology Study (EPS): A test in which thin wires (electrodes) are passed through the veins to the heart, recording its electrical signals and identifying the pathway causing the rapid heartbeat.
9. Blood Tests: To rule out other conditions that might be causing the symptoms, such as thyroid diseases.
10. Intracardiac Tracings: Acquired during an EPS, these detailed electrical tracings can confirm the diagnosis of AVNRT.

Treating AVNRT

Medications for AVNRT:

1. Adenosine is a fast-acting medication that slows the electrical conduction through the AV node, often used in emergencies to terminate an AVNRT episode.
2. Beta-Blockers (such as metoprolol or atenolol): These medications slow down the heart rate and can be used to prevent AVNRT episodes.
3. Calcium Channel Blockers (such as verapamil or diltiazem): Similar to beta-blockers, these medications also slow down the heart rate and can be used to prevent AVNRT episodes.
4. Antiarrhythmic Drugs (such as flecainide or propafenone): These medications can prevent AVNRT episodes by slowing down the electrical conduction in the heart.
5. Digoxin: This medication slows the heart rate by increasing the refractory period of the AV node, which can help prevent AVNRT episodes.
6. Amiodarone: A potent antiarrhythmic drug that can be used in severe cases to control AVNRT.
7. Dofetilide: An antiarrhythmic drug used to maintain normal heart rhythm in patients with frequent episodes of AVNRT.
8. Sotalol: A beta-blocker with antiarrhythmic properties that can be used to manage AVNRT.
9. Ranolazine: An antianginal medication that also has antiarrhythmic properties.
10. Edoxaban and other anticoagulants: If the patient has a high risk of developing blood clots due to AVNRT, these medications may be used to prevent clot formation.

Other Treatment Options for AVNRT:

1. Vagal Maneuvers: Techniques such as bearing down or immersing the face in cold water stimulate the vagus nerve and can often halt an AVNRT episode.
2. Cardioversion: A procedure that delivers a shock to the heart to restore normal rhythm, used in emergencies if medication is impractical.
3. Radiofrequency Catheter Ablation: A procedure that uses heat to destroy the abnormal electrical pathway in the heart, effectively curing AVNRT in most cases.
4. Cryoablation: Similar to radiofrequency ablation, but uses cold energy to destroy the abnormal pathway.
5. Pacemaker Implantation: In rare cases, if medication and ablation are ineffective, a pacemaker may be implanted to control the heart’s rhythm.
6. Lifestyle Changes: Avoiding triggers such as caffeine, alcohol, and stress can help reduce the frequency of AVNRT episodes.
7. Regular Exercise: Regular physical activity can help maintain a healthy heart and reduce the frequency of AVNRT episodes.
8. Healthy Diet: A heart-healthy diet can help prevent other heart conditions that might exacerbate AVNRT.
9. Stress Management Techniques: Yoga, meditation, and deep breathing can help manage stress and potentially reduce AVNRT episodes.
10. Regular Medical Follow-up: Regular appointments with a cardiologist are necessary to monitor the condition and adjust treatment as necessary.

Prevention

1. Healthy Diet: A heart-healthy diet rich in fruits, vegetables, lean proteins, and whole grains can help maintain a healthy heart.
2. Avoid Stimulants: Limit the intake of caffeine, alcohol, and tobacco, which can trigger an AVNRT episode.
3. Regular Exercise: Regular physical activity helps maintain a healthy weight and reduce the risk of heart disease.
4. Stress Management: Learn yoga, meditation, or deep-breathing exercises to reduce stress.
5. Control Blood Pressure: Regularly monitor and control blood pressure levels. High blood pressure can increase the risk of heart conditions.
6. Maintain a Healthy Weight: Obesity can strain the heart and increase the risk of heart disease. Aim for a healthy weight through a balanced diet and regular exercise.
7. Regular Check-ups: Regular health check-ups can detect any underlying heart conditions early, reducing the risk of AVNRT.
8. Medication Management: If you’re on medication, especially heart medication, ensure you use it correctly. Misuse can trigger AVNRT.
9. Stay Hydrated: Dehydration can cause electrolyte imbalances, which may trigger AVNRT. Drink plenty of fluids, especially during physical activity.
10. Limit Over-the-Counter Medications: Some over-the-counter medications, especially cold and allergy drugs, can trigger AVNRT. Always consult a healthcare provider before starting any new medication.

References:

1. American Heart Association – Supraventricular Tachycardia
2. Mayo Clinic – Supraventricular Tachycardia
3. Johns Hopkins Medicine – Atrioventricular Nodal Reentry Tachycardia
4. American College of Cardiology – Atrioventricular Nodal Reentrant Tachycardia
5. Cleveland Clinic – Atrioventricular Nodal Reentrant Tachycardia

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Disclaimer: This article is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your healthcare provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you’ve read on this website.