Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is an umbrella term for abnormally fast heart rhythms originating from the upper part of the heart, specifically the atria or the atrioventricular (AV) node. This condition contrasts with ventricular tachycardia, which arises from the lower chambers of the heart. SVT encompasses several specific arrhythmias, including atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia (PSVT), and Wolff-Parkinson-White syndrome.

Signs and Symptoms

SVT symptoms can appear suddenly and may resolve without intervention. They can be triggered by stress, exercise, or emotional factors, and episodes can last from a few minutes to several days. Common symptoms include palpitations, feeling faint, sweating, shortness of breath, chest pain, rapid breathing, dizziness, and, in severe cases, loss of consciousness. In infants and toddlers, symptoms may manifest as a lack of interest in feeding, shallow breathing, lethargy, vomiting, and decreased responsiveness.

Lead II electrocardiogram strip showing PSVT with a heart rate of about 180

Pathophysiology

SVT mechanisms include re-entry circuits and increased automaticity of cardiac muscle cells. The AV node acts as a gating mechanism, limiting the number of impulses that pass to the ventricles. However, accessory pathways, such as in Wolff-Parkinson-White syndrome, can bypass this protection, leading to faster ventricular rates.

Mechanisms of supraventricular tachycardias

Diagnosis

Diagnosis of SVT typically involves an electrocardiogram (ECG), Holter monitor, or event monitor. Subtypes of SVT can be distinguished by their ECG characteristics, with most presenting narrow QRS complexes. In cases of electrical conduction abnormalities, a wide QRS complex may mimic ventricular tachycardia. Algorithms exist to differentiate between supraventricular and ventricular tachycardia, very important as they require different treatments.

Holter monitor - Imaging with start (red arrow) and end (blue arrow) of a SV-tachycardia with a pulse frequency of about 128/min

A 12-lead ECG showing paroxysmal supraventricular tachycardia at about 180 beats per minute

Classification

SVT can be classified by their specific site of origin. Subtypes include sinoatrial nodal reentrant tachycardia (SNRT), ectopic (unifocal) atrial tachycardia (EAT), multifocal atrial tachycardia (MAT), and atrioventricular reentrant tachycardia (AVRT), among others. Each subtype has distinct ECG features and mechanisms.

Treatment

Treatment of SVT depends on the subtype and severity. Initial management may include vagal manoeuvres, which stimulate the vagus nerve to slow heart rate, and medications such as adenosine, beta-blockers, or calcium channel blockers for rate control. For recurrent or persistent SVT, catheter ablation may be considered. Radiofrequency ablation uses a catheter to destroy abnormal electrical pathways, offering a high success rate for certain SVT types. Cryoablation, an alternative to radiofrequency ablation, uses extreme cold to ablate tissue with a lower risk of damaging the AV node.

Prevention

Preventive measures may involve lifestyle changes, medications, or medical procedures. For those with infrequent or minimally symptomatic episodes, observation may suffice. More frequent or disabling symptoms may require beta-blockers, antiarrhythmic drugs, or catheter ablation.

Impulse arising in SA node, traversing atria to AV node, then entering ventricle. Rhythm originating at or above AV node constitutes SVT

Notable Cases

Several public figures have been diagnosed with SVT, including Tony Blair, Miley Cyrus, and various athletes. Their experiences highlight the condition's impact on diverse populations.

Note: This summary is intended to inform UK dentists preparing for professional exams about SVT in general medicine and surgery.

Self-assessment MCQs (single best answer)

Which of the following conditions is not considered a type of supraventricular tachycardia (SVT)?

score 0 / 1. running total: 0 / 0

What is the primary difference between supraventricular tachycardia (SVT) and ventricular tachycardia?

score 0 / 1. running total: 0 / 0

Which symptom is not commonly associated with SVT?

score 0 / 1. running total: 0 / 0

Which diagnostic tool is most commonly used to identify SVT?

score 0 / 1. running total: 0 / 0

In Wolff-Parkinson-White syndrome, what is the main mechanism causing SVT?

score 0 / 1. running total: 0 / 0

What is the typical appearance of SVT on an ECG?

score 0 / 1. running total: 0 / 0

Which of the following is a first-line intervention for acute management of SVT?

score 0 / 1. running total: 0 / 0

Which of the following treatment options involves using extreme cold to destroy abnormal electrical pathways?

score 0 / 1. running total: 0 / 0

Which lifestyle factor is least likely to trigger an episode of SVT?

score 0 / 1. running total: 0 / 0

Which subtype of SVT is characterised by multiple atrial foci causing irregular atrial rhythms?

score 0 / 1. running total: 0 / 0