Picture Quiz

A young athlete with bradycardia

BMJ 2013; 347 doi: http://dx.doi.org/10.1136/bmj.f4258 (Published 4 July 2013)
Cite this as: BMJ 2013;347:f4258

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  1. Nabeel Sheikh, cardiology specialist registrar,
  2. Sanjay Sharma, professor of cardiology
  1. 1St George’s Hospital, London SW17 0QT, UK
  1. Correspondence to: N Sheikh; nabeelsheikh99{at}yahoo.com

A 17 year old male athlete was referred for specialist investigation after an abnormal electrocardiogram (ECG) was found on routine pre-participation cardiovascular evaluation. He swam for 20 hours a week during peak training at club level, in addition to cycling for six hours a week. He was asymptomatic apart from occasional dizziness after exercise. He had no medical, drug, or family history of note. Examination was normal apart from bradycardia of 40 beats/min. Figure 1 shows the 12 lead electrocardiography trace. A two dimensional transthoracic echocardiogram showed a structurally normal heart.

Questions

  • 1 What is the electrocardiographic diagnosis?

  • 2 What is the atrioventricular conduction ratio?

  • 3 What is the likely clinical diagnosis?

  • 4 What further investigations would confirm the diagnosis and level of block?

  • 5 How would you manage this young athlete?

Answers

1 What is the electrocardiographic diagnosis?

Short answer

Second degree atrioventricular block.

Long answer

The ECG shows second degree atrioventricular block but this cannot be classified further into Mobitz type 1 (Wenckebach) or type 2 block.

Mobitz type 1 block usually occurs in the atrioventricular node and is most commonly caused by functional suppression of nodal conduction—for example, by drugs, ischaemia, or increased vagal tone. Under these circumstances, nodal cells exhibit progressive fatigue—seen on the ECG as a gradually increasing PR interval—which eventually culminates in failure of conduction and a “dropped” beat. Subsequent recovery of the nodal cells occurs during the ensuing pause, resulting in shortening of the next conducted PR interval. Although this is the typical “textbook” definition, atypical patterns are also seen, and in some instances (particularly when associated with a broad (≥120 msec) QRS complex) type 1 block can occur in the His-Purkinje system.1 Nodal type 1 block is usually reversible and benign.

In contrast, Mobitz type 2 atrioventricular block is an “all or nothing” phenomenon, resulting from disease in the His-Purkinje system. Cells …

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