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Atrioventricular nodal reentrant tachycardia (AVNRT)

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Atrioventricular nodal reentrant tachycardia (AVNRT)

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USMLE® Step 1 style questions USMLE

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A 34-year-old male presents to the emergency department with palpitations. He states he drank his morning coffee, went out for a jog, but he suddenly became lightheaded and noted a fluttering sensation in his chest. He had a similar episode in the past, which self-resolved without intervention. Past medical history is noncontributory, and he does not take any medications. Temperature is 37.0°C (98.6°F), pulse is 175/min, respirations are 14/min, and blood pressure is 124/72 mmHg. Physical exam is otherwise unremarkable, and initial electrocardiogram is demonstrated below:  


Image reproduced from Wikimedia Commons  

Based on this patient's clinical presentation, which of the following is the most likely diagnosis?  

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Content Reviewers

Rishi Desai, MD, MPH,Tanner Marshall, MS

The atria are the heart’s upper chambers; the ventricles are the lower chambers. Reentrant tachycardias are fast heart rates caused by electrical signals that loop back on themselves.

Normally, an electrical signal starts at the sinoatrial or SA node in the right atrium and propagates out through both atria, including bachmann’s bundle in the left atrium, and then contracts both atria. It’s then delayed just a little bit as it goes through the atrioventricular, or AV node, before it passes through the Bundle of His and on to the Purkinje fibers of the left and right ventricles, causing them to contract as well.

Usually, the only place where a signal can go from the atria to the ventricles is at the AV node, and once that signal gets to the purkinje fibers, it stops and the heart tissue waits for another signal from the SA node. With an atrioventricular reentrant tachycardia, or AVRT, the electrical signal actually uses a separate accessory pathway to get back up from the ventricles to the atria, which causes the atria to contract before the SA node sends out another signal. The signal then moves back down the AV node to the ventricles and purkinje fibers, contracts the ventricles, and goes back up that accessory pathway. This cycle repeats, which is why AVRT can result in rates as high as 200-300 bpm. This type of tachycardia is known as a supraventricular tachycardia because the signal causing the fast rate originates above the ventricles. The most common type of AVRT is Wolff-Parkinson-White syndrome, where the accessory pathway is called the Bundle of Kent. This type of reentry is known as an anatomical reentrant circuit because the accessory pathway is a fixed, anatomically-defined pathway.

Another type of reentrant circuit is atrioventricular nodal reentrant tachycardia, or AVNRT. AVNRT, just like AVRT, is a type of supraventricular tachycardia; however, with AVNRT it’s in or near the AV node, which similarly contracts the ventricle and the atria every time it goes around.

Sources

  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "Differentiation of Slow-Slow Form of AVNRT from AVRT through a Posteroseptal Accessory Pathway by Retrograde P-Wave Amplitude" Pacing and Clinical Electrophysiology (2016)
  5. "Atrioventricular Reciprocating Tachycardia/Atrioventricular Reentrant Tachycardia (AVRT)" StatPearls Publishing (2020 Jan)