Shown below is an EKG recorded in a middle-aged woman treated for atrial fibrillation. The patient was doing well when this electrocardiogram was taken, and was taking digoxin and flecainide . The electrocardiogram shows an irregular rhythm which appears to be sinus. The grouping of the QRS complexes suggests a Mobitz type I AV block. In this case though, no AV block is seen and this may represent a sinus node exit block.

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Shown below is an EKG recording from a middle aged woman with recurrent atrial fibrillation. She was treated with flecainide with some improvement of her symptoms. The above is a recording taken in the cardiac clinic. It shows group beating with sinus rhythm. There are missing P waves. This suggests that there is sinus node arrest or that this is sinus node exit block.

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Shown below is a Holter recording from a patient that illustrates a bradycardia after the termination of a tachycardia. This has been called the “tachy/brady syndrome”. In this case the tachy part is atrial fibrillation, which is followed by a long pause and then a nodal escape at about 35/min. Patients are often symptomatic from the pause and may have dizziness or syncope on termination of the tachycardia.

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