Paroxysmal Supraventricular Tachycardia Workup

Updated: Apr 05, 2017
  • Author: Monika Gugneja, MD; Chief Editor: Mikhael F El-Chami, MD  more...
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Workup

Approach Considerations

Laboratory studies

A cardiac enzyme evaluation should be ordered for patients with chest pain, patients with risk factors for myocardial infarction, and patients who are otherwise unstable and present with heart failure, hypotension, or pulmonary edema. Young patients with no structural heart defects have a very low risk of myocardial infarction.

Other laboratory tests include the following:

  • Electrolyte levels - Should be checked because electrolyte abnormalities can contribute to paroxysmal supraventricular tachycardia (paroxysmal SVT)
  • Complete blood count (CBC) - Helps to assess whether anemia is contributing to the tachycardia or ischemia
  • Thyroid studies - The results are rarely diagnostic of hyperthyroidism
  • Digoxin level - Obtain for patients on digoxin, because paroxysmal SVT is one of the many dysrhythmias that can be caused by supratherapeutic levels of this drug

Electrophysiology

Electrophysiologic studies have dramatically changed the diagnosis of SVT. Intracardiac recordings have helped to map accessory pathways and reentry circuits in patients, and they have also assisted cardiologists and electrophysiologists in understanding the mechanisms behind these tachyarrhythmias.

In a prospective registry, Lauschke et al compared the prevalence of inducible arrhythmias and the clinical outcome in 525 patients with and without ECG documentation. Results showed that a substantial proportion of patients with suspected paroxysmal tachycardia, but without ECG documentation, had inducible supraventricular tachycardias (SVTs) and clinically benefited from an electrophysiological study (EPS). [69]

At present, electrophysiologic studies are generally performed in combination with radiofrequency catheter ablation.

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Imaging Studies

Chest radiography

Obtain a chest radiograph to assess for the presence of pulmonary edema and cardiomegaly. In certain cases, infections such as pneumonia are also associated with paroxysmal SVT and can be confirmed with chest radiography. [9, 10, 11, 40, 41]

Transthoracic echocardiography

A transthoracic echocardiogram may be helpful if structural or congenital heart disease is suggested.

Magnetic resonance imaging

Cardiac magnetic resonance imaging (MRI) can be useful, especially if a congenital heart disease is being considered.

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Electrocardiography

Electrocardiographic findings permit classification of the tachyarrhythmia, and they may allow a precise diagnosis. P waves may not be visible; when present, they may be normal or abnormal, depending on the mechanism of atrial depolarization. [9, 10, 35]

Electrocardiographic characteristics of the various SVTs are as follows:

  • Sinus tachycardia - Heart rate greater than 100 bpm; P waves similar to sinus rhythm
  • Inappropriate sinus tachycardia (IST) - Findings similar to sinus tachycardia; P waves similar to sinus rhythm
  • Sinus nodal reentrant tachycardia (SNRT) - P waves similar to sinus rhythm; abrupt onset and offset
  • Atrial tachycardia - Heart rate 120-250 bpm; P-wave morphology different from sinus rhythm; long RP interval (in general); AV block does not terminate tachycardia
  • Multifocal atrial tachycardia - Heart rate 100-200 bpm; 3 or more different P-wave morphologies
  • Atrial flutter- Atrial rate of 200-300 bpm; flutter waves; AV conduction of 2:1 or 4:1
  • Atrial fibrillation - Irregularly irregular rhythm; lack of discernible P waves
  • AV nodal reentrant tachycardia (AVNRT) - Heart rate of 150-200 bpm; P wave located either within the QRS complex or shortly after the QRS complex; short RP interval in typical AVNRT and long RP interval in atypical AVNRT
  • AV reentrant tachycardia (AVRT) - Heart rate of 150-250 bpm; narrow QRS complex in orthodromic conduction and wide QRS in antidromic conduction; diagnosis excluded by AV block during SVT; P wave after QRS complex

Following the termination of the tachycardia, an ECG should be performed during the sinus rhythm to screen for WPW syndrome. Holter monitoring also may be useful as it can help to assess the frequency and duration of SVT episodes, although they have a low yield. Echocardiography may be helpful in screening for structural or congenital heart disease.

Characterizing a patient’s SVT by comparing the RP interval to the PR interval is helpful. Long RP tachycardias result when atrial activity precedes the QRS complex. In short RP tachycardias, atrial activity occurs with or shortly after ventricle excitation, and the P wave is found within the QRS complex or shortly after the QRS complex. [9, 10, 40, 41] The classifications of SVTs based on the RP interval are as follows:

  • Short RP tachycardias – Typical AVNRT, AVRT, junctional ectopic tachycardia (JET), and nonparoxysmal junctional tachycardia (NPJT)
  • Long RP tachycardias – Sinus tachycardia, SNRT, atrial tachycardia, atrial flutter, atypical AVNRT, and a permanent form of junctional reciprocating tachycardia

Two consecutive P waves without an intervening QRS complex may be due to atrial tachycardias, in some cases, AVNRT, but they are unlikely to be due to AVRT. Vagal maneuvers and nodal blocking agents like adenosine work in AVNRT in some cases, but not in atrial tachycardias. Blocking the tachycardia with adenosine or vagal maneuvers may assist in diagnosing the rhythm as well as treating it.

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