Supraventricular tachycardia, also known as (SVT), is a type of abnormal cardiac rhythm (arrhythmia) characterized by a rapid heartbeat that originates above the ventricles. The sinoatrial (SA) node, the heart’s natural pacemaker, is the starting point of the synchronized electrical signals that flow through the heart during a typical heartbeat. These impulses cause the atria to contract followed by the ventricles, resulting in a steady beating. 

In SVT, the electrical signals in the heart’s upper chambers (atria) become abnormal, causing them to beat rapidly and irregularly. This can result in a heart rate of more than 100 beats per minute, and in some cases, 200 bpm. SVT bouts can be brief or persistent, and symptoms may include palpitations, chest pain, shortness of breath, dizziness. 

There are several types of SVT, including: 

• Atrioventricular nodal reentrant tachycardia (AVNRT): The atrioventricular (AV) node’s aberrant electrical route produces a reentrant circuit that generates fast heartbeats, which is the most prevalent kind of SVT. 
• Atrioventricular reentrant tachycardia (AVRT): Rapid heartbeats are caused when there is an additional electrical route that connects the ventricles and atria, enabling electrical signals to flow in a circular manner between these chambers. 
• Atrial tachycardia: This type of SVT originates from abnormal electrical signals originating in the atria outside of the normal SA node, causing rapid heartbeats. 
• Atrial fibrillation and atrial flutter: While not always classified as SVT, these conditions involve rapid and irregular heartbeats originating from the atria. 

Prevalence: 

• SVT is a relatively common arrhythmia, and its prevalence increases with age. 
• The overall population is estimated to be around 2.25 per 1000 persons. 

Age Distribution: 

• SVT can occur at any age, but it is often diagnosed in young adults. 
• Atrial fibrillation and atrial flutter, which are considered forms of SVT, are more prevalent in older adults. 

Risk Factors: 

• The development of SVT may be predisposed by a number of factors, such as structural heart defects, family record , and specific medical disorders. 
• Emotional stress, excessive caffeine or alcohol consumption, and stimulant medications can trigger SVT episodes in susceptible individuals. 

Incidence: 

• The incidence of SVT is influenced by factors such as lifestyle,genetics, and the presence of other cardiovascular conditions. 
• The incidence may be higher in individuals with congenital heart abnormalities or other structural heart diseases. 

Normal Cardiac Conduction: 

• The natural pacemaker of the heart, the sinoatrial (SA) node, produces electrical impulses that pass through the atria and activate the atrioventricular (AV) node in a healthy heart. 

Initiation of SVT: 

• SVT typically involves the abnormal initiation of electrical impulses, often in areas other than the SA node. 
• In AVRT, an extra accessory pathway exists that allows the electrical impulse to travel in a loop between the atria and ventricles, bypassing the usual pathway through the AV node. 
• In AVNRT, there is a reentrant circuit within the AV node itself, causing a rapid loop of electrical conduction. 

Reentry Circuits: 

• The hallmark of SVT is the presence of reentry circuits, where electrical impulses circulate in a loop, causing a rapid and sustained heartbeat. 
• Abnormal pathways, either within the AV node or due to accessory pathways, create the conditions for reentry. 

Shortened Refractory Period: 

• The refractory period is the time during which a cardiac cell cannot be stimulated again. In SVT, the refractory period may be shortened, allowing rapid reentry of electrical impulses. 

Impaired Automaticity: 

• In some cases, SVT may result from increased automaticity of certain cells in the atria, causing them to initiate electrical impulses at a faster rate than normal. 

Abnormal Electrical Pathways: 

• Atrioventricular Reentrant Tachycardia (AVRT): This occurs when there is an abnormal accessory pathway between the atria and ventricles. 
• Atrioventricular Nodal Reentrant Tachycardia (AVNRT): It involves an abnormal pathway within the atrioventricular node. 

Reentry Circuits: 

• SVT can occur due to reentry circuits where electrical signals circulate abnormally within the heart, leading to a rapid heartbeat. 

Atrioventricular Node Dysfunction: 

• SVT can be caused by dysfunction of the atrioventricular (AV) node, a vital component of the electrical conduction system of the heart. 

Irritability of Heart Cells: 

• Enhanced automaticity of cells in the atria can lead to rapid and irregular heartbeats. 

Heart Diseases: 

• The risk of SVT can be raised by structural heart problems such congenital heart abnormalities, cardiomyopathy, and coronary artery disease. 

Thyroid Disorders: 

• Individuals with hyperthyroidism, defined as an overactive thyroid gland, may be prone to SVT. 

Stress and Anxiety: 

• Emotional stress and worry can cause SVT in vulnerable people. 

• Type of SVT: The specific type of SVT can influence the prognosis. Examples of common forms of tachycardias with positive prognoses are atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT), especially when treated appropriately. 
• Underlying Heart Conditions: The presence of underlying structural heart disease or congenital heart abnormalities may impact the prognosis. Individuals with a structurally normal heart generally have a better prognosis. 
• Age of Onset: The age at which SVT first presents can be a factor. SVT that presents in childhood may have different implications than SVT that develops later in life. 
• Symptom Severity: The severity of symptoms can differ among individuals with SVT. While some may experience occasional and tolerable symptoms, others may have more frequent and bothersome episodes. 
• Response to Treatment: The response to medical therapy or interventions such as catheter ablation can influence the prognosis. Successful treatment that effectively controls or eliminates SVT episodes contributes to a better prognosis. 

Age Group: 

• Infants and Children: SVT can occur in infants and children, often presenting as sudden-onset episodes of rapid heart rate. 
• Adolescents and Young Adults: SVT is commonly diagnosed in this age group. 
• Middle-Aged Adults: SVT can continue to manifest in this age group. Individuals may experience chest discomfort,palpitations, and dizziness. 
• Elderly: SVT can occur in older adults, although it may be less common. 

Associated Comorbidities or Activities: 

• Heart Disease: People who have underlying heart conditions, such as coronary artery disease or cardiomyopathy, may be more susceptible to SVT. 
• Thyroid Disorders: It is associated with an increased risk of SVT. 
• Structural Heart Abnormalities: Congenital heart defects or acquired structural abnormalities may predispose individuals to SVT. 
• Stress and Anxiety: Anxiety and Emotional stress can trigger SVT episodes in susceptible individuals. 
• Pregnancy: SVT can occur during pregnancy, potentially due to hormonal changes and increased blood volume. 

Acuity of Presentation: 

• Acute Onset: SVT episodes often have a sudden and rapid onset.  
• Chronic or Recurrent: Some individuals may have a history of chronic or recurrent SVT episodes. Chronic SVT can manifest with ongoing or intermittent symptoms over an extended period. 
• Syncope or Near-Syncope: In some cases, SVT may lead to syncope (fainting) or near-syncope due to the rapid and inefficient heart rate. 
• Asymptomatic: Certain people with SVT might not exhibit any symptoms at all, particularly if their heart rate stays within a manageable range. 

Vital Signs: 

• Heart Rate: Assess the patient’s heart rate. SVT is characterized by a rapid and regular heartbeat. 
• Blood Pressure: Measure blood pressure to evaluate perfusion and rule out hypertension-related complications. 

Cardiac Auscultation: 

• Listen to the heart sounds using a stethoscope. 
• Identify any abnormal heart sounds (murmurs, gallops) or irregular rhythms. 

Peripheral Pulses: 

• Evaluate peripheral pulses to assess the strength and regularity. 

Respiratory Rate: 

• Assess the respiratory rate and look for signs of respiratory distress, which may occur if SVT affects cardiac output. 

Jugular Venous Distension (JVD): 

• Check for JVD, which may be a sign of impaired cardiac function. 

Skin Examination: 

• Assess the skin for signs of poor perfusion, such as pallor or cyanosis. 
• Note any diaphoresis (excessive sweating) or cool extremities. 

Neurological Examination: 

• Evaluate the patient’s mental status, as decreased cerebral perfusion may lead to confusion or altered consciousness. 
• Assess for symptoms of syncope or near-syncope. 

• Vagal Maneuvers: Techniques such as the Valsalva maneuver, carotid sinus massage, or diving reflex may be attempted to stimulate the vagus nerve and slow down the heart rate. These maneuvers are more effective for certain types of SVT, such as AV nodal reentrant tachycardia (AVNRT). 
• Adenosine: Adenosine is often used for acute termination of SVT. It is administered rapidly through an intravenous (IV) line and can interrupt the abnormal electrical pathways in the heart, restoring normal sinus rhythm. 
• Calcium Channel Blockers: Drugs such as verapamil and diltiazem, can be used to reduce the heart rate and stop SVT episodes. These medications are commonly used for patients with atrioventricular reentrant tachycardia (AVRT). 
• Beta-Blockers: Another family of drugs which may be used to lower heart rate and lessen the rate of SVT episodes are beta-blockers, including propranolol or metoprolol. 
• Antiarrhythmic Medications: For long-term care or in situations when other medicines are ineffective, more powerful antiarrhythmic medications such amiodarone, propafenone, or flecainide may be taken into consideration. However, these treatments may have negative effects and must be carefully monitored. 
• Catheter Ablation: It is a method that involves using a catheter to provide electricity to parts of the heart that are causing abnormal electrical pathways.  
• Implantable Devices: For long-term care, an implanted cardioverter-defibrillator (ICD) or pacemaker may be recommended in some situations, particularly for patients with symptomatic and recurrent SVT. 
• Lifestyle Modifications: Identifying and eliminating triggers, such as coffee or stress, can assist to prevent SVT episodes. 

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• Vagal Maneuvers: Techniques like the Valsalva maneuver, carotid sinus massage, or diving reflex can stimulate the vagus nerve and help terminate SVT episodes in some cases. 
• Catheter Ablation: It is a highly effective non-pharmacological treatment for SVT. It involves inserting catheters into the heart and using radiofrequency energy to destroy or isolate the abnormal electrical pathways responsible for the arrhythmia. Catheter ablation has a high success rate and can provide long-term relief from SVT symptoms. 

• Atrioventricular Node Ablation with Pacemaker Implantation: In cases where SVT is refractory to other treatments or when catheter ablation is not feasible, atrioventricular (AV) node ablation may be considered. This procedure involves ablating the AV node, the electrical connection between the ventricles and atria, and implanting a permanent pacemaker to regulate the heart rate. While this approach effectively prevents SVT episodes, it also eliminates the possibility of normal AV conduction, necessitating permanent pacing. 
• Surgical Maze Procedure: The surgical maze procedure is a surgical intervention used to treat various types of arrhythmias, including SVT. During the procedure, surgeons create a series of scar lines in the atria to disrupt abnormal electrical pathways and restore normal rhythm. 
• Lifestyle Modifications: Lifestyle changes, such as avoiding triggers like caffeine, alcohol, and stress, can help reduce the frequency and severity of SVT episodes. Additionally, maintaining a healthy weight, regular exercise, and stress management techniques may contribute to overall heart health and symptom management. 
• Biofeedback and Relaxation Techniques: Techniques such as meditation,biofeedback and deep breathing exercises can help individuals manage stress and anxiety, which may exacerbate SVT episodes. Learning to recognize and control physiological responses to stressors can be beneficial in preventing arrhythmia triggers. 

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Antiarrhythmic medicines are used extensively to treat supraventricular tachycardia (SVT). These drugs aim to regulate the cardiac rhythm and prevent arrhythmias from recurring. Here’s a breakdown of the role of antiarrhythmic drugs in SVT treatment along with examples of commonly used medications: 

Class I Antiarrhythmics: These drugs block sodium channels in cardiac cells, which can help stabilize the heart’s electrical activity. Examples include: 

• Flecainide: Flecainide is used to treat various types of SVT, including atrial fibrillation, atrial flutter, and atrioventricular nodal reentrant tachycardia (AVNRT). It works by slowing conduction in the heart. 
• Propafenone: Propafenone is similar to flecainide and is used to treat similar types of SVT. It can also be effective in terminating acute SVT episodes. 

Class III Antiarrhythmics: These medications increase the length of cardiac cells’ action potentials and refractory periods, which can assist avoid electrical impulse reentry. Examples include: 

• Amiodarone: Amiodarone is a potent antiarrhythmic drug used to treat various types of SVT, including atrial fibrillation and atrial flutter. It has a broad range of action and can be useful in individuals with resistant or recurrent arrhythmias. 
• Dronedarone: Dronedarone is a newer antiarrhythmic medication related to amiodarone. It is used to treat atrial fibrillation and may be considered in patients with paroxysmal SVT. 

Class IV Antiarrhythmics: These drugs block calcium channels in cardiac cells, leading to decreased conduction through the AV node and slowing of the heart rate. Examples include: 

• Verapamil: It is a calcium channel blocker used to treat SVT, particularly AVNRT. It can be administered orally or intravenously to terminate acute episodes or prevent recurrences. 
• Diltiazem: Diltiazem is another calcium channel blocker that is effective in treating SVT. It works similarly to verapamil and is commonly used in patients who cannot tolerate or do not respond to other antiarrhythmic medications. 

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Calcium channel blockers are mostly used in the treatment of supraventricular tachycardia (SVT), particularly for certain types of SVT where slowing the conduction through the atrioventricular (AV) node is beneficial. These medications are effective in controlling heart rate and preventing the recurrence of SVT episodes.  

Drugs such as verapamil and diltiazem, primarily target the L-type calcium channels in cardiac cells. By blocking these channels, they reduce the influx of calcium ions during each cardiac cycle. This causes the AV node to carry electrical impulses less efficiently, which lowers heart rate. 

They are particularly effective in treating SVT types that involve the AV node. Conditions such as atrioventricular nodal reentrant tachycardia (AVNRT) and atrial fibrillation with rapid ventricular response (AFib with RVR) often respond well to calcium channel blockers. 

Two main calcium channel blockers used in SVT treatment are verapamil and diltiazem. 

• Verapamil: It is effective in slowing the heart rate and terminating SVT episodes. Verapamil is available in both immediate-release and sustained-release formulations. 
• Diltiazem: Similar to verapamil, diltiazem is used to slow down the heart rate and control SVT. It is available in both oral and intravenous formulations, making it suitable for acute management of SVT. Calcium channel blockers can be administered orally for long-term management of SVT or intravenously for acute termination of SVT episodes. In emergency cases or when a quick reaction is necessary, an intravenous drug is frequently used. 

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Beta blockers, also known as beta-adrenergic blockers, are mostly used in the treatment of supraventricular tachycardia (SVT). These medications work by blocking the effects of the hormone adrenaline (epinephrine) on the heart, leading to a reduction in heart rate and blood pressure. Beta blockers are particularly effective in managing SVT by slowing the conduction of electrical impulses through the atrioventricular (AV) node. 

Beta blockers block beta receptors in the heart, which are normally stimulated by adrenaline. By inhibiting the effects of adrenaline, beta blockers reduce the heart rate, myocardial contractility, and the automaticity of the heart, thereby helping to control SVT.Beta blockers can be administered orally for long-term management of SVT or intravenously for acute termination of SVT episodes. The intravenous route is commonly used in emergency situations or when a rapid response is needed. 

• Metoprolol: Metoprolol is a selective beta-1 receptor blocker and is often used for SVT management. Both extended-release and immediate-release formulations are available for it. 
• Propranolol: It is a non-selective beta blocker which affects both beta-1 and beta-2 receptors. It is used in SVT treatment and is available in various formulations. 

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Adenosine is a naturally occurring nucleoside that acts on specific receptors in the heart, known as adenosine receptors. When administered, adenosine slows down the conduction through the AV node and interrupts the abnormal electrical pathway responsible for SVT. It does so by hyperpolarizing the AV node cells and inhibiting the release of neurotransmitters. Adenosine  

is typically administered as a rapid intravenous (IV) bolus in a medical setting. The administration is done through a large-bore IV line, often in the antecubital vein of the arm closest to the heart. The rapid bolus is followed by a saline flush. 

The standard initial dose of adenosine is usually 6 mg, administered rapidly over 1-2 seconds. If there is no response or incomplete response, a second dose of 12 mg may be given in the same manner. It’s important to note that adenosine has a very short half-life (seconds), and its effects are transient. 

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Catheter Ablation: 

• It is a minimally invasive procedure performed in a electrophysiology (EP) laboratory by a trained cardiac electrophysiologist. 
• During the procedure, thin, flexible tubes called catheters are inserted into the blood vessels of the heart, usually accessed via the groin or neck. 
• Using advanced mapping techniques, the electrophysiologist locates the abnormal electrical pathways responsible for SVT. 
• Once the abnormal site is identified, energy, such as radiofrequency (RF) or cryoablation, is delivered through the catheter to destroy or ablate the tissue causing the arrhythmia. 
• By ablating the abnormal pathway, the conduction of electrical impulses is interrupted, thereby preventing the recurrence of SVT. 

Types of SVT Treated with Catheter Ablation: 

• Catheter ablation is effective for various types of SVT, including atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), and atrial tachycardias. 
• The specific type of SVT and the location of the abnormal pathway determine the approach and success rate of catheter ablation. 

Success Rate and Risks: 

• Catheter ablation is highly successful in treating SVT, with success rates exceeding 90% in many cases. 
• The procedure is generally safe, but like any invasive procedure, it carries some risks, including bleeding, infection, damage to blood vessels or heart structures, and the development of new arrhythmias. 
• Risks are minimized through careful patient selection, skilled procedural techniques, and post-procedural monitoring. 

Post-procedural Care: 

• Following catheter ablation, patients are typically monitored overnight in the hospital to ensure stability and detect any potential complications. 
• Though intense activity may be prohibited for a brief while, most patients are able to return to their regular activities in a few of days. 
• A cardiac electrophysiologist must perform a long-term follow-up to evaluate the procedure’s effectiveness and keep an eye out for any SVT recurrence. 

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Acute Intervention Phase: 

• Recognition of Symptoms: Recognizing the symptoms of SVT is crucial for prompt intervention. Common symptoms include palpitations, rapid heart rate, chest discomfort, and dizziness. 
• Vagal Maneuvers: Simple maneuvers, such as the Valsalva maneuver, carotid sinus massage, or immersion in cold water, may be attempted to stimulate the vagus nerve and terminate SVT episodes. 
• Pharmacological Intervention: Intravenous administration of medications like adenosine, calcium channel blockers, beta-blockers can be used to acutely terminate SVT episodes. 

Transition to Maintenance Phase: 

• Determination of SVT Type: Identifying the specific type of SVT is important for tailoring the treatment plan. This may involve an electrophysiological study to map the abnormal pathways. 
• Medication Selection: Based on the type of SVT, a healthcare provider may prescribe antiarrhythmic medications such as calcium channel blockers, beta blockers other specific agents for long-term prevention. 
• Patient Education: Informing the patient about the condition, triggers, and the importance of adherence to medications is crucial during this phase. 

Long-Term Prevention Phase: 

• Medication Adherence: Consistent and proper use of prescribed medications is essential for preventing the recurrence of SVT episodes. Adjustments to medication dosage or changes in medication may be made during follow-up appointments based on the patient’s response. 
• Regular Follow-up: Periodic follow-up visits with a healthcare provider are necessary to monitor the patient’s response to medication, assess for any side effects, and make adjustments to the treatment plan as needed. 
• Consideration of Non-pharmacological Interventions: In cases where medications are not effective or not well-tolerated, or if there is a preference for non-pharmacological approaches, catheter ablation may be considered as a long-term solution. 

Lifestyle Modification Phase: 

• Identification of Triggers: Identifying and avoiding triggers that may induce SVT episodes is an important aspect of long-term management. Common triggers include stress, caffeine, and certain medications. 

Crisis Management Phase: 

• Emergency Preparedness: In cases where SVT episodes persist or become more severe, patients should be educated on when to seek emergency medical attention.