Cardiology · Arrhythmias
The facts most likely to be tested
The classic ECG presentation of paroxysmal supraventricular tachycardia (PSVT) is a narrow-complex tachycardia with a regular rhythm and absent P waves.
Vagal maneuvers, such as carotid sinus massage or the Valsalva maneuver, are the first-line intervention for a hemodynamically stable patient.
Adenosine is the drug of choice for terminating AV nodal reentrant tachycardia (AVNRT) due to its ultra-short half-life and ability to cause a transient AV nodal block.
Synchronized electrical cardioversion is the mandatory treatment for any patient presenting with hemodynamic instability, characterized by hypotension, altered mental status, or acute heart failure.
Wolff-Parkinson-White (WPW) syndrome is a pre-excitation syndrome characterized by a delta wave and a short PR interval on ECG.
Adenosine is contraindicated in patients with WPW syndrome presenting with atrial fibrillation because it can promote conduction through the accessory pathway and trigger ventricular fibrillation.
Radiofrequency catheter ablation is the definitive, curative treatment for patients with recurrent, symptomatic PSVT.
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A 28-year-old woman presents to the emergency department with a 30-minute history of palpitations and lightheadedness. She denies chest pain or shortness of breath. Her blood pressure is 118/76 mmHg and her heart rate is 175 bpm. The ECG reveals a narrow-complex tachycardia with no visible P waves and a regular R-R interval. The patient is alert and oriented.
What is the most appropriate initial management for this patient?
Vagal maneuvers
The patient is hemodynamically stable with a narrow-complex tachycardia, making vagal maneuvers the appropriate first-line intervention before pharmacological therapy with adenosine.
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Etiology / Epidemiology
Common in young, healthy patients with accessory pathways or AV nodal re-entry.
Clinical Manifestations
Presents as palpitations, tachycardia-bradycardia syndrome, and narrow QRS complex.
Diagnosis
Electrocardiogram is the gold standard; look for rate >150 bpm and absent P waves.
Treatment
Use vagal maneuvers first, followed by adenosine for stable patients; avoid in asthma.
Prognosis
Generally benign; catheter ablation is curative for recurrent, symptomatic cases.
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Epidemiology & Etiology
Most common in patients with AVNRT or AVRT, often triggered by caffeine, alcohol, or stress. It is frequently seen in patients with Wolff-Parkinson-White syndrome. Younger patients are more commonly affected than the elderly population.
Pertinent Anatomy
The re-entrant circuit typically involves the AV node or an accessory pathway (e.g., Bundle of Kent). Understanding the location of the circuit is essential for planning catheter ablation.
Pathophysiology
A re-entrant circuit is established when an electrical impulse travels in a continuous loop. This leads to rapid, regular atrial depolarization and subsequent ventricular response. The hallmark is a narrow QRS complex because the conduction system is activated normally.
Clinical Manifestations
Patients report sudden onset of palpitations, lightheadedness, or dyspnea. Physical exam reveals a regular, rapid heart rate often exceeding 150 bpm. Syncope or chest pain indicates hemodynamic instability requiring immediate intervention.
Diagnosis
The 12-lead ECG is the gold standard for diagnosis. Look for a narrow QRS complex (<0.12s) and absent P waves or retrograde P waves. A rate of 150-250 bpm is classic for paroxysmal supraventricular tachycardia.
Treatment
Stable patients receive vagal maneuvers (e.g., carotid massage) followed by adenosine (6mg rapid IV push). Adenosine is contraindicated in asthma due to potential bronchospasm. Unstable patients require synchronized cardioversion.
Prognosis
Most episodes are self-limiting or easily terminated. Catheter ablation provides a >95% success rate for recurrent cases. Long-term monitoring is required if the patient remains symptomatic despite initial management.
Differential Diagnosis
Atrial Fibrillation: Irregularly irregular rhythm with absent P waves
Atrial Flutter: Sawtooth P waves with a fixed AV block
Sinus Tachycardia: Gradual onset with identifiable P waves
Ventricular Tachycardia: Wide QRS complex (>0.12s) and AV dissociation
Wolff-Parkinson-White: Delta wave on baseline ECG