A 65-year-old man was admitted to the emergency room for dizziness. The patient was alert and oriented. Cardiopulmonary examination showed bilateral air entry with no adventitious sounds and normal heart sounds without murmurs, gallop, or rub. There was no peripheral edema. Analysis of the ECG (Figure 1, top) showed constant sinus bradycardia (42 beats per minute), with normal atrioventricular and intraventricular conduction. The patient was hemodynamically stable (blood pressure 120/80mmHg). Curiously, during observation, abrupt changes in heart rate was recorded. The ECG on the bottom of Figure 1 shows a phase of unexpected slowing of the heart rate.

Figure 1

(0.98MB).

How can you define this arrhythmia?

• 1)

  Respiratory sinus arrhythmia

• 2)

  Sympathovagal imbalance

• 3)

  Sinoatrial 2:1 block

• 4)

  Concealed atrioventricular node reentry

Suggest a solution to this ECG Contest at http://www.revespcardiol.org/en/electroreto/72/10. The answer will be published in the next issue (November 2019). #EKGchallenge.