Supraventricular Tachycardia (AVNRT)
A 21-year-old man reports three episodes of abrupt palpitations with brief loss of consciousness. During an episode his blood pressure is 105/70 mm Hg and the monitor shows a regular narrow QRS complex tachycardia at 230 beats/min with no discernible P waves and no beat-to-beat variability. The rhythm terminates suddenly with carotid sinus massage. Which is the most likely diagnosis?
- A.Sinus tachycardia
- B.Atrial fibrillation with rapid ventricular response
- C.Atrial flutter with two-to-one conduction
- D.Atrioventricular nodal reentrant tachycardiaCorrect
Explanation
A regular narrow complex tachycardia at 220 to 250 beats/min in a young patient with abrupt onset and offset, absent visible P waves, and termination with vagal manoeuvres is typical atrioventricular nodal reentrant tachycardia, the commonest form of paroxysmal supraventricular tachycardia. The mechanism is reentry within dual atrioventricular nodal pathways, with slow pathway antegrade and fast pathway retrograde conduction, so the atria and ventricles depolarise almost simultaneously and the retrograde P wave is buried in the QRS or appears as a pseudo R prime in lead V1. Because the atrioventricular node forms an obligatory limb of the circuit, vagal manoeuvres or adenosine 6 mg rapid intravenous push interrupt the circuit and terminate the arrhythmia abruptly, which is both diagnostic and therapeutic. Syncope occurs when the very rapid rate shortens diastolic filling and drops cardiac output. Haemodynamically unstable patients receive immediate synchronised cardioversion, and recurrent symptomatic cases are cured by catheter ablation of the slow pathway with success rates above 95 percent. Atrial fibrillation is irregularly irregular with no organised atrial activity and rarely reaches this rate in a structurally normal 21-year-old heart. Atrial flutter with two-to-one block gives a regular rate near 150 beats/min with sawtooth flutter waves that are unmasked but not terminated by adenosine. Sinus tachycardia has visible P waves, rarely exceeds 220 minus age, and slows gradually rather than stopping abruptly.
Why each option
- A.
- Sinus tachycardia has visible P waves, a rate below about 200 beats/min at this age, and slows gradually with vagal stimulation.
- B.
- Atrial fibrillation is irregularly irregular and does not terminate abruptly with carotid sinus massage.
- C.
- Atrial flutter with two-to-one conduction gives a rate near 150 beats/min; adenosine reveals sawtooth waves but does not terminate it.
- D.
- Correct. Abrupt onset and offset, rate over 220 beats/min, absent P waves, and termination with vagal manoeuvres define atrioventricular nodal reentrant tachycardia.
Reference: 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia
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