Tachycardia

Tachycardia is defined by a heart rate ≥100 beats per minute. Most tachyarrhythmias occur as a result of triggered activity, increased automaticity, or re-entry circuits. A 12-lead ECG is essential to determining the type of tachyarrhythmia present. Wide complex tachycardia must be worked up and treated as ventricular tachycardia until proven otherwise.

Differential Diagnosis

• Sinus tachycardia
  –Regular rhythm, narrow QRS complex
  –Originates at sinus node (normal P waves)
  –Occurs in response to physiologic stimuli (e.g., volume depletion, fever, pain, thyrotoxicosis)

• Atrial flutter
  –Narrow QRS complex
  –Usually regular, but may be irregular
  –Caused by a re-entrant circuit in atrium
  –Characteristic “sawtooth” pattern on ECG
  –Atrial rate typically 250–350 bpm
  –Ventricular rate usually 1/2 atrial rate (2:1 block), but may be 3:1, 4:1, etc.

Workup and Diagnosis

• History and physical examination
  –Associated symptoms may include lightheadedness, palpitations, dyspnea, chest pain, and syncope
  –Assess for hemodynamic instability (blood pressure, level of consciousness) and jugular venous pulsations (cannon A waves are highly suggestive of AV dissociation)
• ECG is the key tool for establishing diagnosis
  –Determining supraventricular versus ventricular origin is the most critical distinction
  –Adenosine IV push may be used to transiently block the AV node to identify underlying rhythms
• Any wide-QRS complex tachycardia (QRS >0.12 seconds) is considered ventricular tachycardia until proven otherwise
  –Nonsustained VT lasts <30 seconds and is asymptomatic
  –Sustained VT lasts >30 seconds or results in hemodynamic compromise
  –Monomorphic VT is a single stable QRS complex
  –Polymorphic VT is a changing QRS morphology and axis—may have normal or prolonged QT interval (e.g., torsade de pointes) on baseline ECG

Treatment

• Ventricular tachycardia must be treated emergently
  –Unstable VT with hypotension or cardiac ischemia requires immediate cardioversion
  –IV amiodarone or lidocaine if cardioversion fails
  –Stable VT should be treated initially with antiarrhythmic medications (e.g., IV amiodarone, lidocaine, procainamide), correction of electrolyte abnormalities, and/or IV magnesium; cardiovert if there is no response

• Supraventricular tachycardias
  –Control rate, terminate rhythm, prevent recurrence
  –Vagal maneuvers (e.g., carotid sinus massage) to transiently block AV node may be useful (avoid in elderly, carotid bruits, or known carotid artery stenosis)
  –Medications include AV nodal blocking drugs (e.g., β-blockers): Slow conduction to ventricles; antiarrhythmics terminate rhythm, prevent recurrence
  –Cardioversion is reserved for symptomatic patients
  –Radiofrequency ablation is more definitive means of terminating arrhythmias and preventing recurrences

Book Source Details

• Book Title: In a Page: Signs and Symptoms
• Author(s): Scott Kahan, Ellen G. Smith
• Year of Publication: 2004
• Copyright Details: In a Page: Signs and Symptoms, Copyright © 2004 Lippincott Williams & Wilkins.

Other Book Chapters Related to Atrial fibrillation

Read excerpts from these other book chapters related to Atrial fibrillation:

Copyright Details: In a Page: Signs and Symptoms, Copyright © 2008 Williams & Wilkins.

More About Causes of Atrial fibrillation

• Back to symptom: Atrial fibrillation: Introduction (review 77 causes)
• Next Book Extract About Atrial fibrillation: Murmurs - Diastolic (In a Page: Signs and Symptoms)
• All Book Extracts: All Online Book Extracts for Atrial fibrillation

More About This Book: Title: In a Page: Signs and Symptoms Authors: Scott Kahan, Ellen G. Smith Publisher: Lippincott Williams & Wilkins Copyright: 2004 ISBN: 1-4051-0368-X

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